An intercomparison and validation of satellite-based surface radiative energy flux estimates over the Arctic

NASA Astrophysics Data System (ADS)

Riihelä, Aku; Key, Jeffrey R.; Meirink, Jan Fokke; Kuipers Munneke, Peter; Palo, Timo; Karlsson, Karl-Göran

2017-05-01

Accurate determination of radiative energy fluxes over the Arctic is of crucial importance for understanding atmosphere-surface interactions, melt and refreezing cycles of the snow and ice cover, and the role of the Arctic in the global energy budget. Satellite-based estimates can provide comprehensive spatiotemporal coverage, but the accuracy and comparability of the existing data sets must be ascertained to facilitate their use. Here we compare radiative flux estimates from Clouds and the Earth's Radiant Energy System (CERES) Synoptic 1-degree (SYN1deg)/Energy Balanced and Filled, Global Energy and Water Cycle Experiment (GEWEX) surface energy budget, and our own experimental FluxNet / Satellite Application Facility on Climate Monitoring cLoud, Albedo and RAdiation (CLARA) data against in situ observations over Arctic sea ice and the Greenland Ice Sheet during summer of 2007. In general, CERES SYN1deg flux estimates agree best with in situ measurements, although with two particular limitations: (1) over sea ice the upwelling shortwave flux in CERES SYN1deg appears to be underestimated because of an underestimated surface albedo and (2) the CERES SYN1deg upwelling longwave flux over sea ice saturates during midsummer. The Advanced Very High Resolution Radiometer-based GEWEX and FluxNet-CLARA flux estimates generally show a larger range in retrieval errors relative to CERES, with contrasting tendencies relative to each other. The largest source of retrieval error in the FluxNet-CLARA downwelling shortwave flux is shown to be an overestimated cloud optical thickness. The results illustrate that satellite-based flux estimates over the Arctic are not yet homogeneous and that further efforts are necessary to investigate the differences in the surface and cloud properties which lead to disagreements in flux retrievals.

The Surface Energy Balance at Local and Regional Scales-A Comparison of General Circulation Model Results with Observations.

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Krummel, P. B.; Kowalczyk, E. A.

1993-06-01

Aspects of the mean monthly energy balance at continental surfaces are examined by appeal to the results of general circulation model (GCM) simulations, climatological maps of surface fluxes, and direct observations. Emphasis is placed on net radiation and evaporation for (i) five continental regions (each approximately 20°×150°) within Africa, Australia, Eurasia, South America, and the United States; (ii) a number of continental sites in both hemispheres. Both the mean monthly values of the local and regional fluxes and the mean monthly diurnal cycles of the local fluxes are described. Mostly, GCMs tend to overestimate the mean monthly levels of net radiation by about 15% -20% on an annual basis, for observed annual values in the range 50 to 100 Wm2. This is probably the result of several deficiencies, including (i) continental surface albedos being undervalued in a number of the models, resulting in overestimates of the net shortwave flux at the surface (though this deficiency is steadily being addressed by modelers); (ii) incoming shortwave fluxes being overestimated due to uncertainties in cloud schemes and clear-sky absorption; (iii) land-surface temperatures being under-estimated resulting in an underestimate of the outgoing longwave flux. In contrast, and even allowing for the poor observational base for evaporation, there is no obvious overall bias in mean monthly levels of evaporation determined in GCMS, with one or two exceptions. Rather, and far more so than with net radiation, there is a wide range in values of evaporation for all regions investigated. For continental regions and at times of the year of low to moderate rainfall, there is a tendency for the simulated evaporation to be closely related to the precipitation-this is not surprising. In contrast, for regions where there is sufficient or excessive rainfall, the evaporation tends to follow the behavior of the net radiation. Again, this is not surprising given the close relation between potential evaporation and net radiation, as discussed by Priestley and Taylor. Finally, the introduction into GCMs of an `improved' surface scheme (incorporating more realistic representations of soil and canopy processes and revised albedos) does tend to improve the calculations of both regional net radiation and evaporation.

Tidal and atmospheric forcing of the upper ocean in the Gulf of California. 2: Surface heat flux

NASA Technical Reports Server (NTRS)

Paden, Cynthia A.; Winant, Clinton D.; Abbott, Mark R.

1993-01-01

Satellite infrared imagery and coastal meteorological data for March 1984 through February 1985 are used to estimate the net annual surface heat flux for the northern Gulf of California. The average annual surface heat flux for the area north of Guaymas and Santa Rosalia is estimated to be +74 W/sq m for the 1984-1985 time period. This is comparable to the +20-50 W/sq m previously obtained from heat and freshwater transport estimates made with hydrographic surveys from different years and months. The spatial distribution of the net surface heat flux shows a net gain of heat over the whole northern gulf. Except for a local maximum near San Esteban Island, the largest heat gain (+110-120 W/sq m) occurs in the Ballenas and Salsipuedes channels, where strong tidal mixing produces anomalously cold sea surface temperatures (SSTs) over much of the year. The lowest heat gain occurs in the Guayamas Basin (+40-50 W/sq m), where SSTs are consistently warmer. In the relatively shallow northern basin the net surface heat flux is farily uniform, with a net annual gain of approxmately +70 W/sq m. A local minimum in heat gain (approximately +60 W/sq m) is observed over the shelf in the northwest, where spring and summer surface temperatures are particularly high. A similar minimum in heat gain over the shelf was observed in a separate study in which historical SSTs and 7 years (1979-1986) of meteorological data from Puerto Penasco were used to estimate the net surface heat flux for the northern basin. In that study, however, the heat fluxes were higher, with a gain of +100 W/sq m over the shelf and +114 W/sq m in the northern basin. These larger values are directly attributable to the higher humidities in the 1979-1986 study compared to the 1984-1985 satellite study. High humidities reduce evaporation and the associated latent heat loss, promoting a net annual heat gain. In the norther Gulf of California, however, tidal mixing appears to play a key role in the observed gain of heat. Deep mixing in the island region produces a persistent pool of cold water which is mixed horizontally by the large-scale circulation, lowering surface temperatures over most of the northern gulf. These cold SSTs decrease evaporation by reducing the saturation vapor pressure of the overlying air. As a result, heat loss is substantially reduced, even when humidities are low. By removing heat from the surface, tidal mixing alters the time scale of air-sea interaction and reduces or possibly even inhibits the formation of deep water masses via convection.

Thermocouple frequency response compensation leads to convergence of the surface renewal alpha calibration

USDA-ARS?s Scientific Manuscript database

Sensible heat flux measurements are used in conjunction with net radiation and ground heat flux measurements to determine the latent heat flux as the energy balance residual. Surface renewal is a relatively inexpensive technique for sensible heat flux estimation because it requires only a fast-resp...

Influence of water table fluctuations on subsurface methane dynamics and surface fluxes in seasonally flooded subtropical pastures.

NASA Astrophysics Data System (ADS)

Chamberlain, S.; Gomez-Casanovas, N.; Boughton, E.; Keel, E.; Walter, M. T.; Groffman, P. M.; Sparks, J. P.

2015-12-01

Seasonally flooded subtropical pastures are major sources of methane (CH4), and periodic flooding drives complex emission dynamics from these ecosystems. Understanding the mechanisms of belowground CH4 dynamics driving soil surface fluxes is needed to better understand emissions from these systems and their response to environmental change. We investigated subsurface CH4 dynamics in relation to net surface fluxes using laboratory water table manipulations and compared these results to eddy covariance-measured fluxes to link within-soil CH4 dynamics to observed ecosystem fluxes. Pronounced hysteresis was observed in ecosystem CH4 fluxes during precipitation driven flooding events. This dynamic was replicated in mesocosm experiments, with maximum CH4 fluxes observed during periods of water table recession. Hysteresis dynamics were best explained by oxygen dynamics during precipitation recharge events and the oxidation of CH4 produced in organic soil horizons during water table recession. We observed distinct CH4 dynamics between surface organic and deeper mineral soil horizons. In surface organic soil horizons, high levels of CH4 production were temporally linked to observed surface emissions. In contrast, high concentrations of CH4 observed in deeper mineral soils did not contribute to surface fluxes. Methane production potentials in surface organic soils were orders of magnitude higher than in mineral soils, suggesting that over longer flooding regimes CH4 produced in mineral horizons is unlikely to be a significant component of net surface emissions. Our results demonstrate that distinct CH4 dynamics may be stratified by depth, and flooding of the near-surface organic soils drives the high magnitude CH4 fluxes observed from subtropical pastures. These results suggest that relatively small changes in pasture water table dynamics can drive large changes in net CH4 emissions if surface organic soils remain saturated over longer time scales.

Surface Net Solar Radiation Estimated from Satellite Measurements: Comparisons with Tower Observations

NASA Technical Reports Server (NTRS)

Li, Zhanqing; Leighton, H. G.; Cess, Robert D.

1993-01-01

A parameterization that relates the reflected solar flux at the top of the atmosphere to the net solar flux at the surface in terms of only the column water vapor amount and the solar zenith angle was tested against surface observations. Net surface fluxes deduced from coincidental collocated satellite-measured radiances and from measurements from towers in Boulder during summer and near Saskatoon in winter have mean differences of about 2 W/sq m, regardless of whether the sky is clear or cloudy. Furthermore, comparisons between the net fluxes deduced from the parameterization and from surface measurements showed equally good agreement when the data were partitioned into morning and afternoon observations. This is in contrast to results from an empirical clear-sky algorithm that is unable to account adequately for the effects of clouds and that shows, at Boulder, a distinct morning to afternoon variation, which is presumably due to the predominance of different cloud types throughout the day. It is also demonstrated that the parameterization may be applied to irradiances at the top of the atmosphere that have been temporally averaged by using the temporally averaged column water vapor amount and the temporally averaged cosine of the solar zenith angle. The good agreement between the results of the parameterization and surface measurements suggests that the algorithm is a useful tool for a variety of climate studies.

Estimating surface fluxes over middle and upper streams of the Heihe River Basin with ASTER imagery

NASA Astrophysics Data System (ADS)

Ma, W.; Ma, Y.; Hu, Z.; Su, B.; Wang, J.; Ishikawa, H.

2009-06-01

Surface fluxes are important boundary conditions for climatological modeling and the Asian monsoon system. Recent availability of high-resolution, multi-band imagery from the ASTER (Advanced Space-borne Thermal Emission and Reflection Radiometer) sensor has enabled us to estimate surface fluxes to bridge the gap between local scale flux measurements using micrometeorological instruments and regional scale land-atmosphere exchanges of water and heat fluxes that are fundamental for the understanding of the water cycle in the Asian monsoon system. A Surface Energy Balance System (SEBS) method based on ASTER data and field observations has been proposed and tested for deriving net radiation flux (Rn), soil heat flux (G0), sensible heat flux (H) and latent heat flux (λ E) over heterogeneous land surface in this paper. As a case study, the methodology was applied to the experimental area of the WATER (Watershed Allied Telemetry Experimental Research), located at the mid-to-upstream sections of the Heihe River, northwest China. The ASTER data of 3 May and 4 June in 2008 was used in this paper for the case of mid-to-upstream sections of the Heihe River Basin. To validate the proposed methodology, the ground-measured land surface heat fluxes (net radiation flux (Rn), soil heat flux (G0), sensible heat flux (H) and latent heat flux (λ E)) were compared to the ASTER derived values. The results show that the derived surface variables and land surface heat fluxes in different months over the study area are in good accordance with the land surface status. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface heat fluxes using the ASTER data and filed observation over the study area.

Sea Ice, Clouds, Sunlight, and Albedo: The Umbrella Versus the Blanket

NASA Astrophysics Data System (ADS)

Perovich, D. K.

2017-12-01

The Arctic sea ice cover has undergone a major decline in recent years, with reductions in ice extent, ice thickness, and ice age. Understanding the feedbacks and forcing driving these changes is critical in improving predictions. The surface radiation budget plays a central role in summer ice melt and is governed by clouds and surface albedo. Clouds act as an umbrella reducing the downwelling shortwave, but also serve as a blanket increasing the downwelling longwave, with the surface albedo also determining the net balance. Using field observations from the SHEBA program, pairs of clear and cloudy days were selected for each month from May through September and the net radiation flux was calculated for different surface conditions and albedos. To explore the impact of albedo we calculated a break even albedo, where the net radiation for cloudy skies is the same as clear skies. For albedos larger than the break-even value the net radiation flux is smaller under clear skies compared to cloudy skies. Break-even albedos ranged from 0.30 in September to 0.58 in July. For snow covered or bare ice, clear skies always resulted in less radiative heat input. In contrast, leads always had, and ponds usually had, more radiative heat input under clear skies than cloudy skies. Snow covered ice had a net radiation flux that was negative or near zero under clear skies resulting in radiative cooling. We combined the albedo of individual ice types with the area of those ice types to calculate albedos averaged over a 50 km x 50 km area. The July case had the smallest areally averaged albedo of 0.50. This was less than the breakeven albedo, so cloudy skies had a smaller net radiation flux than clear skies. For the cases from the other four months, the areally averaged albedo was greater than the break-even albedo. The areally averaged net radiation flux was negative under clear skies for the May and September cases.

An inter-comparison of surface energy flux measurement systems used during FIFE, 1987

NASA Technical Reports Server (NTRS)

Nie, D.; Kanemasu, E. T.; Fritschen, L. J.; Weaver, H.; Smith, E. A.; Verma, S. B.; Field, R. T.; Kustas, W.; Stewart, J. B.

1990-01-01

During the first International Satellite Land Surface Climatology Program Field Experiment (FIFE-87), surface energy fluxes were measured at 22 flux sites by nine groups of scientists using different measuring systems. A rover Bowen ratio station was taken to nearly all the flux stations to serve as a reference for estimating the instrument related differences. The rover system was installed within a few meters from the host instrument of a site. Net radiation, Bowen ratio, and latent heat fluxes were compared between the rover and the host for the stations visited. Linear regression analysis was used to examine the relationship between rover measurements and host measurements. These inter-comparisons are needed to examine the influence of instrumentation on measurement uncertainty. Highly significant effects of instrument type were detected from these comparisons. Instruments of the same type showed average differences of less than 5 percent for net radiation, 10 percent for Bowen ratio, and 6 percent for latent heat flux. The corresponding average differences for different types of instruments can be up to 10, 30, and 20 percent respectively. The Didcot net radiometer gave higher net radiation while the Swissteco type showed lower values, as compared to the corrected REBS model. The 4-way components methed and the Thornswaite type give similar values to the REBS. The SERBS type Bowen ratio systems exhibit slightly lower Bowen ratios and thus higher latent heat fluxes, compared to the AZET systems. Eddy correlation systems showed slightly lower latent heat flux in comparison to the Bowen ratio systems.

Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa

NASA Astrophysics Data System (ADS)

Majozi, Nobuhle P.; Mannaerts, Chris M.; Ramoelo, Abel; Mathieu, Renaud; Nickless, Alecia; Verhoef, Wouter

2017-07-01

Flux towers provide essential terrestrial climate, water, and radiation budget information needed for environmental monitoring and evaluation of climate change impacts on ecosystems and society in general. They are also intended for calibration and validation of satellite-based Earth observation and monitoring efforts, such as assessment of evapotranspiration from land and vegetation surfaces using surface energy balance approaches. In this paper, 15 years of Skukuza eddy covariance data, i.e. from 2000 to 2014, were analysed for surface energy balance closure (EBC) and partitioning. The surface energy balance closure was evaluated using the ordinary least squares regression (OLS) of turbulent energy fluxes (sensible (H) and latent heat (LE)) against available energy (net radiation (Rn) less soil heat (G)), and the energy balance ratio (EBR). Partitioning of the surface energy during the wet and dry seasons was also investigated, as well as how it is affected by atmospheric vapour pressure deficit (VPD), and net radiation. After filtering years with low-quality data (2004-2008), our results show an overall mean EBR of 0.93. Seasonal variations of EBR also showed the wet season with 1.17 and spring (1.02) being closest to unity, with the dry season (0.70) having the highest imbalance. Nocturnal surface energy closure was very low at 0.26, and this was linked to low friction velocity during night-time, with results showing an increase in closure with increase in friction velocity. The energy partition analysis showed that sensible heat flux is the dominant portion of net radiation, especially between March and October, followed by latent heat flux, and lastly the soil heat flux, and during the wet season where latent heat flux dominated sensible heat flux. An increase in net radiation was characterized by an increase in both LE and H, with LE showing a higher rate of increase than H in the wet season, and the reverse happening during the dry season. An increase in VPD is correlated with a decrease in LE and increase in H during the wet season, and an increase in both fluxes during the dry season.

Refining surface net radiation estimates in arid and semi-arid climates of Iran

NASA Astrophysics Data System (ADS)

Golkar, Foroogh; Rossow, William B.; Sabziparvar, Ali Akbar

2018-06-01

Although the downwelling fluxes exhibit space-time scales of dependency on characteristic of atmospheric variations, especially clouds, the upward fluxes and, hence the net radiation, depends on the variation of surface properties, particularly surface skin temperature and albedo. Evapotranspiration at the land surface depends on the properties of that surface and is determined primarily by the net surface radiation, mostly absorbed solar radiation. Thus, relatively high spatial resolution net radiation data are needed for evapotranspiration studies. Moreover, in more arid environments, the diurnal variations of surface (air and skin) temperature can be large so relatively high (sub-daily) time resolution net radiation is also needed. There are a variety of radiation and surface property products available but they differ in accuracy, space-time resolution and information content. This situation motivated the current study to evaluate multiple sources of information to obtain the best net radiation estimate with the highest space-time resolution from ISCCP FD dataset. This study investigates the accuracy of the ISCCP FD and AIRS surface air and skin temperatures, as well as the ISCCP FD and MODIS surface albedos and aerosol optical depths as the leading source of uncertainty in ISCCP FD dataset. The surface air temperatures, 10-cm soil temperatures and surface solar insolation from a number of surface sites are used to judge the best combinations of data products, especially on clear days. The corresponding surface skin temperatures in ISCCP FD, although they are known to be biased somewhat high, disagreed more with AIRS measurements because of the mismatch of spatial resolutions. The effect of spatial resolution on the comparisons was confirmed using the even higher resolution MODIS surface skin temperature values. The agreement of ISCCP FD surface solar insolation with surface measurements is good (within 2.4-9.1%), but the use of MODIS aerosol optical depths as an alternative was checked and found to not improve the agreement. The MODIS surface albedos differed from the ISCCP FD values by no more than 0.02-0.07, but because these differences are mostly at longer wavelengths, they did not change the net solar radiation very much. Therefore to obtain the best estimate of surface net radiation with the best combination of spatial and temporal resolution, we developed a method to adjust the ISCCP FD surface longwave fluxes using the AIRS surface air and skin temperatures to obtain the higher spatial resolution of the latter (45 km), while retaining the 3-h time intervals of the former. Overall, the refinements reduced the ISCCP FD longwave flux magnitudes by about 25.5-42.1 W/m2 RMS (maximum difference -27.5 W/m2 for incoming longwave radiation and -59 W/m2 for outgoing longwave radiation) with the largest differences occurring at 9:00 and 12:00 UTC near local noon. Combining the ISCCP FD net shortwave radiation data and the AIRS-modified net longwave radiation data changed the total net radiation for summertime by 4.64 to 61.5 W/m2 and for wintertime by 1.06 to 41.88 W/m2 (about 11.1-39.2% of the daily mean).

Mixed Layer Temperature Budget for the Northward Propagating Summer Monsoon Intraseasonal Oscillation (MISO) in the Central Bay of Bengal

NASA Astrophysics Data System (ADS)

Girishkumar, M. S.; Joseph, J.; Thangaprakash, V. P.; Pottapinjara, V.; McPhaden, M. J.

2017-11-01

Composite analyses of mixed layer temperature (MLT) budget terms from near-surface meteorological and oceanic observations in the central Bay of Bengal are utilized to evaluate the modulation of air-sea interactions and MLT processes in response to the summer monsoon intraseasonal oscillation (MISO). For this purpose, we use moored buoy data at 15°N, 12°N, and 8°N along 90°E together with TropFlux meteorological parameters and the Ocean Surface Current Analyses Real-time (OSCAR) current product. Our analysis shows a strong cooling tendency in MLT with maximum amplitude in the central and northern BoB during the northward propagation of enhanced convective activity associated with the active phase of the MISO; conversely, warming occurs during the suppressed phase of the MISO. The surface mixed layer is generally heated during convectively inactive phases of the MISO primarily due to increased net surface heat flux into the ocean. During convectively active MISO phases, the surface mixed layer is cooled by the combined influence of net surface heat loss to the atmosphere and entrainment cooling at the base of mixed layer. The variability of net surface heat flux is primarily due to modulation of latent heat flux and shortwave radiation. Shortwave is mostly controlled by an enhancement or reduction of cloudiness during the active and inactive MISO phases and latent heat flux is mostly controlled by variations in air-sea humidity difference.

A Sensitivity Analysis of the Impact of Rain on Regional and Global Sea-Air Fluxes of CO2

PubMed Central

Shutler, J. D.; Land, P. E.; Woolf, D. K.; Quartly, G. D.

2016-01-01

The global oceans are considered a major sink of atmospheric carbon dioxide (CO2). Rain is known to alter the physical and chemical conditions at the sea surface, and thus influence the transfer of CO2 between the ocean and atmosphere. It can influence gas exchange through enhanced gas transfer velocity, the direct export of carbon from the atmosphere to the ocean, by altering the sea skin temperature, and through surface layer dilution. However, to date, very few studies quantifying these effects on global net sea-air fluxes exist. Here, we include terms for the enhanced gas transfer velocity and the direct export of carbon in calculations of the global net sea-air fluxes, using a 7-year time series of monthly global climate quality satellite remote sensing observations, model and in-situ data. The use of a non-linear relationship between the effects of rain and wind significantly reduces the estimated impact of rain-induced surface turbulence on the rate of sea-air gas transfer, when compared to a linear relationship. Nevertheless, globally, the rain enhanced gas transfer and rain induced direct export increase the estimated annual oceanic integrated net sink of CO2 by up to 6%. Regionally, the variations can be larger, with rain increasing the estimated annual net sink in the Pacific Ocean by up to 15% and altering monthly net flux by > ± 50%. Based on these analyses, the impacts of rain should be included in the uncertainty analysis of studies that estimate net sea-air fluxes of CO2 as the rain can have a considerable impact, dependent upon the region and timescale. PMID:27673683

Downwelling Longwave Fluxes at Continental Surfaces-A Comparison of Observations with GCM Simulations and Implications for the Global Land-Surface Radiation Budget.

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Prata, A. J.

1996-03-01

Previous work suggests that general circulation (global climate) models have excess net radiation at land surfaces, apparently due to overestimates in downwelling shortwave flux and underestimates in upwelling long-wave flux. Part of this excess, however, may be compensated for by an underestimate in downwelling longwave flux. Long term observations of the downwelling longwave component at several land stations in Europe, the United States, Australia, and Antarctica suggest that climate models (four are used, as in previous studies) underestimate this flux component on an annual basis by up to 10 W m2, yet with low statistical significance. It is probable that the known underestimate in boundary-layer air temperature contributes to this, as would low model cloudiness and neglect of minor gases such as methane, nitrogen oxide, and the freons. The bias in downwelling longwave flux, together with those found earlier for downwelling shortwave and upwlling long-wave fluxes, are consistent with the model bias found previously for net radiation. All annually averaged fluxes and biases are deduced for global land as a whole.

Dynamics behind warming of the southeastern Arabian Sea and its interruption based on in situ measurements

NASA Astrophysics Data System (ADS)

Mathew, Simi; Natesan, Usha; Latha, Ganesan; Venkatesan, Ramasamy

2018-05-01

A study of the inter-annual variability of the warming of the southeastern Arabian Sea (SEAS) during the spring transition months was carried out from 2013 to 2015 based on in situ data from moored buoys. An attempt was made to identify the roles of the different variables in the warming of the SEAS (e.g., net heat flux, advection, entrainment, and thickness of the barrier layer during the previous northeast monsoon season). The intense freshening of the SEAS (approximately 2 PSU) occurring in each December, together with the presence of a downwelling Rossby wave, supports the formation of a thick barrier layer during the northeast monsoon season. It is known that the barrier layer thickness, varying each year, plays a major role in the spring warming of the SEAS. Interestingly, an anomalously thick barrier layer occurred during the northeast monsoon season of 2012-2013. However, the highest sea surface temperature (31 °C) was recorded during the last week of April 2015, while the lowest sea surface temperature (29.7 °C) was recorded during the last week of May 2013. The mixed layer heat budget analysis during the spring transition months proved that the intense warming has been mainly supported by the net heat flux, not by other factors like advection and entrainment. The inter-annual variability analysis of the net heat flux and its components, averaged over a box region of the SEAS, showed a substantial latent heat flux release and a reduction in net shortwave radiation in 2013. Both factors contributed to the negative net heat flux. Strong breaks in the warming were also observed in May due to the entrainment of cold sub-surface waters. These events are associated with the cyclonic eddy persisting over the SEAS during the same time. The entrainment term, favoring the cooling, was stronger in 2015 than that in 2013 and 2014. The surface temperatures measured in 2013 were lower than those in 2014 and 2015 despite the presence of a thick barrier layer. The substantial decrease in net heat flux along with entrainment cooling has been identified as causes for this behavior.

Surface energy budget and turbulent fluxes at Arctic terrestrial sites

NASA Astrophysics Data System (ADS)

Grachev, Andrey; Persson, Ola; Uttal, Taneil; Konopleva-Akish, Elena; Crepinsek, Sara; Cox, Christopher; Fairall, Christopher; Makshtas, Alexander; Repina, Irina

2017-04-01

Determination of the surface energy budget (SEB) and all SEB components at the air-surface interface are required in a wide variety of applications including atmosphere-land/snow simulations and validation of the surface fluxes predicted by numerical models over different spatial and temporal scales. Here, comparisons of net surface energy budgets at two Arctic sites are made using long-term near-continuous measurements of hourly averaged surface fluxes (turbulent, radiation, and soil conduction). One site, Eureka (80.0 N; Nunavut, Canada), is located in complex topography near a fjord about 200 km from the Arctic Ocean. The other site, Tiksi (71.6 N; Russian East Siberia), is located on a relatively flat coastal plain less than 1 km from the shore of Tiksi Bay, a branch of the Arctic Ocean. We first analyzed diurnal and annual cycles of basic meteorological parameters and key SEB components at these locations. Although Eureka and Tiksi are located on different continents and at different latitudes, the annual course of the surface meteorology and SEB components are qualitatively similar. Surface energy balance closure is a formulation of the conservation of energy principle. Our direct measurements of energy balance for both Arctic sites show that the sum of the turbulent sensible and latent heat fluxes and the ground (conductive) heat flux systematically underestimate the net radiation by about 25-30%. This lack of energy balance closure is a fundamental and pervasive problem in micrometeorology. We discuss a variety of factors which may be responsible for the lack of SEB closure. In particular, various storage terms (e.g., air column energy storage due to radiative and/or sensible heat flux divergence, ground heat storage above the soil flux plate, energy used in photosynthesis, canopy biomass heat storage). For example, our observations show that the photosynthesis storage term is relatively small (about 1-2% of the net radiation), but about 8-12% of the imbalance magnitude. All turbulent fluxes are highly correlated with net radiation because this balance between solar and longwave radiation is the principal energy source for daytime surface warming, evaporation, and photosynthesis. We find that turbulent fluxes of carbon dioxide and sensible heat are closely linked and, on average, change sign synchronously during the diurnal and annual cycles. The work is supported by the NOAA Climate Program Office, the U.S. National Science Foundation (NSF) with award ARC 11-07428, and by the U.S. Civilian Research & Development Foundation (CRDF) with award RUG1-2976-ST-10.

Surface Meteorological Station - ANL 10m, (1) Sonics, (1) EBBR, Physics site-3 - Raw Data

DOE Data Explorer

Muradyan, Paytsar

2017-10-23

Sonic anemometers from Physics Site-3 and Site-9 provide wind components and virtual temperature. The energy balance Bowen ratio (EBBR) station at Physics site-3 provides measurements of the surface fluxes of latent and sensible heat, net radiation, and surface soil heat flux.

Surface Meteorological Station - ANL 10m, (1) Sonic, Physics site-9 - Raw Data

DOE Data Explorer

Muradyan, Paytsar

2017-10-23

Sonic anemometers from Physics Site-3 and Site-9 provide wind components and virtual temperature. The energy balance Bowen ratio (EBBR) station at Physics site-3 provides measurements of the surface fluxes of latent and sensible heat, net radiation, and surface soil heat flux.

Surface Meteorological Station - ANL 10m, (1) Sonics, (1) EBBR, Physics site-3 - Reviewed Data

DOE Data Explorer

Muradyan, Paytsar

2018-03-14

Sonic anemometers from Physics Site-3 and Site-9 provide wind components and virtual temperature. The energy balance Bowen ratio (EBBR) station at Physics site-3 provides measurements of the surface fluxes of latent and sensible heat, net radiation, and surface soil heat flux.

Surface Meteorological Station - ANL 10m, (1) Sonic, Physics site-9 - Reviewed Data

DOE Data Explorer

Muradyan, Paytsar

2018-03-14

Sonic anemometers from Physics Site-3 and Site-9 provide wind components and virtual temperature. The energy balance Bowen ratio (EBBR) station at Physics site-3 provides measurements of the surface fluxes of latent and sensible heat, net radiation, and surface soil heat flux.

Understanding the Temporal Variation of CO2 and CH4 Fluxes in a Subtropical Seasonal Wetland

NASA Astrophysics Data System (ADS)

Gomez-Casanovas, N.; DeLucia, N.; DeLucia, E. H.; Boughton, E.; Bernacchi, C.

2017-12-01

The magnitude of the net greenhouse gas (GHG) sink strength of wetlands and mechanisms driving C fluxes remain uncertain, particularly for subtropical and tropical wetlands that are responsible for the majority of wetland CH4 emissions globally. We determined the exchange of CO2 and CH4 fluxes between a subtropical wetland and the atmosphere, and investigated how changes in water table (WT), soil temperature (ST), and Gross Primary Productivity (GPP) alter CH4 fluxes. Measurements were made using the eddy covariance technique from June, 2013 to December, 2015. As GPP was greater than ecosystem respiration, wetland was consistently a net sink of CO2 from the atmosphere (-480 gC m-2 in 2013, -275 gC m-2 in 2014 and -258 gC m-2 in 2015). Though variable among years, wetland was a net source of CH4 to the atmosphere (24.5 gC m-2 in 2013, 26.1 gC m-2 in 2014, 32.7 gC m-2 in 2015). WT and ST were strong drivers of net CH4 fluxes. Fluxes of CH4 exponentially increased with WT near the soil surface, and they were maximal and sustained after 3 days or more of preceding flooding suggesting that flooding duration and intensity drives CH4 emissions in this system. GPP also exerted a strong control on these fluxes, particularly when water was near the soil surface. The system emitted an average of 2 g more C-CH4 m-2 during the wet seasons of 2013 and 2015 than the wet season of 2014 due to higher WT, and increases in flooding days and cumulative GPP for days with water at near-surface (GPPWT). Although WT was higher during the dry season of 2015 than the wet season of 2014, CH4 fluxes were similar likely because of increased ST and GPPWT in the wet season of 2014. The contribution of CH4 fluxes during the dry season to annual fluxes was 41% in 2014 and 48% in 2015. Wetland was a strong sink of C, and it was a net sink of GHGs in 2014 and a net source in 2015 mainly attributable to increases in net CH4 emissions. Climate models predict that subtropical and tropical regions will experience more frequent floods and droughts as well as higher temperatures, conditions that will likely alter ecosystem attributes such as GPP. Our results indicate that CH4 emissions from subtropical wetlands will likely respond to projected changes in precipitation, temperature and productivity, substantially affecting the net GHG sink strength of these systems in future climate scenarios.

Investigation of Seepage Meter Measurements in Steady Flow and Wave Conditions.

PubMed

Russoniello, Christopher J; Michael, Holly A

2015-01-01

Water exchange between surface water and groundwater can modulate or generate ecologically important fluxes of solutes across the sediment-water interface. Seepage meters can directly measure fluid flux, but mechanical resistance and surface water dynamics may lead to inaccurate measurements. Tank experiments were conducted to determine effects of mechanical resistance on measurement efficiency and occurrence of directional asymmetry that could lead to erroneous net flux measurements. Seepage meter efficiency was high (average of 93%) and consistent for inflow and outflow under steady flow conditions. Wave effects on seepage meter measurements were investigated in a wave flume. Seepage meter net flux measurements averaged 0.08 cm/h-greater than the expected net-zero flux, but significantly less than theoretical wave-driven unidirectional discharge or recharge. Calculations of unidirectional flux from pressure measurements (Darcy flux) and theory matched well for a ratio of wave length to water depth less than 5, but not when this ratio was greater. Both were higher than seepage meter measurements of unidirectional flux made with one-way valves. Discharge averaged 23% greater than recharge in both seepage meter measurements and Darcy calculations of unidirectional flux. Removal of the collection bag reduced this net discharge. The presence of a seepage meter reduced the amplitude of pressure signals at the bed and resulted in a nearly uniform pressure distribution beneath the seepage meter. These results show that seepage meters may provide accurate measurements of both discharge and recharge under steady flow conditions and illustrate the potential measurement errors associated with dynamic wave environments. © 2014, National Ground Water Association.

Drivers of Arctic Ocean warming in CMIP5 models

NASA Astrophysics Data System (ADS)

Burgard, Clara; Notz, Dirk

2017-05-01

We investigate changes in the Arctic Ocean energy budget simulated by 26 general circulation models from the Coupled Model Intercomparison Project Phase 5 framework. Our goal is to understand whether the Arctic Ocean warming between 1961 and 2099 is primarily driven by changes in the net atmospheric surface flux or by changes in the meridional oceanic heat flux. We find that the simulated Arctic Ocean warming is driven by positive anomalies in the net atmospheric surface flux in 11 models, by positive anomalies in the meridional oceanic heat flux in 11 models, and by positive anomalies in both energy fluxes in four models. The different behaviors are mainly characterized by the different changes in meridional oceanic heat flux that lead to different changes in the turbulent heat loss to the atmosphere. The multimodel ensemble mean is hence not representative of a consensus across the models in Arctic climate projections.

SIERRA-Flux: Measuring Regional Surface Fluxes of Carbon Dioxide, Methane, and Water Vapor from an Unmanned Aircraft System

NASA Technical Reports Server (NTRS)

Fladeland; Yates, Emma Louise; Bui, Thaopaul Van; Dean-Day, Jonathan; Kolyer, Richard

2011-01-01

The Eddy-Covariance Method for quantifying surface-atmosphere fluxes is a foundational technique for measuring net ecosystem exchange and validating regional-to-global carbon cycle models. While towers or ships are the most frequent platform for measuring surface-atmosphere exchange, experiments using aircraft for flux measurements have yielded contributions to several large-scale studies including BOREAS, SMACEX, RECAB by providing local-to-regional coverage beyond towers. The low-altitude flight requirements make airborne flux measurements particularly dangerous and well suited for unmanned aircraft.

Measurement of Net Fluxes of Ammonium and Nitrate at the Surface of Barley Roots Using Ion-Selective Microelectrodes 1

PubMed Central

Henriksen, Gordon H.; Raman, D. Raj; Walker, Larry P.; Spanswick, Roger M.

1992-01-01

Net fluxes of NH4+ and NO3− into roots of 7-day-old barley (Hordeum vulgare L. cv Prato) seedlings varied both with position along the root axis and with time. These variations were not consistent between replicate plants; different roots showed unique temporal and spatial patterns of uptake. Axial scans of NH4+ and NO3− net fluxes were conducted along the apical 7 centimeters of seminal roots of intact barley seedlings in solution culture using ion-selective microelectrodes in the unstirred layer immediately external to the root surface. Theoretically derived relationships between uptake and concentration gradients, combined with experimental observations of the conditions existing in our experimental system, permitted evaluation of the contribution of bulk water flow to ion movement in the unstirred layer, as well as a measure of the spatial resolution of the microelectrode flux estimation technique. Finally, a method was adopted to assess the accuracy of this technique. PMID:16668947

Cabauw experimental results from the Project for Intercomparison of Land-Surface Parameterization Schemes

USGS Publications Warehouse

Chen, T.H.; Henderson-Sellers, A.; Milly, P.C.D.; Pitman, A.J.; Beljaars, A.C.M.; Polcher, J.; Abramopoulos, F.; Boone, A.; Chang, S.; Chen, F.; Dai, Y.; Desborough, C.E.; Dickinson, R.E.; Dumenil, L.; Ek, M.; Garratt, J.R.; Gedney, N.; Gusev, Y.M.; Kim, J.; Koster, R.; Kowalczyk, E.A.; Laval, K.; Lean, J.; Lettenmaier, D.; Liang, X.; Mahfouf, Jean-Francois; Mengelkamp, H.-T.; Mitchell, Ken; Nasonova, O.N.; Noilhan, J.; Robock, A.; Rosenzweig, C.; Schaake, J.; Schlosser, C.A.; Schulz, J.-P.; Shao, Y.; Shmakin, A.B.; Verseghy, D.L.; Wetzel, P.; Wood, E.F.; Xue, Y.; Yang, Z.-L.; Zeng, Q.

1997-01-01

In the Project for Intercomparison of Land-Surface Parameterization Schemes phase 2a experiment, meteorological data for the year 1987 from Cabauw, the Netherlands, were used as inputs to 23 land-surface flux schemes designed for use in climate and weather models. Schemes were evaluated by comparing their outputs with long-term measurements of surface sensible heat fluxes into the atmosphere and the ground, and of upward longwave radiation and total net radiative fluxes, and also comparing them with latent heat fluxes derived from a surface energy balance. Tuning of schemes by use of the observed flux data was not permitted. On an annual basis, the predicted surface radiative temperature exhibits a range of 2 K across schemes, consistent with the range of about 10 W m-2 in predicted surface net radiation. Most modeled values of monthly net radiation differ from the observations by less than the estimated maximum monthly observational error (±10 W m-2). However, modeled radiative surface temperature appears to have a systematic positive bias in most schemes; this might be explained by an error in assumed emissivity and by models' neglect of canopy thermal heterogeneity. Annual means of sensible and latent heat fluxes, into which net radiation is partitioned, have ranges across schemes of 30 W m-2 and 25 W m-2, respectively. Annual totals of evapotranspiration and runoff, into which the precipitation is partitioned, both have ranges of 315 mm. These ranges in annual heat and water fluxes were approximately halved upon exclusion of the three schemes that have no stomatal resistance under non-water-stressed conditions. Many schemes tend to underestimate latent heat flux and overestimate sensible heat flux in summer, with a reverse tendency in winter. For six schemes, root-mean-square deviations of predictions from monthly observations are less than the estimated upper bounds on observation errors (5 W m-2 for sensible heat flux and 10 W m-2 for latent heat flux). Actual runoff at the site is believed to be dominated by vertical drainage to groundwater, but several schemes produced significant amounts of runoff as overland flow or interflow. There is a range across schemes of 184 mm (40% of total pore volume) in the simulated annual mean root-zone soil moisture. Unfortunately, no measurements of soil moisture were available for model evaluation. A theoretical analysis suggested that differences in boundary conditions used in various schemes are not sufficient to explain the large variance in soil moisture. However, many of the extreme values of soil moisture could be explained in terms of the particulars of experimental setup or excessive evapotranspiration.

Cabauw Experimental Results from the Project for Intercomparison of Land-Surface Parameterization Schemes.

NASA Astrophysics Data System (ADS)

Chen, T. H.; Henderson-Sellers, A.; Milly, P. C. D.; Pitman, A. J.; Beljaars, A. C. M.; Polcher, J.; Abramopoulos, F.; Boone, A.; Chang, S.; Chen, F.; Dai, Y.; Desborough, C. E.; Dickinson, R. E.; Dümenil, L.; Ek, M.; Garratt, J. R.; Gedney, N.; Gusev, Y. M.;  Kim, J.;  Koster, R.;  Kowalczyk, E. A.;  Laval, K.;  Lean, J.;  Lettenmaier, D.;  Liang, X.;  Mahfouf, J.-F.;  Mengelkamp, H.-T.;  Mitchell, K.;  Nasonova, O. N.;  Noilhan, J.;  Robock, A.;  Rosenzweig, C.;  Schaake, J.;  Schlosser, C. A.;  Schulz, J.-P.;  Shao, Y.;  Shmakin, A. B.;  Verseghy, D. L.;  Wetzel, P.;  Wood, E. F.;  Xue, Y.;  Yang, Z.-L.;  Zeng, Q.

1997-06-01

In the Project for Intercomparison of Land-Surface Parameterization Schemes phase 2a experiment, meteorological data for the year 1987 from Cabauw, the Netherlands, were used as inputs to 23 land-surface flux schemes designed for use in climate and weather models. Schemes were evaluated by comparing their outputs with long-term measurements of surface sensible heat fluxes into the atmosphere and the ground, and of upward longwave radiation and total net radiative fluxes, and also comparing them with latent heat fluxes derived from a surface energy balance. Tuning of schemes by use of the observed flux data was not permitted. On an annual basis, the predicted surface radiative temperature exhibits a range of 2 K across schemes, consistent with the range of about 10 W m2 in predicted surface net radiation. Most modeled values of monthly net radiation differ from the observations by less than the estimated maximum monthly observational error (±10 W m2). However, modeled radiative surface temperature appears to have a systematic positive bias in most schemes; this might be explained by an error in assumed emissivity and by models' neglect of canopy thermal heterogeneity. Annual means of sensible and latent heat fluxes, into which net radiation is partitioned, have ranges across schemes of30 W m2 and 25 W m2, respectively. Annual totals of evapotranspiration and runoff, into which the precipitation is partitioned, both have ranges of 315 mm. These ranges in annual heat and water fluxes were approximately halved upon exclusion of the three schemes that have no stomatal resistance under non-water-stressed conditions. Many schemes tend to underestimate latent heat flux and overestimate sensible heat flux in summer, with a reverse tendency in winter. For six schemes, root-mean-square deviations of predictions from monthly observations are less than the estimated upper bounds on observation errors (5 W m2 for sensible heat flux and 10 W m2 for latent heat flux). Actual runoff at the site is believed to be dominated by vertical drainage to groundwater, but several schemes produced significant amounts of runoff as overland flow or interflow. There is a range across schemes of 184 mm (40% of total pore volume) in the simulated annual mean root-zone soil moisture. Unfortunately, no measurements of soil moisture were available for model evaluation. A theoretical analysis suggested that differences in boundary conditions used in various schemes are not sufficient to explain the large variance in soil moisture. However, many of the extreme values of soil moisture could be explained in terms of the particulars of experimental setup or excessive evapotranspiration.

Surface-air mercury fluxes across Western North America: A synthesis of spatial trends and controlling variables

USGS Publications Warehouse

Eckley, Chris S.; Tate, Michael T.; Lin, Che-Jen; Gustin, Mae S.; Dent, Stephen; Eagles-Smith, Collin A.; Lutz, Michelle A; Wickland, Kimberly; Wang, Bronwen; Gray, John E.; Edwards, Grant; Krabbenhoft, David P.; Smith, David

2016-01-01

Mercury (Hg) emission and deposition can occur to and from soils, and are an important component of the global atmospheric Hg budget. This paper focuses on synthesizing existing surface-air Hg flux data collected throughout the Western North American region and is part of a series of geographically focused Hg synthesis projects. A database of existing Hg flux data collected using the dynamic flux chamber (DFC) approach from almost a thousand locations was created for the Western North America region. Statistical analysis was performed on the data to identify the important variables controlling Hg fluxes and to allow spatiotemporal scaling. The results indicated that most of the variability in soil-air Hg fluxes could be explained by variations in soil-Hg concentrations, solar radiation, and soil moisture. This analysis also identified that variations in DFC methodological approaches were detectable among the field studies, with the chamber material and sampling flushing flow rate influencing the magnitude of calculated emissions. The spatiotemporal scaling of soil-air Hg fluxes identified that the largest emissions occurred from irrigated agricultural landscapes in California. Vegetation was shown to have a large impact on surface-air Hg fluxes due to both a reduction in solar radiation reaching the soil as well as from direct uptake of Hg in foliage. Despite high soil Hg emissions from some forested and other heavily vegetated regions, the net ecosystem flux (soil flux + vegetation uptake) was low. Conversely, sparsely vegetated regions showed larger net ecosystem emissions, which were similar in magnitude to atmospheric Hg deposition (except for the Mediterranean California region where soil emissions were higher). The net ecosystem flux results highlight the important role of landscape characteristics in effecting the balance between Hg sequestration and (re-)emission to the atmosphere.

Surface-Air Mercury Fluxes Across Western North America: A Synthesis of Spatial Trends and Controlling Variables.

NASA Astrophysics Data System (ADS)

Eckley, C.; Tate, M.; Lin, C. J.; Gustin, M. S.; Dent, S.; Eagles-Smith, C.; Lutz, M.; Wickland, K.; Wang, B.; Gray, J.; Edwards, G. C.; Krabbenhoft, D. P.; Smith, D. B.

2016-12-01

Mercury (Hg) emission and deposition can occur to and from soils and are an important component of the global atmospheric Hg budget. This presentation focuses on synthesizing existing surface-air Hg flux data collected throughout the Western North American region and is part of a series of geographically focused Hg synthesis projects. A database of existing Hg flux data collected using the dynamic flux chamber (DFC) approach from almost a thousand locations was created for the Western North America region. Statistical analysis was performed on the data to identify the important variables controlling Hg fluxes and to allow spatiotemporal scaling. The results indicated that most of the variability in soil-air Hg fluxes could be explained by variations in soil-Hg concentrations, solar radiation, and soil moisture. This analysis also identified that variations in DFC methodological approaches were detectable among the field studies, with the chamber material and sampling flushing flow rate influencing the magnitude of calculated emissions. The spatiotemporal scaling of soil-air Hg fluxes identified that the largest emissions occurred from irrigated agricultural landscapes in California. Vegetation was shown to have a large impact on surface-air Hg fluxes due to both a reduction in solar radiation reaching the soil as well as from direct uptake of Hg in foliage. Despite high soil Hg emissions from some forested and other heavily vegetated regions, the net ecosystem flux (soil flux + vegetation uptake) was low. Conversely, sparsely vegetated regions showed larger net ecosystem emissions, which were similar in magnitude to atmospheric Hg deposition (except for the Mediterranean California region where soil emissions were higher). The net ecosystem flux results highlight the important role of landscape characteristics in effecting the balance between Hg sequestration and (re-)emission to the atmosphere.

The Influence of a Sandy Substrate, Seagrass, or Highly Turbid Water on Albedo and Surface Heat Flux

NASA Astrophysics Data System (ADS)

Fogarty, M. C.; Fewings, M. R.; Paget, A. C.; Dierssen, H. M.

2018-01-01

Sea-surface albedo is a combination of surface-reflected and water-leaving irradiance, but water-leaving irradiance typically contributes less than 15% of the total albedo in open-ocean conditions. In coastal systems, however, the bottom substrate or suspended particulate matter can increase the amount of backscattered light, thereby increasing albedo and decreasing net shortwave surface heat flux. Here a sensitivity analysis using observations and models predicts the effect of light scattering on albedo and the net shortwave heat flux for three test cases: a bright sand bottom, a seagrass canopy, and turbid water. After scaling to the full solar shortwave spectrum, daytime average albedo for the test cases is up to 0.20 and exceeds the value of 0.05 predicted using a commonly applied parameterization. Daytime net shortwave heat flux into the water is significantly reduced, particularly for waters with bright sediments, dense horizontal seagrass canopies < 0.25 m from the sea surface, or highly turbid waters with suspended particulate matter concentration ≥ 50 g m-3. Observations of a more vertical seagrass canopy within 0.2 and 1 m of the surface indicate the increase in albedo compared to the common parameterization is negligible. Therefore, we suggest that the commonly applied albedo lookup table can be used in coastal heat flux estimates in water as shallow as 1 m unless the bottom substrate is highly reflective or the water is highly turbid. Our model results provide guidance to researchers who need to determine albedo in highly reflective or highly turbid conditions but have no direct observations.

Relationship Between Sea Surface Temperature and Surface Heat Balance Trends in the Tropical Oceans: The Crucial Role of Surface Wind Trends

NASA Astrophysics Data System (ADS)

Cook, K. H.; Vizy, E. K.; Sun, X.

2016-12-01

Multiple atmospheric and ocean reanalyses are analyzed for 1980-2015 to understand annual-mean adjustments of the surface heat balance over the tropical oceans as the climate warms. Linear trends are examined, with statistical significance evaluated. While surface heat budgets and sea surface temperatures are mutually adjusted fields, insights into the physical processes of this adjustment and the implications for temperature trends can be identified. Two second-generation reanalyses, ERA-Interim and JRA-55, agree well on the distributions and magnitudes of trends in the net heat flux from the atmosphere to the ocean. Trends in the net longwave and sensible heat fluxes are generally small, and trends in solar radiation absorbed are only influential regionally and vary among the reanalyses. The largest contribution is from latent heat flux trends. Contributions to these trends associated with surface temperature (thermal-driving), 10-m wind (dynamical-driving) and specific humidity (hydrological-driving) trends are estimated. The dynamically-driven latent heat flux dominates and explains much of the regionality of the multi-decadal heat flux trends. However, trends in the net surface heat flux alone do not match the observed SSTs trends well, indicating that the redistribution of heat within the ocean mixed layer is also important. Ocean mixed layer heat budgets in various ocean reanalyses are examined to understand this redistribution, and we again identify a crucial role for changes in the surface wind. Acceleration of the tropical easterlies is associated with strengthening of the equatorial undercurrents in both the tropical Pacific and Atlantic. In the Pacific, where the EUC is also shoaling, the result is enhanced warm-water advection into the central Pacific. This advective warming is superimposed on cooling due to enhanced evaporation and equatorial upwelling, which are also associated with wind trends, to determine the observed pattern of SST trends.

Measuring surface fluxes in CAPE

NASA Technical Reports Server (NTRS)

Kanemasu, E. T.; D-Shah, T.; Nie, Dalin

1992-01-01

Two stations (site 1612 and site 2008) were operated by the University of Georgia group from 6 July 1991 to 18 August 1991. The following data were collected continuously: surface energy fluxes (i.e., net radiation, soil heat fluxes, sensible heat flux and latent heat flux), air temperature, vapor pressure, soil temperature (at 1 cm depth), and precipitation. Canopy reflectance and light interception data were taken three times at each site between 6 July and 18 August. Soil moisture content was measured twice at each site.

Studies of the net surface radiative flux from satellite radiances during FIFE

NASA Technical Reports Server (NTRS)

Frouin, Robert

1993-01-01

Studies of the net surface radiative flux from satellite radiances during First ISLSCP Field Experiment (FIFE) are presented. Topics covered include: radiative transfer model validation; calibration of VISSR and AVHRR solar channels; development and refinement of algorithms to estimate downward solar and terrestrial irradiances at the surface, including photosynthetically available radiation (PAR) and surface albedo; verification of these algorithms using in situ measurements; production of maps of shortwave irradiance, surface albedo, and related products; analysis of the temporal variability of shortwave irradiance over the FIFE site; development of a spectroscopy technique to estimate atmospheric total water vapor amount; and study of optimum linear combinations of visible and near-infrared reflectances for estimating the fraction of PAR absorbed by plants.

Anthropogenic disturbance of element cycles at the Earth's surface.

PubMed

Sen, Indra S; Peucker-Ehrenbrink, Bernhard

2012-08-21

The extent to which humans are modifying Earth's surface chemistry can be quantified by comparing total anthropogenic element fluxes with their natural counterparts (Klee and Graedel, 2004). We quantify anthropogenic mass transfer of 77 elements from mining, fossil fuel burning, biomass burning, construction activities, and human apportionment of terrestrial net primary productivity, and compare it to natural mass transfer from terrestrial and marine net primary productivity, riverine dissolved and suspended matter fluxes to the ocean, soil erosion, eolian dust, sea-salt spray, cosmic dust, volcanic emissions, and for helium, hydrodynamic escape from the Earth's atmosphere. We introduce an approach to correct for losses during industrial processing of elements belonging to geochemically coherent groups, and explicitly incorporate uncertainties of element mass fluxes through Monte Carlo simulations. We find that at the Earth's surface anthropogenic fluxes of iridium, osmium, helium, gold, ruthenium, antimony, platinum, palladium, rhenium, rhodium and chromium currently exceed natural fluxes. For these elements mining is the major factor of anthropogenic influence, whereas petroleum burning strongly influences the surficial cycle of rhenium. Our assessment indicates that if anthropogenic contributions to soil erosion and eolian dust are considered, anthropogenic fluxes of up to 62 elements surpass their corresponding natural fluxes.

Energy transfers in internal tide generation, propagation and dissipation in the deep ocean

NASA Astrophysics Data System (ADS)

Floor, J. W.; Auclair, F.; Marsaleix, P.

The energy transfers associated with internal tide (IT) generation by a semi-diurnal surface tidal wave impinging on a supercritical meridionally uniform deep ocean ridge on the f-plane, and subsequent IT-propagation are analysed using the Boussinesq, free-surface, terrain-following ocean model Symphonie. The energy diagnostics are explicitly based on the numerical formulation of the governing equations, permitting a globally conservative, high-precision analysis of all physical and numerical/artificial energy transfers in a sub-domain with open lateral boundaries. The net primary energy balances are quantified using a moving average of length two tidal periods in a simplified control simulation using a single time-step, minimal diffusion, and a no-slip sea floor. This provides the basis for analysis of enhanced vertical and horizontal diffusion and a free-slip bottom boundary condition. After a four tidal period spin-up, the tidally averaged (net) primary energy balance in the generation region, extending ±20 km from the ridge crest, shows that the surface tidal wave loses approximately C = 720 W/m or 0.3% of the mean surface tidal energy flux (2.506 × 10 5 W/m) in traversing the ridge. This corresponds mainly to the barotropic-to-baroclinic energy conversion due to stratified flow interaction with sloping topography. Combined with a normalised net advective flux of baroclinic potential energy of 0.9 × C this causes a net local baroclinic potential energy gain of 0.72 × C and a conversion into baroclinic kinetic energy through the baroclinic buoyancy term of 1.18 × C. Tidally averaged, about 1.14 × C is radiated into the abyssal ocean through the total baroclinic flux of internal pressure associated with the IT- and background density field. This total baroclinic pressure flux is therefore not only determined by the classic linear surface-to-internal tide conversion, but also by the net advection of baroclinic (background) potential energy, indicating the importance of local processes other than linear IT-motion. In the propagation region (PR), integrated over the areas between 20 and 40 km from the ridge crest, the barotropic and baroclinic tide are decoupled. The net incoming total baroclinic pressure flux is balanced by local potential energy gain and outward baroclinic flux of potential energy associated with the total baroclinic density. The primary net energy balances are robust to changes in the vertical diffusion coefficient, whereas relatively weak horizontal diffusion significantly reduces the outward IT energy flux. Diapycnal mixing due to vertical diffusion causes an available potential energy loss of about 1% of the total domain-averaged potential energy gain, which matches {km-1}/{km}ρ0KVN2 to within 0.5%, for km linearly distributed grid-levels and constant background density ρ0, vertical diffusivity ( KV) and buoyancy frequency ( N).

Observed Screen (Air) and GCM Surface/Screen Temperatures: Implications for Outgoing Longwave Fluxes at the Surface.

NASA Astrophysics Data System (ADS)

Garratt, J. R.

1995-05-01

There is direct evidence that excess net radiation calculated in general circulation models at continental surfaces [of about 11-17 W m2 (20%-27%) on an annual ~1 is not only due to overestimates in annual incoming shortwave fluxes [of 9-18 W m2 (6%-9%)], but also to underestimates in outgoing longwave fluxes. The bias in the outgoing longwave flux is deduced from a comparison of screen-air temperature observations, available as a global climatology of mean monthly values, and model-calculated surface and screen-air temperatures. An underestimate in the screen temperature computed in general circulation models over continents, of about 3 K on an annual basis, implies an underestimate in the outgoing longwave flux, averaged in six models under study, of 11-15 W m2 (3%-4%). For a set of 22 inland stations studied previously, the residual bias on an annual basis (the residual is the net radiation minus incoming shortwave plus outgoing longwave) varies between 18 and 23 W m2 for the models considered. Additional biases in one or both of the reflected shortwave and incoming longwave components cannot be ruled out.

Sensitivity of the Tropical Pacific Ocean to Precipitation Induced Freshwater Flux

NASA Technical Reports Server (NTRS)

Yang, Song; Lau, K.-M.; Schopf, Paul S.

1999-01-01

We have performed a series of experiments using an ocean model to study the sensitivity of tropical Pacific Ocean to variations in precipitation induced freshwater fluxes. Variations in these fluxes arise from natural causes on all time scales. In addition, estimates of these fluxes are uncertain because of differences among measurement techniques. The model used is a quasi-isopycnal model, covering the Pacific from 40 S to 40 N. The surface forcing is constructed from observed wind stress, evaporation, precipitation, and surface temperature (SST) fields. The heat flux is produced with an iterative technique so as to maintain the model close to the observed climatology, but with only a weak damping to that climatology. Climatological estimates of evaporation are combined with various estimates of precipitation to determine the net surface freshwater flux. Results indicate that increased freshwater input decreases salinity as expected, but increases temperatures in the upper ocean. Using the freshwater flux estimated from the Microwave Sounding Unit leads to a warming of up to 0.6 C in the western Pacific over a case with zero net freshwater flux. SST is sensitive to the discrepancies among different precipitation observations, with root-mean-square differences in SST on the order of 0.2-0.3 C. The change in SST is more pronounced in the eastern Pacific, with differences of over 1 C found among the various precipitation products. Interannual variation in precipitation during El Nino events leads to increased warming. During the winter of 1982-83, freshwater flux accounts for about 0.4 C (approximately 10-15% of the maximum warming) of the surface warming in the central-eastern Pacific. Thus, the error of SST caused by the discrepancies in precipitation products is more than half of the SST anomaly produced by the interannual variability of observed precipitation. Further experiments, in which freshwater flux anomalies are imposed in the western, central, and eastern Pacific, show that the influence of net freshwater flux is also spatially dependent. The imposition of freshwater flux in the far western Pacific leads to a trapping of salinity anomaly to the surface layers near the equator. An identical flux imposed in the central Pacific produces deeper and off-equatorial salinity anomalies. The contrast between these two simulations is consistent with other simulations of the western Pacific barrier layer information.

Potential, Current, and Ionic Fluxes across the Isolated Retinal Pigment Epithelium and Choroid

PubMed Central

Lasansky, Arnaldo; de Fisch, Felisa W.

1966-01-01

A flux chamber was utilized for in vitro studies of a membrane formed by the retinal pigment epithelium and choroid of the eye of the toad (Bufo arenarum and Bufo marinus). A transmembrane potential of 20 to 30 mv was found, the pigment epithelium surface positive with respect to the choroidal surface. Unidirectional fluxes of chloride, sodium, potassium, and calcium were determined in the absence of an electrochemical potential difference. A net transfer of chloride from pigment epithelium to choroid accounted for a major fraction of the mean short-circuit current. A small net flux of sodium from choroid to pigment epithelium was detected in Bufo marinus. In both species of toads, however, about one-third of the mean short-circuit current remained unaccounted for. Manometric determinations of bicarbonate suggested an uptake of this ion at the epithelial surface of the membrane but did not provide evidence of a relationship between this process and the short-circuit current. PMID:5961357

The Impact of Moisture Intrusions from Lower Latitudes on Arctic Net Surface Radiative Fluxes and Sea Ice Growth in Fall and Winter

NASA Astrophysics Data System (ADS)

Hegyi, B. M.; Taylor, P. C.

2017-12-01

The fall and winter seasons mark an important period in the evolution of Arctic sea ice, where energy is transferred away from the surface to facilitate the cooling of the surface and the growth of Arctic sea ice extent and thickness. Climatologically, these seasons are characterized by distinct periods of increased and reduced surface cooling and sea ice growth. Periods of reduced sea ice growth and surface cooling are associated with cloudy conditions and the transport of warm and moist air from lower latitudes, termed moisture intrusions. In the research presented, we explore the regional and Arctic-wide impact of moisture intrusions on the surface net radiative fluxes and sea ice growth for each fall and winter season from 2000/01-2015/16, utilizing MERRA2 reanalysis data, PIOMAS sea ice thickness data, and daily CERES radiative flux data. Consistent with previous studies, we find that positive anomalies in downwelling longwave surface flux are associated with increased temperature and water vapor content in the atmospheric column contained within the moisture intrusions. Interestingly, there are periods of increased downwelling LW flux anomalies that persist for one week or longer (i.e. longer than synoptic timescales) that are associated with persistent poleward flux of warm, moist air from lower latitudes. These persistent anomalies significantly reduce the regional growth of Arctic sea ice, and may in part explain the interannual variability of fall and winter Arctic sea ice growth.

Influence of snow cover changes on surface radiation and heat balance based on the WRF model

NASA Astrophysics Data System (ADS)

Yu, Lingxue; Liu, Tingxiang; Bu, Kun; Yang, Jiuchun; Chang, Liping; Zhang, Shuwen

2017-10-01

The snow cover extent in mid-high latitude areas of the Northern Hemisphere has significantly declined corresponding to the global warming, especially since the 1970s. Snow-climate feedbacks play a critical role in regulating the global radiation balance and influencing surface heat flux exchange. However, the degree to which snow cover changes affect the radiation budget and energy balance on a regional scale and the difference between snow-climate and land use/cover change (LUCC)-climate feedbacks have been rarely studied. In this paper, we selected Heilongjiang Basin, where the snow cover has changed obviously, as our study area and used the WRF model to simulate the influences of snow cover changes on the surface radiation budget and heat balance. In the scenario simulation, the localized surface parameter data improved the accuracy by 10 % compared with the control group. The spatial and temporal analysis of the surface variables showed that the net surface radiation, sensible heat flux, Bowen ratio, temperature and percentage of snow cover were negatively correlated and that the ground heat flux and latent heat flux were positively correlated with the percentage of snow cover. The spatial analysis also showed that a significant relationship existed between the surface variables and land cover types, which was not obviously as that for snow cover changes. Finally, six typical study areas were selected to quantitatively analyse the influence of land cover types beneath the snow cover on heat absorption and transfer, which showed that when the land was snow covered, the conversion of forest to farmland can dramatically influence the net radiation and other surface variables, whereas the snow-free land showed significantly reduced influence. Furthermore, compared with typical land cover changes, e.g., the conversion of forest into farmland, the influence of snow cover changes on net radiation and sensible heat flux were 60 % higher than that of land cover changes, indicating the importance of snow cover changes in the surface-atmospheric feedback system.

A Study of Surface Temperatures, Clouds and Net Radiation

NASA Technical Reports Server (NTRS)

Dhuria, Harbans

1996-01-01

This study focused on the seasonal relationships and interactions of climate parameters such as the surface temperatures, net radiation, long wave flux, short wave flux, and clouds on a global basis. Five years of observations (December 1984 to November 1989) from the Earth Radiation Budget Experiment (ERBE) and the International Satellite Cloud Climatology Program (ISCCP) were used to study both seasonal variations and interannual variations by use of a basic radiation budget equation. In addition, the study was extended to include an analysis of the cloud forcing due El-Nino's impact on the ERBE parameters.

Recent trends (2003-2013) of land surface heat fluxes on the southern side of the central Himalayas, Nepal

NASA Astrophysics Data System (ADS)

Amatya, Pukar Man; Ma, Yaoming; Han, Cunbo; Wang, Binbin; Devkota, Lochan Prasad

2015-12-01

Novice efforts have been made in order to study the regional distribution of land surface heat fluxes on the southern side of the central Himalayas utilizing high-resolution remotely sensed products, but these have been on instantaneous scale. In this study the Surface Energy Balance System model is used to obtain annual averaged maps of the land surface heat fluxes for 11 years (2003-2013) and study their annual trends on the central Himalayan region. The maps were derived at 5 km resolution using monthly input products ranging from satellite derived to Global Land Data Assimilation System meteorological data. It was found that the net radiation flux is increasing as a result of decreasing precipitation (drier environment). The sensible heat flux did not change much except for the northwestern High Himalaya and High Mountains. In northwestern High Himalaya sensible heat flux is decreasing because of decrease in wind speed, ground-air temperature difference, and increase in winter precipitation, whereas in High Mountains it is increasing due to increase in ground-air temperature difference and high rate of deforestation. The latent heat flux has an overall increasing trend with increase more pronounced in the lower regions compared to high elevated regions. It has been reported that precipitation is decreasing with altitude in this region. Therefore, the increasing trend in latent heat flux can be attributed to increase in net radiation flux under persistent forest cover and irrigation land used for agriculture.

The Surface Energy Budget and Precipitation Efficiency for Convective Systems During TOGA, COARE, GATE, SCSMEX and ARM: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, W.-K.; Shie, C.-L.; Johnson, D; Simpson, J.; Starr, David OC. (Technical Monitor)

2002-01-01

A two-dimensional version of the Goddard Cumulus Ensemble (GCE) Model is used to simulate convective systems that developed in various geographic locations. Observed large-scale advective tendencies for potential temperature, water vapor mixing ratio, and horizontal momentum derived from field campaigns are used as the main forcing. By examining the surface energy budgets, the model results show that the two largest terms are net condensation (heating/drying) and imposed large-scale forcing (cooling/moistening) for tropical oceanic cases. These two terms arc opposite in sign, however. The contributions by net radiation and latent heat flux to the net condensation vary in these tropical cases, however. For cloud systems that developed over the South China Sea and eastern Atlantic, net radiation (cooling) accounts for about 20% or more of the net condensation. However, short-wave heating and long-wave cooling are in balance with each other for cloud systems over the West Pacific region such that the net radiation is very small. This is due to the thick anvil clouds simulated in the cloud systems over the Pacific region. Large-scale cooling exceeds large-scale moistening in the Pacific and Atlantic cases. For cloud systems over the South China Sea, however, there is more large-scale moistening than cooling even though the cloud systems developed in a very moist environment. though For three cloud systems that developed over a mid-latitude continent, the net radiation and sensible and latent heat fluxes play a much more important role. This means the accurate measurement of surface fluxes and radiation is crucial for simulating these mid-latitude cases.

Variation and significance of surface heat after the mechanical sand control of Qinghai-Tibet Railway was covered with sandy sediments

NASA Astrophysics Data System (ADS)

Xie, Shengbo; Qu, Jianjun; Mu, Yanhu; Xu, Xiangtian

Mechanical control of drifting sand used to protect the Qinghai-Tibet Railway from sand damage inevitably results in sand deposition, and the change in radiation and heat flux after the ground surface is covered with sandy sediments remains unclear. These variations were studied in this work through field observations along with laboratory analyses and tests. After the ground surface was covered with sandy sediments produced by the mechanical control of sand in the Qinghai-Tibet Railway, the reflectivity increased, and the annual average reflectivity on the surface covered with sandy sediments was higher than that without sandy sediments, with the value increasing by 0.043. Moreover, the surface shortwave radiation increased, whereas the surface net radiation decreased. The annual average value of the surface shortwave radiant flux density on the sandy sediments was higher than that without sandy sediments, with the value increasing by 7.291 W·m-2. The annual average value of the surface net radiant flux density on the sandy sediments decreased by 9.639 W·m-2 compared with that without sandy sediments. The soil heat flux also decreased, and the annual average value of the heat flux in the sandy sediments decreased by 0.375 W·m-2 compared with that without sandy sediments. These variations caused the heat source on the surface of sandy sediments underground to decrease, which is beneficial for preventing permafrost from degradation in the section of sand control of the railway.

Air-sea heat flux climatologies in the Mediterranean Sea: Surface energy balance and its consistency with ocean heat storage

NASA Astrophysics Data System (ADS)

Song, Xiangzhou; Yu, Lisan

2017-05-01

This study provides an analysis of the Mediterranean Sea surface energy budget using nine surface heat flux climatologies. The ensemble mean estimation shows that the net downward shortwave radiation (192 ± 19 W m-2) is balanced by latent heat flux (-98 ± 10 W m-2), followed by net longwave radiation (-78 ± 13 W m-2) and sensible heat flux (-13 ± 4 W m-2). The resulting net heat budget (Qnet) is 2 ± 12 W m-2 into the ocean, which appears to be warm biased. The annual-mean Qnet should be -5.6 ± 1.6 W m-2 when estimated from the observed net transport through the Strait of Gibraltar. To diagnose the uncertainty in nine Qnet climatologies, we constructed Qnet from the heat budget equation by using historic hydrological observations to determine the heat content changes and advective heat flux. We also used the Qnet from a data-assimilated global ocean state estimation as an additional reference. By comparing with the two reference Qnet estimates, we found that seven products (NCEP 1, NCEP 2, CFSR, ERA-Interim, MERRA, NOCSv2.0, and OAFlux+ISCCP) overestimate Qnet, with magnitude ranging from 6 to 27 W m-2, while two products underestimate Qnet by -6 W m-2 (JRA55) and -14 W m-2 (CORE.2). Together with the previous warm pool work of Song and Yu (2013), we show that CFSR, MERRA, NOCSv2.0, and OAFlux+ISCCP are warm-biased not only in the western Pacific warm pool but also in the Mediterranean Sea, while CORE.2 is cold-biased in both regions. The NCEP 1, 2, and ERA-Interim are cold-biased over the warm pool but warm-biased in the Mediterranean Sea.

Air-sea Exchange of Polycyclic Aromatic Hydrocarbons (PAHs), Polychlorinated Biphenyls (PCBs), Organochlorine Pesticides (OCPs) and Polybrominated Diphenyl Ethers (PBDEs) in the Mediterranean Sea

NASA Astrophysics Data System (ADS)

Lammel, G. P.; Heil, A.; Kukucka, P.; Meixner, F. X.; Mulder, M. D.; Prybilova, P.; Prokes, R.; Rusina, T. S.; Song, G. Z.; Vrana, B.

2015-12-01

The marine atmospheric environment is a receptor for persistent organic pollutants (POPs) which are advected from sources on land, primary, such as biomass burning by-products (PAHs, dioxins), and secondary, such as volatilization from contaminated soils (PCBs, pesticides). Primary sources do not exist in the marine environment, except for PAHs (ship engines) but following previous atmospheric deposition, the sea surface may turn to a secondary source by reversal of diffusive air-sea mass exchange. No monitoring is in place. We studied the vertical fluxes of a wide range of primary and secondary emitted POPs based on measurements in air and surface seawater at a remote coastal site in the eastern Mediterranean (2012). To this end, silicon rubbers were used as passive water samplers, vertical concentration gradients were determined in air and fluxes were quantified based on Eddy covariance. Diffusive air-sea exchange fluxes of hexachlorocyclohexanes (HCHs) and semivolatile PAHs were found close to phase equilibrium, except one PAH, retene, a wood burning tracer, was found seasonally net-volatilisational. Some PCBs, p,p'-DDE, penta- and hexachlorobenzene (PeCB, HCB) were mostly net-depositional, while PBDEs were net-volatilizational. Fluxes determined at a a remote coastal site ranged -33 - +2.4 µg m-2 d-1 for PAHs and -4.0 - +0.3 µg m-2 d-1for halogenated compounds (< 0 means net-deposition, > 0 means net-volatilization). It is concluded that nowadays in open seas more pollutants are undergoing reversal of the direction of air-sea exchange. Recgional fire activity records in combination with box model simulations suggest that deposition of retene during summer is followed by a reversal of air-sea exchange. The seawater surface as secondary source of pollution should be assessed based on flux measurements across seasons and over longer time periods.

Why is there net surface heating over the Antarctic Circumpolar Current?

NASA Astrophysics Data System (ADS)

Czaja, Arnaud; Marshall, John

2015-05-01

Using a combination of atmospheric reanalysis data, climate model outputs and a simple model, key mechanisms controlling net surface heating over the Southern Ocean are identified. All data sources used suggest that, in a streamline-averaged view, net surface heating over the Antarctic Circumpolar Current (ACC) is a result of net accumulation of solar radiation rather than a result of heat gain through turbulent fluxes (the latter systematically cool the upper ocean). It is proposed that the fraction of this net radiative heat gain realized as net ACC heating is set by two factors. First, the sea surface temperature at the southern edge of the ACC. Second, the relative strength of the negative heatflux feedbacks associated with evaporation at the sea surface and advection of heat by the residual flow in the oceanic mixed layer. A large advective feedback and a weak evaporative feedback maximize net ACC heating. It is shown that the present Southern Ocean and its circumpolar current are in this heating regime.

Surface Meteorological Station - ARL 2m, ancillary flux, Prineville - Reviewed Data

DOE Data Explorer

Clawson, Kirk

2017-10-23

These data contain measurements from a four-component net radiometer, as well as 2-m temperature, pressure, and relative humidity. In addition, soil moisture and temperature measurements and soil heat fluxes are included.

Surface Meteorological Station - ARL 2m, ancillary flux, Boardman - Raw Data

DOE Data Explorer

Clawson, Kirk

2017-10-23

These data contain measurements from a four-component net radiometer, as well as 2-m temperature, pressure, and relative humidity. In addition, soil moisture and temperature measurements and soil heat fluxes are included.

Surface Meteorological Station - ARL 2m, ancillary flux, Boardman - Reviewed Data

DOE Data Explorer

Clawson, Kirk

2017-10-23

These data contain measurements from a four-component net radiometer, as well as 2-m temperature, pressure, and relative humidity. In addition, soil moisture and temperature measurements and soil heat fluxes are included.

Global Surface Net-Radiation at 5 km from MODIS Terra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verma, Manish; Fisher, Joshua; Mallick, Kaniska

Reliable and fine resolution estimates of surface net-radiation are required for estimating latent and sensible heat fluxes between the land surface and the atmosphere. However, currently, fine resolution estimates of net-radiation are not available and consequently it is challenging to develop multi-year estimates of evapotranspiration at scales that can capture land surface heterogeneity and are relevant for policy and decision-making. We developed and evaluated a global net-radiation product at 5 km and 8-day resolution by combining mutually consistent atmosphere and land data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board Terra. Comparison with net-radiation measurements from 154 globally distributedmore » sites (414 site-years) from the FLUXNET and Surface Radiation budget network (SURFRAD) showed that the net-radiation product agreed well with measurements across seasons and climate types in the extratropics (Wilmott's index ranged from 0.74 for boreal to 0.63 for Mediterranean sites). Mean absolute deviation between the MODIS and measured net-radiation ranged from 38.0 ± 1.8 W.m -2 in boreal to 72.0 ± 4.1 W.m -2 in the tropical climates. The mean bias was small and constituted only 11%, 0.7%, 8.4%, 4.2%, 13.3%, and 5.4% of the mean absolute error in daytime net-radiation in boreal, Mediterranean, temperate-continental, temperate, semi-arid, and tropical climate, respectively. To assess the accuracy of the broader spatiotemporal patterns, we upscaled error-quantified MODIS net-radiation and compared it with the net-radiation estimates from the coarse spatial (1° x 1°) but high temporal resolution gridded net-radiation product from the Clouds and Earth's Radiant Energy System (CERES). Our estimates agreed closely with the net-radiation estimates from the CERES. Difference between the two was less than 10W.m -2 in 94% of the total land area. MODIS net-radiation product will be a valuable resource for the science community studying turbulent fluxes and energy budget at the Earth's surface.« less

Global Surface Net-Radiation at 5 km from MODIS Terra

DOE PAGES

Verma, Manish; Fisher, Joshua; Mallick, Kaniska; ...

2016-09-06

Reliable and fine resolution estimates of surface net-radiation are required for estimating latent and sensible heat fluxes between the land surface and the atmosphere. However, currently, fine resolution estimates of net-radiation are not available and consequently it is challenging to develop multi-year estimates of evapotranspiration at scales that can capture land surface heterogeneity and are relevant for policy and decision-making. We developed and evaluated a global net-radiation product at 5 km and 8-day resolution by combining mutually consistent atmosphere and land data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board Terra. Comparison with net-radiation measurements from 154 globally distributedmore » sites (414 site-years) from the FLUXNET and Surface Radiation budget network (SURFRAD) showed that the net-radiation product agreed well with measurements across seasons and climate types in the extratropics (Wilmott's index ranged from 0.74 for boreal to 0.63 for Mediterranean sites). Mean absolute deviation between the MODIS and measured net-radiation ranged from 38.0 ± 1.8 W.m -2 in boreal to 72.0 ± 4.1 W.m -2 in the tropical climates. The mean bias was small and constituted only 11%, 0.7%, 8.4%, 4.2%, 13.3%, and 5.4% of the mean absolute error in daytime net-radiation in boreal, Mediterranean, temperate-continental, temperate, semi-arid, and tropical climate, respectively. To assess the accuracy of the broader spatiotemporal patterns, we upscaled error-quantified MODIS net-radiation and compared it with the net-radiation estimates from the coarse spatial (1° x 1°) but high temporal resolution gridded net-radiation product from the Clouds and Earth's Radiant Energy System (CERES). Our estimates agreed closely with the net-radiation estimates from the CERES. Difference between the two was less than 10W.m -2 in 94% of the total land area. MODIS net-radiation product will be a valuable resource for the science community studying turbulent fluxes and energy budget at the Earth's surface.« less

Understanding the behavior of carbon dioxide and surface energy fluxes in semiarid Salt Lake Valley, Utah, USA

NASA Astrophysics Data System (ADS)

Ramamurthy, Prathap

This dissertation reports the findings from the Salt Lake Valley flux study. The Salt Lake Valley flux study was designed to improve our understanding of the complex land-atmosphere interactions in urban areas. The flux study used the eddy covariance technique to quantify carbon dioxide and surface energy budget in the semiarid Salt Lake Valley. Apart from quantifying fluxes, the study has also added new insight into the nature of turbulent scalar transport in urban areas and has addressed some of the complications in using Eddy Covariance technique in urban areas. As part of this experiment, eddy fluxes of CO2 and surface energy fluxes were measured at two sites, with distinct urban landforms; One site was located in a suburban neighborhood with substantial vegetative cover, prototypical of many residential neighborhoods in the valley. The other CO2 site was in a preurban surrounding that resembled the Salt Lake Valley before it was urbanized. The two sites were intentionally chosen to illustrate the impact of urbanization on CO 2 and surface energy flux cycles. Results indicate that the suburban site acted as a sink of CO2 during the midday period due to photosynthesis and acted as a source of CO2 during the evening and nighttime periods. The vegetative cover around the suburban site also had a significant impact on the surface energy fluxes. Contribution from latent heat flux was substantially high at the suburban site during the summer months compared to sensible heat. The turbulence investigation found that the general behavior of turbulence was very much influenced by local factors and the statistics did not always obey Monin-Obukhov Similarity parameters. This investigation also found that the scalar (co)spectra observed at the suburban site were characterized by multiple peaks and were different compared to (co)spectra reported over forest and crop canopies. The study also observed multiscale CO2 transport at the suburban site during the convective period. While the suburban site acted as a net sink of CO2 during the midday periods, CO2 was transported positively at lower frequencies. Also, during the evening transition period, when the site switched from a sink of CO2 to a source, the net upward transport of CO2 was cancelled by the net downward transport of CO2. This balance caused the total net transport reduce to zero. Overall this research, apart from characterizing the behavior of scalar fluxes at a suburban site in a semiarid desert city has also added some valuable insight on the complex nature of urban scalar transport.

An Analysis of Inter-annual Variability and Uncertainty of Continental Surface Heat Fluxes

NASA Astrophysics Data System (ADS)

Huang, S. Y.; Deng, Y.; Wang, J.

2016-12-01

The inter-annual variability and the corresponding uncertainty of land surface heat fluxes during the first decade of the 21st century are re-evaluated at continental scale based on the heat fluxes estimated by the maximum entropy production (MEP) model. The MEP model predicted heat fluxes are constrained by surface radiation fluxes, automatically satisfy surface energy balance, and are independent of temperature/moisture gradient, wind speed, and roughness lengths. The surface radiation fluxes and temperature data from Clouds and the Earth's Radiant Energy System and the surface specific humidity data from Modern-Era Retrospective analysis for Research and Applications were used to reproduce the global surface heat fluxes with land-cover data from the NASA Energy and Water cycle Study (NEWS). Our analysis shows that the annual means of continental latent heat fluxes have increasing trends associated with increasing trends in surface net radiative fluxes. The sensible heat fluxes also have increasing trends over most continents except for South America. Ground heat fluxes have little trends. The continental-scale analysis of the MEP fluxes are compared with other existing global surface fluxes data products and the implications of the results for inter-annual to decadal variability of regional surface energy budget are discussed.

Quantifying isentropic stratosphere-troposphere exchange of ozone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Huang; Chen, Gang; Tang, Qi

There is increased evidence that stratosphere-troposphere exchange (STE) of ozone has a significant impact on tropospheric chemistry and radiation. Traditional diagnostics of STE consider the ozone budget in the lowermost stratosphere (LMS) as a whole. However, this can only render the hemispherically integrated ozone flux and therefore does not distinguish the exchange of ozone into low latitudes from that into high latitudes. The exchange of ozone at different latitudes may have different tropospheric impacts. This present study extends the traditional approach from the entire LMS to individual isentropic layers in the LMS and therefore gives the meridional distribution of STEmore » by the latitudes where each isentropic surface intersects the tropopause. The specified dynamics version of the Whole Atmosphere Community Climate Model is used to estimate the STE ozone flux on each isentropic surface. It is found that net troposphere-to-stratosphere ozone transport occurs in low latitudes along the 350–380 K isentropic surfaces and that net stratosphere-to-troposphere ozone transport takes place in the extratropics along the 280–350 K isentropes. Particularly, the seasonal cycle of extratropical STE ozone flux in the Northern Hemisphere displays a maximum in late spring and early summer, following the seasonal migration of the upper tropospheric jet and associated isentropic mixing. Moreover, differential diabatic heating and isentropic mixing tend to induce STE ozone fluxes in opposite directions, but the net effect results in a spatiotemporal pattern similar to the STE ozone flux associated with isentropic mixing.« less

Quantifying isentropic stratosphere-troposphere exchange of ozone

DOE PAGES

Yang, Huang; Chen, Gang; Tang, Qi; ...

2016-03-25

There is increased evidence that stratosphere-troposphere exchange (STE) of ozone has a significant impact on tropospheric chemistry and radiation. Traditional diagnostics of STE consider the ozone budget in the lowermost stratosphere (LMS) as a whole. However, this can only render the hemispherically integrated ozone flux and therefore does not distinguish the exchange of ozone into low latitudes from that into high latitudes. The exchange of ozone at different latitudes may have different tropospheric impacts. This present study extends the traditional approach from the entire LMS to individual isentropic layers in the LMS and therefore gives the meridional distribution of STEmore » by the latitudes where each isentropic surface intersects the tropopause. The specified dynamics version of the Whole Atmosphere Community Climate Model is used to estimate the STE ozone flux on each isentropic surface. It is found that net troposphere-to-stratosphere ozone transport occurs in low latitudes along the 350–380 K isentropic surfaces and that net stratosphere-to-troposphere ozone transport takes place in the extratropics along the 280–350 K isentropes. Particularly, the seasonal cycle of extratropical STE ozone flux in the Northern Hemisphere displays a maximum in late spring and early summer, following the seasonal migration of the upper tropospheric jet and associated isentropic mixing. Moreover, differential diabatic heating and isentropic mixing tend to induce STE ozone fluxes in opposite directions, but the net effect results in a spatiotemporal pattern similar to the STE ozone flux associated with isentropic mixing.« less

On the energy balance closure and net radiation in complex terrain

PubMed Central

Wohlfahrt, Georg; Hammerle, Albin; Niedrist, Georg; Scholz, Katharina; Tomelleri, Enrico; Zhao, Peng

2017-01-01

In complex, sloping terrain, horizontal measurements of net radiation are not reflective of the radiative energy available for the conductive and convective heat exchange of the underlying surface. Using data from a grassland site on a mountain slope characterised by spatial heterogeneity in inclination and aspect, we tested the hypothesis that a correction of the horizontal net radiation measurements which accounts for the individual footprint contributions of the various surfaces to the measured sensible and latent heat eddy covariance fluxes will yield more realistic slope-parallel net radiation estimates compared to a correction based on the average inclination and aspect of the footprint. Our main result is that both approaches led to clear, but very similar improvements in the phase between available energy and the sum of the latent and sensible heat fluxes. As a consequence the variance in the sum of latent and sensible heat flux explained by available radiation improved by >10 %, while energy balance closure improved only slightly. This is shown to be mainly due to the average inclination and aspect corresponding largely with the inclination and aspect of the main flux source area in combination with a limited sensitivity of the slope correction to small angular differences in, particularly, inclination and aspect. We conclude with a discussion of limitations of the present approach and future research directions. PMID:28066093

Characteristics of urban-ecosystem atmosphere fluxes of CO2, CH4, N2O, and et over Denver, Colorado

USGS Publications Warehouse

Anderson, D.E.; Alvarez, C.; Thienelt, T.

2004-01-01

The characteristics of urban ecosystems fluxes of carbon dioxide, methane, nitrous oxide, and evapotranspiration (ET) over Denver, Colorado were discussed. These atmospheric fluxes were measured using a methodology that included a combination of eddy covariance sensors at two levels on a tall tower and chamber measurements at 33 locations on the soil surface. There was both strong temporal and spatial heterogeneity of fluxes owing to characteristics of natural and anthropogenic ecosystem components. Although the urban ecosystem was a net carbon dioxide source, tower-based eddy covariance measurements showed it to be a net vegetative sink during the majority of mid-say summer hours.

Surface Meteorological Station - ARL 2m, ancillary flux, Prineville - Raw Data

DOE Data Explorer

Clawson, kirk

2017-10-23

These data contain measurements from a 4-component net radiometer, as well as 2-m temperature, pressure, and relative humidity (RH). Measurements of soil moisture and temperature and soil heat fluxes also are included in the dataset.

Quantifying the Terrestrial Surface Energy Fluxes Using Remotely-Sensed Satellite Data

NASA Astrophysics Data System (ADS)

Siemann, Amanda Lynn

The dynamics of the energy fluxes between the land surface and the atmosphere drive local and regional climate and are paramount to understand the past, present, and future changes in climate. Although global reanalysis datasets, land surface models (LSMs), and climate models estimate these fluxes by simulating the physical processes involved, they merely simulate our current understanding of these processes. Global estimates of the terrestrial, surface energy fluxes based on observations allow us to capture the dynamics of the full climate system. Remotely-sensed satellite data is the source of observations of the land surface which provide the widest spatial coverage. Although net radiation and latent heat flux global, terrestrial, surface estimates based on remotely-sensed satellite data have progressed, comparable sensible heat data products and ground heat flux products have not progressed at this scale. Our primary objective is quantifying and understanding the terrestrial energy fluxes at the Earth's surface using remotely-sensed satellite data with consistent development among all energy budget components [through the land surface temperature (LST) and input meteorology], including validation of these products against in-situ data, uncertainty assessments, and long-term trend analysis. The turbulent fluxes are constrained by the available energy using the Bowen ratio of the un-constrained products to ensure energy budget closure. All final products are within uncertainty ranges of literature values, globally. When validated against the in-situ estimates, the sensible heat flux estimates using the CFSR air temperature and constrained with the products using the MODIS albedo produce estimates closest to the FLUXNET in-situ observations. Poor performance over South America is consistent with the largest uncertainties in the energy budget. From 1984-2007, the longwave upward flux increase due to the LST increase drives the net radiation decrease, and the decrease in the available energy balances the decrease in the sensible heat flux. These datasets are useful for benchmarking climate models and LSM output at the global annual scale and the regional scale subject to the regional uncertainties and performance. Future work should improve the input data, particularly the temperature gradient and Zilitinkevich empirical constant, to reduce uncertainties.

Air-surface exchange measurements of gaseous elemental mercury over naturally enriched and background terrestrial landscapes in Australia

NASA Astrophysics Data System (ADS)

Edwards, G. C.; Howard, D. A.

2012-10-01

This paper presents the first gaseous elemental mercury (GEM) air-surface exchange measurements obtained over naturally enriched and background (< 0.1 μg g-1 Hg) terrestrial landscapes in Australia. Two pilot field studies were carried out during the Australian autumn and winter periods at a copper-gold-cobalt-arsenic-mercury mineral field near Pulganbar, NSW. GEM fluxes using a dynamic flux chamber approach were measured, along with controlling environmental parameters over three naturally enriched and three background substrates. The enriched sites results showed net emission to the atmosphere and a strong correlation between flux and substrate Hg concentration, with average fluxes ranging from 14 ± 1 ng m-2 h-1 to 113 ± 6 ng m-2 h-1. Measurements at background sites showed both emission and deposition. The average Hg flux from all background sites showed an overall net emission of 0.36 ± 0.06 ng m-2 h-1. Fluxes show strong relationships with temperature, radiation, and substrate parameters. A compensation point of 2.48, representative of bare soils was determined. Comparison of the Australian data to North American data confirmed the need for Australian specific mercury air-surface exchange data representative of Australia's unique climatic conditions, vegetation types, land use patterns, and soils.

Impact of fire on global land surface air temperature and energy budget for the 20th century due to changes within ecosystems

NASA Astrophysics Data System (ADS)

Li, Fang; Lawrence, David M.; Bond-Lamberty, Ben

2017-04-01

Fire is a global phenomenon and tightly interacts with the biosphere and climate. This study provides the first quantitative assessment and understanding of fire’s influence on the global annual land surface air temperature and energy budget through its impact on terrestrial ecosystems. Fire impacts are quantified by comparing fire-on and fire-off simulations with the Community Earth System Model (CESM). Results show that, for the 20th century average, fire-induced changes in terrestrial ecosystems significantly increase global land annual mean surface air temperature by 0.18 °C, decrease surface net radiation and latent heat flux by 1.08 W m-2 and 0.99 W m-2, respectively, and have limited influence on sensible heat flux (-0.11 W m-2) and ground heat flux (+0.02 W m-2). Fire impacts are most clearly seen in the tropical savannas. Our analyses suggest that fire increases surface air temperature predominantly by reducing latent heat flux, mainly due to fire-induced damage to the vegetation canopy, and decreases net radiation primarily because fire-induced surface warming significantly increases upward surface longwave radiation. This study provides an integrated estimate of fire and induced changes in ecosystems, climate, and energy budget at a global scale, and emphasizes the importance of a consistent and integrated understanding of fire effects.

Surface Energy Exchanges during Pre-monsoon Thunderstorm Activity over a Tropical Station Kharagpur

NASA Astrophysics Data System (ADS)

Tyagi, Bhishma; Satyanarayana, A. N. V.; Rajvanshi, R. K.; Mandal, M.

2014-07-01

In the present study an attempt has been made to understand the variation of surface energy fluxes such as net radiation, sensible, latent and soil heat during different epochs of thunderstorm activity at Kharagpur. The study also focuses in delineating the difference in the surface energy budget from the days of thunderstorm activity to fair weather days in the pre-monsoon months (April and May) which is locally known as thunderstorm season. For this purpose, experimental data obtained from the Severe Thunderstorms- Observations and Regional Modeling (STORM) programme during pre-monsoon months of 2007, 2009 and 2010 at Kharagpur (22°30'N, 87°20'E), West Bengal, India are used. The present study reveals quick response, in the order of a few days, in the variations of transport of energy fluxes at soil-atmosphere interface to the upper atmosphere vis-à-vis to the occurrence of thunderstorm activity. Rise of surface sensible heat flux to the level of surface latent heat flux a day or two before the occurrence of a thunderstorm has been identified as a precursor signal for the thunderstorm occurrence over Kharagpur. Distinguishable differences are found in the partitioning of the surface energy fluxes to that of net radiation between thunderstorm and non-thunderstorm days. The present study reveals more Bowen's ratio during thunderstorm days to that of nonthunderstorm days. These results are useful in validating mesoscale model simulations of thunderstorm activity.

Analysis of Near-Surface Oceanic Measurements Obtained During the Low-Wind Component of the Coupled Boundary Layers and Air-Sea Transfer (CBLAST) Experiment

DTIC Science & Technology

2006-09-30

temperature and the upwelling IR radiative heat flux were obtained from a pyrometer . The heat fluxes are combined to compute the net heat flux into or out...sampled acoustic Doppler velocimeters (ADVs) and thermistors (Figure 1b). These measurements provide inertial-range estimates of dissipation rates...horizontal velocity at the sea surface were obtained with a “fanbeam” acoustic Doppler current profiler (ADCP), which produces spatial maps of the

Energy Balance Bowen Ratio (EBBR) Handbook

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, D. R.

2016-01-01

The Energy Balance Bowen Ratio (EBBR) system produces 30-minute estimates of the vertical fluxes of sensible and latent heat at the local surface. Flux estimates are calculated from observations of net radiation, soil surface heat flux, and the vertical gradients of temperature and relative humidity (RH). Meteorological data collected by the EBBR are used to calculate bulk aerodynamic fluxes, which are used in the Bulk Aerodynamic Technique (BA) EBBR value-added product (VAP) to replace sunrise and sunset spikes in the flux data. A unique aspect of the system is the automatic exchange mechanism (AEM), which helps to reduce errors frommore » instrument offset drift.« less

Energy Balance Bowen Ratio Station (EBBR) Handbook

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, DR

2011-02-23

The energy balance Bowen ratio (EBBR) system produces 30-minute estimates of the vertical fluxes of sensible and latent heat at the local surface. Flux estimates are calculated from observations of net radiation, soil surface heat flux, and the vertical gradients of temperature and relative humidity (RH). Meteorological data collected by the EBBR are used to calculate bulk aerodynamic fluxes, which are used in the Bulk Aerodynamic Technique (BA) EBBR value-added product (VAP) to replace sunrise and sunset spikes in the flux data. A unique aspect of the system is the automatic exchange mechanism (AEM), which helps to reduce errors frommore » instrument offset drift.« less

Tests of a robust eddy correlation system for sensible heat flux

NASA Astrophysics Data System (ADS)

Blanford, J. H.; Gay, L. W.

1992-03-01

Sensible heat flux estimates from a simple, one-propeller eddy correlation system (OPEC) were compared with those from a sonic anemometer eddy correlation system (SEC). In accordance with similarity theory, the performance of the OPEC system improved with increasing height of the sensor above the surface. Flux totals from the two systems at sites with adequate fetch were in excellent agreement after frequency response corrections were applied. The propeller system appears suitable for long periods of unattended measurement. The sensible heat flux measurements can be combined with net radiation and soil heat flux measurements to estimate latent heat as a residual in the surface energy balance.

Sustained Observations of Air-Sea Fluxes and Air-Sea Interaction at the Stratus Ocean Reference Station

NASA Astrophysics Data System (ADS)

Weller, Robert

2014-05-01

Since October 2000, a well-instrumented surface mooring has been maintained some 1,500 km west of the coast of northern Chile, roughly in the location of the climatological maximum in marine stratus clouds. Statistically significant increases in wind stress and decreases in annual net air-sea heat flux and in latent heat flux have been observed. If the increased oceanic heat loss continues, the region will within the next decade change from one of net annual heat gain by the ocean to one of neat annual heat loss. Already, annual evaporation of about 1.5 m of sea water a year acts to make the warm, salty surface layer more dense. Of interest is examining whether or not increased oceanic heat loss has the potential to change the structure of the upper ocean and potentially remove the shallow warm, salty mixed layer that now buffers the atmosphere from the interior ocean. Insights into how that warm, shallow layer is formed and maintained come from looking at oceanic response to the atmosphere at diurnal tie scales. Restratification each spring and summer is found to depend upon the occurrence of events in which the trade winds decay, allowing diurnal warming in the near-surface ocean to occur, and when the winds return resulting in a net upward step in sea surface temperature. This process is proving hard to accurately model.

An Economical Analytical Equation for the Integrated Vertical Overlap of Cumulus and Stratus

NASA Astrophysics Data System (ADS)

Park, Sungsu

2018-03-01

By extending the previously proposed heuristic parameterization, the author derived an analytical equation computing the overlap areas between the precipitation (or radiation) areas and the cloud areas in a cloud system consisting of cumulus and stratus. The new analytical equation is accurate and much more efficient than the previous heuristic equation, which suffers from the truncation error in association with the digitalization of the overlap areas. Global test simulations with the new analytical formula in an offline mode showed that the maximum cumulus overlap simulates more surface precipitation flux than the random cumulus overlap. On the other hand, the maximum stratus overlap simulates less surface precipitation flux than random stratus overlap, which is due to the increase in the evaporation rate of convective precipitation from the random to maximum stratus overlap. The independent precipitation approximation (IPA) marginally decreases the surface precipitation flux, implying that IPA works well with other parameterizations. In contrast to the net production rate of precipitation and surface precipitation flux that increase when the cumulus and stratus are maximally and randomly overlapped, respectively, the global mean net radiative cooling and longwave cloud radiative forcing (LWCF) increase when the cumulus and stratus are randomly overlapped. On the global average, the vertical cloud overlap exerts larger impacts on the precipitation flux than on the radiation flux. The radiation scheme taking the subgrid variability of water vapor between the cloud and clear portions into account substantially increases the global mean LWCF in tropical deep convection and midlatitude storm track regions.

Global fields of soil moisture and land surface evapotranspiration derived from observed precipitation and surface air temperature

NASA Technical Reports Server (NTRS)

Mintz, Y.; Walker, G. K.

1993-01-01

The global fields of normal monthly soil moisture and land surface evapotranspiration are derived with a simple water budget model that has precipitation and potential evapotranspiration as inputs. The precipitation is observed and the potential evapotranspiration is derived from the observed surface air temperature with the empirical regression equation of Thornthwaite (1954). It is shown that at locations where the net surface radiation flux has been measured, the potential evapotranspiration given by the Thornthwaite equation is in good agreement with those obtained with the radiation-based formulations of Priestley and Taylor (1972), Penman (1948), and Budyko (1956-1974), and this provides the justification for the use of the Thornthwaite equation. After deriving the global fields of soil moisture and evapotranspiration, the assumption is made that the potential evapotranspiration given by the Thornthwaite equation and by the Priestley-Taylor equation will everywhere be about the same; the inverse of the Priestley-Taylor equation is used to obtain the normal monthly global fields of net surface radiation flux minus ground heat storage. This and the derived evapotranspiration are then used in the equation for energy conservation at the surface of the earth to obtain the global fields of normal monthly sensible heat flux from the land surface to the atmosphere.

Assessment of Global Annual Atmospheric Energy Balance from Satellite Observations

NASA Technical Reports Server (NTRS)

Lin, Bing; Stackhouse, Paul; Minnis, Patrick; Wielicki, Bruce A.; Hu, Yongxiang; Sun, Wenbo; Fan, Tai-Fang (Alice); Hinkelman, Laura

2008-01-01

Global atmospheric energy balance is one of the fundamental processes for the earth's climate system. This study uses currently available satellite data sets of radiative energy at the top of atmosphere (TOA) and surface and latent and sensible heat over oceans for the year 2000 to assess the global annual energy budget. Over land, surface radiation data are used to constrain assimilated results and to force the radiation, turbulent heat, and heat storage into balance due to a lack of observation-based turbulent heat flux estimations. Global annual means of the TOA net radiation obtained from both direct measurements and calculations are close to zero. The net radiative energy fluxes into the surface and the surface latent heat transported into the atmosphere are about 113 and 86 Watts per square meter, respectively. The estimated atmospheric and surface heat imbalances are about -8 9 Watts per square meter, values that are within the uncertainties of surface radiation and sea surface turbulent flux estimates and likely systematic biases in the analyzed observations. The potential significant additional absorption of solar radiation within the atmosphere suggested by previous studies does not appear to be required to balance the energy budget the spurious heat imbalances in the current data are much smaller (about half) than those obtained previously and debated at about a decade ago. Progress in surface radiation and oceanic turbulent heat flux estimations from satellite measurements significantly reduces the bias errors in the observed global energy budgets of the climate system.

[Characteristics of water and heat fluxes and its footprint climatology on farmland in low hilly region of red soil].

PubMed

Li, Yang; Jing, Yuan Shu; Qin, Ben Ben

2017-01-01

The analysis of the characteristics and footprint climatology of farmland water and heat fluxes has great significance to strengthen regional climate resource management and improve the hydrothermal resource utilization in the region of red soil. Based on quality controlled data from large aperture scintillometer and automatic meteorological station in hilly region of red soil, this paper analyzed in detail the characteristics of farmland water and heat fluxes at different temporal scales and the corresponding source area distribution of flux measurement in the non-rainy season and crop growth period in hilly region of red soil. The results showed that the diurnal variation of water and heat fluxes showed a unimodal trend, but compared with the sunny day, the diurnal variation curves fluctuated more complicatedly on cloudy day. In the whole, either ten-day periods or month scale, the water and heat fluxes were greater in August than in September, while the net radiation flux was more distributed to latent heat exchange. The proportion of net radiation to latent heat flux decreased in September compared to August, but the sensible heat flux was vice versa. With combined effects of weather conditions (particularly wind), stability, and surface condition, the source areas of flux measurement at different temporal scales showed different distribution characteristics. Combined with the underlying surface crops, the source areas at different temporal scales also had different contribution sources.

Eddy covariance measurements of the net turbulent methane flux in the city centre - results of 2-year campaign in Łódź, Poland

NASA Astrophysics Data System (ADS)

Pawlak, Włodzimierz; Fortuniak, Krzysztof

2016-07-01

To investigate temporal variability of methane (CH4) fluxes in an urban environment, air-surface exchange fluxes of CH4 were continuously measured using eddy covariance techniques at a city-centre site in Łódź, Poland, from July 2013 to August 2015. In the immediate vicinity of the measurement site, potential methane sources include vehicle traffic, dense sewerage infrastructure and natural gas networks. Sensible and latent heat fluxes have also been measured since 2000 and carbon dioxide fluxes since 2007 at this site. Upward CH4 fluxes dominated during the measurement period, indicating that the city centre is a net source of CH4 to the troposphere. The highest monthly fluxes were observed in winter (2.0 to 2.7 g m-2 month-1) and the lowest in summer (0.8 to 1.0 g m-2 month-1). Fluxes on working days were around 6 % higher than on weekends. The cumulative flux indicates that the city centre emitted a net quantity of nearly 18 g m-2 of CH4 in 2014. Stable values of the FCO2/ FCH4 ratio in months (minimum 2.41 × 10-3, maximum 5.3 × 10-3) and the lack of a clear annual course suggest comparable magnitude of both fluxes.

A Restricted Boltzman Neural Net to Infer Carbon Uptake from OCO-2 Satellite Data

NASA Astrophysics Data System (ADS)

Halem, M.; Dorband, J. E.; Radov, A.; Barr-Dallas, M.; Gentine, P.

2015-12-01

For several decades, scientists have been using satellite observations to infer climate budgets of terrestrial carbon uptake employing inverse methods in conjunction with ecosystem models and coupled global climate models. This is an extremely important Big Data calculation today since the net annual photosynthetic carbon uptake changes annually over land and removes on average ~20% of the emissions from human contributions to atmospheric loading of CO2 from fossil fuels. Unfortunately, such calculations have large uncertainties validated with in-situ networks of measuring stations across the globe. One difficulty in using satellite data for these budget calculations is that the models need to assimilate surface fluxes of CO2 as well as soil moisture, vegatation cover and the eddy covariance of latent and sensible heat to calculate the carbon fixed in the soil while satellite spectral observations only provide near surface concentrations of CO2. In July 2014, NASA successfully launched OCO-2 which provides 3km surface measurements of CO2 over land and oceans. We have collected nearly one year of Level 2 XCO2 data from the OCO-2 satellite for 3 sites of ~200 km2 at equatorial, temperate and high latitudes. Each selected site was part of the Fluxnet or ARM system with tower stations for measuring and collecting CO2 fluxes on an hourly basis, in addition to eddy transports of the other parameters. We are also planning to acquire the 4km NDVI products from MODIS and registering the data to the 3km XCO2 footprints for the three sites. We have implemented a restricted Boltzman machine on the quantum annealing D-Wave computer, a novel deep learning neural net, to be used for training with station data to infer CO2 fluxes from collocated XCO2, MODIS vegetative land cover and MERRA reanalysis surface exchange products. We will present performance assessments of the D-Wave Boltzman machine for generating XCO2 fluxes from the OCO-2 satellite observations for the 3 sites by validating with monthly station flux data for one year as a potential assimilation input to the LIS model for obtaining the Net Ecosystem Exchange.

The imprint of surface fluxes and transport on variations in total column carbon dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keppel-Aleks, G; Wennberg, PO; Washenfelder, RA

2012-01-01

New observations of the vertically integrated CO{sub 2} mixing ratio, , from ground-based remote sensing show that variations in are primarily determined by large-scale flux patterns. They therefore provide fundamentally different information than observations made within the boundary layer, which reflect the combined influence of large-scale and local fluxes. Observations of both and CO{sub 2} concentrations in the free troposphere show that large-scale spatial gradients induce synoptic-scale temporal variations in in the Northern Hemisphere midlatitudes through horizontal advection. Rather than obscure the signature of surface fluxes on atmospheric CO{sub 2}, these synoptic-scale variationsmore » provide useful information that can be used to reveal the meridional flux distribution. We estimate the meridional gradient in from covariations in and potential temperature, {theta}, a dynamical tracer, on synoptic timescales to evaluate surface flux estimates commonly used in carbon cycle models. We find that simulations using Carnegie Ames Stanford Approach (CASA) biospheric fluxes underestimate both the seasonal cycle amplitude throughout the Northern Hemisphere midlatitudes and the meridional gradient during the growing season. Simulations using CASA net ecosystem exchange (NEE) with increased and phase-shifted boreal fluxes better fit the observations. Our simulations suggest that climatological mean CASA fluxes underestimate boreal growing season NEE (between 45-65{sup o} N) by {approx}40%. We describe the implications for this large seasonal exchange on inference of the net Northern Hemisphere terrestrial carbon sink.« less

The imprint of surface fluxes and transport on variations in total column carbon dioxide

NASA Astrophysics Data System (ADS)

Keppel-Aleks, G.; Wennberg, P. O.; Washenfelder, R. A.; Wunch, D.; Schneider, T.; Toon, G. C.; Andres, R. J.; Blavier, J.-F.; Connor, B.; Davis, K. J.; Desai, A. R.; Messerschmidt, J.; Notholt, J.; Roehl, C. M.; Sherlock, V.; Stephens, B. B.; Vay, S. A.; Wofsy, S. C.

2012-03-01

New observations of the vertically integrated CO2 mixing ratio, ⟨CO2⟩, from ground-based remote sensing show that variations in CO2⟩ are primarily determined by large-scale flux patterns. They therefore provide fundamentally different information than observations made within the boundary layer, which reflect the combined influence of large-scale and local fluxes. Observations of both ⟨CO2⟩ and CO2 concentrations in the free troposphere show that large-scale spatial gradients induce synoptic-scale temporal variations in ⟨CO2⟩ in the Northern Hemisphere midlatitudes through horizontal advection. Rather than obscure the signature of surface fluxes on atmospheric CO2, these synoptic-scale variations provide useful information that can be used to reveal the meridional flux distribution. We estimate the meridional gradient in ⟨CO2⟩ from covariations in ⟨CO2⟩ and potential temperature, θ, a dynamical tracer, on synoptic timescales to evaluate surface flux estimates commonly used in carbon cycle models. We find that simulations using Carnegie Ames Stanford Approach (CASA) biospheric fluxes underestimate both the ⟨CO2⟩ seasonal cycle amplitude throughout the Northern Hemisphere midlatitudes and the meridional gradient during the growing season. Simulations using CASA net ecosystem exchange (NEE) with increased and phase-shifted boreal fluxes better fit the observations. Our simulations suggest that climatological mean CASA fluxes underestimate boreal growing season NEE (between 45-65° N) by ~40%. We describe the implications for this large seasonal exchange on inference of the net Northern Hemisphere terrestrial carbon sink.

Heat transfer in melt ponds with convection and radiative heating: observationally-inspired modelling

NASA Astrophysics Data System (ADS)

Wells, A.; Langton, T.; Rees Jones, D. W.; Moon, W.; Kim, J. H.; Wilkinson, J.

2016-12-01

Melt ponds have key impacts on the evolution of Arctic sea ice and summer ice melt. Small changes to the energy budget can have significant consequences, with a net heat-flux perturbation of only a few Watts per square metre sufficient to explain the thinning of sea ice over recent decades. Whilst parameterisations of melt-pond thermodynamics often assume that pond temperatures remain close to the freezing point, recent in-situ observations show more complex thermal structure with significant diurnal and synoptic variability. We here consider the energy budget of melt ponds and explore the role of internal convective heat transfer in determining the thermal structure within the pond in relatively calm conditions with low winds. We quantify the energy fluxes and temperature variability using two-dimensional direct numerical simulations of convective turbulence within a melt pond, driven by internal radiative heating and surface fluxes. Our results show that the convective flow dynamics are modulated by changes to the incoming radiative flux and sensible heat flux at the pond surface. The evolving pond surface temperature controls the outgoing longwave emissions from the pond. Hence the convective flow modifies the net energy balance of a melt pond, modulating the relative fractions of the incoming heat flux that is re-emitted to the atmosphere or transferred downward into the sea ice to drive melt.

Evaluation of surface energy and radiation balance systems for FIFE

NASA Technical Reports Server (NTRS)

Fritschen, Leo J.; Qian, Ping

1988-01-01

The energy balance and radiation balance components were determined at six sites during the First International Satellite Land Surface Climatology Project Field Experiment (FIFE) conducted south of Manhattan, Kansas during the summer of 1987. The objectives were: to determine the effect of slope and aspect, throughout a growing season, on the magnitude of the surface energy balance fluxes as determined by the Energy Balance Method (EBM); to investigate the calculation of the soil heat flux density at the surface as calculated from the heat capacity and the thermal conductivity equations; and to evaluate the performance of the Surface Energy and Radiation Balance System (SERBS). A total of 17 variables were monitored at each site. They included net, solar (up and down), total hemispherical (up and down), and diffuse radiation, soil temperature and heat flux density, air and wet bulb temperature gradients, wind speed and direction, and precipitation. A preliminary analysis of the data, for the season, indicate that variables including net radiation, air temperature, vapor pressure, and wind speed were quite similar at the sites even though the sites were as much as 16 km apart and represented four cardinal slopes and the top of a ridge.

The role of global cloud climatologies in validating numerical models

NASA Technical Reports Server (NTRS)

HARSHVARDHAN

1991-01-01

Reliable estimates of the components of the surface radiation budget are important in studies of ocean-atmosphere interaction, land-atmosphere interaction, ocean circulation and in the validation of radiation schemes used in climate models. The methods currently under consideration must necessarily make certain assumptions regarding both the presence of clouds and their vertical extent. Because of the uncertainties in assumed cloudiness, all these methods involve perhaps unacceptable uncertainties. Here, a theoretical framework that avoids the explicit computation of cloud fraction and the location of cloud base in estimating the surface longwave radiation is presented. Estimates of the global surface downward fluxes and the oceanic surface net upward fluxes were made for four months (April, July, October and January) in 1985 to 1986. These estimates are based on a relationship between cloud radiative forcing at the top of the atmosphere and the surface obtained from a general circulation model. The radiation code is the version used in the UCLA/GLA general circulation model (GCM). The longwave cloud radiative forcing at the top of the atmosphere as obtained from Earth Radiation Budget Experiment (ERBE) measurements is used to compute the forcing at the surface by means of the GCM-derived relationship. This, along with clear-sky fluxes from the computations, yield maps of the downward longwave fluxes and net upward longwave fluxes at the surface. The calculated results are discussed and analyzed. The results are consistent with current meteorological knowledge and explainable on the basis of previous theoretical and observational works; therefore, it can be concluded that this method is applicable as one of the ways to obtain the surface longwave radiation fields from currently available satellite data.

Annual Cycle of Surface Longwave Radiation

NASA Technical Reports Server (NTRS)

Mlynczak, Pamela E.; Smith, G. Louis; Wilber, Anne C.; Stackhouse, Paul W.

2011-01-01

The annual cycles of upward and downward longwave fluxes at the Earth s surface are investigated by use of the NASA/GEWEX Surface Radiation Budget Data Set. Because of the immense difference between the heat capacity of land and ocean, the surface of Earth is partitioned into these two categories. Principal component analysis is used to quantify the annual cycles. Over land, the first principal component describes over 95% of the variance of the annual cycle of the upward and downward longwave fluxes. Over ocean the first term describes more than 87% of these annual cycles. Empirical orthogonal functions show the corresponding geographical distributions of these cycles. Phase plane diagrams of the annual cycles of upward longwave fluxes as a function of net shortwave flux show the thermal inertia of land and ocean.

Closing the Seasonal Ocean Surface Temperature Balance in the Eastern Tropical Oceans from Remote Sensing and Model Reanalyses

NASA Technical Reports Server (NTRS)

Roberts, J. Brent; Clayson, Carol A.

2012-01-01

The Eastern tropical ocean basins are regions of significant atmosphere-ocean interaction and are important to variability across subseasonal to decadal time scales. The numerous physical processes at play in these areas strain the abilities of coupled general circulation models to accurately reproduce observed upper ocean variability. Furthermore, limitations in the observing system of important terms in the surface temperature balance (e.g., turbulent and radiative heat fluxes, advection) introduce uncertainty into the analyses of processes controlling sea surface temperature variability. This study presents recent efforts to close the surface temperature balance through estimation of the terms in the mixed layer temperature budget using state-of-the-art remotely sensed and model-reanalysis derived products. A set of twelve net heat flux estimates constructed using combinations of radiative and turbulent heat flux products - including GEWEX-SRB, ISCCP-SRF, OAFlux, SeaFlux, among several others - are used with estimates of oceanic advection, entrainment, and mixed layer depth variability to investigate the seasonal variability of ocean surface temperatures. Particular emphasis is placed on how well the upper ocean temperature balance is, or is not, closed on these scales using the current generation of observational and model reanalysis products. That is, the magnitudes and spatial variability of residual imbalances are addressed. These residuals are placed into context within the current uncertainties of the surface net heat fluxes and the role of the mixed layer depth variability in scaling the impact of those uncertainties, particularly in the shallow mixed layers of the Eastern tropical ocean basins.

A quantitative determination of air-water heat fluxes in Hermit Lake, New Hampshire under varying meteorological conditions, time of day, and time of year

NASA Astrophysics Data System (ADS)

Kyper, Nicholas D.

An extensive heat flux study is performed at Hermit Lake, New Hampshire from May 26, 2010 till November 7, 2010 to determine the effects of the five individual heat fluxes on Hermit Lake and the surrounding amphibian community. Hermit Lake was chosen due to the relatively long meteorological observations record within the White Mountains of New Hampshire, a new lakeside meteorological station, and ongoing phenology studies of the surrounding eco-system. Utilizing meteorological data from the lakeside weather station and moored water temperature sensors, the incident (Qi), blackbody ( Qbnet ), latent (Qe), sensible (Q s), and net (Qn) heat fluxes are calculated. The incident heat flux is the dominate term in the net flux, accounting for 93% of the variance found in Qn and producing a heat gain of ˜ 19x108 J m-2 throughout the period of study. This large gain produces a net gain of heat in the lake until October 1, 2010, where gains by Qi are offset by the large combined losses of Qbnet , Qs, and Qe thereby producing a gradual decline of heat within the lake. The latent and blackbody heat fluxes produce the largest losses of heat in the net heat flux with a total losses of ˜ -8x108 J m-2 and ˜ -7x108 J m-2, respectively. The sensible heat flux is negligible, producing a total minimal loss of ˜ -1x108 J m-2. Overall the net heat produces a net gain of heat of 2x108 J m-2 throughout the study period. Frog calls indicative of breeding are recorded from May 26, 2010 until August 16, 2010. The spring peeper, American toad, and green frog each produced enough actively calling days to be compared to air temperature, surface water temperature, and wind speed data, as well as data from the five heat fluxes. Linear regression analysis reveals that certain water temperature thresholds affect the calling activities of the spring peeper and green frog, while higher wind speeds have a dramatic effect on the calling activities of both the green frog and American toad. All three frog species phenological activities are also affected by certain thresholds in the incident, blackbody, latent, sensible, and net heat

Seasonal reversal of temperature-moisture response of net carbon exchange of biocrusted soils in a cool desert ecosystem.

NASA Astrophysics Data System (ADS)

Tucker, C.; Reed, S.; Howell, A.

2017-12-01

Carbon cycling associated with biological soil crusts, which occur in interspaces between vascular plants in drylands globally, may be an important part of the coupled climate-carbon cycle of the Earth system. A major challenge to understanding CO2 fluxes in these systems is that much of the biotic and biogeochemical activity occurs in the upper few mm of the soil surface layer (i.e., the `mantle of fertility'), which exhibits highly dynamic and difficult to measure temperature and moisture fluctuations. Here, we report data collected in a cool desert ecosystem over one year using a multi-sensor approach to simultaneously measuring temperature and moisture of the biocrust surface layer (0-2 mm), and the deeper soil profile (5-20 cm), concurrent with automated measurement of surface soil CO2 effluxes. Our results illuminate robust relationships between microclimate and field CO2 pulses that have previously been difficult to detect and explain. The temperature of the biocrust surface layer was highly variable, ranging from minimum of -9 °C in winter to maximum of 77 °C in summer with a maximum diurnal range of 61 °C. Temperature cycles were muted deeper in the soil profile. During summer, biocrust and soils were usually hot and dry and CO2 fluxes were tightly coupled to pulse wetting events experienced at the biocrust surface, which consistently resulted in net CO2 efflux (i.e., respiration). In contrast, during the winter, biocrust and soils were usually cold and moist, and there was sustained net CO2 uptake via photosynthesis by biocrust organisms, although during cold dry periods CO2 fluxes were minimal. During the milder spring and fall seasons, short wetting events drove CO2 loss, while sustained wetting events resulted in net CO2 uptake. Thus, the upper and lower bounds of net CO2 exchange at a point in time were functions of the seasonal temperature regime, while the actual flux within those bounds was determined by the magnitude and duration of biocrust and soil wetting events. These patterns reflect both the low temperature sensitivity and slow initiation in response to wetting of photosynthesis compared to respiration by biocrust organisms. Our study highlights the importance of cool and cold periods for C uptake in biocrusted soils of the Colorado Plateau.

Net Ecosystem Fluxes of Hydrocarbons from a Ponderosa Pine Forest in Colorado

NASA Astrophysics Data System (ADS)

Rhew, R. C.; Turnipseed, A. A.; Ortega, J. V.; Smith, J. N.; Guenther, A. B.; Shen, S.; Martinez, L.; Koss, A.; Warneke, C.; De Gouw, J. A.; Deventer, M. J.

2015-12-01

Light (C2-C4) alkenes, light alkanes and isoprene (C5H8) are non-methane hydrocarbons that play important roles in the photochemical production of tropospheric ozone and in the formation of secondary organic aerosols. Natural terrestrial fluxes of the light hydrocarbons are poorly characterized, with global emission estimates based on limited field measurements. In 2014, net fluxes of these compounds were measured at the Manitou Experimental Forest Observatory, a semi-arid ponderosa pine forest in the Colorado Rocky Mountains and site of the prior BEACHON campaigns. Three field intensives were conducted between June 17 and August 10, 2014. Net ecosystem flux measurements utilized a relaxed eddy accumulation system coupled to an automated gas chromatograph. Summertime average emissions of ethene and propene were up to 90% larger than those observed from a temperate deciduous forest. Ethene and propene fluxes were also correlated to each other, similar to the deciduous forest study. Emissions of isoprene were small, as expected for a coniferous forest, and these fluxes were not correlated with either ethene or propene. Unexpected emissions of light alkanes were also observed, and these showed a distinct diurnal cycle. Understory flux measurements allowed for the partitioning of fluxes between the surface and the canopy. Full results from the three field intensives will be compared with environmental variables in order to parameterize the fluxes for use in modeling emissions.

Impact of water use efficiency on eddy covariance flux partitioning using correlation structure analysis

NASA Astrophysics Data System (ADS)

Anderson, Ray; Skaggs, Todd; Alfieri, Joseph; Kustas, William; Wang, Dong; Ayars, James

2016-04-01

Partitioned land surfaces fluxes (e.g. evaporation, transpiration, photosynthesis, and ecosystem respiration) are needed as input, calibration, and validation data for numerous hydrological and land surface models. However, one of the most commonly used techniques for measuring land surface fluxes, Eddy Covariance (EC), can directly measure net, combined water and carbon fluxes (evapotranspiration and net ecosystem exchange/productivity). Analysis of the correlation structure of high frequency EC time series (hereafter flux partitioning or FP) has been proposed to directly partition net EC fluxes into their constituent components using leaf-level water use efficiency (WUE) data to separate stomatal and non-stomatal transport processes. FP has significant logistical and spatial representativeness advantages over other partitioning approaches (e.g. isotopic fluxes, sap flow, microlysimeters), but the performance of the FP algorithm is reliant on the accuracy of the intercellular CO2 (ci) concentration used to parameterize WUE for each flux averaging interval. In this study, we tested several parameterizations for ci as a function of atmospheric CO2 (ca), including (1) a constant ci/ca ratio for C3 and C4 photosynthetic pathway plants, (2) species-specific ci/ca-Vapor Pressure Deficit (VPD) relationships (quadratic and linear), and (3) generalized C3 and C4 photosynthetic pathway ci/ca-VPD relationships. We tested these ci parameterizations at three agricultural EC towers from 2011-present in C4 and C3 crops (sugarcane - Saccharum officinarum L. and peach - Prunus persica), and validated again sap-flow sensors installed at the peach site. The peach results show that the species-specific parameterizations driven FP algorithm came to convergence significantly more frequently (~20% more frequently) than the constant ci/ca ratio or generic C3-VPD relationship. The FP algorithm parameterizations with a generic VPD relationship also had slightly higher transpiration (5 Wm-2 difference) than the constant ci/ca ratio. However, photosynthesis and respiration fluxes over sugarcane were ~15% lower with a VPD-ci/ca relationship than a constant ci/ca ratio. The results illustrate the importance of combining leaf-level physiological observations with EC to improve the performance of the FP algorithm.

Relating Cirrus Cloud Properties to Observed Fluxes: A Critical Assessment.

NASA Astrophysics Data System (ADS)

Vogelmann, A. M.; Ackerman, T. P.

1995-12-01

The accuracy needed in cirrus cloud scattering and microphysical properties is quantified such that the radiative effect on climate can he determined. Our ability to compute and observe these properties to within needed accuracies is assessed, with the greatest attention given to those properties that most affect the fluxes.Model calculations indicate that computing net longwave fluxes at the surface to within ±5% requires that cloud temperature be known to within as little as ±3 K in cold climates for extinction optical depths greater than two. Such accuracy could be more difficult to obtain than that needed in the values of scattering parameters. For a baseline case (defined in text), computing net shortwave fluxes at the surface to within ±5% requires accuracies in cloud ice water content that, when the optical depth is greater than 1.25, are beyond the accuracies of current measurements. Similarly, surface shortwave flux computations require accuracies in the asymmetry parameter that are beyond our current abilities when the optical depth is greater than four. Unless simplifications are discovered, the scattering properties needed to compute cirrus cloud fluxes cannot be obtained explicitly with existing scattering algorithms because the range of crystal sizes is too great and crystal shapes are too varied to be treated computationally. Thus, bulk cirrus scattering properties might be better obtained by inverting cirrus cloud fluxes and radiances. Finally, typical aircraft broadband flux measurements are not sufficiently accurate to provide a convincing validation of calculations. In light of these findings we recommend a reexamination of the methodology used in field programs such as FIRE and suggest a complementary approach.

The imprint of surface fluxes and transport on variations in total column carbon dioxide

NASA Astrophysics Data System (ADS)

Keppel-Aleks, G.; Wennberg, P. O.; Washenfelder, R. A.; Wunch, D.; Schneider, T.; Toon, G. C.; Andres, R. J.; Blavier, J.-F.; Connor, B.; Davis, K. J.; Desai, A. R.; Messerschmidt, J.; Notholt, J.; Roehl, C. M.; Sherlock, V.; Stephens, B. B.; Vay, S. A.; Wofsy, S. C.

2011-07-01

New observations of the vertically integrated CO2 mixing ratio, ⟨CO2⟩, from ground-based remote sensing show that variations in ⟨CO2⟩ are primarily determined by large-scale flux patterns. They therefore provide fundamentally different information than observations made within the boundary layer, which reflect the combined influence of large scale and local fluxes. Observations of both ⟨CO2⟩ and CO2 concentrations in the free troposphere show that large-scale spatial gradients induce synoptic-scale temporal variations in ⟨CO2⟩ in the Northern Hemisphere midlatitudes through horizontal advection. Rather than obscure the signature of surface fluxes on atmospheric CO2, these synoptic-scale variations provide useful information that can be used to reveal the meridional flux distribution. We estimate the meridional gradient in ⟨CO2⟩ from covariations in ⟨CO2⟩ and potential temperature, θ, a dynamical tracer, on synoptic timescales to evaluate surface flux estimates commonly used in carbon cycle models. We find that Carnegie Ames Stanford Approach (CASA) biospheric fluxes underestimate both the ⟨CO2⟩ seasonal cycle amplitude throughout the Northern Hemisphere midlatitudes as well as the meridional gradient during the growing season. Simulations using CASA net ecosystem exchange (NEE) with increased and phase-shifted boreal fluxes better reflect the observations. Our simulations suggest that boreal growing season NEE (between 45-65° N) is underestimated by ~40 % in CASA. We describe the implications for this large seasonal exchange on inference of the net Northern Hemisphere terrestrial carbon sink.

Net ecosystem exchange and energy fluxes measured with the eddy covariance technique in a western Siberian bog

NASA Astrophysics Data System (ADS)

Alekseychik, Pavel; Mammarella, Ivan; Karpov, Dmitry; Dengel, Sigrid; Terentieva, Irina; Sabrekov, Alexander; Glagolev, Mikhail; Lapshina, Elena

2017-08-01

Very few studies of ecosystem-atmosphere exchange involving eddy covariance data have been conducted in Siberia, with none in the western Siberian middle taiga. This work provides the first estimates of carbon dioxide (CO2) and energy budgets in a typical bog of the western Siberian middle taiga based on May-August measurements in 2015. The footprint of measured fluxes consisted of a homogeneous mixture of tree-covered ridges and hollows with the vegetation represented by typical sedges and shrubs. Generally, the surface exchange rates resembled those of pine-covered bogs elsewhere. The surface energy balance closure approached 100 %. Net CO2 uptake was comparatively high, summing up to 202 gC m-2 for the four measurement months, while the Bowen ratio was seasonally stable at 28 %. The ecosystem turned into a net CO2 source during several front passage events in June and July. The periods of heavy rain helped keep the water table at a sustainably high level, preventing a usual drawdown in summer. However, because of the cloudy and rainy weather, the observed fluxes might rather represent the special weather conditions of 2015 than their typical magnitudes.

The role of global cloud climatologies in validating numerical models

NASA Technical Reports Server (NTRS)

HARSHVARDHAN

1992-01-01

Global maps of the monthly mean net upward longwave radiation flux at the ocean surface were obtained for April, July, October 1985 and January 1986. These maps were produced by blending information obtained from a combination of general circulation model cloud radiative forcing fields, the top of the atmosphere cloud radiative forcing from ERBE and TOVS profiles and sea surface temperature on ISCCP C1 tapes. The fields are compatible with known meteorological regimes of atmospheric water vapor content and cloudiness. There is a vast area of high net upward longwave radiation flux (greater than 80/sq Wm) in the eastern Pacific Ocean throughout most of the year. Areas of low net upward longwave radiation flux ((less than 40/sq Wm) are the tropical convective regions and extra tropical regions that tend to have persistent low cloud cover.The technique used relies on General Circulation Model simulations and so is subject to some of the uncertainties associated with the model. However, all input information regarding temperature, moisture, and cloud cover is from satellite data having near global coverage. This feature of the procedure alone warrants its consideration for further use in compiling global maps of longwave radiation.

A global model simulation for 3-D radiative transfer impact on surface hydrology over the Sierra Nevada and Rocky Mountains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, W. -L.; Gu, Y.; Liou, K. N.

2015-05-19

We investigate 3-D mountain effects on solar flux distributions and their impact on surface hydrology over the western United States, specifically the Rocky Mountains and the Sierra Nevada, using the global CCSM4 (Community Climate System Model version 4; Community Atmosphere Model/Community Land Model – CAM4/CLM4) with a 0.23° × 0.31° resolution for simulations over 6 years. In a 3-D radiative transfer parameterization, we have updated surface topography data from a resolution of 1 km to 90 m to improve parameterization accuracy. In addition, we have also modified the upward-flux deviation (3-D–PP (plane-parallel)) adjustment to ensure that the energy balance atmore » the surface is conserved in global climate simulations based on 3-D radiation parameterization. We show that deviations in the net surface fluxes are not only affected by 3-D mountains but also influenced by feedbacks of cloud and snow in association with the long-term simulations. Deviations in sensible heat and surface temperature generally follow the patterns of net surface solar flux. The monthly snow water equivalent (SWE) deviations show an increase in lower elevations due to reduced snowmelt, leading to a reduction in cumulative runoff. Over higher-elevation areas, negative SWE deviations are found because of increased solar radiation available at the surface. Simulated precipitation increases for lower elevations, while it decreases for higher elevations, with a minimum in April. Liquid runoff significantly decreases at higher elevations after April due to reduced SWE and precipitation.« less

Boreal peatland pools C release: implication for the contemporary C exchange

NASA Astrophysics Data System (ADS)

Pelletier, L.; Strachan, I. B.; Garneau, M.; Roulet, N. T.

2013-12-01

Peatland ecosystems are considered to be net-sinks for carbon, with long-term accumulation rates ranging between 3 and 71 g C m-2 yr-1. However, the net carbon exchange rates vary significantly across the surface of these ecosystems, both in terms of magnitude and direction of the fluxes. Boreal peatlands are characterized by microforms ranging from dry hummocks, to lawns, to wet hollows and pools, which have distinct physical and chemical properties. While the hummocks and lawns absorb C due to the positive balance between gross primary production (CO2 uptake) and respiration (CO2 and CH4 release), pools represent net sources of carbon to the atmosphere. Annual pool C fluxes have been poorly documented and their contribution to the ecosystem level C budget is often ignored, even if they cover a significant portion of the peatland surface. Furthermore, the net ecosystem CO2 exchange (NEE) of these peatlands remains largely unknown. In this study, we examine the dynamics of the atmospheric exchange of CO2 and CH4 from peatland pools. Dissolved CO2 and CH4 were measured sporadically in five pools using the headspace technique and continuously with an NDIR sensor (CO2 for one pool only) over a 16-month period. Fluxes were calculated using the thin boundary layer model. We measured spring release and growing season (May to October) NEE-CO2 and CH4 fluxes in the same peatland using an eddy covariance tower to see how the presence of pools impacts the contemporary C exchange at the ecosystem level.

A study of the surface energy balance on slopes in a tallgrass prairie

NASA Technical Reports Server (NTRS)

Nie, D.; Demetriades-Shah, T.; Kanemasu, E. T.

1990-01-01

Four slopes (north, south, east, and west) were selected on the Konza Prairie Research Natural Area to study the effect of topography on surface energy balance and other micrometeorological variables. Energy fluxes, air temperature, and vapor pressure were measured on the sloped throughout the 1988 growing season. Net radiation was the highest on the south-facing slope and lowest on the north-facing slope, and the difference was more than 150 W/sq m (20 to 30 percent) at solar noon. For daily averages, the difference was 25 W/sq m (15 percent) early in the season and increased to 60 W/sq m (30 to 50 percent) in September. The east-facing and west-facing slopes had the same daily average net radiation, but the time of day when maximum net radiation occurred was one hour earlier for the east-facing slope and one hour later for the west-facing slope relative to solar noon. Soil heat fluxes were similar for all the slopes. The absolute values of sensible heat flux (h) was consistently lower on the north-facing slope compared with other slopes. Typical difference in the values of H between the north-facing and the south-facing slopes was 15 to 30 W/sq m. The south-facing slope had the greatest day to day fluctuation in latent heat flux as a result of interaction of net radiation, soil moisture, and green leaf area. The north-facing slope had higher air temperatures during the day and higher vapor pressures both during the day and at night when the wind was from the south.

Simulating the effects of fire disturbance and vegetation recovery on boreal ecosystem carbon fluxes

NASA Astrophysics Data System (ADS)

Yi, Y.; Kimball, J. S.; Jones, L. A.; Zhao, M.

2011-12-01

Fire related disturbance and subsequent vegetation recovery has a major influence on carbon storage and land-atmosphere CO2 fluxes in boreal ecosystems. We applied a synthetic approach combining tower eddy covariance flux measurements, satellite remote sensing and model reanalysis surface meteorology within a terrestrial carbon model framework to estimate fire disturbance and recovery effects on boreal ecosystem carbon fluxes including gross primary production (GPP), ecosystem respiration and net CO2 exchange (NEE). A disturbance index based on MODIS land surface temperature and NDVI was found to coincide with vegetation recovery status inferred from tower chronosequence sites. An empirical algorithm was developed to track ecosystem recovery status based on the disturbance index and used to nudge modeled net primary production (NPP) and surface soil organic carbon stocks from baseline steady-state conditions. The simulations were conducted using a satellite based terrestrial carbon flux model driven by MODIS NDVI and MERRA reanalysis daily surface meteorology inputs. The MODIS (MCD45) burned area product was then applied for mapping recent (post 2000) regional disturbance history, and used with the disturbance index to define vegetation disturbance and recovery status. The model was then applied to estimate regional patterns and temporal changes in terrestrial carbon fluxes across the entire northern boreal forest and tundra domain. A sensitivity analysis was conducted to assess the relative importance of fire disturbance and recovery on regional carbon fluxes relative to assumed steady-state conditions. The explicit representation of disturbance and recovery effects produces more accurate NEE predictions than the baseline steady-state simulations and reduces uncertainty regarding the purported missing carbon sink in the high latitudes.

Projected Impact of Climate Change on the Energy Budget of the Arctic Ocean by a Global Climate Model

NASA Technical Reports Server (NTRS)

Miller, James R.; Russell, Gary L.; Hansen, James E. (Technical Monitor)

2001-01-01

The annual energy budget of the Arctic Ocean is characterized by a net heat loss at the air-sea interface that is balanced by oceanic heat transport into the Arctic. The energy loss at the air-sea interface is due to the combined effects of radiative, sensible, and latent heat fluxes. The inflow of heat by the ocean can be divided into two components: the transport of water masses of different temperatures between the Arctic and the Atlantic and Pacific Oceans and the export of sea ice, primarily through Fram Strait. Two 150-year simulations (1950-2099) of a global climate model are used to examine how this balance might change if atmospheric greenhouse gases (GHGs) increase. One is a control simulation for the present climate with constant 1950 atmospheric composition, and the other is a transient experiment with observed GHGs from 1950 to 1990 and 0.5% annual compounded increases of CO2 after 1990. For the present climate the model agrees well with observations of radiative fluxes at the top of the atmosphere, atmospheric advective energy transport into the Arctic, and surface air temperature. It also simulates the seasonal cycle and summer increase of cloud cover and the seasonal cycle of sea-ice cover. In addition, the changes in high-latitude surface air temperature and sea-ice cover in the GHG experiment are consistent with observed changes during the last 40 and 20 years, respectively. Relative to the control, the last 50-year period of the GHG experiment indicates that even though the net annual incident solar radiation at the surface decreases by 4.6 W(per square meters) (because of greater cloud cover and increased cloud optical depth), the absorbed solar radiation increases by 2.8 W(per square meters) (because of less sea ice). Increased cloud cover and warmer air also cause increased downward thermal radiation at the surface so that the net radiation into the ocean increases by 5.0 Wm-2. The annual increase in radiation into the ocean, however, is compensated by larger increases in sensible and latent heat fluxes out of the ocean. Although the net energy loss from the ocean surface increases by 0.8 W (per square meters), this is less than the interannual variability, and the increase may not indicate a long-term trend. The seasonal cycle of heat fluxes is significantly enhanced. The downward surface heat flux increases in summer (maximum 2 of 19 W per square meters or 23% in June) while the upward heat flux increases in winter (maximum of 16 W per square meters or 28% in November). The increased downward flux in summer is due to a combination of increases in absorbed solar and thermal radiation and smaller losses of sensible and latent heat. The increased heat loss in winter is due to increased sensible and latent heat fluxes, which in turn are due to reduced sea-ice cover. On the other hand, the seasonal cycle of surface air temperature is damped, as there is a large increase in winter temperature but little change in summer.

Application of the two-source energy balance model to partition evapotranspiration in an arid wine vineyard

NASA Astrophysics Data System (ADS)

Kool, Dilia; Kustas, William P.; Agam, Nurit

2016-04-01

The partitioning of evapotranspiration (ET) into transpiration (T), a productive water use, and soil water evaporation (E), which is generally considered a water loss, is highly relevant to agriculture in the light of increasing desertification and water scarcity. This task is challenged by the complexity of soil and plant interactions, coupled with changes in atmospheric and soil water content conditions. Many of the processes controlling water/energy exchange are not adequately modeled. The two-source energy balance model (TSEB) was evaluated and adapted for independent E and T estimations in an isolated drip-irrigated wine vineyard in the arid Negev desert. The TSEB model estimates ET by computing vegetation and soil energy fluxes using remotely sensed composite surface temperature, local weather data (solar radiation, air temperature and humidity, and wind speed), and vegetation metrics (row spacing, canopy height and width, and leaf area). The soil and vegetation energy fluxes are computed numerically using a system of temperature gradient and resistance equations; where soil and canopy temperatures are derived from the composite surface temperature. For estimation of ET, the TSEB model has been shown to perform well for various agricultural crops under a wide range of environmental conditions, but validation of T and E fluxes is limited to one study in a well-watered cotton crop. Extending the TSEB approach to water-limited vineyards demands careful consideration regarding how the complex canopy structure of vineyards will influence the accuracy of the partitioning between E and T. Data for evaluation of the TSEB model were collected over a season (bud break till harvest). Composite, canopy, and soil surface temperatures were measured using infrared thermometers. The composite vegetation and soil surface energy fluxes were assessed using independent measurements of net radiation, and soil, sensible and latent heat flux. The below canopy energy balance was assessed at the dry midrow position as well as the wet irrigated position directly underneath the vine row, where net radiation and soil heat flux were measured, sensible heat flux was computed indirectly, and E was calculated as the residual. While the below canopy energy balance approach used in this study allowed continuous assessment of E at daily intervals, instantaneous E fluxes could not be assessed due to vertical variability in shading below the canopy. Seasonal partitioning indicated that total E amounted to 9-11% of ET. Initial evaluation of the TSEB model indicated that discrepancies between modeled and measured fluxes can largely be attributed to net radiation partitioning. In addition, large diurnal variation at the soil surface requires adaptation of the soil heat flux formulations. Improved estimation of energy fluxes by accounting for the relatively complex canopy structure of vineyards will be highlighted.

Oceanic Emissions and Atmospheric Depositions of Volatile Organic Compounds

NASA Astrophysics Data System (ADS)

Yang, M.; Blomquist, B.; Beale, R.; Nightingale, P. D.; Liss, P. S.

2015-12-01

Atmospheric volatile organic compounds (VOCs) affect the tropospheric oxidative capacity due to their ubiquitous abundance and relatively high reactivity towards the hydroxyal radical. Over the ocean and away from terrestrial emission sources, oxygenated volatile organic compounds (OVOCs) make up a large fraction of VOCs as airmasses age and become more oxidized. In addition to being produced or destroyed in the marine atmosphere, OVOCs can also be emitted from or deposited to the surface ocean. Here we first present direct air-sea flux measurements of three of the most abundant OVOCs - methanol, acetone, and acetaldehyde, by the eddy covariance technique from two cruises in the Atlantic: the Atlantic Meridional Transect in 2012 and the High Wind Gas Exchange Study in 2013. The OVOC mixing ratios were quantified by a high resolution proton-reaction-transfer mass spectrometer with isotopically labeled standards and their air-sea (net) fluxes were derived from the eddy covariance technique. Net methanol flux was consistently from the atmosphere to the surface ocean, while acetone varied from supersaturation (emission) in the subtropics to undersaturation (deposition) in the higher latitudes of the North Atlantic. The net air-sea flux of acetaldehyde is near zero through out the Atlantic despite the apparent supersaturation of this compound in the surface ocean. Knowing the dissolved concentrations and in situ production rates of these compounds in seawater, we then estimate their bulk atmospheric depositions and oceanic emissions. Lastly, we summarize the state of knowledge on the air-sea transport of a number of organic gasses, and postulate the magnitude and environmental impact of total organic carbon transfer between the ocean and the atmosphere.

The effects of clouds on CO2 forcing

NASA Technical Reports Server (NTRS)

Randall, David A.

1990-01-01

The cloud radiative forcing (CRF) is the difference between the radiative flux (at the top of the atmosphere) which actually occurs in the presence of clouds, and that which would occur if the clouds were removed but the atmospheric state were otherwise unchanged. The CO2 forcing is defined, in analogy with the cloud forcing, as the difference in fluxes and/or infrared heating rates obtained by instantaneously changing CO2 concentration (doubling it) without changing anything else, i.e., without allowing any feedback. An increased CO2 concentration leads to a reduced net upward longwave flux at the Earth's surface. This induced net upward flux is due to an increased downward emission by the CO2 in the atmosphere above. The negative increment to the net upward flux becomes more intense at higher levels in the troposphere, reaching a peak intensity roughly at the tropopause. It then weakens with height in the stratosphere. This profile implies a warming of the troposphere and cooling of the stratosphere. The CSU GCM was recently used to make some preliminary CO2 forcing calculations, for a single simulated, for July conditions. The longwave radiation routine was called twice, to determine the radiative fluxes and heating rates for both 2 x CO2 and 1 x CO2. As diagnostics, the 2-D distributions of the longwave fluxes at the surface and the top of atmosphere, as well as the 3-D distribution of the longwave cooling in the interior was saved. In addition, the pressure was saved (near the tropopause) where the difference in the longwave flux due to CO2 doubling has its largest magnitude. For convenience, this level is referred to as the CO2 tropopause. The actual difference in the flux at that level was also saved. Finally, all of these fields were duplicated for the hypothetical case of no cloudiness (clear sky), so that the effects of the clouds can be isolated.

Air-surface exchange measurements of gaseous elemental mercury over naturally enriched and background terrestrial landscapes in Australia

NASA Astrophysics Data System (ADS)

Edwards, G. C.; Howard, D. A.

2013-05-01

This paper presents the first gaseous elemental mercury (GEM) air-surface exchange measurements obtained over naturally enriched and background (<0.1 μg g-1 Hg) terrestrial landscapes in Australia. Two pilot field studies were carried out during the Australian autumn and winter periods at a copper-gold-cobalt-arsenic-mercury mineral field near Pulganbar, NSW. GEM fluxes using a dynamic flux chamber approach were measured, along with controlling environmental parameters over three naturally enriched and three background substrates. The enriched sites results showed net emission to the atmosphere and a strong correlation between flux and substrate Hg concentration, with average fluxes ranging from 14 ± 1 ng m-2 h-1 to 113 ± 6 ng m-2 h-1. Measurements at background sites showed both emission and deposition. The average Hg flux from all background sites showed an overall net emission of 0.36 ± 0.06 ng m-2 h-1. Fluxes show strong relationships with temperature, radiation, and substrate parameters. A compensation point of 2.48, representative of bare soils was determined. For periods of deposition, dry deposition velocities ranged from 0.00025 cm s-1 to 0.0083 cm s-1 with an average of 0.0041 ± 0.00018 cm s-1, representing bare soil, nighttime conditions. Comparison of the Australian data to North American data suggests the need for Australian-specific mercury air-surface exchange data representative of Australia's unique climatic conditions, vegetation types, land use patterns and soils.

Comparison of Radiative Energy Flows in Observational Datasets and Climate Modeling

NASA Technical Reports Server (NTRS)

Raschke, Ehrhard; Kinne, Stefan; Rossow, William B.; Stackhouse, Paul W. Jr.; Wild, Martin

2016-01-01

This study examines radiative flux distributions and local spread of values from three major observational datasets (CERES, ISCCP, and SRB) and compares them with results from climate modeling (CMIP3). Examinations of the spread and differences also differentiate among contributions from cloudy and clear-sky conditions. The spread among observational datasets is in large part caused by noncloud ancillary data. Average differences of at least 10Wm(exp -2) each for clear-sky downward solar, upward solar, and upward infrared fluxes at the surface demonstrate via spatial difference patterns major differences in assumptions for atmospheric aerosol, solar surface albedo and surface temperature, and/or emittance in observational datasets. At the top of the atmosphere (TOA), observational datasets are less influenced by the ancillary data errors than at the surface. Comparisons of spatial radiative flux distributions at the TOA between observations and climate modeling indicate large deficiencies in the strength and distribution of model-simulated cloud radiative effects. Differences are largest for lower-altitude clouds over low-latitude oceans. Global modeling simulates stronger cloud radiative effects (CRE) by +30Wmexp -2) over trade wind cumulus regions, yet smaller CRE by about -30Wm(exp -2) over (smaller in area) stratocumulus regions. At the surface, climate modeling simulates on average about 15Wm(exp -2) smaller radiative net flux imbalances, as if climate modeling underestimates latent heat release (and precipitation). Relative to observational datasets, simulated surface net fluxes are particularly lower over oceanic trade wind regions (where global modeling tends to overestimate the radiative impact of clouds). Still, with the uncertainty in noncloud ancillary data, observational data do not establish a reliable reference.

The effects of ecological restoration on CO2 fluxes from a climatically marginal upland blanket bog

NASA Astrophysics Data System (ADS)

Dixon, Simon; Qassim, Suzane; Rowson, James; Worrall, Fred; Evans, Martin

2013-04-01

A legacy of gully incision, deposition of industrially-derived aerial pollutants, inappropriate management and wildfire has left large expanses of the topographic Bleaklow Plateau (Peak District National Park, England, UK) bare of vegetation and susceptible to massive erosion of the peat soils. The consequence of such degradation has been to decrease the capacity of the peatland on the plateau to provide important ecosystem services including; loss of net C sink function, discolouration of surface waters, mobilisation to surface waters of stored heavy metals and infilling of upland reservoirs with peat-derived sediment. In response to on-going and worsening degradation a programme of ecological restoration has been undertaken. Restoration methods include: seeding with a lawn grass mix; liming; fertilisation; slope stabilisation; and gully blocking. This talk will present data from a five-year, observational-study of CO2 fluxes from eight sites, with four sites sampling different restoration treatments and four sampling bare and least disturbed areas. The results of the analysis reveal that sites with revegetation alongside slope stabilisation were most productive and were the largest net (daylight hours) sinks of CO2. Unrestored, bare sites, while having relatively low gross fluxes of CO2 were the largest net sources of CO2. Revegetation without slope stabilisation took longer (~18 months) to show an impact on CO2 flux in comparison to the sites with slope stabilisation. Binary logistic regression indicated that a ten centimetre increase in water table depth decreases the odds of observing a net CO2 sink, on a given site, by up to 30%. Sites with slope stabilisation were between 5-8x more likely to be net CO2 sinks than the bare sites. Sites without slope stabilisation were only 2-2.3x more likely to be net CO2 sinks compared to the bare sites. The most important conclusion of this research is that revegetation appears to be effective at increasing the likelihood of net CO2 behaviour on degraded, climatically marginal blanket peat, with revegetation alongside slope stabilisation having the greatest impact.

An assessment of TropFlux and NCEP air-sea fluxes on ROMS simulations over the Bay of Bengal region

NASA Astrophysics Data System (ADS)

Dey, Dipanjan; Sil, Sourav; Jana, Sudip; Pramanik, Saikat; Pandey, P. C.

2017-12-01

This study presents an assessment of the TropFlux and the National Centers for Environmental Prediction (NCEP) reanalysis air-sea fluxes in simulating the surface and subsurface oceanic parameters over the Bay of Bengal (BoB) region during 2002-2014 using the Regional Ocean Modelling System (ROMS). The assessment has been made by comparing the simulated fields with in-situ and satellite observations. The simulated surface and subsurface temperatures in the TropFlux forced experiment (TropFlux-E) show better agreement with the Research Moored Array for African-Asian-Australian Monsoon Analysis (RAMA) and Argo observations than the NCEP forced experiment (NCEP-E). The BoB domain averaged sea surface temperature (SST) simulated in the NCEP-E is consistently cooler than the satellite SST, with a root mean square error (RMSE) of 0.79 °C. Moreover, NCEP-E shows a limitation in simulating the observed seasonal cycle of the SST due to substantial underestimation of the pre-monsoon SST peak. These limitations are mostly due to the lower values of the NCEP net heat flux. The seasonal and interannual variations of SST in the TropFlux-E are better comparable to the observations with correlations and skills more than 0.80 and 0.90 respectively. However, SST is overestimated during summer monsoon periods mainly due to higher net heat flux. The superiority of TropFlux forcing over the NCEP reanalysis can also be seen when simulating the interannual variabilities of the magnitude and vertical extent of Wyrtki jets at two equatorial RAMA buoy locations. The jet is weaker in the NCEP-E relative to the TropFlux-E and observations. The simulated sea surface height anomalies (SSHA) from both the experiments are able to capture the regions of positive and negative SSHA with respect to satellite-derived altimeter data with better performance in the TropFlux-E. The speed of the westward propagating Rossby wave along 18°N in the TropFlux-E is found to be about 4.7 cm/s, which is close to the theoretical phase speed of Rossby waves.

Mapping surface energy balance components by combining Landsat Thematic Mapper and ground-based meteorological data

NASA Technical Reports Server (NTRS)

Moran, M. Susan; Jackson, Ray D.; Raymond, Lee H.; Gay, Lloyd W.; Slater, Philip N.

1989-01-01

Surface energy balance components were evaluated by combining satellite-based spectral data with on-site measurements of solar irradiance, air temperature, wind speed, and vapor pressure. Maps of latent heat flux density and net radiant flux density were produced using Landsat TM data for three dates. The TM-based estimates differed from Bowen-ratio and aircraft-based estimates by less than 12 percent over mature fields of cotton, wheat, and alfalfa.

Regional difference of the vertical structure of seasonal thermocline and its impact on sea surface temperature in the North Pacific

NASA Astrophysics Data System (ADS)

Yamaguchi, R.; Suga, T.

2016-12-01

Recent observational studies show that, during the warming season, a large amount of heat flux is penetrated through the base of thin mixed layer by vertical eddy diffusion, in addition to penetration of solar radiation [1]. In order to understand this heat penetration process due to vertical eddy diffusivity and its contribution to seasonal variation of sea surface temperature, we investigated the evolution of thermal stratification below the summertime thin mixed layer (i.e. evolution of seasonal thermocline) and its vertical structure in the North Pacific using high vertical resolution temperature profile observed by Argo floats. We quantified the vertical structure of seasonal thermocline as deviations from the linear structure where the vertical gradient of temperature is constant, that is, "shape anomaly". The shape anomaly is variable representing the extent of the bend of temperature profiles. We found that there are larger values of shape anomaly in the region where the seasonal sea surface temperature warming is relatively faster. To understand the regional difference of shape anomalies, we investigated the relationship between time changes in shape anomalies and net surface heat flux and surface kinetic energy flux. From May to July, the analysis indicated that, in a large part of North Pacific, there's a tendency for shape anomalies to develop strongly (weakly) under the conditions of large (small) downward net surface heat flux and small (large) downward surface kinetic energy flux. Since weak (strong) development of shape anomalies means efficient (inefficient) downward heat transport from the surface, these results suggest that the regional difference of the downward heat penetration below mixed layer is explained reasonably well by differences in surface heat forcing and surface wind forcing in a vertical one dimensional framework. [1] Hosoda et al. (2015), J. Oceanogr., 71, 541-556.

The relevance of rooftops: Analyzing the microscale surface energy balance in the Chicago region

NASA Astrophysics Data System (ADS)

Khosla, Radhika

Spatial structure in climate variables often exist over very short length scales within an urban area, and this structure is a result of various site-specific features. In order to analyze the seasonal and diurnal energy flows that take place at a microclimatic surface, this work develops a semi-empirical energy balance model. For this, radiation fluxes and meteorological measurements are determined by direct observation; sensible heat and latent heat fluxes by parameterizations; and the heat storage flux by a 1-D mechanistic model that allows analysis of the temperature profile and heat storage within an underlying slab. Two sites receive detailed study: an anthropogenic site, being a University of Chicago building rooftop, and a natural site, outside Chicago in the open country. Two identical sets of instruments record measurements contemporaneously from these locations during June-November 2007, the entire period for which analyses are carried out. The study yields seasonal trends in surface temperature, surface-to-air temperature contrast and net radiation. At both sites, a temporal hysteresis between net radiation and heat storage flux indicates that surplus energy absorbed during daylight is released to the atmosphere later in the evening. The surface energy balance model responds well to site specific features for both locations. An analysis of the surface energy balance shows that the flux of sensible heat is the largest non-radiative contributor to the roof's surface cooling, while the flux of latent heat (also referred to as evaporative cooling) is the largest heat sink for the soil layer. In the latter part of the study, the surface energy balance model is upgraded by adding the capability to compute changes in surface temperature and non-radiative fluxes for any specified set of thermal and reflective roof properties. The results of this analysis allow an examination of the relationship between the roof temperature, the heat flux entering the building interior through the roof, and the physical properties of the surface. These results hold particular relevance for urban heat island mitigation strategies. Based on the results of this work, recommendations are proposed for widespread adoption of various techniques that enhance building energy efficiency (particularly targeting rooftops), mitigate the negative impacts of the urban heat island, and overcome the current barriers to transforming the market.

Application of self-preservation in the diurnal evolution of the surface energy budget to determine daily evaporation

NASA Technical Reports Server (NTRS)

Brutsaert, Wilfried; Sugita, Michiaki

1992-01-01

Evaporation from natural land surfaces often exhibits a strong variation during the course of a day, mostly in response to the daily variation of radiative energy input at the surface. This makes it difficult to derive the total daily evaporation, when only one or a few instantaneous estimates of evaporation are available. It is often possible to resolve this difficulty by assuming self-preservation in the diurnal evolution of the surface energy budget. Thus if the relative partition of total incoming energy flux among the different components remains the same, the ratio of latent heat flux and any other flux component can be taken as constant through the day. This concept of constant flux ratios is tested by means of data obtained during the First ISLSCP Field Experiment; the instantaneous evaporation values were calculated by means of the atmospheric boundary layer bulk similarity approach with radiosonde profiles and radiative surface temperatures. Good results were obtained for evaporative flux ratios with available energy flux, with net radiation, and with incoming shortwave radiation.

Diurnal Variations of the Flux Imbalance Over Homogeneous and Heterogeneous Landscapes

NASA Astrophysics Data System (ADS)

Zhou, Yanzhao; Li, Dan; Liu, Heping; Li, Xin

2018-05-01

It is well known that the sum of the turbulent sensible and latent heat fluxes as measured by the eddy-covariance method is systematically lower than the available energy (i.e., the net radiation minus the ground heat flux). We examine the separate and joint effects of diurnal and spatial variations of surface temperature on this flux imbalance in a dry convective boundary layer using the Weather Research and Forecasting model. Results show that, over homogeneous surfaces, the flux due to turbulent-organized structures is responsible for the imbalance, whereas over heterogeneous surfaces, the flux due to mesoscale or secondary circulations is the main contributor to the imbalance. Over homogeneous surfaces, the flux imbalance in free convective conditions exhibits a clear diurnal cycle, showing that the flux-imbalance magnitude slowly decreases during the morning period and rapidly increases during the afternoon period. However, in shear convective conditions, the flux-imbalance magnitude is much smaller, but slightly increases with time. The flux imbalance over heterogeneous surfaces exhibits a diurnal cycle under both free and shear convective conditions, which is similar to that over homogeneous surfaces in free convective conditions, and is also consistent with the general trend in the global observations. The rapid increase in the flux-imbalance magnitude during the afternoon period is mainly caused by the afternoon decay of the turbulent kinetic energy (TKE). Interestingly, over heterogeneous surfaces, the flux imbalance is linearly related to the TKE and the difference between the potential temperature and surface temperature, ΔT; the larger the TKE and ΔT values, the smaller the flux-imbalance magnitude.

Variability in carbon dioxide fluxes for dense urban, suburban and woodland environments in southern England

NASA Astrophysics Data System (ADS)

Ward, Helen; Kotthaus, Simone; Grimmond, C. Sue; Bjorkegren, Alex; Wilkinson, Matt; Morrison, Will; Evans, Jon; Morison, James; Christen, Andreas

2014-05-01

The net exchange of carbon dioxide between the surface and atmosphere can be measured using the eddy covariance technique. Fluxes from a dense urban environment (central London), a suburban landscape (Swindon) and a woodland ecosystem (Alice Holt) are compared. All sites are located in southern England and experience similar climatic and meteorological conditions, yet have very different land cover. The signatures of anthropogenic and biogenic processes are explored at various (daily, seasonal and annual) timescales. Particular emphasis is placed on identifying the mixture of controls that determine the flux. In summer, there are clear similarities between the suburban and woodland sites, as the diurnal behaviour is dominated by photosynthetic uptake. In winter, however, vegetation is largely dormant and human activity determines the pattern of fluxes at the urban and suburban sites. Emissions from building heating augment the net release of carbon dioxide in cold months. Road use is a major contributor to the total emissions, and the diurnal cycle in the observed fluxes reflects this: in central London roads are busy throughout the day, whereas in Swindon a double-peaked rush-hour signal is evident. The net exchange of carbon dioxide is estimated for each site and set in context with other studies around the world. Central London has the smallest proportion of vegetation and largest emissions amongst study sites in the literature to date. Although Swindon's appreciable vegetation fraction helps to offset the anthropogenic emissions, even in summertime the 24h total flux is usually positive, indicating carbon release. Comparison of these three sites in a similar region demonstrates the effects of increasing urban density and changing land use on the atmosphere. Findings are relevant in terms of characterising the behaviour of urban surfaces and for quantifying the impact of anthropogenic activities.

Escape of magnetic toroids from the Sun

NASA Technical Reports Server (NTRS)

Bieber, John W.; Rust, David M.

1995-01-01

Analysis of heliospheric magnetic fields at 1 AU shows that 10(exp 24) Mx of net azimuthal flux escapes from the Sun per solar cycle. This rate is consistent with rates derived from other indicators of flux escape, including coronal mass ejections and filament eruptions. The toroidal flux escape rate is compared with the apparent rate of flux emergence at the solar surface, and it is concluded that escaping toroids will remove at least 20% of the emerging flux, and may remove as much as 100% of emerging flux if multiple eruptions occur on the toroids. The data imply that flux escapes the Sun with an efficiency far exceeding Parker's upper limit estimate of 3%. Toroidal flux escape is almost certainly the source of the observed overwinding of the interplanetary magnetic field spiral. Two mechanisms to facilitate net flux escape are discussed: helicity charging to push open the fields and flux transport with reconnection to close them off. We estimate the Sun will shed approximately 2 x 10(exp 45) of magnetic helicity per solar cycle, leading to a mean helicity density of 100 Mx(exp 2)cm(exp -3) at 1 AU, which agrees well with observations.

A study of oceanic surface heat fluxes in the Greenland, Norwegian, and Barents Seas

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa; Cavalieri, Donald J.

1989-01-01

This study examines oceanic surface heat fluxes in the Norwegian, Greenland, and Barents seas using the gridded Navy Fleet Numerical Oceanography Central surface analysis and the First GARP Global Experiment (FGGE) IIc cloudiness data bases. Monthly and annual means of net and turbulent heat fluxes are computed for the FGGE year 1979. The FGGE IIb data base consisting of individual observations provides particularly good data coverage in this region for a comparison with the gridded Navy winds and air temperatures. The standard errors of estimate between the Navy and FGGE IIb winds and air temperatures are 3.6 m/s and 2.5 C, respectively. The computations for the latent and sensible heat fluxes are based on bulk formulas with the same constant heat exchange coefficient of 0.0015. The results show extremely strong wintertime heat fluxes in the northern Greenland Sea and especially in the Barents Sea in contrast to previous studies.

Estimating the Soil Temperature Profile from a Single Depth Observation: A Simple Empirical Heatflow Solution

NASA Technical Reports Server (NTRS)

Holmes, Thomas; Owe, Manfred; deJeu, Richard

2007-01-01

Two data sets of experimental field observations with a range of meteorological conditions are used to investigate the possibility of modeling near-surface soil temperature profiles in a bare soil. It is shown that commonly used heat flow methods that assume a constant ground heat flux can not be used to model the extreme variations in temperature that occur near the surface. This paper proposes a simple approach for modeling the surface soil temperature profiles from a single depth observation. This approach consists of two parts: 1) modeling an instantaneous ground flux profile based on net radiation and the ground heat flux at 5cm depth; 2) using this ground heat flux profile to extrapolate a single temperature observation to a continuous near surface temperature profile. The new model is validated with an independent data set from a different soil and under a range of meteorological conditions.

Mass and Ozone Fluxes from the Lowermost Stratosphere

NASA Technical Reports Server (NTRS)

Schoeberl, Mark R.; Olsen, Mark A.

2004-01-01

Net mass flux from the stratosphere to the troposphere can be computed from the heating rate along the 380K isentropic surface and the time rate of change of the mass of the lowermost stratosphere (the region between the tropopause and the 380K isentrope). Given this net mass flux and the cross tropopause diabatic mass flux, the residual adiabatic mass flux across the tropopause can also be estimated. These fluxes have been computed using meteorological fields from a free-running general circulation model (FVGCM) and two assimilation data sets, FVDAS, and UKMO. The data sets tend to agree that the annual average net mass flux for the Northern Hemisphere is about 1P10 kg/s. There is less agreement on the southern Hemisphere flux that might be half as large. For all three data sets, the adiabatic mass flux is computed to be from the upper troposphere into the lowermost stratosphere. This flux will dilute air entering from higher stratospheric altitudes. The mass fluxes are convolved with ozone mixing ratios from the Goddard 3D CTM (which uses the FVGCM) to estimate the cross-tropopause transport of ozone. A relatively large adiabatic flux of tropospheric ozone from the tropical upper troposphere into the extratropical lowermost stratosphere dilutes the stratospheric air in the lowermost stratosphere. Thus, a significant fraction of any measured ozone STE may not be ozone produced in the higher Stratosphere. The results also illustrate that the annual cycle of ozone concentration in the lowermost stratosphere has as much of a role as the transport in the seasonal ozone flux cycle. This implies that a simplified calculation of ozone STE mass from air mass and a mean ozone mixing ratio may have a large uncertainty.

A 10 Year Climatology of Arctic Cloud Fraction and Radiative Forcing at Barrow, Alaska

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Xiquan; Xi, Baike; Crosby, Kathryn

2010-09-15

A 10-yr record of Arctic cloud fraction and surface radiation budget has been generated using data collected from June 1998 to May 2008 at the Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA) site and the nearby NOAA Barrow Observatory (BRW). The record includes the seasonal variations of cloud fraction (CF), cloud liquid water path (LWP), precipitable water vapor (PWV), surface albedo, shortwave (SW) and longwave (LW) fluxes and cloud radative forcings (CRFs), as well as their decadal variations. Values of CF derived from different instruments and methods agree well, having an annual average of ~0.74. Cloudiness increases frommore » March to May, remains high (~0.8-0.9) from May to October, and then decreases over winter. More clouds and higher LWP and PWV occurred during the warm season (May-October) than the cold season (November-April). These results are strongly associated with southerly flow which transports warm, moist air masses to Barrow from the North Pacific and over area of Alaska already free of snow during the warm season and with a dipole pattern of pressure in which a high is centered over the Beaufort Sea and low over the Aleutians during the cold season. The monthly means of estimated clear-sky and measured allsky SW-down and LW-down fluxes at the two facilities are almost identical with the annual mean differences less than 1.6 W m-2. The downwelling and upwelling LW fluxes remain almost constant from January to March, then increase from March and peak during July-August. SW-down fluxes are primarily determined by seasonal changes in the intensity and duration of insolation over Northern Alaska, and are also strongly dependent on cloud fraction and optical depth, and surface albedo. The monthly variations of NET CRF generally follow the cycle of SW CRF, modulated by LW effects. On annual average, the negative SW CRF and positive LW CRF tend to cancel, resulting in annual average NET CRF of 2-4.5 Wm-2. Arctic clouds have a 3 net warming effect on the surface throughout the year, with exception of the snow-free period from middle June to middle September when there tends to be a cooling effect. The daily average surface albedos agree well at the two sites remaining high (>0.8) until late May, dropping below 0.2 after the snow melts around June and increasing during autumn once snow begins to accumulate. On the basis of long-term regression analyses CF has decreased by about 0.048 while temperature has risen by ≈1.1 K over the 10-yr period, which can be characterized by tendencies of warming mainly during December and April. With regard to the 2007 record minimum Arctic ice extent, this study provides additional empirical evidence that decreased cloud cover and increased SW-down flux during summer contributed to anomalous ice melt in the region north of Barrow. At Barrow, average June-August CF decreased by 0.062 in 2007 from the 10-yr mean, while SW-down and NET fluxes increased by 28.4 Wm-2 and 11.3 Wm-2, respectively. The increase in the NET radiative flux during summer 2007 most likely contributed to an increase in surface air temperature of 1.6 K.« less

Quantifying the Uncertainties of Reanalyzed Arctic Cloud-radiation Properties Using Satellite-surface Observations

NASA Astrophysics Data System (ADS)

Huang, Y.; Dong, X.; Xi, B.; Dolinar, E. K.; Stanfield, R.

2015-12-01

Cloud and radiation processes are very important issues in Arctic climate system. Reanalyses have proved to be the essential tools to study extreme weather and climate events, especially in data-sparse region like the Arctic. Before using reanalyses products, their strengths and uncertainties should be identified. In this study, five recent reanalyses (JRA55, 20CR V2c, CFSR, ERA-Interim and MERRA) are compared with NASA CERES satellite observations with respect of cloud fraction (CF), top-of-atmosphere (TOA) and surface longwave (LW)/shortwave (SW) radiation fluxes during the period of 03/2000-02/2012 over the Arctic (70-90°N). 20CR V2c, CFSR, ERA-Interim and MERRA overestimate CFs, particularly during the cold season, with the positive biases of annual means from +9.6% (MERRA) to +22.9% (20CR V2c). Only JRA55 can represent its overall seasonal variation and spatial distribution but with large negative biases (nearly -15%). All reanalyses can well capture the seasonal trend of TOA SW/LW upwelling fluxes. However, in all-sky condition, all of them show positive biases of TOA SW upwelling flux along northern and eastern coasts in Greenland during the warm season (JJA). There is a good agreement between reanalyses and observation in seasonal cycle of net TOA cloud radiative effects (CRE), which are calculated by TOA SW/LW fluxes. The spatial distributions of net TOA CRE in warm season show that only JRA55 and ERA-Interim are relatively consistent with their reanalyzed CFs. As for the surface radiation, the satellite-derived results were firstly validated by Baseline Surface Radiation Network (BSRN) ground-based observations. It illustrates that average biases of satellite retrievals are +9.85 W/m2 for surface downward SW flux and +0.39 W/m2 for downward LW flux in warm season within the Arctic. The seasonal variation of SW/LW fluxes can be well represented by four of five reanalyses except MERRA. Reanalyzed surface downward SW flux in JRA55, CFSR and ERA-Interim are relatively consistent with their CF results among these reanalyses. However, the biases in TOA and surface radiation fluxes cannot only explained by biased CFs in some of reanalyses.

Analysis of Surface Albedo to Improve Upper-Ocean Heat Budget Calculations

NASA Astrophysics Data System (ADS)

Hogikyan, A.; Zhang, D.; Cronin, M. F.

2016-12-01

Over 90% of the Earth's energy imbalance is stored in the oceans, so it is important to understand the ocean-atmosphere heat transfer. The Ocean Climate Stations group (OCS) at the Pacific Marine Environmental Laboratory maintains two moored surface buoys in the North Pacific (PAPA and KEO) as air-sea flux reference sites. The goal of the reference sites is to validate global air-sea flux products from atmospheric reanalyses and satellite products, that are critical to understand and model the variability and trend of the earth climate. As other air-sea flux reference buoys in the world ocean, PAPA and KEO only measure downward shortwave radiation (SWdown), but utilize the albedo and the directly measured SWdown to calculate the SWup. Since the open ocean albedo is small, the errors associated with this practice are thought to be comparable or smaller than the instrumentation errors in the air-sea flux measurements. In addition, it is generally accepted that ocean surface albedos can be derived with reasonable confidence from surface radiative fluxes in satellite products such as the Clouds and the Earth's Radiant Energy System (CERES) and the International Satellite Cloud Climatology Project (ISCCP). This project developed a CERES-based albedo product for derivation of SWnet at PAPA and KEO, and assessed the impact of CERES-based albedo on the net surface heat fluxes relative to the currently used ISCCP-based albedo in the OCS air-sea flux data (http://www.pmel.noaa.gov/ocs/data/fluxdisdel/). The high-resolution surface fluxes from CERES are more frequently updated, and consider more physical factors in the approximation, than those from ISCCP. There was a greater change between ISCCP and CERES albedo during wintertime than during summer. There was a greater change at Station PAPA in the northeastern sub-Arctic Pacific, than at Station KEO in the northwestern subtropical Pacific. The rate of temperature change of the mixed-layer is shown to increase based on the new source of albedo data, .08 and .5 °C/year at KEO and PAPA, respectively. The differences in the net surface heat flux due to different albedos used in this study suggest that more comprehensive investigations of the albedo in different products and radiative models, and their impacts on oceanic and atmospheric processes are needed.

Micrometeorological, evapotranspiration, and soil-moisture data at the Amargosa Desert Research site in Nye County near Beatty, Nevada, 2006-11

USGS Publications Warehouse

Arthur, Jonathan M.; Johnson, Michael J.; Mayers, C. Justin; Andraski, Brian J.

2012-11-13

This report describes micrometeorological, evapotranspiration, and soil-moisture data collected since 2006 at the Amargosa Desert Research Site adjacent to a low-level radio-active waste and hazardous chemical waste facility near Beatty, Nevada. Micrometeorological data include precipitation, solar radiation, net radiation, air temperature, relative humidity, saturated and ambient vapor pressure, wind speed and direction, barometric pressure, near-surface soil temperature, soil-heat flux, and soil-water content. Evapotranspiration (ET) data include latent-heat flux, sensible-heat flux, net radiation, soil-heat flux, soil temperature, air temperature, vapor pressure, and other principal energy-budget data. Soil-moisture data include periodic measurements of volumetric water-content at experimental sites that represent vegetated native soil, devegetated native soil, and simulated waste disposal trenches - maximum measurement depths range from 5.25 to 29.25 meters. All data are compiled in electronic spreadsheets that are included with this report.

Experimental assessment of the performance of ablative heat shield materials from plasma wind tunnel testing

NASA Astrophysics Data System (ADS)

Löhle, S.; Hermann, T.; Zander, F.

2018-06-01

A method for assessing the performance of typical heat shield materials is presented in this paper. Three different material samples, the DLR material Zuram, the Airbus material Asterm and the carbon preform Calcarb were tested in the IRS plasma wind tunnel PWK1 at the same nominal condition. State of the art diagnostic tools, i.e., surface temperature with pyrometry and thermography and boundary layer optical emission spectroscopy were completed by photogrammetric surface recession measurements. These data allow the assessment of the net heat flux for each material. The analysis shows that the three materials each have a different effect on heat flux mitigation with ASTERM showing the largest reduction in surface heat flux. The effect of pyrolysis and blowing is clearly observed and the heat flux reduction can be determined from an energy balance.

Advanced high performance horizontal piezoelectric hybrid synthetic jet actuator

NASA Technical Reports Server (NTRS)

Xu, Tian-Bing (Inventor); Jiang, Xiaoning (Inventor); Su, Ji (Inventor)

2012-01-01

The present invention comprises a high performance, horizontal, zero-net mass-flux, synthetic jet actuator for active control of viscous, separated flow on subsonic and supersonic vehicles. The present invention is a horizontal piezoelectric hybrid zero-net mass-flux actuator, in which all the walls of the chamber are electrically controlled synergistically to reduce or enlarge the volume of the synthetic jet actuator chamber in three dimensions simultaneously and to reduce or enlarge the diameter of orifice of the synthetic jet actuator simultaneously with the reduction or enlargement of the volume of the chamber. The present invention is capable of installation in the wing surface as well as embedding in the wetted surfaces of a supersonic inlet. The jet velocity and mass flow rate for the SJA-H will be several times higher than conventional piezoelectric actuators.

SW radiative effect of aerosol in GRAPES_GFS

NASA Astrophysics Data System (ADS)

Chen, Qiying

2017-04-01

The aerosol particles can scatter and absorb solar radiation, and so change the shortwave radiation absorbed by the atmosphere, reached the surface and that reflected back to outer space at TOA. Since this process doesn't interact with other processes, it is called direct radiation effect. The clear sky downward SW and net SW fluxes at the surface in GRAPES_GFS of China Meteorological Administration are overestimated in Northern multitudes and Tropics. The main source of these errors is the absence of aerosol SW effect in GRAPES_GFS. The climatic aerosol mass concentration data, which include 13 kinds of aerosol and their 14 SW bands optical properties are considered in GRAPES_GFS. The calculated total optical depth, single scatter albedo and asymmetry factor are used as the input to radiation scheme. Compared with the satellite observation from MISER, the calculated total optical depth is in good consistent. The seasonal experiments show that, the summer averaged clear sky radiation fluxes at the surface are improved after including the SW effect of aerosol. The biases in the clear sky downward SW and net SW fluxes at the surface in Northern multitudes and Tropic reduced obviously. Furthermore, the weather forecast experiments also show that the skill scores in Northern hemisphere and East Asia also become better.

Surface energy fluxes on four slope sites during FIFE 1988

NASA Technical Reports Server (NTRS)

Nie, D.; Demetriades-Shah, T.; Kanemasu, E. T.

1992-01-01

Four slopes (facing north, south, east, and west) in the Konza Prairie Research Natural Area were selected to study the effect of topography on surface energy balance and other micrometeorological variables. Energy fluxes, air temperature, and vapor pressure were measured on the slopes throughout the 1988 growing season. Net radiation was highest on the south facing slope and lowest on the north facing slope, and the difference was more than 150 W/sq m (20-30 percent) at solar noon. For daily averages the difference was about 25 W/sq m (15 percent) early in the season and increased to about 60 W/sq m (30-50 percent) in September. Soil heat fluxes were similar for all the slopes. The absolute values of sensible heat flux were consistently lower on the north facing slope compared with other slopes. The south facing slope had the greatest day-to-day fluctuation in latent heat flux as a result of the interaction of net radiation, soil moisture, and green leaf area. Differences were found in the partitioning of the available energy among the slopes, and the north facing slope had a higher percentage of energy dissipated into latent heat flux. The north facing slope had higher air temperatures during the day and higher vapor pressures both during the day and at night when the wind was from the south.

Stimulation of Mojave Desert net ecosystem CO2 uptake after winter precipitation with the opposite effect after summer rains based on 7 years of flux data

NASA Astrophysics Data System (ADS)

Jasoni, Richard; Arnone, John; Fenstermaker, Lynn; Wohlfahrt, Georg

2014-05-01

Eddy covariance measurements of net ecosystem CO2 exchange (NEE) in the Mojave Desert (Jasoni et al. 2005-Global Change Biology 11:749-756; Wohlfahrt et al. 2008-Global Change Biology 14:1475-1487), and in other deserts of the world (e.g., Hastings et al. 2005- Global Change Biology 14:927-939, indicate greater rates of net CO2 uptake (more negative NEE values) and net ecosystem productivity (NEP) than would have been expected for deserts (as high as -120 g C m-2 year-1). We continue to observe high rates of NEE and NEP and seek explanations for these findings at interannual, seasonal, and sub-seasonal time scales. Because moisture availability most strongly constrains biological activity in deserts, responses to rains probably play a significant role in defining components of NEE-namely net primary productivity (NPP, or roughly net photosynthesis by vascular and non-vascular plants) and heterotrophic respiration (Rh, mainly by soil microorganisms). Most precipitation in the Mojave Desert falls from October through April and periodically in the summer as convective storms. The main objective of this study was to quantify the extent to which NEE and the net flux of CO2 from/to biological soil crust (BSC) covered soil surfaces respond to rain pulses occurring during cool/cold and warm/hot times of the year. Flux data from 7 years (2005-2011) of measurements at our shub land desert site (average 150 mm rain per year) located 120 km northwest of Las Vegas showed a range in NEP from -111±34 to -47±28 g C m-2 year-1. Cool season rains usually stimulated NEE (more negative NEE values or net CO2 uptake) while warm season rains reversed this effect and led to positive NEE values (net ecosystem CO2 efflux. Cool season stimulation of NEE often occurred in the absence of green leaves on vascular plants, suggesting that photosynthesis of BSCs (up to 70% of soil surface covered by cyanobacteria, mosses, and lichens) were responsible for this net uptake. At other times during the cool season, herbaceous vascular plants also contributed to increases in NEE. Parallel experiments in which we simulated rain pulses (10 mm) in the cool (February) and warm (May) seasons and measured net CO2 fluxes from BSC covered soil surfaces showed responses similar to those observed at the level of the ecosystem. Earlier continuous measurements of soil air relative humidity (RH; 2001-2006) showed that soil moisture increases occurring after rains in the cool season persist up to 3 weeks after events (a total of 48-108 day equivalent per year at >98% RH) indicating conditions favorable for photosynthetic activity. Thus, net CO2 uptake by BSCs during cool months may largely determine large NEEs measured under moist conditions during this time of year and, together with NPP of herbaceous vascular plants, help explain overall consistently high annual NEP in these ecosystems.

Digestion and nutrient net fluxes across the rumen, and the mesenteric- and portal-drained viscera in sheep fed with fresh forage twice daily: net balance and dynamic aspects.

PubMed

Rémond, Didier; Bernard, Laurence; Chauveau, Béatrice; Nozière, Pierre; Poncet, Claude

2003-05-01

Digestion and portal net flux of nutrients were studied in sheep fed twice daily with fresh orchard-grass. Digestive flows were measured in six fistulated sheep using the double-marker technique. Three sheep were fitted with catheters and blood-flow probes, allowing nutrient net flux measurements across the portal-drained viscera (PDV), the mesenteric-drained viscera (MDV) and the rumen. Total tract apparent digestion of N was similar to portal net appearance of N, calculated as the sum of free amino acids (FAA), peptide amino acids (PAA), NH3, and urea net fluxes. PAA accounted for 25 % of non-protein amino acid net release across the PDV. With the exception of glycine and glutamate, the small intestine was the main contributor to this PAA net release. The essential amino acid (EAA) apparent disappearance between the duodenum and the ileum was lower than the net appearance of EAA (FAA + PAA) across the MDV. The value of PDV:MDV flux of free EAA was, on average, 78 %. The rumen accounted for 30 % of the net uptake of EAA by the PDV tissues not drained by the mesenteric vein. Rumen net release of acetate, propionate, butyrate, 3-hydroxybutyrate, and lactate accounted for 70, 55, 46, 77 and 52 %, respectively, of their portal net releases. Conversely, the small intestine was a net consumer of arterial acetate and 3-hydroxybutyrate. Dynamic study of nutrient net fluxes across the PDV showed that throughout a feeding cycle, the liver faced a constant flux of amino acids (AA), whereas volatile fatty acid and NH3 net fluxes varied in response to the meal. The present study specified, in forage-fed sheep, the partitioning of nutrient net fluxes across the PDV and the role of peptides in portal net release of AA.

Exploiting satellite earth observation to quantify current global oceanic DMS flux and its future climate sensitivity

NASA Astrophysics Data System (ADS)

Land, P. E.; Shutler, J. D.; Bell, T. G.; Yang, M.

2014-11-01

We used coincident Envisat RA2 and AATSR temperature and wind speed data from 2008/2009 to calculate the global net sea-air flux of dimethyl sulfide (DMS), which we estimate to be 19.6 Tg S a-1. Our monthly flux calculations are compared to open ocean eddy correlation measurements of DMS flux from 10 recent cruises, with a root mean square difference of 3.1 μmol m-2 day-1. In a sensitivity analysis, we varied temperature, salinity, surface wind speed, and aqueous DMS concentration, using fixed global changes as well as CMIP5 model output. The range of DMS flux in future climate scenarios is discussed. The CMIP5 model predicts a reduction in surface wind speed and we estimate that this will decrease the global annual sea-air flux of DMS by 22% over 25 years. Concurrent changes in temperature, salinity, and DMS concentration increase the global flux by much smaller amounts. The net effect of all CMIP5 modelled 25 year predictions was a 19% reduction in global DMS flux. 25 year DMS concentration changes had significant regional effects, some positive (Southern Ocean, North Atlantic, Northwest Pacific) and some negative (isolated regions along the Equator and in the Indian Ocean). Using satellite-detected coverage of coccolithophore blooms, our estimate of their contribution to North Atlantic DMS emissions suggests that the coccolithophores contribute only a small percentage of the North Atlantic annual flux estimate, but may be more important in the summertime and in the northeast Atlantic.

UV sensitivity of planktonic net community production in ocean surface waters

NASA Astrophysics Data System (ADS)

Regaudie-de-Gioux, Aurore; Agustí, Susana; Duarte, Carlos M.

2014-05-01

The net plankton community metabolism of oceanic surface waters is particularly important as it more directly affects the partial pressure of CO2 in surface waters and thus the air-sea fluxes of CO2. Plankton communities in surface waters are exposed to high irradiance that includes significant ultraviolet blue (UVB, 280-315 nm) radiation. UVB radiation affects both photosynthetic and respiration rates, increase plankton mortality rates, and other metabolic and chemical processes. Here we test the sensitivity of net community production (NCP) to UVB of planktonic communities in surface waters across contrasting regions of the ocean. We observed here that UVB radiation affects net plankton community production at the ocean surface, imposing a shift in NCP by, on average, 50% relative to the values measured when excluding partly UVB. Our results show that under full solar radiation, the metabolic balance shows the prevalence of net heterotrophic community production. The demonstration of an important effect of UVB radiation on NCP in surface waters presented here is of particular relevance in relation to the increased UVB radiation derived from the erosion of the stratospheric ozone layer. Our results encourage design future research to further our understanding of UVB effects on the metabolic balance of plankton communities.

Soil water evaporation during the dry season in an arid zone

NASA Astrophysics Data System (ADS)

Agam (Ninari), Nurit; Berliner, Pedro R.; Zangvil, Abraham; Ben-Dor, Eyal

2004-08-01

The objective of this study was to assess the relative magnitude of latent heat flux density over a bare loess soil in the Negev desert throughout the dry season, during which the atmospheric models usually assume the lack of latent heat flux. The measurements were carried out in the northern Negev, Israel, over a bare loess soil, during nine 24-hour field campaigns throughout the dry season of 2002. In addition to a micrometeorological station that was set up in the research site, an improved microlysimeter was installed. The representativity of the microlysimeter was assessed by comparing its surface temperature to that of the surrounding surface using thermal images acquired on an hourly basis during several campaigns. It was found that although the water content of the uppermost soil is significantly lower than the wilting point, for which most of the commonly used meteorological models would assume no latent heat flux, the latter was ˜20% of the net-radiation during the night and 10-15% during the day. It is therefore concluded that latent heat flux plays a major role in the dissipation of the net radiation during the dry season in the Negev desert.

Measurement of Urban fluxes of CO2 and water

NASA Astrophysics Data System (ADS)

Grimmond, S.; Crawford, B.; Offerle, B.; Hom, J.

2006-05-01

Measurements of surface-atmosphere fluxes of carbon dioxide (FCO2) and latent heat in urban environments are rare even though cities are a major source of atmospheric CO2 and users of water. In this paper, an overview of urban FCO2 measurements will be presented to illustrate how and where such measurements are being conducted and emerging results to date. Most of these studies have been conducted over short periods of time; few studies have considered annual sources/sinks. More investigations have been conducted, and are planned, in European cities than elsewhere, most commonly in areas of medium density urban development. The most dense urban sites are significant net sources of carbon. However, in areas where there is large amounts of vegetation present, there is a net sink of carbon during the summertime. In the second part of the presentation, more detailed attention will be directed to an ongoing measurement program in Baltimore, MD (part of the Baltimore Ecosystem Study). Eddy covariance instrumentation mounted on a tall-tower at 41.2 m has continuously measured local-scale fluxes of carbon dioxide from a suburban environment since 2001. Several features make this particular study unique: 1) for an urban area, the study site is extensively vegetated, 2) the period of record (2001-2005) is among the longest available for urban FCO2 measurements, 3) both closed-path and open-path infrared gas analyzers are used for observations, and 4) several unique data quality control and gap-filling methods have been developed for use in an urban environment. Additionally, detailed surface datasets and GIS software are used to perform flux source area analysis. Results from Baltimore indicate that FCO2 is very dependent on source area land-cover characteristics, particularly the proportion of vegetated and built surfaces. Over the course of a year, the urban surface is a strong net source of CO2, though there is considerable inter-annual variability depending on environmental conditions (e.g. average temperature, total precipitation, cicada infestation). During the growing season, there is net uptake of CO2 by the surface, but this uptake is less than in forested areas and is not enough to offset CO2 emissions for the entire year

Flux to the atmosphere of CH4 and CO2 from wetland ponds on the Hudson Bay lowlands (HBLs)

NASA Technical Reports Server (NTRS)

Hamilton, J. David; Kelly, Carol A.; Rudd, John W. M.; Hesslein, Raymond H.; Roulet, Nigel T.

1994-01-01

Ponds on peatlands of the Hudson Bay lowlands (HBLs) are complex ecosystems in which the fluxes to the atmosphere of CH4 and CO2 were controlled by interacting physical and biological factors. This resulted in strong diel variations of both dissolved gas concentrations and gas fluxes to the atmosphere, necessitating frequent sampling on a 24-hour schedule to enable accurate estimates of daily fluxes. Ponds at three sites on the HBL were constant net sources of CH4 and CO2 to the atmosphere at mean rates of 110-180 mg CH4 m(exp -2)/d and 3700-11,000 mg CO2 m(exp -2)/d. Rates peaked in August and September. For CH4 the pond fluxes were 3-30 times higher than adjacent vegetated surfaces. For CO2 the net pond fluxes were similar in magnitude to the vegetated fluxes but the direction of the flux was opposite, toward atmosphere. Even though ponds cover only 8-12% of the HBL area, they accounted for 30% of its total CH4 flux to the atmosphere. There is some circumstantial evidence that the ponds are being formed by decomposition of the underlying peat and that this decomposition is being stimulated by the activity of N2 fixing cyanobacteria that grow in mats at the peat-water interface. The fact that the gas fluxes from the ponds were so different from the surrounding vegetated surfaces means that any change in the ratio of pond to vegetated area, as may occur in response to climate change, would affect the total HBL fluxes.

Assessment of the water and energy budget simulation of three land surface models: CLM4.5, CoLM2014, and CoLM2005

NASA Astrophysics Data System (ADS)

Li, C.; Lu, H.; Wen, X.

2015-12-01

Land surface model (LSM), which simulates energy, water and momentum exchanges between land and atmosphere, is an important component of Earth System Models (ESM). As shown in CMIP5, different ESMs usually use different LSMs and represent various land surface status. In order to select a land surface model which could be embedded into the ESM developed in Tsinghua University, we firstly evaluate the performance of three LSMs: Community Land Model (CLM4.5) and two different versions of Common Land Model (CoLM2005 and CoLM2014). All of three models were driven by CRUNCEP data and simulation results from 1980 to 2010 were used in this study. Diagnostic data provided by NCAR, global latent and sensible heat flux map estimated by Jung, net radiation from SRB, and in situ observation collected from FluxNet were used as reference data. Two variables, surface runoff and snow depth, were used for evaluating the model performance in water budget simulation, while three variables including net radiation, sensible heat, and latent heat were used for assessing energy budget simulation. For 30 years averaged runoff, global average value of Colm2014 is 0.44mm/day and close to the diagnostic value of 0.75 mm/day, while that of Colm2005 is 0.44mm/day and that of CLM is 0.20mm/day. For snow depth simulation, three models all have overestimation in the Northern Hemisphere and underestimation in the Southern Hemisphere compare to diagnostic data. For 30 years energy budget simulation, at global scale, CoLM2005 performs best in latent heat estimation, CoLM2014 performs best in sensible heat simulation, and CoLM2005 and CoLM2014 make similar performance in net radiation estimation but is still better than CLM. At regional and local scale, comparing to the four years average of flux tower observation, RMSE of CoLM2005 is the smallest for latent heat (9.717 W/m2) , and for sensible heat simulation, RMSE of CoLM2005 (13.048 W/m2) is slightly greater than CLM(10.767 W/m2) but still better than CoLM2014(30.085 W/m2). Our analysis shows that both CoLM 2005 and CoLM 2014 are able to reproduce comparable land surface water and energy fluxes. It implies that the ESM developed in Tsinghua University may use CoLM, a LSM developed and maintained in China, as the land surface component. .

Estimating surface fluxes over middle and upper streams of the Heihe River Basin with ASTER imagery

NASA Astrophysics Data System (ADS)

Ma, W.; Ma, Y.; Hu, Z.; Su, Z.; Wang, J.; Ishikawa, H.

2011-05-01

Land surface heat fluxes are essential measures of the strengths of land-atmosphere interactions involving energy, heat and water. Correct parameterization of these fluxes in climate models is critical. Despite their importance, state-of-the-art observation techniques cannot provide representative areal averages of these fluxes comparable to the model grid. Alternative methods of estimation are thus required. These alternative approaches use (satellite) observables of the land surface conditions. In this study, the Surface Energy Balance System (SEBS) algorithm was evaluated in a cold and arid environment, using land surface parameters derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data. Field observations and estimates from SEBS were compared in terms of net radiation flux (Rn), soil heat flux (G0), sensible heat flux (H) and latent heat flux (λE) over a heterogeneous land surface. As a case study, this methodology was applied to the experimental area of the Watershed Allied Telemetry Experimental Research (WATER) project, located on the mid-to-upstream sections of the Heihe River in northwest China. ASTER data acquired between 3 May and 4 June 2008, under clear-sky conditions were used to determine the surface fluxes. Ground-based measurements of land surface heat fluxes were compared with values derived from the ASTER data. The results show that the derived surface variables and the land surface heat fluxes furnished by SEBS in different months over the study area are in good agreement with the observed land surface status under the limited cases (some cases looks poor results). So SEBS can be used to estimate turbulent heat fluxes with acceptable accuracy in areas where there is partial vegetation cover in exceptive conditions. It is very important to perform calculations using ground-based observational data for parameterization in SEBS in the future. Nevertheless, the remote-sensing results can provide improved explanations of land surface fluxes over varying land coverage at greater spatial scales.

Sources of Uncertainty in Predicting Land Surface Fluxes Using Diverse Data and Models

NASA Technical Reports Server (NTRS)

Dungan, Jennifer L.; Wang, Weile; Michaelis, Andrew; Votava, Petr; Nemani, Ramakrishma

2010-01-01

In the domain of predicting land surface fluxes, models are used to bring data from large observation networks and satellite remote sensing together to make predictions about present and future states of the Earth. Characterizing the uncertainty about such predictions is a complex process and one that is not yet fully understood. Uncertainty exists about initialization, measurement and interpolation of input variables; model parameters; model structure; and mixed spatial and temporal supports. Multiple models or structures often exist to describe the same processes. Uncertainty about structure is currently addressed by running an ensemble of different models and examining the distribution of model outputs. To illustrate structural uncertainty, a multi-model ensemble experiment we have been conducting using the Terrestrial Observation and Prediction System (TOPS) will be discussed. TOPS uses public versions of process-based ecosystem models that use satellite-derived inputs along with surface climate data and land surface characterization to produce predictions of ecosystem fluxes including gross and net primary production and net ecosystem exchange. Using the TOPS framework, we have explored the uncertainty arising from the application of models with different assumptions, structures, parameters, and variable definitions. With a small number of models, this only begins to capture the range of possible spatial fields of ecosystem fluxes. Few attempts have been made to systematically address the components of uncertainty in such a framework. We discuss the characterization of uncertainty for this approach including both quantifiable and poorly known aspects.

Wind Effects on Flow Patterns and Net Fluxes in Density-Driven High-Latitude Channel Flow

NASA Astrophysics Data System (ADS)

Huntley, Helga S.; Ryan, Patricia

2018-01-01

A semianalytic two-dimensional model is used to analyze the interplay between the different forces acting on density-driven flow in high-latitude channels. In particular, the balance between wind stress, viscous forces, baroclinicity, and sea surface slope adjustments under specified flux conditions is examined. Weak winds are found not to change flow patterns appreciably, with minimal (<7%) adjustments to horizontal velocity maxima. In low-viscosity regimes, strong winds change the flow significantly, especially at the surface, by either strengthening the dual-jet pattern, established without wind, by a factor of 2-3 or initiating return flow at the surface. A nonzero flux does not result in the addition of a uniform velocity throughout the channel cross section, but modifies both along-channel and cross-channel velocities to become more symmetric, dominated by a down-channel jet centered in the domain and counter-clockwise lateral flow. We also consider formulations of the model that allow adjustments of the net flux in response to the wind. Flow patterns change, beyond uniform intensification or weakening, only for strong winds and high Ekman number. Comparisons of the model results to observational data collected in Nares Strait in the Canadian Archipelago in the summer of 2007 show rough agreement, but the model misses the upstream surface jet on the east side of the strait and propagates bathymetric effects too strongly in the vertical for this moderately high eddy viscosity. Nonetheless, the broad strokes of the observed high-latitude flow are reproduced.

Analytic and experimental evaluation of flowing air test conditions for selected metallics in a shuttle TPS application

NASA Technical Reports Server (NTRS)

Schaefer, J. W.; Tong, H.; Clark, K. J.; Suchsland, K. E.; Neuner, G. J.

1975-01-01

A detailed experimental and analytical evaluation was performed to define the response of TD nickel chromium alloy (20 percent chromium) and coated columbium (R512E on CB-752 and VH-109 on WC129Y) to shuttle orbiter reentry heating. Flight conditions important to the response of these thermal protection system (TPS) materials were calculated, and test conditions appropriate to simulation of these flight conditions in flowing air ground test facilities were defined. The response characteristics of these metallics were then evaluated for the flight and representative ground test conditions by analytical techniques employing appropriate thermochemical and thermal response computer codes and by experimental techniques employing an arc heater flowing air test facility and flat face stagnation point and wedge test models. These results were analyzed to define the ground test requirements to obtain valid TPS response characteristics for application to flight. For both material types in the range of conditions appropriate to the shuttle application, the surface thermochemical response resulted in a small rate of change of mass and a negligible energy contribution. The thermal response in terms of surface temperature was controlled by the net heat flux to the surface; this net flux was influenced significantly by the surface catalycity and surface emissivity. The surface catalycity must be accounted for in defining simulation test conditions so that proper heat flux levels to, and therefore surface temperatures of, the test samples are achieved.

Meteorological surface conditions at Kohnen Station, Antarctica

NASA Astrophysics Data System (ADS)

van As, D.; van den Broeke, M. R.

2003-04-01

Only a few detailed meteorological experiments have been performed in the higher regions of the Antarctic ice sheet. This contribution will describe part of such an experiment and its outcome, performed at Kohnen Station (75.00 S, 0.07 E, 2892 m asl.) in the Antarctic summer of 2001-'02. Results from this experiment are to benefit the interpretation of the ice core presently being drilled at this location. Surface conditions in the 40 day period of measurements varied from typically stable to extraordinarily warm and windy. First we focus on the surface energy balance during this summer period. A model with only a few input parameters is used to combine measured net radiation with calculated heat fluxes to iteratively search for a surface temperature for which all components balance out. Calculated components are compared with measurements. In time this model will be functional for weather stations at different locations. Despite the high albedo (0.82 - 0.92) the net shortwave radiation is the largest component at the surface, contributing a maximum of 100 W/m2. Surprisingly small is the latent heat flux, in fair weather no more than a few W/m2. In general the calculations agree well with the measurements. A shallow convective layer developed in the daytime by the sensible heat flux is confirmed by balloon measurements. Linking the surface conditions to measurements outside of the surface layer we find little correlation, as to be expected.

Spectral estimates of net radiation and soil heat flux

USGS Publications Warehouse

Daughtry, C.S.T.; Kustas, William P.; Moran, M.S.; Pinter, P. J.; Jackson, R. D.; Brown, P.W.; Nichols, W.D.; Gay, L.W.

1990-01-01

Conventional methods of measuring surface energy balance are point measurements and represent only a small area. Remote sensing offers a potential means of measuring outgoing fluxes over large areas at the spatial resolution of the sensor. The objective of this study was to estimate net radiation (Rn) and soil heat flux (G) using remotely sensed multispectral data acquired from an aircraft over large agricultural fields. Ground-based instruments measured Rn and G at nine locations along the flight lines. Incoming fluxes were also measured by ground-based instruments. Outgoing fluxes were estimated using remotely sensed data. Remote Rn, estimated as the algebraic sum of incoming and outgoing fluxes, slightly underestimated Rn measured by the ground-based net radiometers. The mean absolute errors for remote Rn minus measured Rn were less than 7%. Remote G, estimated as a function of a spectral vegetation index and remote Rn, slightly overestimated measured G; however, the mean absolute error for remote G was 13%. Some of the differences between measured and remote values of Rn and G are associated with differences in instrument designs and measurement techniques. The root mean square error for available energy (Rn - G) was 12%. Thus, methods using both ground-based and remotely sensed data can provide reliable estimates of the available energy which can be partitioned into sensible and latent heat under nonadvective conditions. ?? 1990.

Assessing the Monthly Averaged Variability of TOA Fluxes from CERES using EBAF, ERBE-like and FLASHFlux Data From 2001 to Present

NASA Astrophysics Data System (ADS)

Stackhouse, Paul; Wong, Takmeng; Kratz, David; Gupta, Shashi; Wiber, Anne; Edwards, Anne

2010-05-01

The FLASHFlux (Fast Longwave and Shortwave radiative Fluxes from CERES and MODIS) project derives daily averaged gridded top-of-atmosphere (TOA) and surface radiative fluxes within one week of observation. Production of CERES based TOA and surface fluxes is achieved by using the latest CERES calibration that is assumed constant in time and by making simplifying assumptions in the computation of time and space averaged quantities. Together these assumptions result in approximately a 1% increase in the uncertainty for FLASHFlux products over CERES. Analysis has clearly demonstrated that the global-annual mean outgoing longwave radiation shows a decrease of ~0.75 Wm-2, from 2007 to 2008, while the global-annual mean reflected shortwave radiation shows a decrease of 0.14 Wm-2 over that same period. Thus, the combined longwave and shortwave changes have resulted in an increase of ~0.89 Wm-2 in net radiation into the Earth climate system in 2008. A time series of TOA fluxes was constructed from CERES EBAF, CERES ERBE-like and FLASHFLUX. Relative to this multi-dataset average from 2001 to 2008, the 2008 global-annual mean anomalies are -0.54/-0.26/+0.80 Wm-2, respectively, for the longwave/shortwave/net radiation. These flux values, which were published in the NOAA 2008 State of the Climate Report, are within their corresponding 2-sigma interannual variabilities for this period. This paper extends these results through 2009, where the net flux is observed to recover. The TOA LW variability is also compared to AIRS OLR showing excellent agreement in the anomalies. The variability appears very well correlated to the to the 2007-2009 La Nina/El Nino cycles, which altered the global distribution of clouds, total column water vapor and temperature. Reassessments of these results are expected when newer Clouds and the Earth's Radiant Energy System (CERES) data are released.

Measures of net oxidant concentration in seawater

NASA Astrophysics Data System (ADS)

Jackson, George A.; Williams, Peter M.

1988-02-01

Dissolved oxygen deficits in the ocean have been used as a measure of the organic matter oxidized in a volume of water. Such organic matter is usually assumed to be predominantly settled particles. Using dissolved oxygen concentration in this way has two problems: first, it does not differentiate between oxidant consumed by the pool of dissolved organic matter present near the ocean surface and oxidant consumed by organic matter contained by falling particles; second, it does not account for other oxidant sources, such as nitrate, which can be as important to organic matter decay as oxygen in low-oxygen water, such as off Peru or in the Southern California submarine basins. New parameters provide better measures of the net oxidant concentration in a water parcel. One such, NetOx, is changed only by gaseous exchange with the atmosphere, exchange with the benthos, or the production or consumption of sinking particles. A simplified version of NetOx, NetOx = [O2] + 1.25[NO3-] - [TOC], where TOC (total organic carbon), the dissolved organic carbon (DOC) plus the suspended particulate organic carbon (POC), provides an index based on the usually dominant variables. Calculation of NetOx and a second property, NetOC ([O2] - [TOC]), for data from GEOSECS and ourselves in the Atlantic and Pacific oceans using property-property graphs show differences from those from oxygen deficits alone. Comparison of NetOx and NetOC concentrations at high and low latitudes of the Pacific Ocean shows the difference in surface water oxidant concentrations is even larger than the difference in oxygen concentration. Vertical particle fluxes off Peru calculated from NetOx gradients are much greater than those calculated from oxygen gradients. The potential value of NetOx and NetOC as parameters to understand particle fluxes implies that determination of TOC should be a routine part of hydrographic measurements.

Real-Time Ocean Prediction System for the East Coast of India

NASA Astrophysics Data System (ADS)

Warrior, H. V.

2016-02-01

The primary objective of the research work reported in this abstract was to develop a Realtime Environmental model for Ocean Dispersion and Impact (as part of an already in-place Decision Support System) for the purpose of radiological safety for the area along Kalpakkam (East Indian) coast. This system involves combining real-time ocean observations with numerical models of ocean processes to provide hindcasts, nowcasts and forecasts of currents, tides and waves. In this work we present the development of an Automated Coupled Atmospheric - Ocean Model (we call it IIT-CAOM) used to forecast the sea surface currents, sea surface temperature (SST) and salinity etc of the Bay of Bengal region under the influence of transient and unsteady atmospheric conditions. This method uses a coupling of Atmosphere and Ocean model. The models used here are the WRF for atmospheric simulations and POM for the ocean counterpart. It has a 3 km X 3 km resolution. This Coupled Model uses GFS (Global Forecast System) Data or FNL (Final Analyses) Data as initial conditions for jump-starting the atmospheric model. The Atmospheric model is run first thus extracting air temperature, wind speed and relative humidity. The heat flux subroutine computes the net heat flux, using above mentioned parameters data. The net heat flux feeds to the ocean model by simply adding net heat flux subroutine to the ocean model code without changing the model original structure. The online forecast of the IIT-CAOM is currently available in the web. The whole system has been automized and runs without any more manual support. The IIT-CAOM simulations have been carried out for Kalpakkam region, which is located on the East coast of India, about 70 km south of Chennai in Tamilnadu State and a three day forecast of sea surface currents, sea surface temperature (SST) and salinity, etc have been obtained.

Fabrication and Testing of a Thin-Film Heat Flux Sensor for a Stirling Convertor

NASA Technical Reports Server (NTRS)

Wilson, Scott D.; Fralick, Gustave; Wrbanek, John; Sayir, Ali

2009-01-01

The NASA Glenn Research Center (GRC) has been testing high efficiency free-piston Stirling convertors for potential use in radioisotope power systems since 1999. Stirling convertors are being operated for many years to demonstrate a radioisotope power system capable of providing reliable power for potential multi-year missions. Techniques used to monitor the convertors for change in performance include measurements of temperature, pressure, energy addition, and energy rejection. Micro-porous bulk insulation is used in the Stirling convertor test set up to minimize the loss of thermal energy from the electric heat source to the environment. The insulation is characterized before extended operation, enabling correlation of the net thermal energy addition to the convertor. Aging microporous bulk insulation changes insulation efficiency, introducing errors in the correlation for net thermal energy addition. A thin-mm heat flux sensor was designed and fabricated to directly measure the net thermal energy addition to the Stirling convertor. The fabrication techniques include slip casting and using Physical Vapor Deposition (PVD). One micron thick noble metal thermocouples measure temperature on the surface of an Alumina ceramic disc and heat flux is calculated. Fabrication, integration, and test results of a thin film heat flux sensor are presented.

Fabrication and Testing of a Thin-Film Heat Flux Sensor for a Stirling Convertor

NASA Technical Reports Server (NTRS)

Wilson, Scott D.; Fralick, Gus c.; Wrbanek, John D.; Sayir, Ali

2010-01-01

The NASA Glenn Research Center (GRC) has been testing high-efficiency free-piston Stirling convertors for potential use in radioisotope power systems since 1999. Stirling convertors are being operated for many years to demonstrate a radioisotope power system capable of providing reliable power for potential multiyear missions. Techniques used to monitor the convertors for change in performance include measurements of temperature, pressure, energy addition, and energy rejection. Micro-porous bulk insulation is used in the Stirling convertor test setup to minimize the loss of thermal energy from the electric heat source to the environment. The insulation is characterized before extended operation, enabling correlation of the net thermal energy addition to the convertor. Aging micro-porous bulk insulation changes insulation efficiency, introducing errors in the correlation for net thermal energy addition. A thin-film heat flux sensor was designed and fabricated to directly measure the net thermal energy addition to the Stirling convertor. The fabrication techniques include slipcasting and using Physical Vapor Deposition (PVD). One-micron-thick noble metal thermocouples measure temperature on the surface of an alumina ceramic disk and heat flux is calculated. Fabrication, integration, and test results of a thin-film heat flux sensor are presented.

Hydraulic and biochemical gradients limit wetland mercury supply to an Adirondack stream

USGS Publications Warehouse

Bradley, Paul M.; Burns, Douglas A.; Harvey, Judson; Journey, Celeste A.; Brigham, Mark E.; Murray, Karen

2016-01-01

Net fluxes (change between upstream and downstream margins) for water, methylmercury (MeHg), total mercury (THg), dissolved organic carbon (DOC), and chloride (Cl) were assessed twice in an Adirondack stream reach (Sixmile Brook, USA), to test the hypothesized importance of wetland-stream hydraulic and chemical gradients as fundamental controls on fluvial mercury (Hg) supply. The 500 m study reach represented less than 4% of total upstream basin area. During a snowmelt high-flow event in May 2009 surface water, DOC, and chloride fluxes increased by 7.1±1.3%, 8.0±1.3%, and 9.0±1.3%, respectively, within the reach, demonstrating that the adjacent wetlands are important sources of water and solutes to the stream. However, shallow groundwater Hg concentrations lower than in the surface water limited groundwater-surface water Hg exchange and no significant changes in Hg (filtered MeHg and THg) fluxes were observed within the reach despite the favorable hydraulic gradient. In August 2009, the lack of significant wetland-stream hydraulic gradient resulted in no net flux of water or solutes (MeHg, THg, DOC, or Cl) within the reach. The results are consistent with the wetland-Hg-source hypothesis and indicate that hydraulic and chemical gradient (direction and magnitude) interactions are fundamental controls on the supply of wetland Hg to the stream.

Effect of cloud cover and surface type on earth's radiation budget derived from the first year of ERBE data

NASA Technical Reports Server (NTRS)

Gibson, G. G.; Denn, F. M.; Young, D. F.; Harrison, E. F.; Minnis, P.; Barkstrom, B. R.

1990-01-01

One year of ERBE data is analyzed for variations in outgoing LW and absorbed solar flux. Differences in land and ocean radiation budgets as well as differences between clear-sky and total scenes, including clouds, are studied. The variation of monthly average radiative parameters is examined for February 1985 through January 1986 for selected study regions and on zonal and global scales. ERBE results show significant seasonal variations in both outgoing LW and absorbed SW flux, and a pronounced difference between oceanic and continental surfaces. The main factors determining cloud radiative forcing in a given region are solar insolation, cloud amount, cloud type, and surface properties. The strongest effects of clouds are found in the midlatitude storm tracks over the oceans. Over much of the globe, LW warming is balanced by SW cooling. The annual-global average net cloud forcing shows that clouds have a net cooling effect on the earth for the year.

Analysis of turbulent heat and momentum transfer in a transitionally rough turbulent boundary layer

NASA Astrophysics Data System (ADS)

Doosttalab, Ali; Dharmarathne, Suranga; Tutkun, Murat; Adrian, Ronald; Castillo, Luciano

2016-11-01

A zero-pressure-gradient (ZPG) turbulent boundary layer over a transitionally rough surface is studied using direct numerical simulation (DNS). The rough surface is modeled as 24-grit sandpaper which corresponds to k+ 11 , where k+ is roughness height. Reynolds number based on momentum thickness is approximately 2400. The walls are isothermal and turbulent flow Prandtl number is 0.71. We simulate temperature as passive scalar. We compute the inner product of net turbulent force (d (u1ui) / dxi) and net turbulent heat flux (d (ui θ / dxi)) in order to investigate (i) the correlation between these vectorial quantities, (II) size of the projection of these fields on each other and (IIi) alignment of momentum and hear flux. The inner product in rough case results in larger projection and better alignment. In addition, our study on the vortices shows that surface roughness promotes production of vortical structures which affects the thermal transport near the wall.

Coccolithophore surface distributions in the North Atlantic and their modulation of the air-sea flux of CO2 from 10 years of satellite Earth observation data

NASA Astrophysics Data System (ADS)

Shutler, J. D.; Land, P. E.; Brown, C. W.; Findlay, H. S.; Donlon, C. J.; Medland, M.; Snooke, R.; Blackford, J. C.

2013-04-01

Coccolithophores are the primary oceanic phytoplankton responsible for the production of calcium carbonate (CaCO3). These climatically important plankton play a key role in the oceanic carbon cycle as a major contributor of carbon to the open ocean carbonate pump (~50%) and their calcification can affect the atmosphere-to-ocean (air-sea) uptake of carbon dioxide (CO2) through increasing the seawater partial pressure of CO2 (pCO2). Here we document variations in the areal extent of surface blooms of the globally important coccolithophore, Emiliania huxleyi, in the North Atlantic over a 10-year period (1998-2007), using Earth observation data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). We calculate the annual mean sea surface areal coverage of E. huxleyi in the North Atlantic to be 474 000 ± 104 000 km2, which results in a net CaCO3 carbon (CaCO3-C) production of 0.14-1.71 Tg CaCO3-C per year. However, this surface coverage (and, thus, net production) can fluctuate inter-annually by -54/+8% about the mean value and is strongly correlated with the El Niño/Southern Oscillation (ENSO) climate oscillation index (r=0.75, p<0.02). Our analysis evaluates the spatial extent over which the E. huxleyi blooms in the North Atlantic can increase the pCO2 and, thus, decrease the localised air-sea flux of atmospheric CO2. In regions where the blooms are prevalent, the average reduction in the monthly air-sea CO2 flux can reach 55%. The maximum reduction of the monthly air-sea CO2 flux in the time series is 155%. This work suggests that the high variability, frequency and distribution of these calcifying plankton and their impact on pCO2 should be considered if we are to fully understand the variability of the North Atlantic air-to-sea flux of CO2. We estimate that these blooms can reduce the annual N. Atlantic net sink atmospheric CO2 by between 3-28%.

A new method for estimating the turbulent heat flux at the bottom of the daily mixed layer

NASA Technical Reports Server (NTRS)

Imawaki, Shiro; Niiler, Pearn P.; Gautier, Catherine H.; Knox, Robert A.; Halpern, David

1988-01-01

Temperature data in the mixed layer and net solar irradiance data at the sea surface are used to estimate the vertical turbulent heat flux at the bottom of the daily mixed layer. The method is applied to data obtained in the eastern tropical Pacific, where the daily cycle in the temperature field is confined to the upper 10-25 m. Equatorial turbulence measurements indicate that the turbulent heat flux is much greater during nighttime than daytime.

Long-terms Change of Sea Surface Temperature in the South China Sea

NASA Astrophysics Data System (ADS)

Park, Y. G.; Choi, A.

2016-02-01

Using the Hadley Centre Global Sea Ice and Sea Surface Temperature (HadISST) the long term trend in the South China Sea (SCS) sea surface temperature (SST) between 1950 and 2008 is investigated. Both in winter and summer SST was increased by comparable amounts, but the warming patterns and the governing processes was different. During winter warming rate was greater in the deep basin in the central part, while during summer near the southern part. In winter the net heat flux into the sea was increased and could contribute to the warming. The pattern of the heat flux, however, was different from that of the warming. The heat flux was increased over the coastal area where warming was weaker, but decreased in deeper part where warming was stronger. The northeasterly monsoon wind weakened to lower the shoreward Ekman transport and the sea surface height gradient. The cyclonic gyre that transports cold northern water to south was weakened to warm the ocean. The effect manifested more strongly southward western boundary currents, and subsequently cold advection. In summer the net surface heat flux, however, was reduced and could not contribute to the warming. Over the southern part of the ocean the weakening of the southwesterly summer monsoon reduced southeastward Ekman transport, which is antiparallel to the mean SST gradient. Firstly, southeastward cold advection is reduced to warm the surface near the southeastern boundary of the SCS. The upwelling southeast of Vietnam was also weakened to raise the SST east of Vietnam. Thus the weakening of the wind in each season was the ultimate cause of the warming, but the responses of the ocean that lead to the warming were different.

Predicting carbon dioxide and energy fluxes across global FLUXNET sites with regression algorithms

DOE PAGES

Tramontana, Gianluca; Jung, Martin; Schwalm, Christopher R.; ...

2016-07-29

Spatio-temporal fields of land–atmosphere fluxes derived from data-driven models can complement simulations by process-based land surface models. While a number of strategies for empirical models with eddy-covariance flux data have been applied, a systematic intercomparison of these methods has been missing so far. In this study, we performed a cross-validation experiment for predicting carbon dioxide, latent heat, sensible heat and net radiation fluxes across different ecosystem types with 11 machine learning (ML) methods from four different classes (kernel methods, neural networks, tree methods, and regression splines). We applied two complementary setups: (1) 8-day average fluxes based on remotely sensed data andmore » (2) daily mean fluxes based on meteorological data and a mean seasonal cycle of remotely sensed variables. The patterns of predictions from different ML and experimental setups were highly consistent. There were systematic differences in performance among the fluxes, with the following ascending order: net ecosystem exchange ( R 2 < 0.5), ecosystem respiration ( R 2 > 0.6), gross primary production ( R 2> 0.7), latent heat ( R 2 > 0.7), sensible heat ( R 2 > 0.7), and net radiation ( R 2 > 0.8). The ML methods predicted the across-site variability and the mean seasonal cycle of the observed fluxes very well ( R 2 > 0.7), while the 8-day deviations from the mean seasonal cycle were not well predicted ( R 2 < 0.5). Fluxes were better predicted at forested and temperate climate sites than at sites in extreme climates or less represented by training data (e.g., the tropics). Finally, the evaluated large ensemble of ML-based models will be the basis of new global flux products.« less

Predicting carbon dioxide and energy fluxes across global FLUXNET sites with regression algorithms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tramontana, Gianluca; Jung, Martin; Schwalm, Christopher R.

Spatio-temporal fields of land–atmosphere fluxes derived from data-driven models can complement simulations by process-based land surface models. While a number of strategies for empirical models with eddy-covariance flux data have been applied, a systematic intercomparison of these methods has been missing so far. In this study, we performed a cross-validation experiment for predicting carbon dioxide, latent heat, sensible heat and net radiation fluxes across different ecosystem types with 11 machine learning (ML) methods from four different classes (kernel methods, neural networks, tree methods, and regression splines). We applied two complementary setups: (1) 8-day average fluxes based on remotely sensed data andmore » (2) daily mean fluxes based on meteorological data and a mean seasonal cycle of remotely sensed variables. The patterns of predictions from different ML and experimental setups were highly consistent. There were systematic differences in performance among the fluxes, with the following ascending order: net ecosystem exchange ( R 2 < 0.5), ecosystem respiration ( R 2 > 0.6), gross primary production ( R 2> 0.7), latent heat ( R 2 > 0.7), sensible heat ( R 2 > 0.7), and net radiation ( R 2 > 0.8). The ML methods predicted the across-site variability and the mean seasonal cycle of the observed fluxes very well ( R 2 > 0.7), while the 8-day deviations from the mean seasonal cycle were not well predicted ( R 2 < 0.5). Fluxes were better predicted at forested and temperate climate sites than at sites in extreme climates or less represented by training data (e.g., the tropics). Finally, the evaluated large ensemble of ML-based models will be the basis of new global flux products.« less

The role of hydrodynamic transport in greenhouse gas fluxes at a wetland with emergent vegetation

NASA Astrophysics Data System (ADS)

Poindexter, C.; Gilson, E.; Knox, S. H.; Matthes, J. H.; Verfaillie, J. G.; Baldocchi, D. D.; Variano, E. A.

2013-12-01

In wetlands with emergent vegetation, the hydrodynamic transport of dissolved gases is often neglected because emergent plants transport gases directly and limit wind-driven air-water gas exchange by sheltering the water surface. Nevertheless, wetland hydrodynamics, and thermally-driven stirring in particular, have the potential to impact gas fluxes in these environments. We are evaluating the importance of hydrodynamic dissolved gas transport at a re-established marsh on Twitchell Island in the Sacramento-San Joaquin Delta (California, USA). At this marsh, the U.S. Geological Survey has previously observed rapid accumulation of organic material (carbon sequestration) as well as very high methane emissions. To assess the role of hydrodynamics in the marsh's greenhouse gas fluxes, we measured dissolved carbon dioxide and methane in the water column on a bi-weekly basis beginning in July 2012. We employed a model for air-water gas fluxes in wetlands with emergent vegetation that predicts gas transfer velocities from meteorological conditions. Modeled air-water gas fluxes were compared with net gas fluxes measured at the marsh via the eddy covariance technique. This comparison revealed that hydrodynamic transport due to thermal convection was responsible for approximately one third of net carbon dioxide and methane fluxes. The cooling at the water surface driving thermal convection occurred each night and was most pronounced during the warmest months of the year. These finding have implications for the prediction and management of greenhouse gas fluxes at re-established marshes in the Sacramento-San Joaquin Delta and other similar wetlands.

Experimental assessment of the performance of ablative heat shield materials from plasma wind tunnel testing

NASA Astrophysics Data System (ADS)

Löhle, S.; Hermann, T.; Zander, F.

2017-12-01

A method for assessing the performance of typical heat shield materials is presented in this paper. Three different material samples, the DLR material uc(Zuram), the Airbus material uc(Asterm) and the carbon preform uc(Calcarb) were tested in the IRS plasma wind tunnel PWK1 at the same nominal condition. State of the art diagnostic tools, i.e., surface temperature with pyrometry and thermography and boundary layer optical emission spectroscopy were completed by photogrammetric surface recession measurements. These data allow the assessment of the net heat flux for each material. The analysis shows that the three materials each have a different effect on heat flux mitigation with ASTERM showing the largest reduction in surface heat flux. The effect of pyrolysis and blowing is clearly observed and the heat flux reduction can be determined from an energy balance.

Upper-Ocean Processed Under the Stratus Cloud Deck in the Southeast Pacific Ocean

DTIC Science & Technology

2010-01-19

based on Woods Hole Oceano - graphic Institution (WHOI) Improved Meteorological (IMET) buoy observations at 20°S, 85°W. Net surface heat fluxes are...Jason-1 and Jason-2 sea surface heights and geostrophic currents (computed from absolute topography) produced by Segment Sol Multimissions d’Altimetrie

Annual net community production and the biological carbon flux in the ocean

NASA Astrophysics Data System (ADS)

Emerson, Steven

2014-01-01

The flux of biologically produced organic matter from the surface ocean (the biological pump), over an annual cycle, is equal to the annual net community production (ANCP). Experimental determinations of ANCP at ocean time series sites using a variety of different metabolite mass balances have made it possible to evaluate the accuracy of sediment trap fluxes and satellite-determined ocean carbon export. ANCP values at the Hawaii Ocean Time-series (HOT), the Bermuda Atlantic Time-series Study (BATS), Ocean Station Papa (OSP) are 3 ± 1 mol C m-2 yr-1—much less variable than presently suggested by satellite remote sensing measurements and global circulation models. ANCP determined from mass balances at these locations are 3-4 times particulate organic carbon fluxes measured in sediment traps. When the roles of dissolved organic carbon (DOC) flux, zooplankton migration, and depth-dependent respiration are considered these differences are reconciled at HOT and OSP but not at BATS, where measured particulate fluxes are about 3 times lower than expected. Even in the cases where sediment trap fluxes are accurate, it is not possible to "scale up" these measurements to determine ANCP without independent determinations of geographically variable DOC flux and zooplankton migration. Estimates of ANCP from satellite remote sensing using net primary production determined by the carbon-based productivity model suggests less geographic variability than its predecessor (the vertically generalized productivity model) and brings predictions at HOT and OSP closer to measurements; however, satellite-predicted ANCP at BATS is still 3 times too low.

Energy exchange of an alpine grassland on the northeastern Qinghai-Tibetan Plateau

NASA Astrophysics Data System (ADS)

Shang, Lunyu; Zhang, Yu; Lv, Shihua; Wang, Shaoying

2014-05-01

The seasonal variability in the surface energy exchange of an alpine grassland on the northeastern Qinghai-Tibetan Plateau was investigated using eddy covariance measurements. Based on the change of air temperature and the seasonal distribution of precipitation, a winter season and wet season were identified, which were separated by transitional periods. For each period, the surface energy exchange exhibited distinct patterns. Daily mean net radiation (Rn) was almost always positive throughout the year. Sensible heat flux (H) was almost always greater than latent heat flux (LE) during the winter season, and LE was always greater than H during the wet season. Ground heat flux (G0) was relatively low throughout the year. The annual mean net radiation was about 39% of the annual mean solar radiation (Rs). Rn was relatively low during the winter season (21% of Rs) compared to the wet season (55% of Rs), which can be explained by the difference in surface albedo and moisture condition between the two seasons. H and LE had different roles during different periods of the year. Annually, the main consumer of net radiation was LE. During the winter season, H was dominant because of the frozen soil condition and lack of precipitation. During the wet season LE was dominant due to increased temperature and sufficient rainfall coupling with vegetation development. LE was strongly controlled by Rn from June to August though surface conductance (gc) and soil water content (θv) were high. During the transitional periods, H and LE were nearly equally partitioned in the energy balance. The results also suggested that the freeze-thaw condition of soil and the seasonal distribution of precipitation had important impacts on the energy exchange in this alpine grassland.

Evaluation of an urban land surface scheme over a tropical suburban neighborhood

NASA Astrophysics Data System (ADS)

Harshan, Suraj; Roth, Matthias; Velasco, Erik; Demuzere, Matthias

2017-07-01

The present study evaluates the performance of the SURFEX (TEB/ISBA) urban land surface parametrization scheme in offline mode over a suburban area of Singapore. Model performance (diurnal and seasonal characteristics) is investigated using measurements of energy balance fluxes, surface temperatures of individual urban facets, and canyon air temperature collected during an 11-month period. Model performance is best for predicting net radiation and sensible heat fluxes (both are slightly overpredicted during daytime), but weaker for latent heat (underpredicted during daytime) and storage heat fluxes (significantly underpredicted daytime peaks and nighttime storage). Daytime surface temperatures are generally overpredicted, particularly those containing horizontal surfaces such as roofs and roads. This result, together with those for the storage heat flux, point to the need for a better characterization of the thermal and radiative characteristics of individual urban surface facets in the model. Significant variation exists in model behavior between dry and wet seasons, the latter generally being better predicted. The simple vegetation parametrization used is inadequate to represent seasonal moisture dynamics, sometimes producing unrealistically dry conditions.

Cloud-radiative effects on implied oceanic energy transport as simulated by atmospheric general circulation models

NASA Technical Reports Server (NTRS)

Gleckler, P. J.; Randall, D. A.; Boer, G.; Colman, R.; Dix, M.; Galin, V.; Helfand, M.; Kiehl, J.; Kitoh, A.; Lau, W.

1995-01-01

This paper summarizes the ocean surface net energy flux simulated by fifteen atmospheric general circulation models constrained by realistically-varying sea surface temperatures and sea ice as part of the Atmospheric Model Intercomparison Project. In general, the simulated energy fluxes are within the very large observational uncertainties. However, the annual mean oceanic meridional heat transport that would be required to balance the simulated surface fluxes is shown to be critically sensitive to the radiative effects of clouds, to the extent that even the sign of the Southern Hemisphere ocean heat transport can be affected by the errors in simulated cloud-radiation interactions. It is suggested that improved treatment of cloud radiative effects should help in the development of coupled atmosphere-ocean general circulation models.

Effects of a clear-cut harvest on soil respiration in a jack pine - Lichen woodland

USGS Publications Warehouse

Striegl, Robert G.; Wickland, K.P.

1998-01-01

Quantification of the components of ecosystem respiration is essential to understanding carbon (C) cycling of natural and disturbed landscapes. Soil respiration, which includes autotrophic and heterotrophic respiration from throughout the soil profile, is the second largest flux in the global carbon cycle. We measured soil respiration (soil CO2 emission) at an undisturbed mature jack pine (Pinus banksiana Lamb.) stand in Saskatchewan (old jack pine, OJP), and at a formerly continuous portion of the stand that was clear-cut during the previous winter (clear-cut, CC). Tree harvesting reduced soil CO2 emission from ???22.5 to ???9.1 mol CO2??m2 for the 1994 growing season. OJP was a small net sink of atmospheric CO2, while CC was a net source of CO2. Winter emissions were similar at both sites. Reduction of soil respiration was attributed to disruption of the soil surface and to the death of tree roots. Flux simulations for CC and OJP identify 40% of CO2 emission at the undisturbed OJP site as near-surface respiration, 25% as deep-soil respiration, and 35% as tree-root respiration. The near-surface component was larger than the estimated annual C input to soil, suggesting fast C turnover and no net C accumulation in these boreal uplands in 1994.

Partitioning of nutrient net fluxes across the portal-drained viscera in sheep fed twice daily: effect of dietary protein degradability.

PubMed

Rémond, Didier; Bernard, Laurence; Savary-Auzeloux, Isabelle; Nozière, Pierre

2009-08-01

Extrusion is used to decrease leguminous seed protein degradability in the rumen in order to shift part of the dietary protein digestion towards the small intestine. The effect of such displacement of digestion site on the partitioning of nutrient net fluxes across the gastrointestinal tract was studied using four sheep fitted with catheters and blood-flow probes, allowing measurements across the rumen, the mesenteric-drained viscera (MDV) and the portal-drained viscera (PDV). Two diets containing 34 % of pea seeds were tested in a crossover design. They differed only according to pea treatment: raw pea (RP) or extruded pea (EP) diet. Rumen undegradable protein (RUP) accounted for 23 and 40 % of dietary crude protein for RP and EP diets, respectively. Across the rumen wall, ammonia net flux was lower with EP diet, whereas urea net flux was not different. Across the MDV, free amino acid (FAA) net flux was greater with EP diet, whereas peptide amino acid net flux was not different, accounting for 7 % of the non-protein amino acid net release. From RP to EP diet, PDV net flux of ammonia decreased by 23 %, whereas FAA net release increased by 21 %. The difference in dietary RUP did not affect the PDV net flux of SCFA, 3-hydroxybutyrate, lactate and glucose. In conclusion, the partial shift in pea protein digestion from the rumen to the small intestine did not affect the portal net balance of N, but decreased N loss from the rumen, and increased amino acid intestinal absorption and portal delivery.

Quantification and mapping of urban fluxes under climate change: Application of WRF-SUEWS model to Greater Porto area (Portugal).

PubMed

Rafael, S; Martins, H; Marta-Almeida, M; Sá, E; Coelho, S; Rocha, A; Borrego, C; Lopes, M

2017-05-01

Climate change and the growth of urban populations are two of the main challenges facing Europe today. These issues are linked as climate change results in serious challenges for cities. Recent attention has focused on how urban surface-atmosphere exchanges of heat and water will be affected by climate change and the implications for urban planning and sustainability. In this study energy fluxes for Greater Porto area, Portugal, were estimated and the influence of the projected climate change evaluated. To accomplish this, the Weather Research and Forecasting Model (WRF) and the Surface Urban Energy and Water Balance Scheme (SUEWS) were applied for two climatological scenarios: a present (or reference, 1986-2005) scenario and a future scenario (2046-2065), in this case the Representative Concentration Pathway RCP8.5, which reflects the worst set of expectations (with the most onerous impacts). The results show that for the future climate conditions, the incoming shortwave radiation will increase by around 10%, the sensible heat flux around 40% and the net storage heat flux around 35%. In contrast, the latent heat flux will decrease about 20%. The changes in the magnitude of the different fluxes result in an increase of the net all-wave radiation by 15%. The implications of the changes of the energy balance on the meteorological variables are discussed, particularly in terms of temperature and precipitation. Copyright © 2017 Elsevier Inc. All rights reserved.

Intermediate-scale community-level flux of CO 2 and CH 4 in a Minnesota peatland: Putting the SPRUCE project in a global context

DOE PAGES

Hanson, Paul J.; Gill, Allison; Xu, Xiaofeng; ...

2016-08-20

Peatland measurements of CO 2 and CH 4 flux were obtained at scales appropriate to the in situ biological community below the tree layer to demonstrate representativeness of the spruce and peatland responses under climatic and environmental change (SPRUCE) experiment. Surface flux measurements were made using dual open-path analyzers over an area of 1.13 m 2 in daylight and dark conditions along with associated peat temperatures, water table height, hummock moisture, atmospheric pressure and incident radiation data. Observations from August 2011 through December 2014 demonstrated seasonal trends correlated with temperature as the dominant apparent driving variable. The S1-Bog for themore » SPRUCE study was found to be representative of temperate peatlands in terms of CO 2 and CH 4 flux. Maximum net CO 2 flux in midsummer showed similar rates of C uptake and loss: daytime surface uptake was -5 to -6 µmol m -2 s -1 and dark period loss rates were 4–5 µmol m -2 s -1 (positive values are carbon lost to the atmosphere). Maximum midsummer CH4-C flux ranged from 0.4 to 0.5 µmol m -2 s -1 and was a factor of 10 lower than dark CO 2–C efflux rates. Midwinter conditions produced near-zero flux for both CO 2 and CH 4 with frozen surfaces. Integrating temperature-dependent models across annual periods showed dark CO 2–C and CH 4–C flux to be 894 ± 34 and 16 ± 2 gC m -2 y -1, respectively. Net ecosystem exchange of carbon from the shrub-forb-Sphagnum-microbial community (excluding tree contributions) ranged from -3.1 gCO2–C m -2 y -1 in 2013, to C losses from 21 to 65 gCO 2–C m -2 y -1 for the other years.« less

A one-layer satellite surface energy balance for estimating evapotranspiration rates and crop water stress indexes.

PubMed

Barbagallo, Salvatore; Consoli, Simona; Russo, Alfonso

2009-01-01

Daily evapotranspiration fluxes over the semi-arid Catania Plain area (Eastern Sicily, Italy) were evaluated using remotely sensed data from Landsat Thematic Mapper TM5 images. A one-source parameterization of the surface sensible heat flux exchange using satellite surface temperature has been used. The transfer of sensible and latent heat is described by aerodynamic resistance and surface resistance. Required model inputs are brightness, temperature, fractional vegetation cover or leaf area index, albedo, crop height, roughness lengths, net radiation, air temperature, air humidity and wind speed. The aerodynamic resistance (r(ah)) is formulated on the basis of the Monin-Obukhov surface layer similarity theory and the surface resistance (r(s)) is evaluated from the energy balance equation. The instantaneous surface flux values were converted into evaporative fraction (EF) over the heterogeneous land surface to derive daily evapotranspiration values. Remote sensing-based assessments of crop water stress (CWSI) were also made in order to identify local irrigation requirements. Evapotranspiration data and crop coefficient values obtained from the approach were compared with: (i) data from the semi-empirical approach "K(c) reflectance-based", which integrates satellite data in the visible and NIR regions of the electromagnetic spectrum with ground-based measurements and (ii) surface energy flux measurements collected from a micrometeorological tower located in the experiment area. The expected variability associated with ET flux measurements suggests that the approach-derived surface fluxes were in acceptable agreement with the observations.

Episodic Southern Ocean Heat Loss and Its Mixed Layer Impacts Revealed by the Farthest South Multiyear Surface Flux Mooring

NASA Astrophysics Data System (ADS)

Ogle, S. E.; Tamsitt, V.; Josey, S. A.; Gille, S. T.; Cerovečki, I.; Talley, L. D.; Weller, R. A.

2018-05-01

The Ocean Observatories Initiative air-sea flux mooring deployed at 54.08°S, 89.67°W, in the southeast Pacific sector of the Southern Ocean, is the farthest south long-term open ocean flux mooring ever deployed. Mooring observations (February 2015 to August 2017) provide the first in situ quantification of annual net air-sea heat exchange from one of the prime Subantarctic Mode Water formation regions. Episodic turbulent heat loss events (reaching a daily mean net flux of -294 W/m2) generally occur when northeastward winds bring relatively cold, dry air to the mooring location, leading to large air-sea temperature and humidity differences. Wintertime heat loss events promote deep mixed layer formation that lead to Subantarctic Mode Water formation. However, these processes have strong interannual variability; a higher frequency of 2 σ and 3 σ turbulent heat loss events in winter 2015 led to deep mixed layers (>300 m), which were nonexistent in winter 2016.

Dry deposition of ammonia, nitric acid, ammonium, and nitrate to alpine tundra at Niwot Ridge, Colorado

USGS Publications Warehouse

Rattray, G.; Sievering, H.

2001-01-01

Micrometeorological measurements and ambient air samples, analyzed for concentrations of NH3, HNO3, NH4+, and NO3-, were collected at an alpine tundra site on Niwot Ridge, Colorado. The measured concentrations were extremely low and ranged between 5 and 70ngNm-3. Dry deposition fluxes of these atmospheric species were calculated using the micrometeorological gradient method. The calculated mean flux for NH3 indicates a net deposition to the surface and indicates that NH3 contributed significantly to the total N deposition to the tundra during the August-September measurement period. Our pre-measurement estimate of the compensation point for NH3 in air above the tundra was 100-200ngNm-3; thus, a net emission of NH3 was expected given the low ambient concentrations of NH3 observed. Based on our results, however, the NH3 compensation point at this alpine tundra site appears to have been at or below about 20ngNm-3. Large deposition velocities (>2cms-1) were determined for nitrate and ammonium and may result from reactions with surface-derived aerosols. Copyright (C) 2001 Elsevier Science B.V.Micrometeorological measurements and ambient air samples, analyzed for concentrations of NH3, HNO3, NH4+, and NO3-, were collected at an alpine tundra site on Niwot Ridge, Colorado. The measured concentrations were extremely low and ranged between 5 and 70 ng N m-3. Dry deposition fluxes of these atmospheric species were calculated using the micrometeorological gradient method. The calculated mean flux for NH3 indicates a net deposition to the surface and indicates that NH3 contributed significantly to the total N deposition to the tundra during the August-September measurement period. Our pre-measurement estimate of the compensation point for NH3 in air above the tundra was 100-200 ng N m-3; thus, a net emission of NH3 was expected given the low ambient concentrations of NH3 observed. Based on our results, however, the NH3 compensation point at this alpine tundra site appears to have been at or below about 20 ng N m-3. Large deposition velocities (>2 cm s-1) were determined for nitrate and ammonium and may result from reactions with surface-derived aerosols.

African tropical rainforest net carbon dioxide fluxes in the twentieth century

PubMed Central

Fisher, Joshua B.; Sikka, Munish; Sitch, Stephen; Ciais, Philippe; Poulter, Benjamin; Galbraith, David; Lee, Jung-Eun; Huntingford, Chris; Viovy, Nicolas; Zeng, Ning; Ahlström, Anders; Lomas, Mark R.; Levy, Peter E.; Frankenberg, Christian; Saatchi, Sassan; Malhi, Yadvinder

2013-01-01

The African humid tropical biome constitutes the second largest rainforest region, significantly impacts global carbon cycling and climate, and has undergone major changes in functioning owing to climate and land-use change over the past century. We assess changes and trends in CO2 fluxes from 1901 to 2010 using nine land surface models forced with common driving data, and depict the inter-model variability as the uncertainty in fluxes. The biome is estimated to be a natural (no disturbance) net carbon sink (−0.02 kg C m−2 yr−1 or −0.04 Pg C yr−1, p < 0.05) with increasing strength fourfold in the second half of the century. The models were in close agreement on net CO2 flux at the beginning of the century (σ1901 = 0.02 kg C m−2 yr−1), but diverged exponentially throughout the century (σ2010 = 0.03 kg C m−2 yr−1). The increasing uncertainty is due to differences in sensitivity to increasing atmospheric CO2, but not increasing water stress, despite a decrease in precipitation and increase in air temperature. However, the largest uncertainties were associated with the most extreme drought events of the century. These results highlight the need to constrain modelled CO2 fluxes with increasing atmospheric CO2 concentrations and extreme climatic events, as the uncertainties will only amplify in the next century. PMID:23878340

Spatiotemporal Variability in Particulate Organic Carbon Export Observed Using Bio-Optical Profiling Floats

NASA Astrophysics Data System (ADS)

Estapa, M. L.

2016-02-01

Autonomous, bio-optical profiling floats are poised to broaden the number and spatiotemporal resolution of observations of the ocean's biological pump. Here, we used multiple optical sensors aboard two bio-optical profiling floats (Navis BGCi, Sea-Bird) deployed in the Sargasso Sea to derive in situ proxies for particulate carbon (PC) flux, sub-mixed layer net community production (NCP) and to drive a model of net primary production (NPP). Profiles were collected at approximately 2-day resolution, and drift-phase PC flux observations were collected at subdaily resolution at a rotating cycle of observation depths between 150 and 1000 m. The magnitudes of NPP, PC flux, and their annually-averaged ratio were generally consistent with observations at the nearby Bermuda Atlantic Timeseries Study (BATS) site. PC flux and the export ratio were enhanced in the autumn as well as in the spring, and varied over short timescales possibly due to the influence of mesoscale eddies. The relatively shallow park depths and short profile cycle lengths allow us to identify ephemeral, subsurface bio-optical features and compare them to measured fluxes and satellite-observed surface properties.

Anticipated Improvements to Net Surface Freshwater Fluxes from GPM

NASA Technical Reports Server (NTRS)

Smith, Eric A.

2005-01-01

Evaporation and precipitation over the oceans play very important roles in the global water cycle, upper-ocean heat budget, ocean dynamics, and coupled ocean-atmosphere dynamics. In the conventional representation of the terrestrial water cycle, the assumed role of the oceans is to act as near-infinite reservoirs of water with the main drivers of the water cycle being land- atmosphere interactions in which excess precipitation (P) over evaporation (E) is returned to the oceans as surface runoff and baseflow. Whereas this perspective is valid for short space and time scales -- fundamental principles, available observed estimates, and results from models indicate that the oceans play a far more important role in the large-scale water cycle at seasonal and longer timescales. Approximately 70-80% of the total global evaporation and precipitation occurs over oceans. Moreover, latent heat release into the atmosphere over the oceans is the major heat source driving global atmospheric circulations, with the moisture transported by circulations from oceans to continents being the major source of water precipitating over land. Notably, the major impediment in understanding and modeling the oceans role in the global water cycle is the lack of reliable net surface freshwater flux estimates (E - P fluxes) at the salient spatial and temporal resolutions, i.e., consistent coupled weekly to monthly E - P gridded datasets.

Energy balance comparison of sorghum and sunflower

NASA Astrophysics Data System (ADS)

Rachidi, F.; Kirkham, M. B.; Kanemasu, E. T.; Stone, L. R.

1993-03-01

An understanding of the energy exchange processes at the surface of the earth is necessary for studies of global climate change. If the climate becomes drier, as is predicted for northern mid-latitudes, it is important to know how major agricultural crops will play a role in the budget of heat and moisture. Thus, the energy balance components of sorghum [ Sorghum bicolor (L.) Moench.] and sunflower ( Helianthus annuus L.), two drought-resistant crops grown in the areas where summertime drying is forecasted, were compared. Soil water content and evapotranspiration ( ET) rates also were determined. Net radiation was measured with net radiometers. Soil heat flux was analyzed with heat flux plates and thermocouples. The Bowen ratio method was used to determine sensible and latent heat fluxes. Sunflower had a higher evapotranspiration rate and depleted more water from the soil than sorghum. Soil heat flux into the soil during the daytime was greater for sorghum than sunflower, which was probably the result of the more erect leaves of sorghum. Nocturnal net radiation loss from the sorghum crop was greater than that from the sunflower crop, perhaps because more heat was stored in the soil under the sorghum crop. But daytime net radiation values were similar for the two crops. The data indicated that models of climate change must differentiate nighttime net radiation of agricultural crops. Sensible heat flux was not always less (or greater) for sorghum compared to sunflower. Sunflower had greater daytime values for latent heat flux, reflecting its greater depletion of water from the soil. Evapotranspiration rates determined by the energy balance method agreed relatively well with those found by the water balance method. For example, on 8 July (43 days after planting), the ET rates found by the energy-balance and water-balance methods were 4.6 vs. 5.5 mm/day for sunflower, respectively; for sorghum, these values were 4.0 vs. 3.5 mm/day, respectively. If the climate does become drier, the lower soil water use and lower latent heat flux of sorghum compared to sunflower suggest that sorghum will be better adapted to the climate change.

Estimation of land surface heat fluxes based on visible infrared imaging radiometer suite data: case study in northern China

NASA Astrophysics Data System (ADS)

Li, Xiaojun; Xin, Xiaozhou; Peng, Zhiqing; Zhang, Hailong; Li, Li; Shao, Shanshan; Liu, Qinhuo

2017-10-01

Evapotranspiration (ET) plays an important role in surface-atmosphere interactions and can be monitored using remote sensing data. The visible infrared imaging radiometer suite (VIIRS) sensor is a generation of optical satellite sensors that provide daily global coverage at 375- to 750-m spatial resolutions with 22 spectral channels (0.412 to 12.05 μm) and capable of monitoring ET from regional to global scales. However, few studies have focused on methods of acquiring ET from VIIRS images. The objective of this study is to introduce an algorithm that uses the VIIRS data and meteorological variables to estimate the energy budgets of land surfaces, including the net radiation, soil heat flux, sensible heat flux, and latent heat fluxes. A single-source model that based on surface energy balance equation is used to obtain surface heat fluxes within the Zhangye oasis in China. The results were validated using observations collected during the HiWATER (Heihe Watershed Allied Telemetry Experimental Research) project. To facilitate comparison, we also use moderate resolution imaging spectrometer (MODIS) data to retrieve the regional surface heat fluxes. The validation results show that it is feasible to estimate the turbulent heat flux based on the VIIRS sensor and that these data have certain advantages (i.e., the mean bias error of sensible heat flux is 15.23 W m-2) compared with MODIS data (i.e., the mean bias error of sensible heat flux is -29.36 W m-2). Error analysis indicates that, in our model, the accuracies of the estimated sensible heat fluxes rely on the errors in the retrieved surface temperatures and the canopy heights.

Carbon Storage and Sequestration in Ecosystems of the Western United States: Finings of a Recent Resource Assessment

NASA Astrophysics Data System (ADS)

Zhu, Z.; Bergamaschi, B. A.; Hawbaker, T. J.; Liu, S.; Sleeter, B. M.; Sohl, T. L.; Stackpoole, S. M.

2012-12-01

A new assessment was conducted covering 2.66 million km2 in the Western United States extending from the Rockies to the Pacific coastal waters, in two time periods: baseline (the first half of the 2000s) and future (projections from baseline to 2050), using in-situ and remotely sensed data together with statistical methods and simulation models. The total carbon storage in the ecosystems of the Western United States in 2005 was approximately 13,920 TgC; distributed in live biomass (38%), soil organic carbon (39%), and woody debris and other surface carbon pools (23%). Estimated mean values of major flux terms included net ecosystem production (-127.2 TgC/yr), inland lateral flux (7.2 TgC/yr) from rivers/streams to coastal areas, emissions from inland water surfaces to the atmosphere (28.2 TgC/yr), and emissions form the wildland fires (10.0 TgC/yr). Average C sequestration rates for the region were estimated: -86.6 TgC/yr in net flux for all terrestrial ecosystems, -2.4 and -2.0 TgC/yr in net burial rates in lakes and reservoirs and in the Pacific coastal waters respectively, for a total sequestration rate of -90.9 TgC/yr across all of the major ecosystems. A negative sign denotes uptake, sequestration, or a carbon sink. Most of the net carbon flux is in forests (62.2%, -72.1 gC/m2/yr), followed by grasslands/shrublands (29.6%, -16.4 gC/m2/yr), agricultural lands (7.1%, -38.3 gC/m2/yr), and wetlands (0.96%, -82.1 gC/m2/yr). Projected on the basis of future land-use and land-cover scenarios and climate projections, the total amount of carbon that potentially could be stored in the ecosystems of the Western United States in 2050 was estimated to range from 13,743 to 19,407 TgC, an increase of 1,325-3,947 TgC (or 10.7 to 25.5 %) from baseline conditions of 2005. The potential mean (averaged between 2006 and 2050) annual net carbon flux in terrestrial ecosystems was projected to range from -113.9 TgC/yr to 2.9 TgC/yr. When compared to the baseline net carbon flux estimates, the projected future carbon-sequestration rates in the Western United States represent a potential decline by 16.5 to 49 TgC/yr. The projected decline is largely associated with grasslands/shrublands and forests in the Rockies. Under future projections of climate change, the GHG combustion emissions from wildfires were projected to increase by 28 to 56 percent, relative to baseline conditions.

A new one-dimensional radiative equilibrium model for investigating atmospheric radiation entropy flux.

PubMed

Wu, Wei; Liu, Yangang

2010-05-12

A new one-dimensional radiative equilibrium model is built to analytically evaluate the vertical profile of the Earth's atmospheric radiation entropy flux under the assumption that atmospheric longwave radiation emission behaves as a greybody and shortwave radiation as a diluted blackbody. Results show that both the atmospheric shortwave and net longwave radiation entropy fluxes increase with altitude, and the latter is about one order in magnitude greater than the former. The vertical profile of the atmospheric net radiation entropy flux follows approximately that of the atmospheric net longwave radiation entropy flux. Sensitivity study further reveals that a 'darker' atmosphere with a larger overall atmospheric longwave optical depth exhibits a smaller net radiation entropy flux at all altitudes, suggesting an intrinsic connection between the atmospheric net radiation entropy flux and the overall atmospheric longwave optical depth. These results indicate that the overall strength of the atmospheric irreversible processes at all altitudes as determined by the corresponding atmospheric net entropy flux is closely related to the amount of greenhouse gases in the atmosphere.

Surface energy fluxes and their representation in CMIP5 models

NASA Astrophysics Data System (ADS)

Wild, M.

2016-12-01

Energy fluxes at the Earth surface play a key role in the determination of surface climate and in the coupling of atmosphere, land and ocean components. Unlike their counterparts at the top of atmosphere (TOA), surface fluxes cannot be directly measured from satellites, but have to be inferred from the space-born observations using additional models to account for atmospheric perturbations, or from the limited number of surface observations. Uncertainties in the energy fluxes at the surface have therefore traditionally been larger than at the TOA, and have limited our knowledge on the distribution of the energy flows within the climate system. Accordingly, current climate models still largely differ in their representation of surface and atmospheric energy fluxes. Since the mid-1990s, accurate flux measurements became increasingly available from surface networks such as BSRN, which allow to better constrain the surface energy fluxes. There is, however, still a lack of flux measurements particularly over oceans. Further, the larger-scale representativeness of the station records needs to be assessed to judge their suitability as anchor sites for gridded flux products inferred from satellites, reanalyses and climate models. In addition, historic records need to be carefully quality-checked and homogeneized. In parallel, satellite-derived products of surface fluxes profit from the great advancement in space-born observations since the turn of the millennium, and from improved validation capabilities with surface observations. Ultimately, it is the combination of surface and space-born observations, reanalyses and modeling approaches that will advance our knowledge on the distribution of the surface energy fluxes. Uncertainties remain in the determination of surface albedo, skin temperatures and the partitioning of surface net radiation into the sensible and latent heat. Climate models over generations up to present day (CMIP5) tend to overestimate the downward shortwave and underestimate the downward longwave radiation. A challenge also remains the consistent representation of the global energy and water cycles. Yet it is shown that those climate models with a realistic surface radiation balance also simulate global precipitation amounts within the uncertainty range of observational estimates.

Radiant Heat Transfer Between Nongray Parallel Plates of Tungsten

NASA Technical Reports Server (NTRS)

Branstetter, J. Robert

1961-01-01

Net radiant heat flow between two infinite, parallel, tungsten plates was computed by summing the monochromatic energy exchange; the results are graphically presented as a function of the temperatures of the two surfaces. In general these fluxes range from approximately a to 25 percent greater than the results of gray-body computations based on the same emissivity data. The selection of spectral emissivity data and the computational procedure are discussed. The present analytical procedure is so arranged that, as spectral emissivity data for a material become available, these data can be readily introduced into the NASA data-reduction equipment, which has been programmed to compute the net heat flux for the particular geometry and basic assumptions cited in the text. Nongray-body computational techniques for determining radiant heat flux appear practical provided the combination of select spectral emissivity data and the proper mechanized data-reduction equipment are brought to bear on the problem.

Large-Eddy Atmosphere-Land-Surface Modelling over Heterogeneous Surfaces: Model Development and Comparison with Measurements

NASA Astrophysics Data System (ADS)

Shao, Yaping; Liu, Shaofeng; Schween, Jan H.; Crewell, Susanne

2013-08-01

A model is developed for the large-eddy simulation (LES) of heterogeneous atmosphere and land-surface processes. This couples a LES model with a land-surface scheme. New developments are made to the land-surface scheme to ensure the adequate representation of atmosphere-land-surface transfers on the large-eddy scale. These include, (1) a multi-layer canopy scheme; (2) a method for flux estimates consistent with the large-eddy subgrid closure; and (3) an appropriate soil-layer configuration. The model is then applied to a heterogeneous region with 60-m horizontal resolution and the results are compared with ground-based and airborne measurements. The simulated sensible and latent heat fluxes are found to agree well with the eddy-correlation measurements. Good agreement is also found in the modelled and observed net radiation, ground heat flux, soil temperature and moisture. Based on the model results, we study the patterns of the sensible and latent heat fluxes, how such patterns come into existence, and how large eddies propagate and destroy land-surface signals in the atmosphere. Near the surface, the flux and land-use patterns are found to be closely correlated. In the lower boundary layer, small eddies bearing land-surface signals organize and develop into larger eddies, which carry the signals to considerably higher levels. As a result, the instantaneous flux patterns appear to be unrelated to the land-use patterns, but on average, the correlation between them is significant and persistent up to about 650 m. For a given land-surface type, the scatter of the fluxes amounts to several hundred W { m }^{-2}, due to (1) large-eddy randomness; (2) rapid large-eddy and surface feedback; and (3) local advection related to surface heterogeneity.

Estimation of sensible and latent heat flux from natural sparse vegetation surfaces using surface renewal

NASA Astrophysics Data System (ADS)

Zapata, N.; Martínez-Cob, A.

2001-12-01

This paper reports a study undertaken to evaluate the feasibility of the surface renewal method to accurately estimate long-term evaporation from the playa and margins of an endorreic salty lagoon (Gallocanta lagoon, Spain) under semiarid conditions. High-frequency temperature readings were taken for two time lags ( r) and three measurement heights ( z) in order to get surface renewal sensible heat flux ( HSR) values. These values were compared against eddy covariance sensible heat flux ( HEC) values for a calibration period (25-30 July 2000). Error analysis statistics (index of agreement, IA; root mean square error, RMSE; and systematic mean square error, MSEs) showed that the agreement between HSR and HEC improved as measurement height decreased and time lag increased. Calibration factors α were obtained for all analyzed cases. The best results were obtained for the z=0.9 m ( r=0.75 s) case for which α=1.0 was observed. In this case, uncertainty was about 10% in terms of relative error ( RE). Latent heat flux values were obtained by solving the energy balance equation for both the surface renewal ( LESR) and the eddy covariance ( LEEC) methods, using HSR and HEC, respectively, and measurements of net radiation and soil heat flux. For the calibration period, error analysis statistics for LESR were quite similar to those for HSR, although errors were mostly at random. LESR uncertainty was less than 9%. Calibration factors were applied for a validation data subset (30 July-4 August 2000) for which meteorological conditions were somewhat different (higher temperatures and wind speed and lower solar and net radiation). Error analysis statistics for both HSR and LESR were quite good for all cases showing the goodness of the calibration factors. Nevertheless, the results obtained for the z=0.9 m ( r=0.75 s) case were still the best ones.

The Surface Radiation Budget over Oceans and Continents.

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Prata, A. J.; Rotstayn, L. D.; McAvaney, B. J.; Cusack, S.

1998-08-01

An updated evaluation of the surface radiation budget in climate models (1994-96 versions; seven datasets available, with and without aerosols) and in two new satellite-based global datasets (with aerosols) is presented. All nine datasets capture the broad mean monthly zonal variations in the flux components and in the net radiation, with maximum differences of some 100 W m2 occurring in the downwelling fluxes at specific latitudes. Using long-term surface observations, both from land stations and the Pacific warm pool (with typical uncertainties in the annual values varying between ±5 and 20 W m2), excess net radiation (RN) and downwelling shortwave flux density (So) are found in all datasets, consistent with results from earlier studies [for global land, excesses of 15%-20% (12 W m2) in RN and about 12% (20 W m2) in So]. For the nine datasets combined, the spread in annual fluxes is significant: for RN, it is 15 (50) W m2 over global land (Pacific warm pool) in an observed annual mean of 65 (135) W m2; for So, it is 25 (60) W m2 over land (warm pool) in an annual mean of 176 (197) W m2.The effects of aerosols are included in three of the authors' datasets, based on simple aerosol climatologies and assumptions regarding aerosol optical properties. They offer guidance on the broad impact of aerosols on climate, suggesting that the inclusion of aerosols in models would reduce the annual So by 15-20 W m2 over land and 5-10 W m2 over the oceans. Model differences in cloud cover contribute to differences in So between datasets; for global land, this is most clearly demonstrated through the effects of cloud cover on the surface shortwave cloud forcing. The tendency for most datasets to underestimate cloudiness, particularly over global land, and possibly to underestimate atmospheric water vapor absorption, probably contributes to the excess downwelling shortwave flux at the surface.

Quantification of dimethyl sulfide (DMS) production in the sea anemone Aiptasia sp. to simulate the sea-to-air flux from coral reefs

NASA Astrophysics Data System (ADS)

Franchini, Filippo; Steinke, Michael

2017-12-01

The production of dimethyl sulfide (DMS) is poorly quantified in tropical reef environments but forms an essential process that couples marine and terrestrial sulfur cycles and affects climate. Here we quantified net aqueous DMS production and the concentration of its cellular precursor dimethylsulfoniopropionate (DMSP) in the sea anemone Aiptasia sp., a model organism to study coral-related processes. Bleached anemones did not show net DMS production whereas symbiotic anemones produced DMS concentrations (mean ± standard error) of 160.7 ± 44.22 nmol g-1 dry weight (DW) after 48 h incubation. Symbiotic and bleached individuals showed DMSP concentrations of 32.7 ± 6.00 and 0.6 ± 0.19 µmol g-1 DW, respectively. We applied these findings to a Monte Carlo simulation to demonstrate that net aqueous DMS production accounts for only 20 % of gross aqueous DMS production. Monte Carlo-based estimations of sea-to-air fluxes of gaseous DMS showed that reefs may release 0.1 to 26.3 µmol DMS m-2 coral surface area (CSA) d-1 into the atmosphere with 40 % probability for rates between 0.5 and 1.5 µmol m-2 CSA d-1. These predictions were in agreement with directly quantified fluxes in previous studies. Conversion to a flux normalised to sea surface area (SSA) (range 0.1 to 17.4, with the highest probability for 0.3 to 1.0 µmol DMS m-2 SSA d-1) suggests that coral reefs emit gaseous DMS at lower rates than the average global oceanic DMS flux of 4.6 µmol m-2 SSA d-1 (19.6 Tg sulfur per year). The large difference between simulated gross and quantified net aqueous DMS production in corals suggests that the current and future potential for its production in tropical reefs is critically governed by DMS consumption processes. Hence, more research is required to assess the sensitivity of DMS-consumption pathways to ongoing environmental change in order to address the impact of predicted degradation of coral reefs on DMS production in tropical coastal ecosystems and its impact on future atmospheric DMS concentrations and climate.

Wind stress and heat fluxes over a Brazilian Coastal Upwelling

NASA Astrophysics Data System (ADS)

Dourado, Marcelo; Candella, Rogério

2017-04-01

Coastal upwelling zones have been intensively studied in the last decades especially due to their importance to the biological cycle. The coastal upwelling system of the Cabo Frio region (east coast of the Rio de Janeiro state, Brazil) keeps the surface water cold during most part of the year, what induces a stable atmospheric boundary layer associated to northeast winds. The main goal of this study is to investigate the wind stress and heat fluxes exchanges between the ocean and the atmosphere in that area. For this purpose, a set of hourly data meteorological and oceanographic data collected by a Wavescan metocean buoy anchored at 23o59S; 42oW, were used, as well as solar radiation and relative humidity from a terrestrial meteorological station from the Instituto Nacional de Meteorologia (InMet). COARE 3.0 algorithm was used to calculate the latent and sensible heat fluxes. In this discussion, positive values represent fluxes towards the ocean. The average net heat flux over our study period is 88 W m-2. The reduction of the net heat flux is due to the increase of the ocean latent heat loss, although a reduction in incoming shortwave radiation and an increase in ocean long wave cooling also contributes. The latent heat is 20 times larger than the sensible heat flux, but the mean value of the latent heat flux, 62 W m-2, is half the typical value found in open ocean. The temporal variability of both sensible and latent heat fluxes reflects their dependence on wind speed and air-sea temperature differences. When upwelling events, here periods when diurnal SST is lower than 18oC, are compared with undisturbed (without upwelling) events, it can be noted the sensible heat fluxes are positives and 10 times greater in magnitude. This is related to an increment, during these upwelling events, of the air-sea temperature difference and an increasing of the wind speed. The cold waters of the upwelling increase the air-sea temperature gradient and, also, the horizontal land-sea gradient. This could intensifies the sea breeze. At the same time, the latent heat flux to the atmosphere is reduced. As expected, cold waters from the upwelling imply in the reduction of the evaporation, and so the latent heat fluxes also reduce significantly. As upwelling events in this region are associated to the presence of the South Atlantic high pressure, NE winds, during these periods of cold water the net heat flux toward the ocean surface is intensified.

Estimating Evapotranspiration Of Orange Orchards Using Surface Renewal And Remote Sensing Techniques

NASA Astrophysics Data System (ADS)

Consoli, S.; Russo, A.; Snyder, R.

2006-08-01

Surface renewal (SR) analysis was utilized to calculate sensible heat flux density from high frequency temperature measurements above orange orchard canopies during 2005 in eastern Sicily (Italy). The H values were employed to estimate latent heat flux density (LE) using measured net radiation (Rn) and soil heat flux density (G) in the energy balance (EB) equation. Crop coefficients were determined by calculating the ratio Kc=ETa/ETo, with reference ETo derived from the daily Penman-Monteith equation. The estimated daily Kc values showed an average of about 0.75 for canopy covers having about 70% ground shading and 80% of PAR light interception. Remote sensing estimates of Kc and ET fluxes were compared with those measured by SR-EB. IKONOS satellite estimates of Kc and NDVI were linearly correlated for the orchard stands.

Field-Based Estimates of Global Warming Potential in Bioenergy Systems of Hawaii: Crop Choice and Deficit Irrigation.

PubMed

Pawlowski, Meghan N; Crow, Susan E; Meki, Manyowa N; Kiniry, James R; Taylor, Andrew D; Ogoshi, Richard; Youkhana, Adel; Nakahata, Mae

2017-01-01

Replacing fossil fuel with biofuel is environmentally viable from a climate change perspective only if the net greenhouse gas (GHG) footprint of the system is reduced. The effects of replacing annual arable crops with perennial bioenergy feedstocks on net GHG production and soil carbon (C) stock are critical to the system-level balance. Here, we compared GHG flux, crop yield, root biomass, and soil C stock under two potential tropical, perennial grass biofuel feedstocks: conventional sugarcane and ratoon-harvested, zero-tillage napiergrass. Evaluations were conducted at two irrigation levels, 100% of plantation application and at a 50% deficit. Peaks and troughs of GHG emission followed agronomic events such as ratoon harvest of napiergrass and fertilization. Yet, net GHG flux was dominated by carbon dioxide (CO2), as methane was oxidized and nitrous oxide (N2O) emission was very low even following fertilization. High N2O fluxes that frequently negate other greenhouse gas benefits that come from replacing fossil fuels with agronomic forms of bioenergy were mitigated by efficient water and fertilizer management, including direct injection of fertilizer into buried irrigation lines. From soil intensively cultivated for a century in sugarcane, soil C stock and root biomass increased rapidly following cultivation in grasses selected for robust root systems and drought tolerance. The net soil C increase over the two-year crop cycle was three-fold greater than the annualized soil surface CO2 flux. Deficit irrigation reduced yield, but increased soil C accumulation as proportionately more photosynthetic resources were allocated belowground. In the first two years of cultivation napiergrass did not increase net greenhouse warming potential (GWP) compared to sugarcane, and has the advantage of multiple ratoon harvests per year and less negative effects of deficit irrigation to yield.

Field-Based Estimates of Global Warming Potential in Bioenergy Systems of Hawaii: Crop Choice and Deficit Irrigation

PubMed Central

Meki, Manyowa N.; Kiniry, James R.; Taylor, Andrew D.; Ogoshi, Richard; Youkhana, Adel; Nakahata, Mae

2017-01-01

Replacing fossil fuel with biofuel is environmentally viable from a climate change perspective only if the net greenhouse gas (GHG) footprint of the system is reduced. The effects of replacing annual arable crops with perennial bioenergy feedstocks on net GHG production and soil carbon (C) stock are critical to the system-level balance. Here, we compared GHG flux, crop yield, root biomass, and soil C stock under two potential tropical, perennial grass biofuel feedstocks: conventional sugarcane and ratoon-harvested, zero-tillage napiergrass. Evaluations were conducted at two irrigation levels, 100% of plantation application and at a 50% deficit. Peaks and troughs of GHG emission followed agronomic events such as ratoon harvest of napiergrass and fertilization. Yet, net GHG flux was dominated by carbon dioxide (CO2), as methane was oxidized and nitrous oxide (N2O) emission was very low even following fertilization. High N2O fluxes that frequently negate other greenhouse gas benefits that come from replacing fossil fuels with agronomic forms of bioenergy were mitigated by efficient water and fertilizer management, including direct injection of fertilizer into buried irrigation lines. From soil intensively cultivated for a century in sugarcane, soil C stock and root biomass increased rapidly following cultivation in grasses selected for robust root systems and drought tolerance. The net soil C increase over the two-year crop cycle was three-fold greater than the annualized soil surface CO2 flux. Deficit irrigation reduced yield, but increased soil C accumulation as proportionately more photosynthetic resources were allocated belowground. In the first two years of cultivation napiergrass did not increase net greenhouse warming potential (GWP) compared to sugarcane, and has the advantage of multiple ratoon harvests per year and less negative effects of deficit irrigation to yield. PMID:28052075

Annual Net Community Production in the Western Subtropical North Pacific Determined from Argo-O2 Measurements

NASA Astrophysics Data System (ADS)

Yang, B.; Emerson, S. R.; Bushinsky, S. M.

2016-02-01

Export of organic carbon from the surface ocean to depth (the biological pump) helps maintain the pCO2 of the atmosphere and the O2 content of the oxygen minimum zones of the ocean. In the upper ocean, at steady state over a seasonal cycle the net organic carbon export is equal to the Annual Net Community Production (ANCP). The geographic distribution of this quantity determined by satellite-predicted Net Primary Production (NPP) and the recycling efficiency in the euphotic zone is more heterogeneous than the limited experimental estimates of ANCP. We evaluate the relationship between these two estimates of ANCP in the subtropical Western North Pacific Ocean ( 165o E and 20o N) using oxygen measurements on Argo Floats. In January of 2015 we deployed four floats with Anderaa oxygen sensors attached to a 60 cm stick on top of the float end cap, which can be readily calibrated against atmospheric pO2. We present data from these floats and air-sea oxygen flux calculations. The degree of oxygen supersaturation in summer is 1-2 percent, and in winter it fluctuates between being over and undersaturated. Evaluating the role of bubbles in winter is critical to an accurate determination of the annual flux. While there is not a full year of data at the time of writing this abstract, there will be when the Ocean Science meeting is held. So far, after nine months of measurements, there is a net flux of oxygen to the atmosphere, indicating that photosynthesis exceeds respiration. In February we will present a full annual cycle of air-sea oxygen flux and an estimate of ANCP in this very rarely studied region of the ocean.

Observation of regional air pollutant transport between the megacity Beijing and the North China Plain

NASA Astrophysics Data System (ADS)

Li, Yingruo; Ye, Chunxiang; Liu, Jun; Zhu, Yi; Wang, Junxia; Tan, Ziqiang; Lin, Weili; Zeng, Limin; Zhu, Tong

2016-11-01

Megacities have strong interactions with the surrounding regions through transport of air pollutants. It has been frequently addressed that the air quality of Beijing is influenced by the influx of air pollutants from the North China Plain (NCP). Estimations of air pollutant cross-boundary transport between Beijing and the NCP are important for air quality management. However, evaluation of cross-boundary transport using long-term observations is very limited. Using the observational results of the gaseous pollutants SO2, NO, NO2, O3, and CO from August 2006 to October 2008 at the Yufa site, a cross-boundary site between the megacity Beijing and the NCP, together with meteorological parameters, we explored a method for evaluating the transport flux intensities at Yufa, as part of the "Campaign of Air Quality Research in Beijing and Surrounding Region 2006-2008" (CAREBeijing 2006-2008). The hourly mean ± SD (median) concentration of SO2, NO, NO2, NOx, O3, Ox, and CO was 15 ± 16 (9) ppb, 12 ± 25 (3) ppb, 24 ± 19 (20) ppb, 36 ± 39 (23) ppb, 28 ± 27 (21) ppb, 52 ± 24 (45) ppb, and 1.6 ± 1.4 (1.2) ppm during the observation period, respectively. The bivariate polar plots showed the dependence of pollutant concentrations on both wind speed and wind direction, and thus inferred their dominant transport directions. Surface flux intensity calculations further demonstrated the regional transport influence of Beijing and the NCP on Yufa. The net surface transport flux intensity (mean ± SD) of SO2, NO, NO2, NOx, O3, Ox, and CO was 6.2 ± 89.5, -4.3 ± 29.5, -0.6 ± 72.3, -4.9 ± 93.0, 14.7 ± 187.8, 14.8 ± 234.9, and 70 ± 2830 µg s-1 m-2 during the observation period, respectively. For SO2, CO, O3, and Ox the surface flux intensities from the NCP to Yufa surpassed those from Beijing to Yufa in all seasons except winter, with the strongest net fluxes largely in summer, which were about 4-8 times those of other seasons. The surface transport flux intensity of NOx from Beijing to Yufa was stronger than that from the NCP to Yufa except in summer, with the strongest net flux in winter, which was about 1.3-8 times that of other seasons. The flux intensities were then assigned to the corresponding trajectories in the potential source contribution function analysis (PSCF), which confirmed the results of flux intensity calculations. Our study also suggested that various factors, such as the wind field, emission inventory, and photochemical reactions, could influence transport of air pollutants. The decrease of surface flux intensity during the Olympic Games implied the role of both local emission reduction and regional cooperation in successful air quality management. Three dimensional observations are needed for further comprehensive discussion of the regional transport between Beijing and the NCP.

Developing multi-tracer approaches to constrain the parameterisation of leaf and soil CO2 and H2O exchange in land surface models

NASA Astrophysics Data System (ADS)

Ogée, Jerome; Wehr, Richard; Commane, Roisin; Launois, Thomas; Meredith, Laura; Munger, Bill; Nelson, David; Saleska, Scott; Zahniser, Mark; Wofsy, Steve; Wingate, Lisa

2016-04-01

The net flux of carbon dioxide between the land surface and the atmosphere is dominated by photosynthesis and soil respiration, two of the largest gross CO2 fluxes in the carbon cycle. More robust estimates of these gross fluxes could be obtained from the atmospheric budgets of other valuable tracers, such as carbonyl sulfide (COS) or the carbon and oxygen isotope compositions (δ13C and δ18O) of atmospheric CO2. Over the past decades, the global atmospheric flask network has measured the inter-annual and intra-annual variations in the concentrations of these tracers. However, knowledge gaps and a lack of high-resolution multi-tracer ecosystem-scale measurements have hindered the development of process-based models that can simulate the behaviour of each tracer in response to environmental drivers. We present novel datasets of net ecosystem COS, 13CO2 and CO18O exchange and vertical profile data collected over 3 consecutive growing seasons (2011-2013) at the Harvard forest flux site. We then used the process-based model MuSICA (multi-layer Simulator of the Interactions between vegetation Canopy and the Atmosphere) to include the transport, reaction, diffusion and production of each tracer within the forest and exchanged with the atmosphere. Model simulations over the three years captured well the impact of diurnally and seasonally varying environmental conditions on the net ecosystem exchange of each tracer. The model also captured well the dynamic vertical features of tracer behaviour within the canopy. This unique dataset and model sensitivity analysis highlights the benefit in the collection of multi-tracer high-resolution field datasets and the developement of multi-tracer land surface models to provide valuable constraints on photosynthesis and respiration across scales in the near future.

CAUSES: On the Role of Surface Energy Budget Errors to the Warm Surface Air Temperature Error Over the Central United States

DOE PAGES

Ma, H. -Y.; Klein, S. A.; Xie, S.; ...

2018-02-27

Many weather forecast and climate models simulate warm surface air temperature (T 2m) biases over midlatitude continents during the summertime, especially over the Great Plains. We present here one of a series of papers from a multimodel intercomparison project (CAUSES: Cloud Above the United States and Errors at the Surface), which aims to evaluate the role of cloud, radiation, and precipitation biases in contributing to the T 2m bias using a short-term hindcast approach during the spring and summer of 2011. Observations are mainly from the Atmospheric Radiation Measurement Southern Great Plains sites. The present study examines the contributions ofmore » surface energy budget errors. All participating models simulate too much net shortwave and longwave fluxes at the surface but with no consistent mean bias sign in turbulent fluxes over the Central United States and Southern Great Plains. Nevertheless, biases in the net shortwave and downward longwave fluxes as well as surface evaporative fraction (EF) are contributors to T 2m bias. Radiation biases are largely affected by cloud simulations, while EF bias is largely affected by soil moisture modulated by seasonal accumulated precipitation and evaporation. An approximate equation based upon the surface energy budget is derived to further quantify the magnitudes of radiation and EF contributions to T 2m bias. Our analysis ascribes that a large EF underestimate is the dominant source of error in all models with a large positive temperature bias, whereas an EF overestimate compensates for an excess of absorbed shortwave radiation in nearly all the models with the smallest temperature bias.« less

CAUSES: On the Role of Surface Energy Budget Errors to the Warm Surface Air Temperature Error Over the Central United States

NASA Astrophysics Data System (ADS)

Ma, H.-Y.; Klein, S. A.; Xie, S.; Zhang, C.; Tang, S.; Tang, Q.; Morcrette, C. J.; Van Weverberg, K.; Petch, J.; Ahlgrimm, M.; Berg, L. K.; Cheruy, F.; Cole, J.; Forbes, R.; Gustafson, W. I.; Huang, M.; Liu, Y.; Merryfield, W.; Qian, Y.; Roehrig, R.; Wang, Y.-C.

2018-03-01

Many weather forecast and climate models simulate warm surface air temperature (T2m) biases over midlatitude continents during the summertime, especially over the Great Plains. We present here one of a series of papers from a multimodel intercomparison project (CAUSES: Cloud Above the United States and Errors at the Surface), which aims to evaluate the role of cloud, radiation, and precipitation biases in contributing to the T2m bias using a short-term hindcast approach during the spring and summer of 2011. Observations are mainly from the Atmospheric Radiation Measurement Southern Great Plains sites. The present study examines the contributions of surface energy budget errors. All participating models simulate too much net shortwave and longwave fluxes at the surface but with no consistent mean bias sign in turbulent fluxes over the Central United States and Southern Great Plains. Nevertheless, biases in the net shortwave and downward longwave fluxes as well as surface evaporative fraction (EF) are contributors to T2m bias. Radiation biases are largely affected by cloud simulations, while EF bias is largely affected by soil moisture modulated by seasonal accumulated precipitation and evaporation. An approximate equation based upon the surface energy budget is derived to further quantify the magnitudes of radiation and EF contributions to T2m bias. Our analysis ascribes that a large EF underestimate is the dominant source of error in all models with a large positive temperature bias, whereas an EF overestimate compensates for an excess of absorbed shortwave radiation in nearly all the models with the smallest temperature bias.

CAUSES: On the Role of Surface Energy Budget Errors to the Warm Surface Air Temperature Error Over the Central United States

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, H. -Y.; Klein, S. A.; Xie, S.

Many weather forecast and climate models simulate warm surface air temperature (T 2m) biases over midlatitude continents during the summertime, especially over the Great Plains. We present here one of a series of papers from a multimodel intercomparison project (CAUSES: Cloud Above the United States and Errors at the Surface), which aims to evaluate the role of cloud, radiation, and precipitation biases in contributing to the T 2m bias using a short-term hindcast approach during the spring and summer of 2011. Observations are mainly from the Atmospheric Radiation Measurement Southern Great Plains sites. The present study examines the contributions ofmore » surface energy budget errors. All participating models simulate too much net shortwave and longwave fluxes at the surface but with no consistent mean bias sign in turbulent fluxes over the Central United States and Southern Great Plains. Nevertheless, biases in the net shortwave and downward longwave fluxes as well as surface evaporative fraction (EF) are contributors to T 2m bias. Radiation biases are largely affected by cloud simulations, while EF bias is largely affected by soil moisture modulated by seasonal accumulated precipitation and evaporation. An approximate equation based upon the surface energy budget is derived to further quantify the magnitudes of radiation and EF contributions to T 2m bias. Our analysis ascribes that a large EF underestimate is the dominant source of error in all models with a large positive temperature bias, whereas an EF overestimate compensates for an excess of absorbed shortwave radiation in nearly all the models with the smallest temperature bias.« less

Radiation Climatology of the Greenland Ice Sheet Derived from Greenland Climate Network Data

NASA Technical Reports Server (NTRS)

Steffen, Konrad; Box, Jason

2003-01-01

The magnitude of shortwave and longwave dative fluxes are critical to surface energy balance variations over the Greenland ice sheet, affecting many aspects of its climate, including melt rates, the nature of low-level temperature inversions, the katabatic wind regime and buoyant stability of the atmosphere. Nevertheless, reliable measurements of the radiative fluxes over the ice sheet are few in number, and have been of limited duration and areal distribution (e.g. Ambach, 1960; 1963, Konzelmann et al., 1994, Harding et al., 1995, Van den Broeke, 1996). Hourly GC-Net radiation flux measurements spanning 1995-2001 period have been used to produce a monthly dataset of surface radiation balance components. The measurements are distributed widely across Greenland and incorporate multiple sensors

Development and evaluation of an ammonia bidirectional flux parameterization for air quality models

NASA Astrophysics Data System (ADS)

Pleim, Jonathan E.; Bash, Jesse O.; Walker, John T.; Cooter, Ellen J.

2013-05-01

is an important contributor to particulate matter in the atmosphere and can significantly impact terrestrial and aquatic ecosystems. Surface exchange between the atmosphere and biosphere is a key part of the ammonia cycle. New modeling techniques are being developed for use in air quality models that replace current ammonia emissions from fertilized crops and ammonia dry deposition with a bidirectional surface flux model including linkage to a detailed biogeochemical and farm management model. Recent field studies involving surface flux measurements over crops that predominate in North America have been crucial for extending earlier bidirectional flux models toward more realistic treatment of NH3 fluxes for croplands. Comparisons of the ammonia bidirection flux algorithm to both lightly fertilized soybeans and heavily fertilized corn demonstrate that the model can capture the magnitude and dynamics of observed ammonia fluxes, both net deposition and evasion, over a range of conditions with overall biases on the order of the uncertainty of the measurements. However, successful application to the field experiment in heavily fertilized corn required substantial modification of the model to include new parameterizations for in-soil diffusion resistance, ground quasi-laminar boundary layer resistance, and revised cuticular resistance that is dependent on in-canopy NH3 concentration and RH at the leaf surface. This new bidirectional flux algorithm has been incorporated in an air quality modeling system, which also includes an implementation of a soil nitrification model.

Application of a dual unscented Kalman filter for simultaneous state and parameter estimation in problems of surface-atmosphere exchange

Treesearch

J.H. Gove; D.Y. Hollinger; D.Y. Hollinger

2006-01-01

A dual unscented Kalman filter (UKF) was used to assimilate net CO2 exchange (NEE) data measured over a spruce-hemlock forest at the Howland AmeriFlux site in Maine, USA, into a simple physiological model for the purpose of filling gaps in an eddy flux time series. In addition to filling gaps in the measurement record, the UKF approach provides continuous estimates of...

Application of Monte Carlo techniques to transient thermal modeling of cavity radiometers having diffuse-specular surfaces

NASA Technical Reports Server (NTRS)

Mahan, J. R.; Eskin, L. D.

1981-01-01

A viable alternative to the net exchange method of radiative analysis which is equally applicable to diffuse and diffuse-specular enclosures is presented. It is particularly more advantageous to use than the net exchange method in the case of a transient thermal analysis involving conduction and storage of energy as well as radiative exchange. A new quantity, called the distribution factor is defined which replaces the angle factor and the configuration factor. Once obtained, the array of distribution factors for an ensemble of surface elements which define an enclosure permits the instantaneous net radiative heat fluxes to all of the surfaces to be computed directly in terms of the known surface temperatures at that instant. The formulation of the thermal model is described, as is the determination of distribution factors by application of a Monte Carlo analysis. The results show that when fewer than 10,000 packets are emitted, an unsatisfactory approximation for the distribution factors is obtained, but that 10,000 packets is sufficient.

Aerosol Radiative Forcing Derived From SeaWIFS - Retrieved Aerosol Optical Properties

NASA Technical Reports Server (NTRS)

Chou, Mong-Dah; Chan, Pui-King; Wang, Menghua; Einaudi, Franco (Technical Monitor)

2000-01-01

To understand climatic implications of aerosols over global oceans, the aerosol optical properties retrieved from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) are analyzed, and the effects of the aerosols on the Earth's radiation budgets (aerosol radiative forcing, ARF) are computed using a radiative transfer model. It is found that the distribution of the SeaWiFS-retrieved aerosol optical thickness is distinctively zonal. The maximum in the equatorial region coincides with the Intertropical Convergence Zone, and the maximum in the Southern Hemispheric high latitudes coincides with the region of prevailing westerlies. The minimum aerosol optical thickness is found in the subtropical high pressure regions, especially in the Southern Hemisphere. These zonal patterns clearly demonstrate the influence of atmospheric circulation on the oceanic aerosol distribution. Over global oceans, aerosols reduce the annual mean net downward solar flux by 5.4 W m-2 at the top of the atmosphere and by 6.1 W m-2 at the surface. The largest ARF is found in the tropical Atlantic, Arabian Sea, Bay of Bengal, the coastal regions of Southeast and East Asia, and the Southern Hemispheric high latitudes. During the period of the Indonesian big fires (September-December 1997), the cooling due to aerosols is greater than 15 W m-2 at the top of the atmosphere and greater than 30 W m(exp -1) at the surface in the vicinity of the maritime continents. The atmosphere receives extra solar radiation by greater than 15 W m(exp -1) over a large area. These large changes in radiative fluxes are expected to have enhanced the atmospheric stability, weakened the atmospheric circulation, and augmented the drought condition during that period. It would be very instructive to simulate the regional climatic. The model-calculated clear sky solar flux at the top of the atmosphere is compared with that derived from the Clouds and the Earth's Radiant Energy System (CERES). The net downward solar flux of CERES is systematically larger than the model calculations by -3 W M-2. In the equatorial region, the CERES-derived net downward solar flux is even larger than the model calculations without including aerosols. It is possible that the CERES incorrectly identified regions of high humidity and high aerosol concentration as being cloud contaminated and, hence, overestimated the clear sky net downward solar flux.

Advances in the Surface Renewal Flux Measurement Method

NASA Astrophysics Data System (ADS)

Shapland, T. M.; McElrone, A.; Paw U, K. T.; Snyder, R. L.

2011-12-01

The measurement of ecosystem-scale energy and mass fluxes between the planetary surface and the atmosphere is crucial for understanding geophysical processes. Surface renewal is a flux measurement technique based on analyzing the turbulent coherent structures that interact with the surface. It is a less expensive technique because it does not require fast-response velocity measurements, but only a fast-response scalar measurement. It is therefore also a useful tool for the study of the global cycling of trace gases. Currently, surface renewal requires calibration against another flux measurement technique, such as eddy covariance, to account for the linear bias of its measurements. We present two advances in the surface renewal theory and methodology that bring the technique closer to becoming a fully independent flux measurement method. The first advance develops the theory of turbulent coherent structure transport associated with the different scales of coherent structures. A novel method was developed for identifying the scalar change rate within structures at different scales. Our results suggest that for canopies less than one meter in height, the second smallest coherent structure scale dominates the energy and mass flux process. Using the method for resolving the scalar exchange rate of the second smallest coherent structure scale, calibration is unnecessary for surface renewal measurements over short canopies. This study forms the foundation for analysis over more complex surfaces. The second advance is a sensor frequency response correction for measuring the sensible heat flux via surface renewal. Inexpensive fine-wire thermocouples are frequently used to record high frequency temperature data in the surface renewal technique. The sensible heat flux is used in conjunction with net radiation and ground heat flux measurements to determine the latent heat flux as the energy balance residual. The robust thermocouples commonly used in field experiments underestimate the sensible heat flux, yielding results that are less than 50% of the sensible heat flux measured with finer sensors. We present the methodology for correcting the thermocouple signal to avoid underestimating the heat flux at both the smallest and the second smallest coherent structure scale.

Evapotranspiration Cycles in a High Latitude Agroecosystem: Potential Warming Role.

PubMed

Ruairuen, Watcharee; Fochesatto, Gilberto J; Sparrow, Elena B; Schnabel, William; Zhang, Mingchu; Kim, Yongwon

2015-01-01

As the acreages of agricultural lands increase, changes in surface energetics and evapotranspiration (ET) rates may arise consequently affecting regional climate regimes. The objective of this study was to evaluate summertime ET dynamics and surface energy processes in a subarctic agricultural farm in Interior Alaska. The study includes micrometeorological and hydrological data. Results covering the period from June to September 2012 and 2013 indicated consistent energy fractions: LE/Rnet (67%), G/Rnet (6%), H/Rnet (27%) where LE is latent heat flux, Rnet is the surface net radiation, G is ground heat flux and H is the sensible heat flux. Additionally actual surface evapotranspiration from potential evaporation was found to be in the range of 59 to 66%. After comparing these rates with those of most prominent high latitude ecosystems it is argued here that if agroecosystem in high latitudes become an emerging feature in the land-use, the regional surface energy balance will significantly shift in comparison to existing Arctic natural ecosystems.

Modeling dynamic exchange of gaseous elemental mercury at polar sunrise.

PubMed

Dastoor, Ashu P; Davignon, Didier; Theys, Nicolas; Van Roozendael, Michel; Steffen, Alexandra; Ariya, Parisa A

2008-07-15

At polar sunrise, gaseous elemental mercury (GEM) undergoes an exceptional dynamic exchange in the air and at the snow surface during which GEM can be rapidly removed from the atmosphere (the so-called atmospheric mercury depletion events (AMDEs)) as well as re-emitted from the snow within a few hours to days in the Polar Regions. Although high concentrations of total mercury in snow following AMDEs is well documented, there is very little data available on the redox transformation processes of mercury in the snow and the fluxes of mercury at the air/snow interface. Therefore, the net gain of mercury in the Polar Regions as a result of AMDEs is still an open question. We developed a new version of the global mercury model, GRAHM, which includes for the first time bidirectional surface exchange of GEM in Polar Regions in spring and summer by developing schemes for mercury halogen oxidation, deposition, and re-emission. Also for the first time, GOME satellite data-derived boundary layer concentrations of BrO have been used in a global mercury model for representation of halogen mercury chemistry. Comparison of model simulated and measured atmospheric concentrations of GEM at Alert, Canada, for 3 years (2002-2004) shows the model's capability in simulating the rapid cycling of mercury during and after AMDEs. Brooks et al. (1) measured mercury deposition, reemission, and net surface gain fluxes of mercury at Barrow, AK, during an intensive measurement campaign for a 2 week period in spring (March 25 to April 7, 2003). They reported 1.7, 1.0 +/- 0.2, and 0.7 +/- 0.2 microg m(-2) deposition, re-emission, and net surface gain, respectively. Using the optimal configuration of the model, we estimated 1.8 microg m(-2) deposition, 1.0 microg m(-2) re-emission, and 0.8 microg m(-2) net surface gain of mercury for the same time period at Barrow. The estimated net annual accumulation of mercury within the Arctic Circle north of 66.5 degrees is approximately 174 t with +/-7 t of interannual variability for 2002-2004 using the optimal configuration. We estimated the uncertainty of the model results to the Hg/Br reaction rate coefficient to be approximately 6%. Springtime is clearly demonstrated as the most active period of mercury exchanges and net surface gain (approximately 46% of annual accumulation) in the Arctic.

Use of ground-based remotely sensed data for surface energy balance evaluation of a semiarid rangeland

USGS Publications Warehouse

Moran, M.S.; Kustas, William P.; Vidal, A.; Stannard, D.I.; Blanford, J.H.; Nichols, W.D.

1994-01-01

An interdisciplinary field experiment was conducted to study the water and energy balance of a semiarid rangeland watershed in southeast Arizona during the summer of 1990. Two subwatersheds, one grass dominated and the other shrub dominated, were selected for intensive study with ground-based remote sensing systems and hydrometeorological instrumentation. Surface energy balance was evaluated at both sites using direct and indirect measurements of the turbulent fluxes (eddy correlation, variance, and Bowen ratio methods) and using an aerodynamic approach based on remote measurements of surface reflectance and temperature and conventional meteorological information. Estimates of net radiant flux density (Rn), derived from measurements of air temperature, incoming solar radiation, and surface temperature and radiance compared well with values measured using a net radiometer (mean absolute difference (MAD) ≃ 50 W/m2 over a range from 115 to 670 W/m2). Soil heat flux density (G) was estimated using a relation between G/Rn and a spectral vegetation index computed from the red and near-infrared surface reflectance. These G estimates compared well with conventional measurements of G using buried soil heat flux plates (MAD ≃ 20 W/m2 over a range from −13 to 213 W/m2). In order to account for the effects of sparse vegetation, semiempirical adjustments to the single-layer bulk aerodynamic resistance approach were required for evaluation of sensible heat flux density (H). This yielded differences between measurements and remote estimates of H of approximately 33 W/m2 over a range from 13 to 303 W/m2. The resulting estimates of latent heat flux density, LE, were of the same magnitude and trend as measured values; however, a significant scatter was still observed: MAD ≃ 40 W/m2 over a range from 0 to 340 W/m2. Because LE was solved as a residual, there was a cumulative effect of errors associated with remote estimates of Rn, G, and H.

Use of MODIS Sensor Images Combined with Reanalysis Products to Retrieve Net Radiation in Amazonia

PubMed Central

de Oliveira, Gabriel; Brunsell, Nathaniel A.; Moraes, Elisabete C.; Bertani, Gabriel; dos Santos, Thiago V.; Shimabukuro, Yosio E.; Aragão, Luiz E. O. C.

2016-01-01

In the Amazon region, the estimation of radiation fluxes through remote sensing techniques is hindered by the lack of ground measurements required as input in the models, as well as the difficulty to obtain cloud-free images. Here, we assess an approach to estimate net radiation (Rn) and its components under all-sky conditions for the Amazon region through the Surface Energy Balance Algorithm for Land (SEBAL) model utilizing only remote sensing and reanalysis data. The study period comprised six years, between January 2001–December 2006, and images from MODIS sensor aboard the Terra satellite and GLDAS reanalysis products were utilized. The estimates were evaluated with flux tower measurements within the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) project. Comparison between estimates obtained by the proposed method and observations from LBA towers showed errors between 12.5% and 16.4% and 11.3% and 15.9% for instantaneous and daily Rn, respectively. Our approach was adequate to minimize the problem related to strong cloudiness over the region and allowed to map consistently the spatial distribution of net radiation components in Amazonia. We conclude that the integration of reanalysis products and satellite data, eliminating the need for surface measurements as input model, was a useful proposition for the spatialization of the radiation fluxes in the Amazon region, which may serve as input information needed by algorithms that aim to determine evapotranspiration, the most important component of the Amazon hydrological balance. PMID:27347957

Use of MODIS Sensor Images Combined with Reanalysis Products to Retrieve Net Radiation in Amazonia.

PubMed

de Oliveira, Gabriel; Brunsell, Nathaniel A; Moraes, Elisabete C; Bertani, Gabriel; Dos Santos, Thiago V; Shimabukuro, Yosio E; Aragão, Luiz E O C

2016-06-24

In the Amazon region, the estimation of radiation fluxes through remote sensing techniques is hindered by the lack of ground measurements required as input in the models, as well as the difficulty to obtain cloud-free images. Here, we assess an approach to estimate net radiation (Rn) and its components under all-sky conditions for the Amazon region through the Surface Energy Balance Algorithm for Land (SEBAL) model utilizing only remote sensing and reanalysis data. The study period comprised six years, between January 2001-December 2006, and images from MODIS sensor aboard the Terra satellite and GLDAS reanalysis products were utilized. The estimates were evaluated with flux tower measurements within the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) project. Comparison between estimates obtained by the proposed method and observations from LBA towers showed errors between 12.5% and 16.4% and 11.3% and 15.9% for instantaneous and daily Rn, respectively. Our approach was adequate to minimize the problem related to strong cloudiness over the region and allowed to map consistently the spatial distribution of net radiation components in Amazonia. We conclude that the integration of reanalysis products and satellite data, eliminating the need for surface measurements as input model, was a useful proposition for the spatialization of the radiation fluxes in the Amazon region, which may serve as input information needed by algorithms that aim to determine evapotranspiration, the most important component of the Amazon hydrological balance.

Measuring and modeling near-surface reflected and emitted radiation fluxes at the FIFE site

NASA Technical Reports Server (NTRS)

Blad, Blaine L.; Walter-Shea, Elizabeth A.; Starks, Patrick J.; Vining, Roel C.; Hays, Cynthia J.; Mesarch, Mark A.

1990-01-01

Information is presented pertaining to the measurement and estimation of reflected and emitted components of the radiation balance. Information is included about reflectance and transmittance of solar radiation from and through the leaves of some grass and forb prairie species, bidirectional reflectance from a prairie canopy is discussed and measured and estimated fluxes are described of incoming and outgoing longwave and shortwave radiation. Results of the study showed only very small differences in reflectances and transmittances for the adaxial and abaxial surfaces of grass species in the visible and infrared wavebands, but some differences in the infrared wavebands were noted for the forbs. Reflectance from the prairie canopy changed as a function of solar and view zenith angles in the solar principal plane with definite asymmetry about nadir. The surface temperature of prairie canopies was found to vary by as much as 5 C depending on view zenith and azimuth position and on the solar azimuth. Aerodynamic temperature calculated from measured sensible heat fluxes ranged from 0 to 3 C higher than nadir-viewed temperatures. Models were developed to estimate incoming and reflected shortwave radiation from data collected with a Barnes Modular Multiband Radiometer. Several algorithms for estimating incoming longwave radiation were evaluated and compared to actual measures of that parameter. Net radiation was calculated using the estimated components of the shortwave radiation streams, determined from the algorithms developed, and from the longwave radiation streams provided by the Brunt, modified Deacon, and the Stefan-Boltzmann models. Estimates of net radiation were compared to measured values and found to be within the measurement error of the net radiometers used in the study.

Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska

NASA Astrophysics Data System (ADS)

Hartery, Sean; Commane, Róisín; Lindaas, Jakob; Sweeney, Colm; Henderson, John; Mountain, Marikate; Steiner, Nicholas; McDonald, Kyle; Dinardo, Steven J.; Miller, Charles E.; Wofsy, Steven C.; Chang, Rachel Y.-W.

2018-01-01

Methane (CH4) is the second most important greenhouse gas but its emissions from northern regions are still poorly constrained. In this study, we analyze a subset of in situ CH4 aircraft observations made over Alaska during the growing seasons of 2012-2014 as part of the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE). Net surface CH4 fluxes are estimated using a Lagrangian particle dispersion model which quantitatively links surface emissions from Alaska and the western Yukon with observations of enhanced CH4 in the mixed layer. We estimate that between May and September, net CH4 emissions from the region of interest were 2.2 ± 0.5 Tg, 1.9 ± 0.4 Tg, and 2.3 ± 0.6 Tg of CH4 for 2012, 2013, and 2014, respectively. If emissions are only attributed to two biogenic eco-regions within our domain, then tundra regions were the predominant source, accounting for over half of the overall budget despite only representing 18 % of the total surface area. Boreal regions, which cover a large part of the study region, accounted for the remainder of the emissions. Simple multiple linear regression analysis revealed that, overall, CH4 fluxes were largely driven by soil temperature and elevation. In regions specifically dominated by wetlands, soil temperature and moisture at 10 cm depth were important explanatory variables while in regions that were not wetlands, soil temperature and moisture at 40 cm depth were more important, suggesting deeper methanogenesis in drier soils. Although similar environmental drivers have been found in the past to control CH4 emissions at local scales, this study shows that they can be used to generate a statistical model to estimate the regional-scale net CH4 budget.

Constraining terrestrial ecosystem CO2 fluxes by integrating models of biogeochemistry and atmospheric transport and data of surface carbon fluxes and atmospheric CO2 concentrations

NASA Astrophysics Data System (ADS)

Zhu, Q.; Zhuang, Q.; Henze, D.; Bowman, K.; Chen, M.; Liu, Y.; He, Y.; Matsueda, H.; Machida, T.; Sawa, Y.; Oechel, W.

2014-09-01

Regional net carbon fluxes of terrestrial ecosystems could be estimated with either biogeochemistry models by assimilating surface carbon flux measurements or atmospheric CO2 inversions by assimilating observations of atmospheric CO2 concentrations. Here we combine the ecosystem biogeochemistry modeling and atmospheric CO2 inverse modeling to investigate the magnitude and spatial distribution of the terrestrial ecosystem CO2 sources and sinks. First, we constrain a terrestrial ecosystem model (TEM) at site level by assimilating the observed net ecosystem production (NEP) for various plant functional types. We find that the uncertainties of model parameters are reduced up to 90% and model predictability is greatly improved for all the plant functional types (coefficients of determination are enhanced up to 0.73). We then extrapolate the model to a global scale at a 0.5° × 0.5° resolution to estimate the large-scale terrestrial ecosystem CO2 fluxes, which serve as prior for atmospheric CO2 inversion. Second, we constrain the large-scale terrestrial CO2 fluxes by assimilating the GLOBALVIEW-CO2 and mid-tropospheric CO2 retrievals from the Atmospheric Infrared Sounder (AIRS) into an atmospheric transport model (GEOS-Chem). The transport inversion estimates that: (1) the annual terrestrial ecosystem carbon sink in 2003 is -2.47 Pg C yr-1, which agrees reasonably well with the most recent inter-comparison studies of CO2 inversions (-2.82 Pg C yr-1); (2) North America temperate, Europe and Eurasia temperate regions act as major terrestrial carbon sinks; and (3) The posterior transport model is able to reasonably reproduce the atmospheric CO2 concentrations, which are validated against Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) CO2 concentration data. This study indicates that biogeochemistry modeling or atmospheric transport and inverse modeling alone might not be able to well quantify regional terrestrial carbon fluxes. However, combining the two modeling approaches and assimilating data of surface carbon flux as well as atmospheric CO2 mixing ratios might significantly improve the quantification of terrestrial carbon fluxes.

CAUSES: On the Role of Surface Energy Budget Errors to the Warm Surface Air Temperature Error Over the Central United States

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, H. -Y.; Klein, S. A.; Xie, S.

Many weather forecasting and climate models simulate a warm surface air temperature (T2m) bias over mid-latitude continents during the summertime, especially over the Great Plains. We present here one of a series of papers from a multi-model intercomparison project (CAUSES: Cloud Above the United States and Errors at the Surface), which aims to evaluate the role of cloud, radiation, and precipitation biases in contributing to T2m bias using a short-term hindcast approach with observations mainly from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site during the period of April to August 2011. The present study examines the contributionmore » of surface energy budget errors to the bias. All participating models simulate higher net shortwave and longwave radiative fluxes at the surface but there is no consistency on signs of biases in latent and sensible heat fluxes over the Central U.S. and ARM SGP. Nevertheless, biases in net shortwave and downward longwave fluxes, as well as surface evaporative fraction (EF) are the main contributors to T2m bias. Radiation biases are largely affected by cloud simulations, while EF is affected by soil moisture modulated by seasonal accumulated precipitation and evaporation. An approximate equation is derived to further quantify the magnitudes of radiation and EF contributions to T2m bias. Our analysis suggests that radiation errors are always an important source of T2m error for long-term climate runs with EF errors either of equal or lesser importance. However, for the short-term hindcasts, EF errors are more important provided a model has a substantial EF bias.« less

Interactions between Lakes and the Atmosphere over the Largest High-Altitude Saline Lake on the Qinghai-Tibet Plateau

NASA Astrophysics Data System (ADS)

Li, X.

2017-12-01

Interactions between lakes and the atmosphere at high-altitudes are still poorly understood due to difficulty in accessibility of direct measurements. This is particularly true for the Qinghai-Tibet Plateau (QTP), where approximately 50% of the lakes in China are located. Continuous direct measurements of the water flux and surface energy budget were made over the largest high-altitude saline lake in China, Qinghai Lake on the northeastern QTP, using the eddy covariance (EC) method from 11 May, 2013 through 10 May, 2015. Results indicated that net radiation and heat storage showed consistent diurnal variation with positive values in the daytime and negative values at night, while latent and sensible heat flux showed little diurnal variation. Nocturnal λE and H contributed to 47.7% and 29.0% of the total heat loss, during the two- year study period. Annual evaporation of Qinghai Lake was 832.5 mm for 2013/2014 and 823.6 mm for 2014/2015, respectively. The surface energy budget and evaporation showed a strong seasonal pattern, with peaks in the latent and sensible heat flux observed in autumn and early winter. There was a 2-3 month delay between the maximum net radiation and maximum latent and sensible heat fluxes. Intraseasonal and seasonal variations in latent and sensible heat flux were strongly affected by different air masses. Westerly cold and dry air masses increased evaporation while southeast moist air mass suppressed evaporation, suggesting that the lakes might serve as an 'air-conditioner' to modify the temporal heat and water flux in QTP. Latent heat flux (λE) during the ice-covered period was less than that during the ice-free period, and lake ice sublimation is perhaps a main possible source for λE during the freeze-up period.

Quantifying the processes controlling intraseasonal mixed-layer temperature variability in the tropical Indian Ocean

NASA Astrophysics Data System (ADS)

Halkides, D. J.; Waliser, Duane E.; Lee, Tong; Menemenlis, Dimitris; Guan, Bin

2015-02-01

Spatial and temporal variation of processes that determine ocean mixed-layer (ML) temperature (MLT) variability on the timescale of the Madden-Julian Oscillation (MJO) in the Tropical Indian Ocean (TIO) are examined in a heat-conserving ocean state estimate for years 1993-2011. We introduce a new metric for representing spatial variability of the relative importance of processes. In general, horizontal advection is most important at the Equator. Subsurface processes and surface heat flux are more important away from the Equator, with surface heat flux being the more dominant factor. Analyses at key sites are discussed in the context of local dynamics and literature. At 0°, 80.5°E, for MLT events > 2 standard deviations, ocean dynamics account for more than two thirds of the net tendency during cooling and warming phases. Zonal advection alone accounts for ˜40% of the net tendency. Moderate events (1-2 standard deviations) show more differences between events, and some are dominated by surface heat flux. At 8°S, 67°E in the Seychelles-Chagos Thermocline Ridge (SCTR) area, surface heat flux accounts for ˜70% of the tendency during strong cooling and warming phases; subsurface processes linked to ML depth (MLD) deepening (shoaling) during cooling (warming) account for ˜30%. MLT is more sensitive to subsurface processes in the SCTR, due to the thin MLD, thin barrier layer and raised thermocline. Results for 8°S, 67°E support assertions by Vialard et al. (2008) not previously confirmed due to measurement error that prevented budget closure and the small number of events studied. The roles of MLD, barrier layer thickness, and thermocline depth on different timescales are examined.

The role of metabolism in modulating CO2 fluxes in boreal lakes

NASA Astrophysics Data System (ADS)

Bogard, Matthew J.; del Giorgio, Paul A.

2016-10-01

Lake CO2 emissions are increasingly recognized as an important component of the global CO2 cycle, yet the origin of these emissions is not clear, as specific contributions from metabolism and in-lake cycling, versus external inputs, are not well defined. To assess the coupling of lake metabolism with CO2 concentrations and fluxes, we estimated steady state ratios of gross primary production to respiration (GPP:R) and rates of net ecosystem production (NEP = GPP-R) from surface water O2 dynamics (concentration and stable isotopes) in 187 boreal lakes spanning long environmental gradients. Our findings suggest that internal metabolism plays a dominant role in regulating CO2 fluxes in most lakes, but this pattern only emerges when examined at a resolution that accounts for the vastly differing relationships between lake metabolism and CO2 fluxes. Fluxes of CO2 exceeded those from NEP in over half the lakes, but unexpectedly, these effects were most common and typically largest in a subset ( 30% of total) of net autotrophic lakes that nevertheless emitted CO2. Equally surprising, we found no environmental characteristics that distinguished this category from the more common net heterotrophic, CO2 outgassing lakes. Excess CO2 fluxes relative to NEP were best predicted by catchment structure and hydrologic properties, and we infer from a combination of methods that both catchment inputs and internal anaerobic processes may have contributed this excess CO2. Together, our findings show that the link between lake metabolism and CO2 fluxes is often strong but can vary widely across the boreal biome, having important implications for catchment-wide C budgets.

Atmospheric deposition and air-sea gas exchange fluxes of DDT and HCH in the Yangtze River Estuary, East China Sea

NASA Astrophysics Data System (ADS)

Li, Zhongxia; Lin, Tian; Li, Yuanyuan; Jiang, Yuqing; Guo, Zhigang

2017-07-01

The Yangtze River Estuary (YRE) is strongly influenced by the Yangtze River and lies on the pathway of the East Asian Monsoon. This study examined atmospheric deposition and air-sea gas exchange fluxes of dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) to determine whether the YRE is a sink or source of selected pesticides at the air-water interface under the influences of river input and atmospheric transport. The air-sea gas exchange of DDT was characterized by net volatilization with a marked difference in its fluxes between summer (140 ng/m2/d) and the other three seasons (12 ng/m2/d), possibly due to the high surface seawater temperatures and larger riverine input in summer. However, there was no obvious seasonal variation in the atmospheric HCH deposition, and the air-sea gas exchange reached equilibrium because of low HCH levels in the air and seawater after the long-term banning of HCH and the degradation. The gas exchange flux of HCH was comparable to the dry and wet deposition fluxes at the air-water interface. This suggests that the influences from the Yangtze River input and East Asian continental outflow on the fate of HCH in the YRE were limited. The gas exchange flux of DDT was about fivefold higher than the total dry and wet deposition fluxes. DDT residues in agricultural soil transported by enhanced riverine runoff were responsible for sustaining such a high net volatilization in summer. Moreover, our results indicated that there were fresh sources of DDT from the local environment to sustain net volatilization throughout the year.

Carbon Fluxes in Dissolved and Gaseous Forms for a Restored Peatland in British Columbia, Canada

NASA Astrophysics Data System (ADS)

D'Acunha, B.; Johnson, M. S.; Lee, S. C.; Christen, A.

2016-12-01

Peatlands are wetlands where gross primary production exceeds organic matter decomposition causing an accumulation of partially decomposed matter, also called peat. These ecosystems can accumulate more carbon than tropical rainforests. However, dissolved and gaseous fluxes of carbon (as dissolved organic carbon (DOC), CO2 and methane (CH4)) must also be considered to determine if these ecosystems are net sinks or sources of greenhouse gases (GHGs) to the atmosphere, which depends in part on the environmental conditions and the state of the ecosystem. We conducted research in Burns Bog, Delta, BC, Canada, a raised domed peat bog located in the Fraser River Delta and one of the largest raised peat bogs on the west coast of the Americas, but which has been heavily impacted by a range of human activities. Currently, ecological restoration efforts are underway by a large-scale ditch blocking program, with the aim to re-establish a high water table. This is approached in partnership with research on the ecosystem services that the bog provides, including its role in a regional GHG inventory. Here we present data on ecosystem-scale fluxes of CO2 and CH4 determined by eddy covariance (EC) on a floating tower platform, and complementary data on (i) evasion fluxes of CO2, CH4 and nitrous oxide (N2O) from the water surface to the atmosphere, and (ii) the flux and composition of dissolved organic carbon in water draining Burns Bog. Concentrations of dissolved CO2, CH4 and N2O were determined by headspace equilibration, and evasion rates from the water surface were quantified and are used to estimate the role of the hydrosphere in the ecosystem-scale measurements. Water samples collected from five saturated areas in the flux tower footprint were analyzed for DOC concentrations and composition. Results indicated that, even though the whole system is a net C sink, the water surface behaved as a source of CO2 and CH4, and a sink for N2O throughout the study period. Drainage waters were high in DOC (> 30 mg L-1). DOC export was found to offset about 20% of the apparent net C uptake determined by EC, indicating that the EC system overestimates carbon accumulation by not accounting for DOC drainage.

Hydrologically transported dissolved organic carbon influences soil respiration in a tropical rainforest

NASA Astrophysics Data System (ADS)

Zhou, Wen-Jun; Lu, Hua-Zheng; Zhang, Yi-Ping; Sha, Li-Qing; Schaefer, Douglas Allen; Song, Qing-Hai; Deng, Yun; Deng, Xiao-Bao

2016-10-01

To better understand the effect of dissolved organic carbon (DOC) transported by hydrological processes (rainfall, throughfall, litter leachate, and surface soil water; 0-20 cm) on soil respiration in tropical rainforests, we detected the DOC flux in rainfall, throughfall, litter leachate, and surface soil water (0-20 cm), compared the seasonality of δ13CDOC in each hydrological process, and δ13C in leaves, litter, and surface soil, and analysed the throughfall, litter leachate, and surface soil water (0-20 cm) effect on soil respiration in a tropical rainforest in Xishuangbanna, south-west China. Results showed that the surface soil intercepted 94.4 ± 1.2 % of the annual litter leachate DOC flux and is a sink for DOC. The throughfall and litter leachate DOC fluxes amounted to 6.81 and 7.23 % of the net ecosystem exchange respectively, indicating that the DOC flux through hydrological processes is an important component of the carbon budget, and may be an important link between hydrological processes and soil respiration in a tropical rainforest. Even the variability in soil respiration is more dependent on the hydrologically transported water than DOC flux insignificantly, soil temperature, and soil-water content (at 0-20 cm). The difference in δ13C between the soil, soil water (at 0-20 cm), throughfall, and litter leachate indicated that DOC is transformed in the surface soil and decreased the sensitivity indices of soil respiration of DOC flux to water flux, which suggests that soil respiration is more sensitive to the DOC flux in hydrological processes, especially the soil-water DOC flux, than to soil temperature or soil moisture.

The MASCOT Radiometer MARA for the Hayabusa 2 Mission

NASA Astrophysics Data System (ADS)

Grott, M.; Knollenberg, J.; Borgs, B.; Hänschke, F.; Kessler, E.; Helbert, J.; Maturilli, A.; Müller, N.

2017-07-01

The MASCOT radiometer MARA is a multi-spectral instrument which measures net radiative flux in six wavelength bands. MARA uses thermopile sensors as sensing elements, and the net flux between the instrument and the surface in the 18° field of view is determined by evaluating the thermoelectric potential between the sensors' absorbing surface and the thermopile's cold-junction. MARA houses 4 bandpass channels in the spectral range of 5.5-7, 8-9.5, 9.5-11.5, and 13.5-15.5 μm, as well as one long-pass channel, which is sensitive in the >3 μm range. In addition, one channel is similar to that used by the Hayabusa 2 orbiter thermal mapper, which uses a wavelength range of 8-12 μm. The primary science objective of the MARA instrument it the determination of the target asteroid's surface brightness temperature, from which surface thermal inertia can be derived. In addition, the spectral bandpass channels will be used to estimate the spectral slope of the surface in the thermal infrared wavelength range. The instrument has been calibrated using a cavity blackbody, and the temperature uncertainty is 1 K in the long pass channel for target temperatures of >173 K. Measurement uncertainty in the spectral bandpasses is 1 K for target temperatures above 273 K.

Effects of Enhanced Thaw Depth on the Composition of Arctic Soil Organic Matter Leachate

NASA Astrophysics Data System (ADS)

Hutchings, J.; Zhang, X.; Bianchi, T. S.; Schuur, E.; Arellano, A. R.; Liu, Y.

2016-12-01

Pan-Arctic permafrost is increasingly susceptible to thaw due to the disproportionally high rate of temperature change in high latitudes. These soils contain a globally significant quantity of organic carbon that, when thawed, interacts with the modern carbon cycle. Current research has focused on atmospheric carbon fluxes and transport by rivers and streams to continental shelves, but has overlooked the lateral flux of carbon within watershed soils, which is the primary link between terrestrial and riverine ecosystems. Understanding the effects of water movement through permafrost soils on dissolved organic carbon is critical to better modelling of lateral carbon fluxes and interpreting the resulting observed riverine carbon fluxes with applications to investigations of the past, present, and future of the pan-Arctic. We conducted a laboratory leaching experiment using active layer soils from the Eight Mile Lake region of interior Alaska. Cores were sampled into surface and deep sections. Surface sections were subjected to a three-stage leaching process using artificial rain, with cores stored frozen overnight between stages (which crudely simulated freeze-thaw mechanisms). Surface leachates were sampled for analysis and the remainder percolated through deep soils using the same three-staged approach. Measurements of surface and deep leachates were selected to characterize transport-related changes to dissolved organic matter and included dissolved organic carbon, fluorescent dissolved organic matter via excitation emission matrices, and molecular composition via Fourier transform ion cyclotron resonance mass spectrometry. Primary findings from the experiment include a net retention of 2.4 to 27% of dissolved organic carbon from surface leachates in deep soils, a net release of fluorescent dissolved organic matter from deep soils that was 43 to 106% greater than surface leachates, increased hydrophobicity during stage three of leaching, and the preferential leaching of lignin- and tannin-like formulas from deep soils, consistent with fluorescence measurements.

The Dynamics of Energy and CO2 Transport above a Subtropical Rice Paddy

NASA Astrophysics Data System (ADS)

Hsieh, C.; Huang, C.; Cheng, S.

2013-12-01

An eddy-covariance system was established to understand the dynamics of turbulent transport of sensible heat, water vapor, and CO2 above a subtropical rice paddy in north Taiwan (24°48'07.958'N, 121°47'58.665'E). The results showed that, during crop season, about 25% of net radiation was used for latent heat flux, 10% for sensible heat flux, and the rest (65%) was absorbed by the water and soil in the rice paddy. However, during fallow period, where there was no rice in the paddy, both water vapor and sensible heat fluxes occupied about 18% of the net radiation. Also, Penman-Monteith equation was found to reproduce the water vapor flux well with surface resistance close to 190 s m-1. We also found that, under small Bowen ratio (< 0.2) conditions, water vapor and CO2 were transported more efficiently than heat. However, when Bowen ration was large (> 0.5), sensible heat was transported about 10% more efficiently than both water vapor and CO2. During crop season the maximum CO2 uptake was about 22 micro mol m-2 s-1. In fallow period, the maximum CO2 emission rate from the soil-water surface was around 5 micro mol m-2 s-1, which was about the same as the growing season.

A Water Balance Model for Hill reservoir - Aquifer Exchange Water Flux Quantification and Uncertainty Analysis - Application to the Kamech catchment, Tunisia

NASA Astrophysics Data System (ADS)

Bouteffeha, Maroua; Dagès, Cécile; Bouhlila, Rachida; Raclot, Damien; Molénat, Jérôme

2013-04-01

In Mediterranean regions, food and water demand increase with population growth leading to considerable changes of the land use and agricultural practices. In North Africa, particularly in the Mediterranean zones, hill reservoirs are water harvesting infrastructures that have been increasingly adopted to mobilize runoff and create alternative water resource that can be used to develop agriculture. Hill reservoirs are also used to prevent from silting of downstream dams. Management of water resources collected in these infrastructures requires a good knowledge of their hydrological functioning. In particular, the rate of water exchanges between the reservoir and the underlying aquifer, called surface-subsurface exchange hereafter, is still an open question. The main purpose of the study is to better know the hydrological functioning of hill reservoirs in quantifying at the annual and intra-annual time scales the flux of surface-subsurface exchange and the uncertainty associated to the flux. The approach is based on the hydrological water balance of the hill reservoir. It was applied to the hill reservoir of the 2.6 km² Kamech catchment (Tunisia), which belongs to the long term Mediterranean hydrological observatory OMERE (Voltz and Albergel, 2002). The dense monitoring of the observation catchment allowed quantifying the fluxes of all hydrological processes governing the reservoir hydrology, and their associated uncertainties. The water balance was established by considering water inputs (direct rainfall, waddy and hillslope runoff, surface-subsurface exchange), water outputs (evaporation, spillway discharge) and hill reservoir water volume changes. The surface-subsurface exchange component was deduced as the default closure term in the water balance. The results first demonstrate the ability of the proposed approach to estimate the net surface-subsurface exchange flux and its uncertainty at various time scales. Its application on the Kamech catchment for two hydrological years (09/2009-08/2010 and 09/2010-08/2011) shows that the net surface-subsurface exchange flux is positive, i.e. the infiltration from the hill reservoir to the aquifer predominates the discharge from the aquifer to the reservoir. Moreover the surface-subsurface exchange constitutes the main output component in the water balance. The annual surface-subsurface exchange flux appeared almost constant from one year to the other one whatever the hydrological conditions variability over the catchment. Moreover, the analysis of the intra-annual variability shows that the flux was nearly constant within every year. Reference: Voltz , M. and Albergel , J., 2002. OMERE : Observatoire Méditerranéen de l'Environnement Rural et de l'Eau - Impact des actions anthropiques sur les transferts de masse dans les hydrosystèmes méditerranéens ruraux. Proposition d'Observatoire de Recherche en Environnement, Ministère de la Recherche.

Long-term accumulation and transport of anthropogenic phosphorus in three river basins

NASA Astrophysics Data System (ADS)

Powers, Stephen M.; Bruulsema, Thomas W.; Burt, Tim P.; Chan, Neng Iong; Elser, James J.; Haygarth, Philip M.; Howden, Nicholas J. K.; Jarvie, Helen P.; Lyu, Yang; Peterson, Heidi M.; Sharpley, Andrew N.; Shen, Jianbo; Worrall, Fred; Zhang, Fusuo

2016-05-01

Global food production depends on phosphorus. Phosphorus is broadly applied as fertilizer, but excess phosphorus contributes to eutrophication of surface water bodies and coastal ecosystems. Here we present an analysis of phosphorus fluxes in three large river basins, including published data on fertilizer, harvested crops, sewage, food waste and river fluxes. Our analyses reveal that the magnitude of phosphorus accumulation has varied greatly over the past 30-70 years in mixed agricultural-urban landscapes of the Thames Basin, UK, the Yangtze Basin, China, and the rural Maumee Basin, USA. Fluxes of phosphorus in fertilizer, harvested crops, food waste and sewage dominate over the river fluxes. Since the late 1990s, net exports from the Thames and Maumee Basins have exceeded inputs, suggesting net mobilization of the phosphorus pool accumulated in earlier decades. In contrast, the Yangtze Basin has consistently accumulated phosphorus since 1980. Infrastructure modifications such as sewage treatment and dams may explain more recent declines in total phosphorus fluxes from the Thames and Yangtze Rivers. We conclude that human-dominated river basins may undergo a prolonged but finite accumulation phase when phosphorus inputs exceed agricultural demand, and this accumulated phosphorus may continue to mobilize long after inputs decline.

Summertime elemental mercury exchange of temperate grasslands on an ecosystem-scale

PubMed Central

Fritsche, J.; Wohlfahrt, G.; Ammann, C.; Zeeman, M.; Hammerle, A.; Obrist, D.; Alewell, C.

2013-01-01

In order to estimate the air-surface mercury exchange of grasslands in temperate climate regions, fluxes of gaseous elemental mercury (GEM) were measured at two sites in Switzerland and one in Austria during summer 2006. Two classic micrometeorological methods (aerodynamic and modified Bowen ratio) have been applied to estimate net GEM exchange rates and to determine the response of the GEM flux to changes in environmental conditions (e.g. heavy rain, summer ozone) on an ecosystem-scale. Both methods proved to be appropriate to estimate fluxes on time scales of a few hours and longer. Average dry deposition rates up to 4.3 ng m−2 h−1 and mean deposition velocities up to 0.10 cm s−1 were measured, which indicates that during the active vegetation period temperate grasslands are a small net sink for atmospheric mercury. With increasing ozone concentrations depletion of GEM was observed, but could not be quantified from the flux signal. Night-time deposition fluxes of GEM were measured and seem to be the result of mercury co-deposition with condensing water. Effects of grass cuts could also be observed, but were of minor magnitude. PMID:24348525

The dominant role of Arctic surface buoyancy fluxes for AMOC slow-down on multi-decadal timescales

NASA Astrophysics Data System (ADS)

Fedorov, A. V.; Sevellec, F.

2016-12-01

One of the most dramatic consequences of the ongoing climate change is the reduction in the Arctic sea ice cover observed over the past few decades. This sea ice loss increases net heat flux into the ocean and at the same time exposes the ocean to additional freshwater flux from the atmosphere. These two effects imply positive anomalies in surface buoyancy fluxes over the Arctic ocean. In this study we estimate the sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to global changes in surface buoyancy forcing, especially in the context of changes in the Arctic. We find that, whereas on decadal timescale the subpolar region (especially east and south of Greenland) is the primarily driver of AMOC weakening due to positive buoyancy fluxes, on multidecadal timescales (longer than 20 years) it is the Arctic region that largely controls the AMOC slow-down. On timescales close to one century surface buoyancy fluxes over the Arctic ocean are nearly twice as effective for weakening the AMOC than those in the subpolar North Atlantic. We also find that the anomalous surface buoyancy fluxes in the Arctic can efficiently weaken poleward heat transport in the North Atlantic on a basin scale (i.e., between 25oN and 50oN). We conclude that such remote control of the AMOC intensity and heat transport by the Arctic ocean is a robust feature of climate change on multi-decadal timescales.

Revisiting the Cause of the 1989-2009 Arctic Surface Warming Using the Surface Energy Budget: Downward Infrared Radiation Dominates the Surface Fluxes

NASA Astrophysics Data System (ADS)

Lee, Sukyoung; Gong, Tingting; Feldstein, Steven B.; Screen, James A.; Simmonds, Ian

2017-10-01

The Arctic has been warming faster than elsewhere, especially during the cold season. According to the leading theory, ice-albedo feedback warms the Arctic Ocean during the summer, and the heat gained by the ocean is released during the winter, causing the cold-season warming. Screen and Simmonds (2010; SS10) concluded that the theory is correct by comparing trend patterns in surface air temperature (SAT), surface turbulence heat flux (HF), and net surface infrared radiation (IR). However, in this comparison, downward IR is more appropriate to use. By analyzing the same data used in SS10 using the surface energy budget, it is shown here that over most of the Arctic the skin temperature trend, which closely resembles the SAT trend, is largely accounted for by the downward IR, not the HF, trend.

Gas exchange and CO2 flux in the tropical Atlantic Ocean determined from Rn-222 and pCO2 measurements

NASA Technical Reports Server (NTRS)

Smethie, W. M., Jr.; Takahashi, T.; Chipman, D. W.; Ledwell, J. R.

1985-01-01

The piston velocity for the tropical Atlantic Ocean has been determined from 29 radon profiles measured during the TTO Tropical Atlantic Study. By combining these data with the pCO2 data measured in the surface water and air samples, the net flux of CO2 across the sea-air interface has been calculated for the tropical Atlantic. The dependence of the piston velocity on wind speed is discussed, and possible causes for the high sea-to-air CO2 flux observed in the equatorial zone are examined.

Nitrate retention in a sand plains stream and the importance of groundwater discharge

Treesearch

Robert S. Stelzer; Damion R. Drover; Susan L. Eggert; Maureen A. Muldoon

2011-01-01

We measured net nitrate retention by mass balance in a 700-m upwelling reach of a third-order sand plains stream, Emmons Creek, from January 2007 to November 2008. Surface water and ground-water fluxes of nitrate were determined from continuous records of discharge and from nitrate concentrations based on weekly and biweekly sampling at three surface water stations and...

Exploiting diurnal variations to evaluate the ISCCP-FD flux calculations and radiative-flux-analysis-processed surface observations from BSRN, ARM, and SURFRAD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yuanchong; Long, Charles N.; Rossow, William B.

2010-01-01

Based on monthly-3-hourly and 3-hourly mean surface radiative fluxes and their associated meteorological parameters for 2004 from the International Satellite Cloud Climatology Project-FD (ISCCP-FD) and the Radiative Flux Analysis method-Produced Surface Observations (RFA-PSO) for 15 high-quality-controlled surface stations, operated by the Baseline Surface Radiation Network (BSRN), the Atmospheric Radiation Measurement (ARM) and the National Oceanic and Atmospheric Administration's Surface Radiation budget network (SURFRAD), this work, goes beyond the previous validation for FD against surface observation by introducing the Meteorological Similarity Comparison Method (MSCM) to make a more precise, mutual evaluation of both FD and PSO products. The comparison results inmore » substantial uncertainty reduction and provides reasonable physical explanations for the flux differences. This approach compares fluxes for cases where the atmospheric and surface physical properties (specifically, the input parameters for radiative transfer model) are as close as possible to the values determined at the observational sites by matching the RFA-produced cloud fraction (CF) and/or optical thickness (Tau), etc., or alternatively, by directly changing the model input variables for FD to match PSO values, and using such-produced matched sub-datasets to make more accurate comparisons based on more similar meteorological environments between FD and PSO. The crucial part is the availability of flux-associated meteorological parameters from RFA-PSO, which was only recently made available that makes this work possible. For surface downwelling shortwave(SW) flux (SWdn) and its two components, diffuse (Dif) and direct (Dir), uncertainty for monthly mean is 15, 15 and 17 W/m 2, respectively, smaller than the separately estimated uncertainty values from both FD and PSO. When applying MSCM by reducing their CF difference, the differences can be reduced by a factor of 2. The strength of MSCM is particularly shown in the comparisons of diurnal variations. For clear sky, reducing the FD values of aerosol optical depth (AOD) by 50% to approximately match the PSO values brings all downward SW flux components into substantial agreement. For cloudy scenes, when both CF and Tau are matched to within 0.1 – 0.25 and ~10, respectively, the majority of the SW flux components have nearly-perfect agreement between FD and PSO. The best restriction differences are not zero indicates the influence of other parameters that are not accounted for yet. For longwave (LW) fluxes, general evaluation also confirms uncertainty values for FD and PSO less than separately estimated. When applying MSCM to CF and surface air temperature, the agreement is substantially improved. For downwelling LW diurnal variation comparison, FD shows good agreement with PSO for both RFA-defined or true clear sky but overestimates the amplitude for cloudy sky by 3-7 W/m 2, which may be caused by different sensitivities to cirrus clouds. For upwelling LW diurnal cycle, the situation is reversed; FD now underestimates the diurnal amplitude for all and clear sky but generally agrees for overcast (CF > 0.7). The combined effect of downwelling and upwelling LW fluxes results in FD's underestimates of the diurnal variation of the net-LW-loss for all the scenes by up to 10 W/m 2, although the daily mean net loss is more accurate. Therefore, in terms of amplitude and phase, both FD and PSO seem to have caught correct diurnal variations.« less

Linking atmospheric synoptic transport, cloud phase, surface energy fluxes, and sea-ice growth: observations of midwinter SHEBA conditions

NASA Astrophysics Data System (ADS)

Persson, P. Ola G.; Shupe, Matthew D.; Perovich, Don; Solomon, Amy

2017-08-01

Observations from the Surface Heat Budget of the Arctic Ocean (SHEBA) project are used to describe a sequence of events linking midwinter long-range advection of atmospheric heat and moisture into the Arctic Basin, formation of supercooled liquid water clouds, enhancement of net surface energy fluxes through increased downwelling longwave radiation, and reduction in near-surface conductive heat flux loss due to a warming of the surface, thereby leading to a reduction in sea-ice bottom growth. The analyses provide details of two events during Jan. 1-12, 1998, one entering the Arctic through Fram Strait and the other from northeast Siberia; winter statistics extend the results. Both deep, precipitating frontal clouds and post-frontal stratocumulus clouds impact the surface radiation and energy budget. Cloud liquid water, occurring preferentially in stratocumulus clouds extending into the base of the inversion, provides the strongest impact on surface radiation and hence modulates the surface forcing, as found previously. The observations suggest a minimum water vapor threshold, likely case dependent, for producing liquid water clouds. Through responses to the radiative forcing and surface warming, this cloud liquid water also modulates the turbulent and conductive heat fluxes, and produces a thermal wave penetrating into the sea ice. About 20-33 % of the observed variations of bottom ice growth can be directly linked to variations in surface conductive heat flux, with retarded ice growth occurring several days after these moisture plumes reduce the surface conductive heat flux. This sequence of events modulate pack-ice wintertime environmental conditions and total ice growth, and has implications for the annual sea-ice evolution, especially for the current conditions of extensive thinner ice.

Eddy covariance flux measurements of net ecosystem carbon dioxide exchange from a lowland peatland flux tower network in England and Wales

NASA Astrophysics Data System (ADS)

Morrison, Ross; Balzter, Heiko; Burden, Annette; Callaghan, Nathan; Cumming, Alenander; Dixon, Simon; Evans, Jonathan; Kaduk, Joerg; Page, Susan; Pan, Gong; Rayment, Mark; Ridley, Luke; Rylett, Daniel; Worrall, Fred; Evans, Christopher

2016-04-01

Peatlands store disproportionately large amounts of soil carbon relative to other terrestrial ecosystems. Over recent decades, the large amount of carbon stored as peat has proved vulnerable to a range of land use pressures as well as the increasing impacts of climate change. In temperate Europe and elsewhere, large tracts of lowland peatland have been drained and converted to agricultural land use. Such changes have resulted in widespread losses of lowland peatland habitat, land subsidence across extensive areas and the transfer of historically accumulated soil carbon to the atmosphere as carbon dioxide (CO2). More recently, there has been growth in activities aiming to reduce these impacts through improved land management and peatland restoration. Despite a long history of productive land use and management, the magnitude and controls on greenhouse gas emissions from lowland peatland environments remain poorly quantified. Here, results of surface-atmosphere measurements of net ecosystem CO2 exchange (NEE) from a network of seven eddy covariance (EC) flux towers located at a range of lowland peatland ecosystems across the United Kingdom (UK) are presented. This spatially-dense peatland flux tower network forms part of a wider observation programme aiming to quantify carbon, water and greenhouse gas balances for lowland peatlands across the UK. EC measurements totalling over seventeen site years were obtained at sites exhibiting large differences in vegetation cover, hydrological functioning and land management. The sites in the network show remarkable spatial and temporal variability in NEE. Across sites, annual NEE ranged from a net sink of -194 ±38 g CO2-C m-2 yr-1 to a net source of 784±70 g CO2-C m-2 yr-1. The results suggest that semi-natural sites remain net sinks for atmospheric CO2. Sites that are drained for intensive agricultural production range from a small net sink to the largest observed source for atmospheric CO2 within the flux tower network. Extensively managed grassland and a site that was restored from intensive arable land use represent modest CO2 sources. Temporal variations in CO2 fluxes at sites with permanent vegetation cover are coupled to seasonal and interannual variations in weather conditions and phenology. The type of crop produced and agricultural management drive large temporal differences in the CO2 fluxes of croplands on drained lowland peat soils. The main environmental controls on the spatial and temporal variations in CO2 exchange processes will be discussed.

Coupled carbon-water exchange of the Amazon rain forest, II. Comparison of predicted and observed seasonal exchange of energy, CO2, isoprene and ozone at a remote site in Rondônia

NASA Astrophysics Data System (ADS)

Simon, E.; Meixner, F. X.; Rummel, U.; Ganzeveld, L.; Ammann, C.; Kesselmeier, J.

2005-04-01

A one-dimensional multi-layer scheme describing the coupled exchange of energy and CO2, the emission of isoprene and the dry deposition of ozone is applied to a rain forest canopy in southwest Amazonia. The model was constrained using mean diel cycles of micrometeorological quantities observed during two periods in the wet and dry season 1999. Predicted net fluxes and concentration profiles for both seasonal periods are compared to observations made at two nearby towers.

The predicted day- and nighttime thermal stratification of the canopy layer is consistent with observations in dense canopies. The observed and calculated net fluxes above and H2O and CO2 concentration profiles within the canopy show a good agreement. The predicted net carbon sink decreases from 2.5 t C ha-1yr-1 for wet season conditions to 1 t C ha-1yr-1 for dry season conditions, whereas observed and predicted midday Bowen ratio increases from 0.5 to 0.8. The evaluation results confirmed a seasonal variability of leaf physiological parameters, as already suggested in the companion study. The predicted midday canopy net flux of isoprene increased from 7.1 mg C m-2h-1 during the wet season to 11.4 mg C m-2h-1 during the late dry season. Applying a constant emission capacity in all canopy layers, resulted in a disagreement between observed and simulated profiles of isoprene concentrations, suggesting a smaller emission capacity of shade adapted leaves and deposition to the soil or leaf surfaces. Assuming a strong light acclimation of emission capacity, equivalent to a 66% reduction of the standard emission factor for leaves in the lower canopy, resulted in a better agreement of observed and calculated concentration profiles and a 30% reduction of the canopy net flux. The mean calculated ozone flux for dry season condition at noontime was ≍12 nmol m-2s-1, agreeing well with observed values. The corresponding deposition velocity increased from 0.8 cm s-1 to >1.6 cm s-1 in the wet season, which can not be explained by increased stomatal uptake. Considering reasonable physiological changes in stomatal regulation, the predicted value was not larger than 1.05 cm s-1. Instead, the observed fluxes could be explained with the model by decreasing the cuticular resistance to ozone deposition from 5000 to 1000 s m-1. For doubled atmospheric CO2 concentrations the model predicts a strong increase of surface temperatures (0.1-1°C) and net assimilation (22%), a considerable shift in the energy budget (≍25% decreasing transpiration and increasing sensible heat), a slight increase of isoprene emissions (10%) and a strong decrease of ozone deposition (35%).

Reviews and syntheses: An empirical spatiotemporal description of the global surface-atmosphere carbon fluxes: opportunities and data limitations

NASA Astrophysics Data System (ADS)

Zscheischler, Jakob; Mahecha, Miguel D.; Avitabile, Valerio; Calle, Leonardo; Carvalhais, Nuno; Ciais, Philippe; Gans, Fabian; Gruber, Nicolas; Hartmann, Jens; Herold, Martin; Ichii, Kazuhito; Jung, Martin; Landschützer, Peter; Laruelle, Goulven G.; Lauerwald, Ronny; Papale, Dario; Peylin, Philippe; Poulter, Benjamin; Ray, Deepak; Regnier, Pierre; Rödenbeck, Christian; Roman-Cuesta, Rosa M.; Schwalm, Christopher; Tramontana, Gianluca; Tyukavina, Alexandra; Valentini, Riccardo; van der Werf, Guido; West, Tristram O.; Wolf, Julie E.; Reichstein, Markus

2017-08-01

Understanding the global carbon (C) cycle is of crucial importance to map current and future climate dynamics relative to global environmental change. A full characterization of C cycling requires detailed information on spatiotemporal patterns of surface-atmosphere fluxes. However, relevant C cycle observations are highly variable in their coverage and reporting standards. Especially problematic is the lack of integration of the carbon dioxide (CO2) exchange of the ocean, inland freshwaters and the land surface with the atmosphere. Here we adopt a data-driven approach to synthesize a wide range of observation-based spatially explicit surface-atmosphere CO2 fluxes from 2001 to 2010, to identify the state of today's observational opportunities and data limitations. The considered fluxes include net exchange of open oceans, continental shelves, estuaries, rivers, and lakes, as well as CO2 fluxes related to net ecosystem productivity, fire emissions, loss of tropical aboveground C, harvested wood and crops, as well as fossil fuel and cement emissions. Spatially explicit CO2 fluxes are obtained through geostatistical and/or remote-sensing-based upscaling, thereby minimizing biophysical or biogeochemical assumptions encoded in process-based models. We estimate a bottom-up net C exchange (NCE) between the surface (land, ocean, and coastal areas) and the atmosphere. Though we provide also global estimates, the primary goal of this study is to identify key uncertainties and observational shortcomings that need to be prioritized in the expansion of in situ observatories. Uncertainties for NCE and its components are derived using resampling. In many regions, our NCE estimates agree well with independent estimates from other sources such as process-based models and atmospheric inversions. This holds for Europe (mean ± 1 SD: 0.8 ± 0.1 PgC yr-1, positive numbers are sources to the atmosphere), Russia (0.1 ± 0.4 PgC yr-1), East Asia (1.6 ± 0.3 PgC yr-1), South Asia (0.3 ± 0.1 PgC yr-1), Australia (0.2 ± 0.3 PgC yr-1), and most of the Ocean regions. Our NCE estimates give a likely too large CO2 sink in tropical areas such as the Amazon, Congo, and Indonesia. Overall, and because of the overestimated CO2 uptake in tropical lands, our global bottom-up NCE amounts to a net sink of -5.4 ± 2.0 PgC yr-1. By contrast, the accurately measured mean atmospheric growth rate of CO2 over 2001-2010 indicates that the true value of NCE is a net CO2 source of 4.3 ± 0.1 PgC yr-1. This mismatch of nearly 10 PgC yr-1 highlights observational gaps and limitations of data-driven models in tropical lands, but also in North America. Our uncertainty assessment provides the basis for setting priority regions where to increase carbon observations in the future. High on the priority list are tropical land regions, which suffer from a lack of in situ observations. Second, extensive pCO2 data are missing in the Southern Ocean. Third, we lack observations that could enable seasonal estimates of shelf, estuary, and inland water-atmosphere C exchange. Our consistent derivation of data uncertainties could serve as prior knowledge in multicriteria optimization such as the Carbon Cycle Data Assimilation System (CCDAS) and atmospheric inversions, without over- or under-stating bottom-up data credibility. In the future, NCE estimates of carbon sinks could be aggregated at national scale to compare with the official national inventories of CO2 fluxes in the land use, land use change, and forestry sector, upon which future emission reductions are proposed.

Flux measurements of energy and trace gases in urban Houston, Texas

NASA Astrophysics Data System (ADS)

Boedeker, I.; Schade, G. W.; Adams, S.; Park, C.

2008-12-01

We describe the setup and some first year results of a new flux measurements tower in an urban area. An existing radio communications tower 4 km north of downtown Houston was equipped with micrometeorological instrumentation and trace gas sampling lines in spring 2007. Wind speed, temperature and relative humidity are recorded at five levels between 12 and 60 m above ground; 3-D wind speed measurements, solar and net radiances, and trace gas sampling are established from the 60 m level. A closed path IRGA is used for CO2 and water vapor fluxes, and independent instrumentation for criteria pollutant and VOC fluxes. Two CSI data loggers and software control the measurements, and EdiRe software is used to analyze turbulence data and compute fluxes. A project description is provided at http://atmo.tamu.edu/yellowcabtower. Surface properties as calculated from the gradient measurements show the site to be surprisingly uniform, with displacement heights between 5 and 9 m and roughness lengths between 0.4 and 0.7 m, despite urban heterogeneity. The latter is investigated through visible/near IR orthoimagery and LIDAR data, which are incorporated into a local GIS. Net radiation was also only marginally affected by surface heterogeneity. At this urban location it is balanced by roughly equal amounts of sensible heat, latent heat, and storage fluxes. Latent heat flux, however, is smaller outside the growing season, with an equivalent increase in winter storage fluxes, as expected. Significant differences are also observed with direction during summer, showing decreased Bowen ratios and lower CO2 emissions from sectors with a larger urban tree canopy cover in the footprint. The largely mature, dominantly oak urban canopy cover alleviates approximately 100 W m- 2 during typical summer days. On the other hand, anthropogenic CO2 emissions dominate over photosynthetic uptake all year round. Measured carbon fluxes peak during morning rush-hour traffic, especially when increasing stretches of the main commuter road fall into the footprint. Outside the rush hour, daytime carbon fluxes typically ranged from 0.4 to 1.6 g C m-2 h-1. A seasonal comparison shows that up to 75% of midday anthropogenic carbon flux is removed via photosynthesis in the dominant wind sector, S, which bears typical tree canopy covers of 25-50% on pervious surfaces.

Multi Seasonal and Diurnal Characterization of Sensible Heat Flux in an Arid Land Environment

NASA Astrophysics Data System (ADS)

Al-Mashharawi, S.; Aragon, B.; McCabe, M.

2017-12-01

In sparsely vegetated arid and semi-arid regions, the available energy is transformed primarily into sensible heat, with little to no energy partitioned into latent heat. The characterization of bare soil arid environments are rather poorly understood in the context of both local, regional and global energy budgets. Using data from a long-term surface layer scintillometer and co-located meteorological installation, we examine the diurnal and seasonal patterns of sensible heat flux and the net radiation to soil heat flux ratio. We do this over a bare desert soil located adjacent to an irrigated agricultural field in the central region of Saudi Arabia. The results of this exploratory analysis can be used to inform upon remote sensing techniques for surface flux estimation, to derive and monitor soil heat flux dynamics, estimate the heat transfer resistance and the thermal roughness length over bare soils, and to better inform efforts that model the advective effects that complicate the accurate representation of agricultural energy budgets in the arid zone.

Effects of ion exchange on stream solute fluxes in a basin receiving highway deicing salts

USGS Publications Warehouse

Shanley, J.B.

1994-01-01

At Fever Brook, a 1260-ha forested basin in central Massachusetts, highway deicing salt application increased the solute flux in streamflow by 120% above background flux (equivalent basis) during a 2-yr period. Attempts to isolate the nonsalt component of stream solute fluxes have commonly subtracted salt contributions based on the net Cl flux (Cl output in streamflow minus Cl input in precipitation). In these studies, any net Na flux in excess of the amount needed to balance the net Cl flux has been attributed to weathering. At Fever Brook, however, the net output of Na was less than the net output of Cl, suggesting a loss of Na within the basin. The Na sink was inferred to be cation exchange of Na for Ca and Mg in the soil. A method was developed to quantify the exchange based on a Na budget, which included an independent estimate of the Na flux from weathering. The amount of exchange was apportioned to Ca and Mg based on their relative concentrations in the stream. The background fluxes of Ca and Mg (i.e., those that would occur in the absence of deicing salts) were calculated by subtracting the amounts from ion exchange plus the much smaller direct contributions in deicing salts from the observed fluxes. Ion exchange and direct salt contributions increased the net output fluxes of Ca and Mg, each by 44% above background. In basins that receive deicing salts, failure to account for cation exchange thus may result in an underestimate of the flux of Na from weathering and overestimates of the fluxes of Ca and Mg from weathering.

Quantification and mapping of urban fluxes under climate change: Application of WRF-SUEWS model to Greater Porto area (Portugal)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rafael, S., E-mail: sandra.rafael@ua.pt

Climate change and the growth of urban populations are two of the main challenges facing Europe today. These issues are linked as climate change results in serious challenges for cities. Recent attention has focused on how urban surface-atmosphere exchanges of heat and water will be affected by climate change and the implications for urban planning and sustainability. In this study energy fluxes for Greater Porto area, Portugal, were estimated and the influence of the projected climate change evaluated. To accomplish this, the Weather Research and Forecasting Model (WRF) and the Surface Urban Energy and Water Balance Scheme (SUEWS) were appliedmore » for two climatological scenarios: a present (or reference, 1986–2005) scenario and a future scenario (2046–2065), in this case the Representative Concentration Pathway RCP8.5, which reflects the worst set of expectations (with the most onerous impacts). The results show that for the future climate conditions, the incoming shortwave radiation will increase by around 10%, the sensible heat flux around 40% and the net storage heat flux around 35%. In contrast, the latent heat flux will decrease about 20%. The changes in the magnitude of the different fluxes result in an increase of the net all-wave radiation by 15%. The implications of the changes of the energy balance on the meteorological variables are discussed, particularly in terms of temperature and precipitation. - Highlights: • Assessment of energy fluxes behaviour under past period and medium-term climate change projection. • Evaluation of climate change at urban scale. • Meteorological variables alters the partitioning of the energy fluxes. • Changes in the partition of the annual energy balance are found between the two analysed periods. • Increase in the magnitude of sensible and storage heat fluxes.« less

Dietary supplementation of branched-chain amino acids increases muscle net amino acid fluxes through elevating their substrate availability and intramuscular catabolism in young pigs.

PubMed

Zheng, Liufeng; Zuo, Fangrui; Zhao, Shengjun; He, Pingli; Wei, Hongkui; Xiang, Quanhang; Pang, Jiaman; Peng, Jian

2017-04-01

Branched-chain amino acids (BCAA) have been clearly demonstrated to have anabolic effects on muscle protein synthesis. However, little is known about their roles in the regulation of net AA fluxes across skeletal muscle in vivo. This study was aimed to investigate the effect and related mechanisms of dietary supplementation of BCAA on muscle net amino acid (AA) fluxes using the hindlimb flux model. In all fourteen 4-week-old barrows were fed reduced-protein diets with or without supplemental BCAA for 28 d. Pigs were implanted with carotid arterial, femoral arterial and venous catheters, and fed once hourly with intraarterial infusion of p-amino hippurate. Arterial and venous plasma and muscle samples were obtained for the measurement of AA, branched-chain α-keto acids (BCKA) and 3-methylhistidine (3-MH). Metabolomes of venous plasma were determined by HPLC-quadrupole time-of-flight-MS. BCAA-supplemented group showed elevated muscle net fluxes of total essential AA, non-essential AA and AA. As for individual AA, muscle net fluxes of each BCAA and their metabolites (alanine, glutamate and glutamine), along with those of histidine, methionine and several functional non-essential AA (glycine, proline and serine), were increased by BCAA supplementation. The elevated muscle net AA fluxes were associated with the increase in arterial and intramuscular concentrations of BCAA and venous metabolites including BCKA and free fatty acids, and were also related to the decrease in the intramuscular concentration of 3-MH. Correlation analysis indicated that muscle net AA fluxes are highly and positively correlated with arterial BCAA concentrations and muscle net BCKA production. In conclusion, supplementing BCAA to reduced-protein diet increases the arterial concentrations and intramuscular catabolism of BCAA, both of which would contribute to an increase of muscle net AA fluxes in young pigs.

Seasonal Variation of Mass Transport Across the Tropopause

NASA Technical Reports Server (NTRS)

Appenzeller, Christof; Holton, James R.; Rosenlof, Karen H.

1996-01-01

The annual cycle of the net mass transport across the extratropical tropopause is examined. Contributions from both the global-scale meridional circulation and the mass variation of the lowermost stratosphere are included. For the northern hemisphere the mass of the lowermost stratosphere has a distinct annual cycle, whereas for the southern hemisphere, the corresponding variation is weak. The net mass transport across the tropopause in the northern hemisphere has a maximum in late spring and a distinct minimum in autumn. This variation and its magnitude compare well with older estimates based on representative Sr-90 mixing ratios. For the southern hemisphere the seasonal cycle of the net mass transport is weaker and follows roughly the annual variation of the net mass flux across a nearby isentropic surface.

ANALYSIS OF WATER AND ENERGY FLUXES USING SATELLITE, ENERGY BALANCE MODELING AND OBSERVATIONS (Invited)

NASA Astrophysics Data System (ADS)

Irmak, A.

2009-12-01

Surface energy fluxes, including net radiation (Rn), sensible heat (H), latent heat (LE), and soil heat flux (G) are critical in surface energy balance of any terrain or landscapes. Estimation or measurement of these energy fluxes is important for completing the water balance in terrestrial ecosystems, and therefore accurately predicting the effects of global climate and land use change. The objectives of this study were to (1) use METRICtm (Mapping Evapotranspiration at high Resolution using Internalized Calibration) model for estimating land surface energy fluxes in Nebraska (NE) by utilizing satellite remote sensing data, (2) identify model bias in energy balance components compared with measurements from Bowen Ratio Energy Balance System (BREBS) in a subsurface drip-irrigated maize field in South-central Nebraska, and (3) understand the partitioning of available energy into latent heat for corn and soybean cropping systems at large scale. A total of 15 Landsat images were processed to estimate instantaneous surface energy fluxes at Landsat overpasses with METRIC model. Results showed that the model predictions of the surface energy fluxes and daily evapotranspiration were correlated well with the BREBS measurements. There is a need, however, to test the performance of the model with in-situ observations in other locations with different dataset before utilizing it for crucial water regulatory and policy decisions. The METRICtm approach illustrated how an ‘off-the-shelf’ model can be applied operationally over a significant time period and how that model behaves. The findings makes considerable contribution to our understanding of estimating land surface energy fluxes using remote sensing approach and experimentally describes the operational characteristics of METRICtm and presents its limitations.

Partitioning of net carbon dioxide flux measured by automatic transparent chamber

NASA Astrophysics Data System (ADS)

Dyukarev, EA

2018-03-01

Mathematical model was developed for describing carbon dioxide fluxes at open sedge-sphagnum fen during growing season. The model was calibrated using the results of observations from automatic transparent chamber and it allows us to estimate autotrophic, heterotrophic and ecosystem respiration fluxes, gross and net primary vegetation production, and the net carbon balance.

Effect of mosaic representation of vegetation in land surface schemes on simulated energy and carbon balances

NASA Astrophysics Data System (ADS)

Li, R.; Arora, V. K.

2011-06-01

Energy and carbon balance implications of representing vegetation using a composite or mosaic approach in a land surface scheme are investigated. In the composite approach the attributes of different plant functional types (PFTs) present in a grid cell are aggregated in some fashion for energy and water balance calculations. The resulting physical environmental conditions (including net radiation, soil moisture and soil temperature) are common to all PFTs and affect their ecosystem processes. In the mosaic approach energy and water balance calculations are performed separately for each PFT tile using its own vegetation attributes, so each PFT "sees" different physical environmental conditions and its carbon balance evolves somewhat differently from that in the composite approach. Simulations are performed at selected boreal, temperate and tropical locations to illustrate the differences caused by using the composite versus the mosaic approaches of representing vegetation. Differences in grid averaged primary energy fluxes are generally less than 5 % between the two approaches. Grid-averaged carbon fluxes and pool sizes can, however, differ by as much as 46 %. Simulation results suggest that differences in carbon balance between the two approaches arise primarily through differences in net radiation which directly affects net primary productivity, and thus leaf area index and vegetation biomass.

High particle export over the continental shelf of the west Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Buesseler, Ken O.; McDonnell, Andrew M. P.; Schofield, Oscar M. E.; Steinberg, Deborah K.; Ducklow, Hugh W.

2010-11-01

Drifting cylindrical traps and the flux proxy 234Th indicate more than an order of magnitude higher sinking fluxes of particulate carbon and 234Th in January 2009 than measured by a time-series conical trap used regularly on the shelf of the west Antarctic Peninsula (WAP). The higher fluxes measured in this study have several implications for our understanding of the WAP ecosystem. Larger sinking fluxes result in a revised export efficiency of at least 10% (C flux/net primary production) and a requisite lower regeneration efficiency in surface waters. High fluxes also result in a large supply of sinking organic matter to support subsurface and benthic food webs on the continental shelf. These new findings call into question the magnitude of seasonal and interannual variability in particle flux and reaffirm the difficulty of using moored conical traps as a quantitative flux collector in shallow waters.

Nitrogen Deposition to and Cycling in a Deciduous Forest

DOE PAGES

Pryor, Sara C.; Barthelmie, Rebecca J.; Carreiro, Margaret; ...

2001-01-01

The project described here seeks to answer questions regarding the role increased nitrogen (N) deposition is playing in enhanced carbon (C) sequestration in temperate mid-latitude forests, using detailed measurements from an AmeriFlux tower in southern Indiana (Morgan-Monroe State Forest, or MMSF). The measurements indicate an average atmosphere-surface N flux of approximately 6 mg-N m -2 day -1 during the 2000 growing season, with approximately 40% coming from dry deposition of ammonia (NH 3 ), nitric acid (HNO 3 ), and particle-bound N. Wet deposition and throughfall measurements indicate significant canopy uptake of N (particularly NH 4 +) at the site,more » leading to a net canopy exchange (NCE) of –6 kg-N ha -1 for the growing season. These data are used in combination with data on the aboveground C:N ratio, litterfall flux, and soil net N mineralization rates to indicate the level of potential perturbation of C sequestration at this site.« less

Exotic geophysical phenomena observed in an environmental neutron flux study using EAS PRISMA detectors

NASA Astrophysics Data System (ADS)

Alekseenko, Victor; Bagrova, Anastasia; Cui, Shuwang; He, Yayun; Li, Bingbing; Ma, Xinhua; Pozdnyakov, Egor; Shchegolev, Oleg; Stenkin, Yuri; Stepanov, Vladimir

2017-06-01

Some exotic geophysical events are observed by a global net of electron-neutron detectors (en-detectors) developed in the framework of the PRISMA EAS project. Our en-detectors running both on the Earth's surface and underground are continuously measuring the environmental thermal neutron flux. Thermal neutrons are in equilibrium with media and are therefore sensitive to many geophysical phenomena, which are exotic for people studying ultra high-energy cosmic rays or carrying out low background experiments deep underground.

Establishment and analysis of a High-Resolution Assimilation Dataset of the water-energy cycle in China

NASA Astrophysics Data System (ADS)

Zhu, X.; Wen, X.; Zheng, Z.

2017-12-01

For better prediction and understanding of land-atmospheric interaction, in-situ observed meteorological data acquired from the China Meteorological Administration (CMA) were assimilated in the Weather Research and Forecasting (WRF) model and the monthly Green Vegetation Coverage (GVF) data, which was calculated using the Normalized Difference Vegetation Index (NDVI) of the Earth Observing System Moderate-Resolution Imaging Spectroradiometer (EOS-MODIS) and Digital Elevation Model (DEM) data of the Shuttle Radar Topography Mission (SRTM) system. Furthermore, the WRF model produced a High-Resolution Assimilation Dataset of the water-energy cycle in China (HRADC). This dataset has a horizontal resolution of 25 km for near surface meteorological data, such as air temperature, humidity, wind vectors and pressure (19 levels); soil temperature and moisture (four levels); surface temperature; downward/upward short/long radiation; 3-h latent heat flux; sensible heat flux; and ground heat flux. In this study, we 1) briefly introduce the cycling 3D-Var assimilation method and 2) compare results of meteorological elements, such as 2 m temperature and precipitation generated by the HRADC with the gridded observation data from CMA, and surface temperature and specific humidity with Global LandData Assimilation System (GLDAS) output data from the National Aeronautics and Space Administration (NASA). We found that the satellite-derived GVF from MODIS increased over southeast China compared with the default model over the whole year. The simulated results of soil temperature, net radiation and surface energy flux from the HRADC are improved compared with the control simulation and are close to GLDAS outputs. The values of net radiation from HRADC are higher than the GLDAS outputs, and the differences in the simulations are large in the east region but are smaller in northwest China and on the Qinghai-Tibet Plateau. The spatial distribution of the sensible heat flux and the ground heat flux from HRADC is consistent with the GLDAS outputs in summer. In general, the simulated results from HRADC are an improvement on the control simulation and can present the characteristics of the spatial and temporal variation of the water-energy cycle in China.

Drivers of inorganic carbon dynamics in first-year sea ice: A model study

NASA Astrophysics Data System (ADS)

Moreau, Sébastien; Vancoppenolle, Martin; Delille, Bruno; Tison, Jean-Louis; Zhou, Jiayun; Kotovitch, Marie; Thomas, David N.; Geilfus, Nicolas-Xavier; Goosse, Hugues

2015-01-01

Sea ice is an active source or a sink for carbon dioxide (CO2), although to what extent is not clear. Here, we analyze CO2 dynamics within sea ice using a one-dimensional halothermodynamic sea ice model including gas physics and carbon biogeochemistry. The ice-ocean fluxes, and vertical transport, of total dissolved inorganic carbon (DIC) and total alkalinity (TA) are represented using fluid transport equations. Carbonate chemistry, the consumption, and release of CO2 by primary production and respiration, the precipitation and dissolution of ikaite (CaCO3·6H2O) and ice-air CO2 fluxes, are also included. The model is evaluated using observations from a 6 month field study at Point Barrow, Alaska, and an ice-tank experiment. At Barrow, results show that the DIC budget is mainly driven by physical processes, wheras brine-air CO2 fluxes, ikaite formation, and net primary production, are secondary factors. In terms of ice-atmosphere CO2 exchanges, sea ice is a net CO2 source and sink in winter and summer, respectively. The formulation of the ice-atmosphere CO2 flux impacts the simulated near-surface CO2 partial pressure (pCO2), but not the DIC budget. Because the simulated ice-atmosphere CO2 fluxes are limited by DIC stocks, and therefore <2 mmol m-2 d-1, we argue that the observed much larger CO2 fluxes from eddy covariance retrievals cannot be explained by a sea ice direct source and must involve other processes or other sources of CO2. Finally, the simulations suggest that near-surface TA/DIC ratios of ˜2, sometimes used as an indicator of calcification, would rather suggest outgassing.

Drivers of inorganic carbon dynamics in first-year sea ice: A model study

NASA Astrophysics Data System (ADS)

Moreau, Sébastien; Vancoppenolle, Martin; Delille, Bruno; Tison, Jean-Louis; Zhou, Jiayun; Kotovich, Marie; Thomas, David; Geilfus, Nicolas-Xavier; Goosse, Hugues

2015-04-01

Sea ice is an active source or a sink for carbon dioxide (CO2), although to what extent is not clear. Here, we analyze CO2 dynamics within sea ice using a one-dimensional halo-thermodynamic sea ice model including gas physics and carbon biogeochemistry. The ice-ocean fluxes, and vertical transport, of total dissolved inorganic carbon (DIC) and total alkalinity (TA) are represented using fluid transport equations. Carbonate chemistry, the consumption and release of CO2 by primary production and respiration, the precipitation and dissolution of ikaite (CaCO3•6H2O) and ice-air CO2 fluxes, are also included. The model is evaluated using observations from a 6-month field study at Point Barrow, Alaska and an ice-tank experiment. At Barrow, results show that the DIC budget is mainly driven by physical processes, wheras brine-air CO2 fluxes, ikaite formation, and net primary production, are secondary factors. In terms of ice-atmosphere CO2 exchanges, sea ice is a net CO2 source and sink in winter and summer, respectively. The formulation of the ice-atmosphere CO2 flux impacts the simulated near-surface CO2 partial pressure (pCO2), but not the DIC budget. Because the simulated ice-atmosphere CO2 fluxes are limited by DIC stocks, and therefore < 2 mmol m-2 day-1, we argue that the observed much larger CO2 fluxes from eddy covariance retrievals cannot be explained by a sea ice direct source and must involve other processes or other sources of CO2. Finally, the simulations suggest that near surface TA/DIC ratios of ~2, sometimes used as an indicator of calcification, would rather suggest outgassing.

Intercomparison of oceanic and atmospheric forced and coupled mesoscale simulations. Part I: Surface fluxes

NASA Astrophysics Data System (ADS)

Josse, P.; Caniaux, G.; Giordani, H.; Planton, S.

1999-04-01

A mesoscale non-hydrostatic atmospheric model has been coupled with a mesoscale oceanic model. The case study is a four-day simulation of a strong storm event observed during the SEMAPHORE experiment over a 500 × 500 km2 domain. This domain encompasses a thermohaline front associated with the Azores current. In order to analyze the effect of mesoscale coupling, three simulations are compared: the first one with the atmospheric model forced by realistic sea surface temperature analyses; the second one with the ocean model forced by atmospheric fields, derived from weather forecast re-analyses; the third one with the models being coupled. For these three simulations the surface fluxes were computed with the same bulk parametrization. All three simulations succeed well in representing the main oceanic or atmospheric features observed during the storm. Comparison of surface fields with in situ observations reveals that the winds of the fine mesh atmospheric model are more realistic than those of the weather forecast re-analyses. The low-level winds simulated with the atmospheric model in the forced and coupled simulations are appreciably stronger than the re-analyzed winds. They also generate stronger fluxes. The coupled simulation has the strongest surface heat fluxes: the difference in the net heat budget with the oceanic forced simulation reaches on average 50 Wm-2 over the simulation period. Sea surface-temperature cooling is too weak in both simulations, but is improved in the coupled run and matches better the cooling observed with drifters. The spatial distributions of sea surface-temperature cooling and surface fluxes are strongly inhomogeneous over the simulation domain. The amplitude of the flux variation is maximum in the coupled run. Moreover the weak correlation between the cooling and heat flux patterns indicates that the surface fluxes are not responsible for the whole cooling and suggests that the response of the ocean mixed layer to the atmosphere is highly non-local and enhanced in the coupled simulation.

Reintroducing radiometric surface temperature into the Penman-Monteith formulation

NASA Astrophysics Data System (ADS)

Mallick, Kaniska; Boegh, Eva; Trebs, Ivonne; Alfieri, Joseph G.; Kustas, William P.; Prueger, John H.; Niyogi, Dev; Das, Narendra; Drewry, Darren T.; Hoffmann, Lucien; Jarvis, Andrew J.

2015-08-01

Here we demonstrate a novel method to physically integrate radiometric surface temperature (TR) into the Penman-Monteith (PM) formulation for estimating the terrestrial sensible and latent heat fluxes (H and λE) in the framework of a modified Surface Temperature Initiated Closure (STIC). It combines TR data with standard energy balance closure models for deriving a hybrid scheme that does not require parameterization of the surface (or stomatal) and aerodynamic conductances (gS and gB). STIC is formed by the simultaneous solution of four state equations and it uses TR as an additional data source for retrieving the "near surface" moisture availability (M) and the Priestley-Taylor coefficient (α). The performance of STIC is tested using high-temporal resolution TR observations collected from different international surface energy flux experiments in conjunction with corresponding net radiation (RN), ground heat flux (G), air temperature (TA), and relative humidity (RH) measurements. A comparison of the STIC outputs with the eddy covariance measurements of λE and H revealed RMSDs of 7-16% and 40-74% in half-hourly λE and H estimates. These statistics were 5-13% and 10-44% in daily λE and H. The errors and uncertainties in both surface fluxes are comparable to the models that typically use land surface parameterizations for determining the unobserved components (gS and gB) of the surface energy balance models. However, the scheme is simpler, has the capabilities for generating spatially explicit surface energy fluxes and independent of submodels for boundary layer developments. This article was corrected on 27 AUG 2015. See the end of the full text for details.

Surface Energy Budget Components Over an Arid Scrubland Site in Idaho

NASA Astrophysics Data System (ADS)

Zurawski, A. M.; Russell, E. S.; Liu, H.; Gao, Z.

2015-12-01

Sagebrush ecosystems comprise a large area of the North American West, and serve as habitat to threatened species such as the sagebrush sparrow. Due to natural and anthropogenic disturbances, these ecosystems are experiencing widespread degradation, causing changes to the ecosystem-atmosphere interactions. Quantifying the surface energy budget components is crucial to understanding the impacts of ecosystem degradation on climate. Eddy covariance data were collected from May through August of 2014 from sensors installed at a height of 16 m over sagebrush-dominated ecosystems near Idaho Falls, Idaho. Our objective is to study how meteorological variables affect the partitioning of surface-based net radiation into latent, sensible, and soil heat fluxes. In this arid region, decrease in soil moisture led to a decrease in latent heat flux, and an increase in sensible heat flux. Air temperature increase had no noticeable effect on latent heat flux, and led to increase in sensible heat flux. Consequently, potential climate warming and drought in this region will likely lead to increased sensible heat flux during the day time. An increase in sensible heat flux will cause an increase in atmospheric heat. This indicates that this ecosystem exhibits a positive feedback to climate warming. Night time data needs to be analyzed to better understand the effect of meteorological variables on heat fluxes during the summer season in this ecosystem.

Actual daily evapotranspiration estimated from MERIS and AATSR data over the Chinese Loess Plateau

NASA Astrophysics Data System (ADS)

Liu, R.; Wen, J.; Wang, X.; Wang, L.; Tian, H.; Zhang, T. T.; Shi, X. K.; Zhang, J. H.; Lu, Sh. N.

2009-02-01

The Loess Plateau is located in north of China and has a significant impact on the climate and ecosystem evolvement over the East Asian continent. Based on the land surface energy balance theory, the potential of using Medium Resolution Imaging Spectrometer (onboard sensor of the Environmental Satellite) remote sensing data on 7, 11 and 27 June 2005 is explored. The "split-window" algorithm is used to retrieve surface temperature from the Advanced the Along-Track Scanning Radiometer, another onboard senor of the Environmental Satellite. Then the near surface net radiation, sensible heat flux and soil heat flux are estimated by using the developed algorithm. We introduce a simple algorithm to predict the heat flux partitioning between the soil and vegetation. Combining the sunshine hours, air temperature, sunshine duration and wind speed measured by weather stations, a model for estimating daily ET is proposed. The instantaneous ET is also converted to daily value. Comparison of latent heats flux retrieved by remote sensing data with ground observation from eddy covariance flux system during Loess Plateau land surface process field Experiment, the maximum and minimum error of this approach are 10.96% and 4.80% respectively, the cause of the bias is also explored and discussed.

The role of local heating in the 2015 Indian Heat Wave.

PubMed

Ghatak, Debjani; Zaitchik, Benjamin; Hain, Christopher; Anderson, Martha

2017-08-09

India faced a major heat wave during the summer of 2015. Temperature anomalies peaked in the dry period before the onset of the summer monsoon, suggesting that local land-atmosphere feedbacks involving desiccated soils and vegetation might have played a role in driving the heat extreme. Upon examination of in situ data, reanalysis, satellite observations, and land surface models, we find that the heat wave included two distinct peaks: one in late May, and a second in early June. During the first peak we find that clear skies led to a positive net radiation anomaly at the surface, but there is no significant sensible heat flux anomaly within the core of the heat wave affected region. By the time of the second peak, however, soil moisture had dropped to anomalously low levels in the core heat wave region, net surface radiation was anomalously high, and a significant positive sensible heat flux anomaly developed. This led to a substantial local forcing on air temperature that contributed to the intensity of the event. The analysis indicates that the highly agricultural landscape of North and Central India can reinforce heat extremes under dry conditions.

Radiative flux opens new window on climate research

NASA Technical Reports Server (NTRS)

Pinker, R. T.; Laszlo, I.; Whitlock, C. H.; Charlock, T. P.

1995-01-01

For several decades, global satellite observations have been made of the rate at which electromagnetic energy (radiative flux) is emerging from the top of the atmosphere of our planet in the spectral range of about 0.2-50.0 microns. At the same time, models have been developed to infer the radiative flux at the surface from the values observed by the satellites at the upper boundary. The balance of incoming and outgoing radiative flux (radiation budget) at both boundaries, determines the net gain or loss of the radiative energy within an atmospheric column. Climate researchers can use the radiative flux as a tool to validate climate models, separate the radiative impact of clouds from surface and atmosphere contributions, and to understand the global hydrological cycle. When applied to physical processes occurring at the surface, information on the radiative flux has the potential to substantially advance our understanding of the transport of heat, moisture, and momentum across the surface/atmosphere interface. Geophysicists of many disciplines stand to benefit from efforts to improve the use of this latter untapped resource. Oceanographers can improve the representation of the selective absorption of radiation in the oceans; biologists and ecologists can improve their models for carbon dioxide exchange and biological heating in oceans; agronomists can model more realistically biomass and crop yields; and environmentalists can obtain better assessment of natural resources of radiation.

Comparisons of Radiative Flux Distributions from Satellite Observations and Global Models

NASA Astrophysics Data System (ADS)

Raschke, Ehrhard; Kinne, Stefan; Wild, Martin; Stackhouse, Paul; Rossow, Bill

2014-05-01

Radiative flux distributions at the top of the atmosphere (TOA) and at the surface are compared between typical data from satellite observations and from global modeling. Averages of CERES, ISCCP and SRB data-products (for the same 4-year period) represent satellite observations. Central values of IPCC-4AR output (over a 12-year period) represent global modeling. At TOA, differences are dominated by differences for cloud-effects, which are extracted from the differences between all-sky and clear-sky radiative flux products. As satellite data are considered as TOA reference, these differences document the poor representation of clouds in global modeling, especially for low altitude clouds over oceans. At the surface the differences, caused by the different cloud treatment are overlaid by a general offset. Satellite products suggest a ca 15Wm-2 stronger surface net-imbalance (and with it stronger precipitation). Since surface products of satellite and modeling are based on simulations and many assumptions, this difference has remained an open issue. BSRN surface monitoring is too short and too sparsely distributed for clear answers to provide a reliable basis for validation.

CARBON STORAGE AND FLUXES IN PONDEROSA PINE AT DIFFERENT SUCCESSIONAL STAGES

EPA Science Inventory

We compared carbon storage and fluxes in young and old ponderosa pine stands in Oregon, including plant and soil storage, net primary productivity, respiration fluxes, and eddy flux estimates of net ecosystem exchange. The young site (Y site) was previously an old-growth pondero...

A new solar cycle model including meridional circulation

NASA Technical Reports Server (NTRS)

Wang, Y.-M.; Sheeley, N. R., Jr.; Nash, A. G.

1991-01-01

A kinematic model is presented for the solar cycle which includes not only the transport of magnetic flux by supergranular diffusion and a poleward bulk flow at the sun's surface, but also the effects of turbulent diffusion and an equatorward 'return flow' beneath the surface. As in the earlier models of Babcock and Leighton, the rotational shearing of a subsurface poloidal field generates toroidal flux that erupts at the surface in the form of bipolar magnetic regions. However, such eruptions do not result in any net loss of toroidal flux from the sun (as assumed by Babcock and Leighton); instead, the large-scale toroidal field is destroyed both by 'unwinding' as the local poloidal field reverses its polarity, and by diffusion as the toroidal flux is transported equatorward by the subsurface flow and merged with its opposite hemisphere counterpart. The inclusion of meridional circulation allows stable oscillations of the magnetic field, accompanied by the equatorward progression of flux eruptions, to be achieved even in the absence of a radial gradient in the angular velocity. An illustrative case in which a subsurface flow speed of order 1 m/s and subsurface diffusion rate of order 10 sq km/s yield 22-yr oscillations in qualitative agreement with observations.

Simulating crop phenology in the Community Land Model and its impact on energy and carbon fluxes

NASA Astrophysics Data System (ADS)

Chen, Ming; Griffis, Tim J.; Baker, John; Wood, Jeffrey D.; Xiao, Ke

2015-02-01

A reasonable representation of crop phenology and biophysical processes in land surface models is necessary to accurately simulate energy, water, and carbon budgets at the field, regional, and global scales. However, the evaluation of crop models that can be coupled to Earth system models is relatively rare. Here we evaluated two such models (CLM4-Crop and CLM3.5-CornSoy), both implemented within the Community Land Model (CLM) framework, at two AmeriFlux corn-soybean sites to assess their ability to simulate phenology, energy, and carbon fluxes. Our results indicated that the accuracy of net ecosystem exchange and gross primary production simulations was intimately connected to the phenology simulations. The CLM4-Crop model consistently overestimated early growing season leaf area index, causing an overestimation of gross primary production, to such an extent that the model simulated a carbon sink instead of the measured carbon source for corn. The CLM3.5-CornSoy-simulated leaf area index (LAI), energy, and carbon fluxes showed stronger correlations with observations compared to CLM4-Crop. Net radiation was biased high in both models and was especially pronounced for soybeans. This was primarily caused by the positive LAI bias, which led to a positive net long-wave radiation bias. CLM4-Crop underestimated soil water content during midgrowing season in all soil layers at the two sites, which caused unrealistic water stress, especially for soybean. Future work regarding the mechanisms that drive early growing season phenology and soil water dynamics is needed to better represent crops including their net radiation balance, energy partitioning, and carbon cycle processes.

Land Use Effects on Net Greenhouse Gas Fluxes in the US Great Plains: Historical Trends and Model Projections

NASA Astrophysics Data System (ADS)

Del Grosso, S. J.; Parton, W. J.; Ojima, D. S.; Mosier, A. R.; Mosier, A. R.; Paustian, K.; Peterson, G. A.

2001-12-01

We present maps showing regional patterns of land use change and soil C levels in the US Great Plains during the 20th century and time series of net greenhouse gas fluxes associated with different land uses. Net greenhouse gas fluxes were calculated by accounting for soil CO2 fluxes, the CO2 equivalents of N2O emissions and CH4 uptake, and the CO2 costs of N fertilizer production. Both historical and modern agriculture in this region have been net sources of greenhouse gases. The primary reason for this, prior to 1950, is that agriculture mined soil C and resulted in net CO2 emissions. When chemical N fertilizer became widely used in the 1950's agricultural soils began to sequester CO2-C but these soils were still net greenhouse gas sources if the effects of increased N2O emissions and decreased CH4 uptake are included. The sensitivity of net greenhouse gas fluxes to conventional and alternative land uses was explored using the DAYCENT ecosystem model. Model projections suggest that conversion to no-till, reduction of the fallow period, and use of nitrification inhibitors can significantly decrease net greenhouse gas emissions in dryland and irrigated systems, while maintaining or increasing crop yields.

Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, X., E-mail: xzm0005@auburn.edu; Maurer, D. A.; Knowlton, S. F.

2015-12-15

Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. The inversion radius of standard sawteeth is used tomore » infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.« less

Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

NASA Astrophysics Data System (ADS)

Ma, X.; Maurer, D. A.; Knowlton, S. F.; ArchMiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; Roberds, N. A.; Traverso, P. J.

2015-12-01

Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. The inversion radius of standard sawteeth is used to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.

Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

DOE PAGES

Ma, X.; Maurer, D. A.; Knowlton, Stephen F.; ...

2015-12-22

Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. Lastly, the inversion radius of standard saw-teeth is usedmore » to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.« less

Measurements of plasma sheath heat flux in the Alcator C-Mod divertor

NASA Astrophysics Data System (ADS)

Brunner, Dan; Labombard, Brian; Terry, Jim; Reinke, Matt

2010-11-01

Heat flux is one of the most important parameters controlling the lifetime of first-wall components in fusion experiments and reactors. The sheath heat flux coefficient (γ) is a parameter relating heat flux (from a plasma to a material surface) to the electron temperature and ion saturation current. Being such a simple expression for a kinetic process, it is of great interest to plasma edge fluid modelers. Under the assumptions of equal ion and electron temperatures, no secondary electron emission, and no net current to the surface the value of γ is approximately 7 [1]. Alcator C-Mod provides a unique opportunity among today's experiments to measure reactor-relevant heat fluxes (100's of MW/m^2 parallel to the magnetic field) in reactor-like divertor geometry. Motivated by the DoE 2010 joint milestone to measure heat flux footprints, the lower outer divertor of Alcator has been instrumented with a suite of Langmuir probes, novel surface thermocouples, and calorimeters in tiles purposefully ramped to eliminate shadowing; all within view of an IR camera. Initial results indicate that the experimentally inferred values of γ are found to agree with simple theory in the sheath limited regime and diverges to lower values as the density increases.

Field-based estimates of global warming potential in bioenergy systems of Hawaii: Crop choice and deficit irrigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pawlowski, Meghan N.; Crow, Susan E.; Meki, Manyowa N.

Replacing fossil fuel with biofuel is environmentally viable from a climate change perspective only if the net greenhouse gas (GHG) footprint of the system is reduced. The effects of replacing annual arable crops with perennial bioenergy feedstocks on net GHG production and soil carbon (C) stock are critical to the system-level balance. Here, we compared GHG flux, crop yield, root biomass, and soil C stock under two potential tropical, perennial grass biofuel feedstocks: conventional sugarcane and ratoon-harvested, zero-tillage napiergrass. Evaluations were conducted at two irrigation levels, 100% of plantation application and at a 50% deficit. Peaks and troughs of GHGmore » emission followed agronomic events such as ratoon harvest of napiergrass and fertilization. Yet, net GHG flux was dominated by carbon dioxide (CO 2), as methane was oxidized and nitrous oxide (N 2O) emission was very low even following fertilization. High N 2O fluxes that frequently negate other greenhouse gas benefits that come from replacing fossil fuels with agronomic forms of bioenergy were mitigated by efficient water and fertilizer management, including direct injection of fertilizer into buried irrigation lines. From soil intensively cultivated for a century in sugarcane, soil C stock and root biomass increased rapidly following cultivation in grasses selected for robust root systems and drought tolerance. The net soil C increase over the two-year crop cycle was three-fold greater than the annualized soil surface CO 2 flux. Furthermore, deficit irrigation reduced yield, but increased soil C accumulation as proportionately more photosynthetic resources were allocated below ground. In the first two years of cultivation napier grass did not increase net greenhouse warming potential (GWP) compared to sugarcane, and has the advantage of multiple ratoon harvests per year and less negative effects of deficit irrigation to yield.« less

Field-based estimates of global warming potential in bioenergy systems of Hawaii: Crop choice and deficit irrigation

DOE PAGES

Pawlowski, Meghan N.; Crow, Susan E.; Meki, Manyowa N.; ...

2017-01-04

Replacing fossil fuel with biofuel is environmentally viable from a climate change perspective only if the net greenhouse gas (GHG) footprint of the system is reduced. The effects of replacing annual arable crops with perennial bioenergy feedstocks on net GHG production and soil carbon (C) stock are critical to the system-level balance. Here, we compared GHG flux, crop yield, root biomass, and soil C stock under two potential tropical, perennial grass biofuel feedstocks: conventional sugarcane and ratoon-harvested, zero-tillage napiergrass. Evaluations were conducted at two irrigation levels, 100% of plantation application and at a 50% deficit. Peaks and troughs of GHGmore » emission followed agronomic events such as ratoon harvest of napiergrass and fertilization. Yet, net GHG flux was dominated by carbon dioxide (CO 2), as methane was oxidized and nitrous oxide (N 2O) emission was very low even following fertilization. High N 2O fluxes that frequently negate other greenhouse gas benefits that come from replacing fossil fuels with agronomic forms of bioenergy were mitigated by efficient water and fertilizer management, including direct injection of fertilizer into buried irrigation lines. From soil intensively cultivated for a century in sugarcane, soil C stock and root biomass increased rapidly following cultivation in grasses selected for robust root systems and drought tolerance. The net soil C increase over the two-year crop cycle was three-fold greater than the annualized soil surface CO 2 flux. Furthermore, deficit irrigation reduced yield, but increased soil C accumulation as proportionately more photosynthetic resources were allocated below ground. In the first two years of cultivation napier grass did not increase net greenhouse warming potential (GWP) compared to sugarcane, and has the advantage of multiple ratoon harvests per year and less negative effects of deficit irrigation to yield.« less

Balance Mass Flux and Velocity Across the Equilibrium Line in Ice Drainage Systems of Greenland

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Giovinetto, Mario B.; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

Estimates of balance mass flux and the depth-averaged ice velocity through the cross-section aligned with the equilibrium line are produced for each of six drainage systems in Greenland. (The equilibrium line, which lies at approximately 1200 m elevation on the ice sheet, is the boundary between the area of net snow accumulation at higher elevations and the areas of net melting at lower elevations around the ice sheet.) Ice drainage divides and six major drainage systems are delineated using surface topography from ERS (European Remote Sensing) radar altimeter data. The net accumulation rate in the accumulation zone bounded by the equilibrium line is 399 Gt/yr and net ablation rate in the remaining area is 231 Gt/yr. (1 GigaTon of ice is 1090 kM(exp 3). The mean balance mass flux and depth-averaged ice velocity at the cross-section aligned with the modeled equilibrium line are 0.1011 Gt kM(exp -2)/yr and 0.111 km/yr, respectively, with little variation in these values from system to system. The ratio of the ice mass above the equilibrium line to the rate of mass output implies an effective exchange time of approximately 6000 years for total mass exchange. The range of exchange times, from a low of 3 ka in the SE drainage system to 14 ka in the NE, suggests a rank as to which regions of the ice sheet may respond more rapidly to climate fluctuations.

New production in the warm waters of the tropical Pacific Ocean

NASA Technical Reports Server (NTRS)

Pena, M. Angelica; Lewis, Marlon R.; Cullen, John J.

1994-01-01

The average depth-integrated rate of new production in the tropical Pacific Ocean was estimated from a calculation of horizontal and vertical nitrate balance over the region enclosed by the climatological 26 C isotherm. The net turbulent flux of nitrate into the region was computed in terms of the climatological net surface heat flux and the nitrate-temperature relationship at the base of the 26 C isotherm. The net advective transport of nitrate into the region was estimated using the mean nitrate distribution obtained from the analysis of historical data and previous results of a general circulation model of the tropical Pacific. The rate of new production resulting from vertical turbulent fluxes of nitrate was found to be similar in magnitude to that due to advective transport. Most (about 75%) of the advective input of nitrate was due to the horizontal transport of nutrient-rich water from the eastern equatorial region rather than from equatorial upwelling. An average rate of new production of 14.5 - 16 g C/sq m/yr was found for the warm waters of the tropical Pacific region. These values are in good agreement with previous estimates for this region and are almost five times less than is estimated for the eastern equatorial Pacific, where most of the nutrient upwelling occurs.

Methane Fluxes at the Tree Stem, Soil, and Ecosystem-scales in a Cottonwood Riparian Forest

NASA Astrophysics Data System (ADS)

Flanagan, L. B.; Nikkel, D. J.; Scherloski, L. M.; Tkach, R. E.; Rood, S. B.

2017-12-01

Trees can emit methane to the atmosphere that is produced by microbes inside their decaying stems or by taking up and releasing methane that is produced by microbes in adjacent, anoxic soil layers. The significance of these two methane production pathways for possible net release to the atmosphere depends on the magnitude of simultaneous oxidation of atmospheric methane that occurs in well-aerated, shallow soil zones. In order to quantify the significance of these processes, we made methane flux measurements using the eddy covariance technique at the ecosystem-scale and via chamber-based methods applied on the soil surface and on tree stems in a riparian cottonwood ecosystem in southern Alberta that was dominated by Populus tree species and their natural hybrids. Tree stem methane fluxes varied greatly among individual Populus trees and changed seasonally, with peak growing season average values of 4 nmol m-2 s-1 (tree surface area basis). When scaled to the ecosystem, the tree stem methane emissions (0.9 nmol m-2 s-1, ground area basis) were slightly higher than average soil surface methane uptake rates (-0.8 nmol m-2 s-1). In addition, we observed regular nighttime increases in methane concentration within the forest boundary layer (by 300 nmol mol-1 on average at 22 m height during July). The majority of the methane concentration build-up was flushed from the ecosystem to the well-mixed atmosphere, with combined eddy covariance and air column storage fluxes reaching values of 70-80 nmol m-2 s-1 for approximately one hour after sunrise. Daily average net methane emission rates at the ecosystem-scale were 4.4 nmol m-2 s-1 during July. Additional lab studies demonstrated that tree stem methane was produced via the CO2-reduction pathway, as tissue in the central stem of living Populus trees was being decomposed. This study demonstrated net methane emission from an upland, cottonwood forest ecosystem, resulting from microbe methane production in tree stems that exceeded simultaneous oxidation of atmospheric methane in shallow, aerobic soils.

Estimation of net ecosystem carbon exchange for the conterminous United States by combining MODIS and AmeriFlux data

Treesearch

Jingfeng Xiao; Qianlai Zhuang; Dennis D. Baldocchi; Beverly E. Law; Andrew D. Richardson; Jiquan Chen; Ram Oren; Gegory Starr; Asko Noormets; Siyan Ma; Sashi B. Verma; Sonia Wharton; Steven C. Wofsy; Paul V. Bolstad; Sean P. Burns; David R. Cook; Peter S. Curtis; Bert G. Drake; Matthias Falk; MArc L. Fischer; David R. Foster; Lianhong Gu; Julian L. Hadley; David Y. Hollinger; Gabriel G. Katul; Marcy Litvak; Timothy Martin; Roser Matamala; Steve McNulty; Tilden P. Meyers; Russell K. Monson; J. William Munger; Walter C. Oechel; Kyaw Tha Paw U; Hans Peter Schmid; Russell L. Scott; Ge Sun; Andrew E. Suyker; Margaret S. Torn

2008-01-01

Eddy covariance flux towers provide continuous measurements of net ecosystem carbon exchange (NEE) for a wide range of climate and biome types. However, these measurements only represent the carbon fluxes at the scale of the tower footprint. To quantify the net exchange of carbon dioxide between the terrestrial biosphere and the atmosphere for regions or continents,...

Chandrasekhar-Kendall modes and Taylor relaxation in an axisymmetric torus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, X.Z.; Boozer, A.H.; Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027

2005-10-01

The helicity-conserving Taylor relaxation of a plasma in a toroidal chamber to a force-free configuration, which means j=(j{sub parallel})/B)B with j{sub parallel}/B independent of position, can be generalized to include the external injection of magnetic helicity. When this is done, j{sub parallel}/B has resonant values, which can be understood using the eigenmodes of Taylor-relaxed plasmas enclosed by a perfectly conducting toroidal shell. These eigenmodes include a toroidal generalization of those found by Chandrasekhar and Kendall (CK) [Astrophys. J. 126, 457 (1957)] for a spherical chamber, which has no externally produced magnetic flux. It is shown that the CK modes inmore » an axisymmetric torus are of three types: (1) helical modes as well as axisymmetric modes that have (2) and have no (3) net toroidal flux. Yoshida and Giga (YG) [Math. Z. 204, 235 (1990)] published a fourth class of modes: axisymmetric modes that have no net toroidal flux in the chamber due to toroidal flux produced by a net poloidal current in the shell canceling the net toroidal flux from the plasma currents. Jensen and Chu [Phys. Fluids 27, 2881 (1984)], as well as Taylor [Rev. Mod. Phys. 58, 741 (1986)], considered modes in which the vector potential was zero on the axisymmetric toroidal chamber. It is shown that these Jensen-Chu-Taylor modes include only the CK helical modes and the CK axisymmetric modes without net toroidal flux. If the toroidal chamber is perfectly conducting except for a cut that prevents a net poloidal current from flowing, resonances in j{sub parallel}/B occur at the eigenvalues of the axisymmetric CK modes. Jensen and Chu studied this type of resonance. Without the cut, so a poloidal current flows to conserve the net toroidal flux, it is shown that j{sub parallel}/B resonances occur at the eigenvalues of the CK modes that have no net toroidal flux and at the eigenvalues of the YG modes, which are upshifted from the eigenvalues of the axisymmetric CK modes that carry net toroidal flux.« less

The surface renewal method for better spatial resolution of evapotranspiration measurements

NASA Astrophysics Data System (ADS)

Suvocarev, K.; Fischer, M.; Massey, J. H.; Reba, M. L.; Runkle, B.

2017-12-01

Evaluating feasible irrigation strategies when water is scarce requires measurements or estimations of evapotranspiration (ET). Direct observations of ET from agricultural fields are preferred, and micrometeorological methods such as eddy covariance (EC) provide a high quality, continuous time series of ET. However, when replicates of the measurements are needed to compare irrigation strategies, the cost of such experiments is often prohibitive and limits experimental scope. An alternative micrometeorological approach to ET, the surface renewal (SR) method, may be reduced to a thermocouple and a propeller anemometer (Castellvi and Snyder, 2009). In this case, net radiation, soil and sensible heat flux (H) are measured and latent heat flux (an energy equivalent for ET) is estimated as the residual of the surface energy-balance equation. In our experiment, thermocouples (Type E Fine-Wire Thermocouple, FW3) were deployed next to the EC system and combined with mean horizontal wind speed measurements to obtain H using SR method for three weeks. After compensating the temperature signal for non-ideal frequency response in the wavelet half-plane and correcting the sonic anemometer for the flow distortion (Horst et al., 2015), the SR H fluxes compared well to those measured by EC (r2 = 0.9, slope = 0.92). This result encouraged us to install thermocouples over 16 rice fields under different irrigation treatments (continuous cascade flood, continuous multiple inlet rice irrigation, alternate wetting and drying, and furrow irrigation). The EC measurements with net radiometer and soil heat flux plates are deployed at three of these fields to provide a direct comparison. The measurement campaign will finish soon and the data will be processed to evaluate the SR approach for ET estimation. The results will be used to show better spatial resolution of ET measurements to support irrigation decisions in agricultural crops.

Influence of crop type specification and spatial resolution on empirical modeling of field-scale Maize and Soybean carbon fluxes in the US Great Plains

NASA Astrophysics Data System (ADS)

McCombs, A. G.; Hiscox, A.; Wang, C.; Desai, A. R.

2016-12-01

A challenge in satellite land surface remote-sensing models of ecosystem carbon dynamics in agricultural systems is the lack of differentiation by crop type and management. This generalization can lead to large discrepancies between model predictions and eddy covariance flux tower observations of net ecosystem exchange of CO2 (NEE). Literature confirms that NEE varies remarkably among different crop types making the generalization of agriculture in remote sensing based models inaccurate. Here, we address this inaccuracy by identifying and mapping net ecosystem exchange (NEE) in agricultural fields by comparing bulk modeling and modeling by crop type, and using this information to develop empirical models for future use. We focus on mapping NEE in maize and soybean fields in the US Great Plains at higher spatial resolution using the fusion of MODIS and LandSAT surface reflectance. MODIS observed reflectance was downscaled using the ESTARFM downscaling methodology to match spatial scales to those found in LandSAT and that are more appropriate for carbon dynamics in agriculture fields. A multiple regression model was developed from surface reflectance of the downscaled MODIS and LandSAT remote sensing values calibrated against five FLUXNET/AMERIFLUX flux towers located on soybean and/or maize agricultural fields in the US Great Plains with multi-year NEE observations. Our new methodology improves upon bulk approximates to map and model carbon dynamics in maize and soybean fields, which have significantly different photosynthetic capacities.

Effects of cold front passage on turbulent fluxes over a large inland water

NASA Astrophysics Data System (ADS)

Zhang, Q.; Liu, H.

2011-12-01

Turbulent fluxes of sensible and latent heat over a large inland water in southern USA were measured using the eddy covariance method through the year of 2008. In addition, net radiation, air temperatures and relative humidity, and water temperature in different depths were also measured. The specific objective of this study is to examine effects of a cold front passage on the surface energy fluxes. For the typical cold front event selected from April 11 to 14, air temperature decreased by 16°C, while surface temperature only dropped 6°C. Atmospheric vapor pressure decreased by 1.6 kPa, while that in the water-air interface dropped 0.7 kPa. The behavior difference in the water-air interface was caused by the passage of cold, dry air masses immediately behind the cold front. During the cold front event, sensible heat and latent heat flux increased by 171 W m-2 and 284 W m-2, respectively. Linear aggression analysis showed that the sensible heat flux was proportional to the product of wind speed and the temperature gradient of water-air interface, with a correlation coefficient of 0.95. Latent heat flux was proportional to the product of wind speed and vapor pressure difference between the water surface and overlaying atmosphere, with a correlation coefficient of 0.81. Also, the correlations between both fluxes and the wind speed were weak. This result indicated that the strong wind associated with the cold front event contributed to the turbulent mixing, which indirectly enhanced surface energy exchange between the water surface and the atmosphere. The relationship between the water heat storage energy and turbulent fluxes was also examined.

Determination of ocean surface heat fluxes by a variational method

NASA Astrophysics Data System (ADS)

Roquet, H.; Planton, S.; Gaspar, P.

1993-06-01

A new technique of determination of the "nonsolar" heat flux (sum of the latent, sensible, and net infrared fluxes) at the ocean surface is proposed. It applies when oceanic advection remains weak and thus relies on a one-dimensional modeling approach. It is based on a variational data assimilation scheme using the adjoint equation formalism. This allows to take advantage of all observed data with their error estimates. Results from experiments performed with station Papa (Gulf of Alaska) and Long-Term Upper Ocean Study (LOTUS, Sargasso Sea) data sets are discussed. The temperature profiles assimilation allows the one-dimensional model to reproduce correctly the temperature evolution at the surface and under the oceanic mixed layer at the two sites. The retrieved fluxes are compared to the fluxes calculated through classical empirical formulae. The diurnal dependence of the fluxes at the LOTUS site is particularly investigated. The results are also compared with those obtained using a simpler technique based on an iterative shooting method and allowing the assimilation of the only sea surface temperature. This second comparison reveals that the variability of the retrieved fluxes is damped when temperature in the inner ocean are assimilated. This is the case for the diurnal cycle at the LOTUS mooring. When the available current data at this site are assimilated, the diurnal variability of the retrieved fluxes is further decreased. This points out a model discrepancy in the representation of mixing processes associated to internal wave activity. The remaining part of the diurnal cycle is significant and could be due to a direct effect of air-sea temperature difference.

Local energy flux estimates for unstable conditions using variance data in semiarid rangelands

USGS Publications Warehouse

Kustas, William P.; Blanford, J.H.; Stannard, D.I.; Daughtry, C.S.T.; Nichols, W.D.; Weltz, M.A.

1994-01-01

A network of meteorological stations was installed during the Monsoon '90 field campaign in the Walnut Gulch experimental watershed. The study area has a fairly complex surface. The vegetation cover is heterogeneous and sparse, and the terrain is mildly hilly, but dissected by ephemeral channels. Besides measurement of some of the standard weather data such as wind speed, air temperature, and solar radiation, these sites also contained instruments for estimating the local surface energy balance. The approach utilized measurements of net radiation (Rn), soil heat flux (G) and Monin-Obukhov similarity theory applied to first- and second-order turbulent statistics of wind speed and temperature for determining the sensible heat flux (H). The latent heat flux (LE) was solved as a residual in the surface energy balance equation, namely, LE = −(Rn + G + H). This procedure (VAR-RESID) for estimating the energy fluxes satisfied monetary constraints and the requirement for low maintenance and continued operation through the harsh environmental conditions experienced in semiarid regions. Comparison of energy fluxes using this approach with more traditional eddy correlation techniques showed differences were within 20% under unstable conditions. Similar variability in flux estimates over the study area was present in the eddy correlation data. Hence, estimates of H and LE using the VAR-RESID approach under unstable conditions were considered satisfactory. Also, with second-order statistics of vertical velocity collected at several sites, the local momentum roughness length was estimated. This is an important parameter used in modeling the turbulent transfer of momentum and sensible heat fluxes across the surface-atmosphere interface.

A novel assessment of the role of land-use and land-cover change in the global carbon cycle, using a new Dynamic Global Vegetation Model version of the CABLE land surface model

NASA Astrophysics Data System (ADS)

Haverd, Vanessa; Smith, Benjamin; Nieradzik, Lars; Briggs, Peter; Canadell, Josep

2017-04-01

In recent decades, terrestrial ecosystems have sequestered around 1.2 PgC y-1, an amount equivalent to 20% of fossil-fuel emissions. This land carbon flux is the net result of the impact of changing climate and CO2 on ecosystem productivity (CO2-climate driven land sink ) and deforestation, harvest and secondary forest regrowth (the land-use change (LUC) flux). The future trajectory of the land carbon flux is highly dependent upon the contributions of these processes to the net flux. However their contributions are highly uncertain, in part because the CO2-climate driven land sink and LUC components are often estimated independently, when in fact they are coupled. We provide a novel assessment of global land carbon fluxes (1800-2015) that integrates land-use effects with the effects of changing climate and CO2 on ecosystem productivity. For this, we use a new land-use enabled Dynamic Global Vegetation Model (DGVM) version of the CABLE land surface model, suitable for use in attributing changes in terrestrial carbon balance, and in predicting changes in vegetation cover and associated effects on land-atmosphere exchange. In this model, land-use-change is driven by prescribed gross land-use transitions and harvest areas, which are converted to changes in land-use area and transfer of carbon between pools (soil, litter, biomass, harvested wood products and cleared wood pools). A novel aspect is the treatment of secondary woody vegetation via the coupling between the land-use module and the POP (Populations Order Physiology) module for woody demography and disturbance-mediated landscape heterogeneity. Land-use transitions to and from secondary forest tiles modify the patch age distribution within secondary-vegetated tiles, in turn affecting biomass accumulation and turnover rates and hence the magnitude of the secondary forest sink. The resulting secondary forest patch age distribution also influences the magnitude of the secondary forest harvest and clearance fluxes, with oldest patches (high biomass) being preferentially harvested, and youngest patches (low biomass) being preferentially cleared. Our results, which agree well with the net land flux derived from the global carbon budget, are used for a process-attribution of the land carbon sink. Use of multiple constraints provides confidence in our process-attribution: we use observation-based data sets to evaluate predictions of global spatial distributions of vegetation cover, evaporation, gross primary production, biomass and soil carbon; interannual variability of the global terrestrial carbon sink; forest allometric relations and age-effects on net primary production.

Effect of distal Sacramento-San Joaquin Delta outflow on suspended-sediment flux in Lower South San Francisco Bay

NASA Astrophysics Data System (ADS)

Livsey, D. N.; Downing-Kunz, M.; Schoellhamer, D. H.; Shellenbarger, G.; Wright, S. A.

2016-12-01

Tidal marshes are an important component of estuarine ecosystems. Within the San Francisco Bay Estuary (SFB) tidal marshes play an important role in food web dynamics, are home to an array of endemic mammals, birds, and fishes, filter pollutants, and dampen coastal flooding. With 80% of SFB tidal marshes lost to human development, numerous restoration efforts are underway. The largest tidal marsh restoration project in SFB, the South Bay Salt Pond Restoration Project, is underway in Lower South San Francisco Bay to restore 60,000 ha of this critical habitat; however, rising sea levels, could jeopardize these gains without concomitant vertical accretion rates of the marsh surface via organic matter accumulation and sediment deposition. Recent work in Lower South Bay using continuously collected data from water years (WY) 2009-11 indicates that the direction of net springtime residual sediment flux is related to the amount of springtime Sacramento-San Joaquin Delta (Delta) outflow. Large outflow freshens the Central Bay, causing a density gradient and inverse gravitational circulation that flushes Lower South Bay. In this study we extend the sediment budget for Lower South Bay from WY 2011 to present using 15-minute turbidity and velocity data paired with Acoustic Doppler Current Profiler cross-sectional measurements and in situ suspended-sediment concentration samples to: 1) further examine the mechanisms controlling net springtime residual sediment flux, and 2) further test the hypothesis that Delta outflow controls the direction of net sediment flux for Lower South Bay.

Evaluation of Deep Learning Models for Predicting CO2 Flux

NASA Astrophysics Data System (ADS)

Halem, M.; Nguyen, P.; Frankel, D.

2017-12-01

Artificial neural networks have been employed to calculate surface flux measurements from station data because they are able to fit highly nonlinear relations between input and output variables without knowing the detail relationships between the variables. However, the accuracy in performing neural net estimates of CO2 flux from observations of CO2 and other atmospheric variables is influenced by the architecture of the neural model, the availability, and complexity of interactions between physical variables such as wind, temperature, and indirect variables like latent heat, and sensible heat, etc. We evaluate two deep learning models, feed forward and recurrent neural network models to learn how they each respond to the physical measurements, time dependency of the measurements of CO2 concentration, humidity, pressure, temperature, wind speed etc. for predicting the CO2 flux. In this paper, we focus on a) building neural network models for estimating CO2 flux based on DOE data from tower Atmospheric Radiation Measurement data; b) evaluating the impact of choosing the surface variables and model hyper-parameters on the accuracy and predictions of surface flux; c) assessing the applicability of the neural network models on estimate CO2 flux by using OCO-2 satellite data; d) studying the efficiency of using GPU-acceleration for neural network performance using IBM Power AI deep learning software and packages on IBM Minsky system.

Interannual Variability in Surface LW Fluxes Over the Tropical Oceans As Seen in ISCCP-FD and GEWEX SRB Data Sets

NASA Technical Reports Server (NTRS)

Robertson, F. R.; Lu, H.-I.

2005-01-01

One notable aspect of Earth s climate is that although the planet appears to be very close to radiative balance at top-of-atmosphere (TOA), the atmosphere itself and underlying surface are not. Profound exchanges of energy between the atmosphere and oceans, land and cryosphere occur over a range of time scales. Recent evidence from broadband satellite measurements suggests that even these TOA fluxes contain some detectable variations. Our ability to measure and reconstruct radiative fluxes at the surface and at the top of atmosphere is improving rapidly. In this work we will evaluate two recently released estimates of radiative fluxes, focusing primarily on surface estimates. The International Satellite Cloud Climatology Project FD radiative flux profiles are available from mid-1 983 to near present and have been constructed by driving the radiative transfer physics from the Goddard Institute for Space Studies (GISS) global model with ISCCP clouds and TOVS (TIROS Operational Vertical Sounder)thermodynamic profiles. Fu!l and clear sky SW and LW fluxes are produced. A similar product from the NASA/GEWEX Surface Radiation Budget Project using different radiative flux codes and thermodynamics from the NAS/Goddard Earth Observing System (GEOS-1) assimilation model makes a similar calculation of surface fluxes. However this data set currently extends only through 1995. Significant differences in both interannual variability as well as trends are found between among these data sets. For radiative fluxes these differences are traced to TOVS thermodynamic soundings used to drive the ISCCP-FD calculations. Errors in near surface temperature and precipitable water cascade into ISCCP upward and downward IR flux components, demonstrably affecting interannual variability. Revised estimates of clear-sky fluxes over ocean are made using statistical algorithms and water vapor from the (SSM/I) Special Sensor Microwave Imager. These calculations show strong near-surface water vapor feedback over the tropical oceans in association with SST changes. However, it is also shown that ISCCP longwave cloud forcing, common to both the ISCCP-FD and GEWEX SRB retrievals, is the main driver of a long-term decrease in net LW flux to the surface during the near-20 year period covered by these revised estimates.

Evaluation of MODIS NPP and GPP products across multiple biomes.

Treesearch

David P. Turner; William D. Ritts; Warren B. Cohen; Stith T. Gower; Steve W. Running; Maosheng Zhao; Marcos H. Costa; Al A. Kirschbaum; Jay M. Ham; Scott R. Saleska; Douglas E. Ahl

2006-01-01

Estimates of daily gross primary production (GPP) and annual net primary production (NPP) at the 1 km spatial resolution are now produced operationally for the global terrestrial surface using imagery from the MODIS (Moderate Resolution Imaging Spectroradiometer) sensor. Ecosystem-level measurements of GPP at eddy covariance flux towers and plot-level measurements of...

Carbon dioxide and water vapor exchange in a warm temperate grassland

Treesearch

K.A. Novick; P.C. Stoy; G.G. Katul; D.S. Ellsworth; M.B.S. Siqueira; J. Juang; R. Oren

2004-01-01

Grasslands cover about 40% of the ice-free global terrestrial surface, but their contribution to local and regional water and carbon fluxes and sensitivity to climatic perturbations such as drought remains uncertain. Here, we assess the direction and magnitude of net ecosystem carbon exchange (NEE) and it components, ecosystem carbon assimilation (Ac...

Carbon fluxes on North American rangelands

Treesearch

Tony Svejcar; Raymond Angell; James A. Bradford; William Dugas; William Emmerich; Albert B. Frank; Tagir Gilmanov; Marshall Haferkamp; Douglas A. Johnson; Herman Mayeux; Pat Mielnick; Jack Morgan; Nicanor Z. Saliendra; Gerald E. Schuman; Phillip L. Sims; Kereith Snyder

2008-01-01

Rangelands account for almost half of the earth's land surface and may play an important role in the global carbon (C) cycle. We studied net ecosystem exchange (NEE) of C on eight North American rangeland sites over a 6-yr period. Management practices and disturbance regimes can influence NEE; for consistency, we compared ungrazed and undisturbed rangelands...

Adjoint-Based Climate Model Tuning: Application to the Planet Simulator

NASA Astrophysics Data System (ADS)

Lyu, Guokun; Köhl, Armin; Matei, Ion; Stammer, Detlef

2018-01-01

The adjoint method is used to calibrate the medium complexity climate model "Planet Simulator" through parameter estimation. Identical twin experiments demonstrate that this method can retrieve default values of the control parameters when using a long assimilation window of the order of 2 months. Chaos synchronization through nudging, required to overcome limits in the temporal assimilation window in the adjoint method, is employed successfully to reach this assimilation window length. When assimilating ERA-Interim reanalysis data, the observations of air temperature and the radiative fluxes are the most important data for adjusting the control parameters. The global mean net longwave fluxes at the surface and at the top of the atmosphere are significantly improved by tuning two model parameters controlling the absorption of clouds and water vapor. The global mean net shortwave radiation at the surface is improved by optimizing three model parameters controlling cloud optical properties. The optimized parameters improve the free model (without nudging terms) simulation in a way similar to that in the assimilation experiments. Results suggest a promising way for tuning uncertain parameters in nonlinear coupled climate models.

Observed and modeled carbon and energy fluxes for agricultural sites under North American Carbon Program site-level interim synthesis

NASA Astrophysics Data System (ADS)

Lokupitiya, E. Y.; Denning, A.

2010-12-01

Croplands are unique, man-made ecosystems with dynamics mostly dependent on human decisions. Crops uptake a significant amount of Carbon dioxide (CO2) during their short growing seasons. Reliability of the available models to predict the carbon exchanges by croplands is important in estimating the cropland contribution towards overall land-atmosphere carbon exchange and global carbon cycle. The energy exchanges from croplands include both sensible and latent heat fluxes. This study focuses on analyzing the performance of 19 land surface models across five agricultural sites under the site-level interim synthesis of North American Carbon Program (NACP). Model simulations were performed using a common simulation protocol and input data, including gap-filled meteorological data corresponding to each site. The net carbon fluxes (i.e. net ecosystem exchange; NEE) and energy fluxes (sensible and latent heat) predicted by 12 models with sub-hourly/hourly temporal resolution and 7 models with daily temporal resolution were compared against the site-specific gap-filled observed flux tower data. Comparisons were made by site and crop type (i.e. maize, soybean, and wheat), mainly focusing on the coefficient of determination, correlation, root mean square error, and standard deviation. Analyses also compared the diurnal, seasonal, and inter-annual variability of the modeled fluxes against the observed data and the mean modeled data.

Improvement of Mars surface snow albedo modeling in LMD Mars GCM with SNICAR

NASA Astrophysics Data System (ADS)

Singh, D.; Flanner, M.; Millour, E.

2017-12-01

The current version of Laboratoire de Météorologie Dynamique (LMD) Mars GCM (original-MGCM) uses annually repeating (prescribed) albedo values from the Thermal Emission Spectrometer observations. We integrate the Snow, Ice, and Aerosol Radiation (SNICAR) model with MGCM (SNICAR-MGCM) to prognostically determine H2O and CO2 ice cap albedos interactively in the model. Over snow-covered regions mean SNICAR-MGCM albedo is higher by about 0.034 than original-MGCM. Changes in albedo and surface dust content also impact the shortwave energy flux at the surface. SNICAR-MGCM model simulates a change of -1.26 W/m2 shortwave flux on a global scale. Globally, net CO2 ice deposition increases by about 4% over one Martian annual cycle as compared to original-MGCM simulations. SNICAR integration reduces the net mean global surface temperature, and the global surface pressure of Mars by about 0.87% and 2.5% respectively. Changes in albedo also show a similar distribution as dust deposition over the globe. The SNICAR-MGCM model generates albedos with higher sensitivity to surface dust content as compared to original-MGCM. For snow-covered regions, we improve the correlation between albedo and optical depth of dust from -0.91 to -0.97 with SNICAR-MGCM as compared to original-MGCM. Using new diagnostic capabilities with this model, we find that cryospheric surfaces (with dust) increase the global surface albedo of Mars by 0.022. The cryospheric effect is severely muted by dust in snow, however, which acts to decrease the planet-mean surface albedo by 0.06.

Effect of land use on methane flux from soil.

PubMed

Chan, A S; Parkin, T B

2001-01-01

The precise effects of natural and disturbed terrestrial systems on the atmospheric CH4 pool are uncertain. This study was conducted to quantify and compare CH4 fluxes from a variety of ecosystems in central Iowa. We investigated agricultural systems under different management practices, a hardwood forest site, native and restored prairies, and a municipal landfill. Flux measurements were obtained using a closed-chamber method, and measurements were compiled by sampling over the 1993 and 1994 growing seasons. In 1993, most of the agricultural sites were net CH4 producers with cumulative CH4 fluxes ranging from -0.02 to 3.19 g m(-2) over the 258-d sampling season, while the natural ecosystems were net CH4 consumers, with cumulative seasonal fluxes ranging from -0.27 to -0.07 g m-2 258 d(-1). In 1994, only the landfill and the agricultural site treated with broadcast liquid swine manure (LSM) were net CH4 producers, while the remainder of the natural and agricultural ecosystems were net CH4 consumers, with mean seasonal flux rates ranging from -0.43 to -0.008 g m(-2) 271 d(-1). We hypothesize that the differences in CH4 fluxes between the two years are due to differences in rainfall. To illustrate the integration between land use and CH4 flux, we computed an area-weighted soil CH4 flux for the state of Iowa. Our calculations yielded a net average soil CH4 flux of 139,000 Mg CH4 for 1993 and 1994.

Non-axisymmetric equilibrium reconstruction on the Compact Toroidal Hybrid Experiment using external magnetic and soft x-ray inversion radius measurements

NASA Astrophysics Data System (ADS)

Ma, X.; Cianciosa, M.; Hanson, J. D.; Hartwell, G. J.; Knowlton, S. F.; Maurer, D. A.; Ennis, D. A.; Herfindal, J. L.

2015-11-01

Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by the driven plasma current. Studies were performed on the Compact Toroidal Hybrid device using the V3FIT reconstruction code incorporating a set of 50 magnetic diagnostics external to the plasma, combined with information from soft X-ray (SXR) arrays. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the outer boundary of these highly non-axisymmetric plasmas. The inversion radius for sawtoothing plasmas is used to identify the location of the q = 1 surface, and thus infer the current profile near the magnetic axis. With external magnetic diagnostics alone, we find the reconstruction to be insufficiently constrained. This work is supported by US Department of Energy Grant No. DE-FG02-00ER54610.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiang, Baoqiang; Zhao, Ming; Held, Isaac M.

The severity of the double Intertropical Convergence Zone (DI) problem in climate models can be measured by a tropical precipitation asymmetry index (PAI), indicating whether tropical precipitation favors the Northern Hemisphere or the Southern Hemisphere. Examination of 19 Coupled Model Intercomparison Project phase 5 models reveals that the PAI is tightly linked to the tropical sea surface temperature (SST) bias. As one of the factors determining the SST bias, the asymmetry of tropical net surface heat flux in Atmospheric Model Intercomparison Project (AMIP) simulations is identified as a skillful predictor of the PAI change from an AMIP to a coupledmore » simulation, with an intermodel correlation of 0.90. Using tropical top-of-atmosphere (TOA) fluxes, the correlations are lower but still strong. However, the extratropical asymmetries of surface and TOA fluxes in AMIP simulations cannot serve as useful predictors of the PAI change. Furthermore, this study suggests that the largest source of the DI bias is from the tropics and from atmospheric models.« less

Variability and trends in surface seawater pCO2 and CO2 flux in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Sutton, A. J.; Wanninkhof, R.; Sabine, C. L.; Feely, R. A.; Cronin, M. F.; Weller, R. A.

2017-06-01

Variability and change in the ocean sink of anthropogenic carbon dioxide (CO2) have implications for future climate and ocean acidification. Measurements of surface seawater CO2 partial pressure (pCO2) and wind speed from moored platforms are used to calculate high-resolution CO2 flux time series. Here we use the moored CO2 fluxes to examine variability and its drivers over a range of time scales at four locations in the Pacific Ocean. There are significant surface seawater pCO2, salinity, and wind speed trends in the North Pacific subtropical gyre, especially during winter and spring, which reduce CO2 uptake over the 10 year record of this study. Starting in late 2013, elevated seawater pCO2 values driven by warm anomalies cause this region to be a net annual CO2 source for the first time in the observational record, demonstrating how climate forcing can influence the timing of an ocean region shift from CO2 sink to source.

Net carbon flux of dead wood in forests of the Eastern US

Treesearch

C.W. Woodall; M.B. Russell; B.F. Walters; A.W. D' Amato; S. Fraver; G.M. Domke

2015-01-01

Downed dead wood (DDW) in forest ecosystems is a C pool whose net flux is governed by a complex of natural and anthropogenic processes and is critical to the management of the entire forest C pool. As empirical examination of DDW C net flux has rarely been conducted across large scales, the goal of this study was to use a remeasured inventory of DDW C and ancillary...

Partitioning net ecosystem carbon exchange into net assimilation and respiration using 13CO2 measurements: A cost-effective sampling strategy

NASA Astrophysics Data System (ADS)

OgéE, J.; Peylin, P.; Ciais, P.; Bariac, T.; Brunet, Y.; Berbigier, P.; Roche, C.; Richard, P.; Bardoux, G.; Bonnefond, J.-M.

2003-06-01

The current emphasis on global climate studies has led the scientific community to set up a number of sites for measuring the long-term biosphere-atmosphere net CO2 exchange (net ecosystem exchange, NEE). Partitioning this flux into its elementary components, net assimilation (FA), and respiration (FR), remains necessary in order to get a better understanding of biosphere functioning and design better surface exchange models. Noting that FR and FA have different isotopic signatures, we evaluate the potential of isotopic 13CO2 measurements in the air (combined with CO2 flux and concentration measurements) to partition NEE into FR and FA on a routine basis. The study is conducted at a temperate coniferous forest where intensive isotopic measurements in air, soil, and biomass were performed in summer 1997. The multilayer soil-vegetation-atmosphere transfer model MuSICA is adapted to compute 13CO2 flux and concentration profiles. Using MuSICA as a "perfect" simulator and taking advantage of the very dense spatiotemporal resolution of the isotopic data set (341 flasks over a 24-hour period) enable us to test each hypothesis and estimate the performance of the method. The partitioning works better in midafternoon when isotopic disequilibrium is strong. With only 15 flasks, i.e., two 13CO2 nighttime profiles (to estimate the isotopic signature of FR) and five daytime measurements (to perform the partitioning) we get mean daily estimates of FR and FA that agree with the model within 15-20%. However, knowledge of the mesophyll conductance seems crucial and may be a limitation to the method.

Experimental study of the impact of large-scale wind farms on land-atmosphere exchanges

NASA Astrophysics Data System (ADS)

Zhang, wei; Markfort, Corey; Porté-Agel, Fernando

2013-04-01

Wind energy is one of the fastest growing sources of renewable energy world-wide, and it is expected that many more large-scale wind farms will be built and cover a significant portion of land and ocean surfaces. By extracting kinetic energy from the atmospheric boundary layer and converting it to electricity, wind farms may affect the transport of momentum, heat, moisture and trace gases (e.g. CO2) between the atmosphere and the land surface locally and globally. Understanding wind farm-atmosphere interactions and subsequent environmental impacts are complicated by the effects of turbine array configuration, wind farm size, land-surface characteristics and atmospheric thermal stability. In particular, surface scalar flux is influenced by wind farms and needs to be appropriately parameterized in meso-scale and/or high-resolution numerical models. Wind-tunnel experiments of model wind farms with perfectly aligned and staggered configurations, having the same turbine distribution density, were conducted in a neutral turbulent boundary layer with a surface heat source. Turbulent flow and fluxes over and through the wind farm were measured using a custom x-wire/cold-wire anemometer; and surface scalar flux was measured with an array of surface-mounted heat flux sensors within the quasi-developed flow regime. Although the overall surface heat flux change produced by the wind farms was found to be small, with a net reduction of 4% for the staggered wind farm and nearly zero for the aligned wind farm, the highly heterogeneous spatial distribution of the surface heat flux, dependent on wind farm layout, is significant. The difference between the minimum and maximum surface heat fluxes could be up to 12% and 7% in aligned and staggered wind farms, respectively. This finding is important for planning intensive agriculture practices and optimizing agricultural land use with regard to wind energy project development. The well-controlled wind-tunnel experiments presented here also provide a first comprehensive dataset on turbulent flow and scalar transport in wind farms, which can be further used to develop and validate new parameterizations for surface scalar fluxes in numerical models.

Hydrogen Fluxes from Photosynthetic Communities: Implications for Early Earth Biogeochemistry

NASA Technical Reports Server (NTRS)

Hoehler, Tori M.; Bebout, Brad M.; DesMarais, David J.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

More than half the history of life on Earth was dominated by photosynthetic microbial mats, which must have represented the preeminent biological influence on global geochemical cycling during that time. In modem analogs of then ancient communities, hypersaline microbial mats from Guerrero Negro, Mexico, we have observed a large flux of molecular hydrogen originating in the cyanobacteria-dominated surface layers. Hydrogen production follows a distinct diel pattern and is sensitive to both oxygen tension and microbial species composition within the mat. On an early Earth dominated by microbial mats, the observed H2 fluxes would scale to global levels far in excess of geothermal emissions. A hydrogen flux of this magnitude represents a profound transmission of reducing power from oxygenic photosynthesis, both to the anaerobic biosphere, where H2 is an almost universally-utilized substrate and regulator of microbial redox chemistry, and to the atmosphere, where subsequent escape to space could provide an important mechanism for the net oxidation of Earth's surface.

Soil-atmosphere exchange of ammonia in a non-fertilized grassland: measured emission potentials and inferred fluxes

NASA Astrophysics Data System (ADS)

Wentworth, G. R.; Murphy, J. G.; Gregoire, P. K.; Cheyne, C. A. L.; Tevlin, A. G.; Hems, R.

2014-10-01

A 50-day field study was carried out in a semi-natural, non-fertilized grassland in south-western Ontario, Canada during the late summer and early autumn of 2012. The purpose was to explore surface-atmosphere exchange processes of ammonia (NH3) with a focus on bi-directional fluxes between the soil and atmosphere. Measurements of soil pH and ammonium concentration ([NH4+]) yielded the first direct quantification of soil emission potential (Γsoil = [NH4+]/[H+]) for this land type, with values ranging from 35 to 1850 (an average of 290). The soil compensation point, the atmospheric NH3 mixing ratio below which net emission from the soil will occur, exhibited both a seasonal trend and diurnal trend. Higher daytime and August compensation points were attributed to higher soil temperature. Soil-atmosphere fluxes were estimated using NH3 measurements from the Ambient Ion Monitor Ion Chromatograph (AIM-IC) and a simple resistance model. Vegetative effects were ignored due to the short canopy height and significant Γsoil. Inferred fluxes were, on average, 2.6 ± 4.5 ng m-2 s-1 in August (i.e. net emission) and -5.8 ± 3.0 ng m-2 s-1 in September (i.e. net deposition). These results are in good agreement with the only other bi-directional exchange study in a semi-natural, non-fertilized grassland. A Lagrangian dispersion model (Hybrid Single-Particle Lagrangian Integrated Trajectory - HYSPLIT) was used to calculate air parcel back-trajectories throughout the campaign and revealed that NH3 mixing ratios had no directional bias throughout the campaign, unlike the other atmospheric constituents measured. This implies that soil-atmosphere exchange over a non-fertilized grassland can significantly moderate near-surface NH3 concentrations. In addition, we provide indirect evidence that dew and fog evaporation can cause a morning increase of [NH3]g. Implications of our findings on current NH3 bi-directional exchange modelling efforts are also discussed.

Net thermal radiation in the atmosphere of Venus

NASA Technical Reports Server (NTRS)

Revercomb, H. E.; Sromovsky, L. A.; Suomi, V. E.; Boese, R. W.

1985-01-01

Estimates of the true atmospheric net fluxes at the four Pioneer Venus entry sites are presently obtained through corrections of measured values that are relatively small for the case of the clouds, but generally large deeper in the atmosphere. The correction procedure for both the small and large probe fluxes used model results near 14 km to establish the size of the correction. The thermal net fluxes obtained imply that the contribution of mode 3 particles to the IR opacity of the middle and lower clouds is smaller than indicated by the Pioneer Venus cloud particle spectrometer measurements, and the day probe results favor a reduction of only about 50 percent. The fluxes at all sites imply that a yet-undetermined source of considerable opacity is present in the upper cloud. Beneath the clouds, the thermal net fluxes generally increase with increasing latitude.

Using NDACC column measurements of carbonyl sulfide to estimate its sources and sinks

NASA Astrophysics Data System (ADS)

Wang, Yuting; Marshall, Julia; Palm, Mathias; Deutscher, Nicholas; Roedenbeck, Christian; Warneke, Thorsten; Notholt, Justus; Baker, Ian; Berry, Joe; Suntharalingam, Parvadha; Jones, Nicholas; Mahieu, Emmanuel; Lejeune, Bernard; Hannigan, James; Conway, Stephanie; Strong, Kimberly; Campbell, Elliott; Wolf, Adam; Kremser, Stefanie

2016-04-01

Carbonyl sulfide (OCS) is taken up by plants during photosynthesis through a similar pathway as carbon dioxide (CO2), but is not emitted by respiration, and thus holds great promise as an additional constraint on the carbon cycle. It might act as a sort of tracer of photosynthesis, a way to separate gross primary productivity (GPP) from the net ecosystem exchange (NEE) that is typically derived from flux modeling. However the estimates of OCS sources and sinks still have significant uncertainties, which make it difficult to use OCS as a photosynthetic tracer, and the existing long-term surface-based measurements are sparse. The NDACC-IRWG measures the absorption of OCS in the atmosphere, and provides a potential long-term database of OCS total/partial columns, which can be used to evaluate OCS fluxes. We have retrieved OCS columns from several NDACC sites around the globe, and compared them to model simulation with OCS land fluxes based on the simple biosphere model (SiB). The disagreement between the measurements and the forward simulations indicates that (1) the OCS land fluxes from SiB are too low in the northern boreal region; (2) the ocean fluxes need to be optimized. A statistical linear flux model describing OCS is developed in the TM3 inversion system, and is used to estimate the OCS fluxes. We performed flux inversions using only NOAA OCS surface measurements as an observational constraint and with both surface and NDACC OCS column measurements, and assessed the differences. The posterior uncertainties of the inverted OCS fluxes decreased with the inclusion of NDACC data comparing to those using surface data only, and could be further reduced if more NDACC sites were included.

Closure of the energy balance equation over bare soil during the formation and evaporation of non-rainfall water inputs

NASA Astrophysics Data System (ADS)

Florentin, Anat; Agam, Nurit

2015-04-01

The Negev desert is characterized by an arid climate (annual mean precipitation is 90 mm) with sea breeze carrying moisture from the Mediterranean Sea during the afternoon regularly. Non-rainfall water inputs (NRWIs) are thus of great importance to the hydrometeorology and the ecological functioning of the region. The small magnitude of NRWIs challenges attempts to quantify these processes. The aim of this research was to test commonly used micrometeorological methods to quantify the energy balance components during the deposition and evaporation of NRWIs. A fully equipped micrometeorological station was set up near the Blaustein Institutes for Desert Research of the Ben-Gurion University of the Negev (30o 51' 35.6" N; 34o 46' 24.8" E) during September-October 2014. Net-radiation was measured with a 4-way net radiometer, and soil heat flux was quantified by the calorimetric method in three replicates. Latent heat was measured using an eddy-covariance (EC) and compared to a micro-lysimeter (ML); sensible heat flux was measured with an EC and a surface layer scintillometer (SLS). Sensible heat fluxes measured by the EC and the SLS showed good agreement. EC latent heat fluxes were in good agreement with those derived by the ML. Nevertheless, derivation of latent heat flux from the SLS measurements through the energy balance equation showed a relatively large deviation from the directly measured latent heat flux. This deviation is likely attributed to measurement errors of the soil heat flux.

Diagnosing the imbalance of Yanamarey Glacier in the Cordillera Blanca of Peru

NASA Astrophysics Data System (ADS)

Hastenrath, Stefan; Ames, Alcides

1995-03-01

A detailed glaciological observation program was conducted on the Yanamarey Glacier in the Cordillera Blanca of Peru, including the monitoring of net balance and ice flow velocity during 1977-1988 and mappings of the surface topography in 1973, 1982, and 1988. These observations are here evaluated to combine net balance, surface lowering, and ice flow into a consistent picture of the mode of operation of a tropical glacier on the scale of a decade. The glacier extends between 5100 and 4500 m with a total area of 9×105 m2 and length of about 1.3 km. Maximum flow velocity is 17.4 m yr-1 and maximum volume flux 336×103 m3 yr-1. In the ablation area, net balance is about -6 m yr-1 and surface lowering 3 m yr-1. About half of the mean annual water discharge from the glacier of 80 L s-1 is not renewed by precipitation but supplied by the ice thinning. The rate of surface lowering of 1.5 m yr-1 liquid water equivalent translates to a glacier average departure heat supply for melting of 16 W m-2. Sensitivity analyses indicate that this could be produced by a cloudiness increase of less than one tenth, an air temperature decrease of 2°C, an increment in specific humidity of less than 1 g kg-1, or some combination of heat budget processes. Such changes in the atmospheric environment would be required to stabilize the glacier at its recent volume. As another indication of the recent imbalance, the maximum volume flux is found some 100 m below the equilibrium line altitude. Under continuation of the recent climatic conditions, the glacier may survive for more than half a century.

A dynamical stabilizer in the climate system: a mechanism suggested by a simple model

NASA Astrophysics Data System (ADS)

Bates, J. R.

1999-05-01

A simple zonally averaged hemispheric model of the climate system is constructed, based on energy equations for two ocean basins separated at 30° latitude with the surface fluxes calculated explicitly. A combination of empirical input and theoretical calculation is used to determine an annual mean equilibrium climate for the model and to study its stability with respect to small perturbations. The insolation, the mean albedos and the equilibrium temperatures for the two model zones are prescribed from observation. The principal agent of interaction between the zones is the vertically integrated poleward transport of atmospheric angular momentum across their common boundary. This is parameterized using an empirical formula derived from a multiyear atmospheric data set. The surface winds are derived from the angular momentum transport assuming the atmosphere to be in a state of dynamic balance on the climatic timescales of interest. A further assumption that the air sea temperature difference and low level relative humidity remain fixed at their mean observed values then allows the surface fluxes of latent and sensible heat to be calculated. Results from a radiative model, which show a positive lower tropospheric water vapour/infrared radiative feedback on SST perturbations in both zones, are used to calculate the net upward infrared radiative fluxes at the surface. In the model's equilibrium climate, the principal processes balancing the solar radiation absorbed at the surface are evaporation in the tropical zone and net infrared radiation in the extratropical zone. The stability of small perturbations about the equilibrium is studied using a linearized form of the ocean energy equations. Ice-albedo and cloud feedbacks are omitted and attention is focussed on the competing effects of the water vapour/infrared radiative feedback and the turbulent surface flux and oceanic heat transport feedbacks associated with the angular momentum cycle. The perturbation equations involve inter-zone coupling and have coefficients dependent on the values of the equilibrium fluxes and the sensitivity of the angular momentum transport. Analytical solutions for the perturbations are obtained. These provide criteria for the stability of the equilibrium climate. If the evaporative feedback on SST perturbations is omitted, the equilibrium climate is unstable due to the influence of the water vapour/infrared radiative feedback, which dominates over the effects of the sensible heat and ocean heat transport feedbacks. The inclusion of evaporation gives a negative feedback which is of sufficient strength to stabilize the system. The stabilizing mechanism involves wind and humidity factors in the evaporative fluxes that are of comparable magnitude. Both factors involve the angular momentum transport. In including angular momentum and calculating the surface fluxes explicitly, the model presented here differs from the many simple climate models based on the Budyko Sellers formulation. In that formulation, an atmospheric energy balance equation is used to eliminate surface fluxes in favour of top-of-the-atmosphere radiative fluxes and meridional atmospheric energy transports. In the resulting models, infrared radiation appears as a stabilizing influence on SST perturbations and the dynamical stabilizing mechanism found here cannot be identified.

Application of a rule-based model to estimate mercury exchange for three background biomes in the continental United States

USGS Publications Warehouse

Hartman, J.S.; Weisberg, P.J.; Pillai, R.; Ericksen, J.A.; Kuiken, T.; Lindberg, S.E.; Zhang, H.; Rytuba, J.J.; Gustin, M.S.

2009-01-01

Ecosystems that have low mercury (Hg) concentrations (i.e., not enriched or impactedbygeologic or anthropogenic processes) cover most of the terrestrial surface area of the earth yet their role as a net source or sink for atmospheric Hg is uncertain. Here we use empirical data to develop a rule-based model implemented within a geographic information system framework to estimate the spatial and temporal patterns of Hg flux for semiarid deserts, grasslands, and deciduous forests representing 45% of the continental United States. This exercise provides an indication of whether these ecosystems are a net source or sink for atmospheric Hg as well as a basis for recommendation of data to collect in future field sampling campaigns. Results indicated that soil alone was a small net source of atmospheric Hg and that emitted Hg could be accounted for based on Hg input by wet deposition. When foliar assimilation and wet deposition are added to the area estimate of soil Hg flux these biomes are a sink for atmospheric Hg. ?? 2009 American Chemical Society.

A comparison between energy transfer and atmospheric turbulent exchanges over alpine meadow and banana plantation

NASA Astrophysics Data System (ADS)

Ding, Zhangwei; Ma, Yaoming; Wen, Zhiping; Ma, Weiqiang; Chen, Shiji

2017-07-01

Banana plantation and alpine meadow ecosystems in southern China and the Tibetan Plateau (TP) are unique in the underlying surfaces they exhibit. In this study, we used eddy covariance and a micrometeorological tower to examine the characteristics of land surface energy exchanges over a banana plantation in southern China and an alpine meadow in the Tibetan Plateau from May 2010 to August 2012. The results showed that the diurnal and seasonal variations in upward shortwave radiation flux and surface soil heat flux were larger over the alpine meadow than over the banana plantation surface. Dominant energy partitioning varied with season. Latent heat flux was the main consumer of net radiation flux in the growing season, whereas sensible heat flux was the main consumer during other periods. The Monin-Obukhov similarity theory was employed for comparative purposes, using sonic anemometer observations of flow over the surfaces of banana plantations in the humid southern China monsoon region and the semi-arid areas of the TP, and was found to be applicable. Over banana plantation and alpine meadow areas, the average surface albedo and surface aerodynamic roughness lengths under neutral atmospheric conditions were ˜0.128 and 0.47 m, and ˜0.223 and 0.01 m, respectively. During the measuring period, the mean annual bulk transfer coefficients for momentum and sensible heat were 1.47 × 10-2 and 7.13 × 10-3, and 2.91 × 10-3 and 1.96 × 10-3, for banana plantation and alpine meadow areas, respectively.

Forcing of global ocean ice models using an atmospheric boundary layer model: assessing consequences for the simulation of the AMOC

NASA Astrophysics Data System (ADS)

Abel, R.; Boning, C. W.

2016-02-01

Current practice in ocean-only model simulations is to force the ocean with a prescribed atmospheric state using bulk formulations. This practice provides a strong thermal restoring to the surface ocean with a typical time-scale of one month. In the real ocean a positive feedback (salinity advection) and a negative feedback (temperature advection) are associated with the Atlantic Meridional Overturning Circulation (AMOC). The surface branch of the AMOC transports warm and salty (relative to the mean conditions) to the subpolar North Atlantic and mix with the near-surface waters. A strong AMOC would therefore warm the subpolar North Atlantic, decrease deep water formation and also reduce AMOC strength (negative feedback). This negative feedback is diminished due to the surface forcing formulation and makes the system excessively sensitive to details in the freshwater fluxes . Instead, additional and unrealistic Sea Surface Salinity (SSS) restoring is applied. There have been several suggestions during the last 20 years for at least partially alleviating the problem. This includes some simplified model of the atmospheric mixed layer (AML) (CheapAML; Deremble et al., 2013) with prescribed winds which allows some feedback of SST anomalies on the near-surface air temperature and humidity needed to calculate the turbulent surface fluxes. We show that if the turbulent heat fluxes are modelled by the simple AML model net-fluxes get more realistic. Commonly ocean models experience an AMOC slowdown if SSS restoring is turned off. In the new system (ORCA05 with turbulent fluxes from CheapAML) this slowdown can be eliminated.

Evaluating the two-source energy balance model using local thermal and surface flux observations in a strongly advective irrigated agricultural area

NASA Astrophysics Data System (ADS)

Kustas, William P.; Alfieri, Joseph G.; Anderson, Martha C.; Colaizzi, Paul D.; Prueger, John H.; Evett, Steven R.; Neale, Christopher M. U.; French, Andrew N.; Hipps, Lawrence E.; Chávez, José L.; Copeland, Karen S.; Howell, Terry A.

2012-12-01

Application and validation of many thermal remote sensing-based energy balance models involve the use of local meteorological inputs of incoming solar radiation, wind speed and air temperature as well as accurate land surface temperature (LST), vegetation cover and surface flux measurements. For operational applications at large scales, such local information is not routinely available. In addition, the uncertainty in LST estimates can be several degrees due to sensor calibration issues, atmospheric effects and spatial variations in surface emissivity. Time differencing techniques using multi-temporal thermal remote sensing observations have been developed to reduce errors associated with deriving the surface-air temperature gradient, particularly in complex landscapes. The Dual-Temperature-Difference (DTD) method addresses these issues by utilizing the Two-Source Energy Balance (TSEB) model of Norman et al. (1995) [1], and is a relatively simple scheme requiring meteorological input from standard synoptic weather station networks or mesoscale modeling. A comparison of the TSEB and DTD schemes is performed using LST and flux observations from eddy covariance (EC) flux towers and large weighing lysimeters (LYs) in irrigated cotton fields collected during BEAREX08, a large-scale field experiment conducted in the semi-arid climate of the Texas High Plains as described by Evett et al. (2012) [2]. Model output of the energy fluxes (i.e., net radiation, soil heat flux, sensible and latent heat flux) generated with DTD and TSEB using local and remote meteorological observations are compared with EC and LY observations. The DTD method is found to be significantly more robust in flux estimation compared to the TSEB using the remote meteorological observations. However, discrepancies between model and measured fluxes are also found to be significantly affected by the local inputs of LST and vegetation cover and the representativeness of the remote sensing observations with the local flux measurement footprint.

Variation of Evaporation Across a Corn-Soybean Production Region in Central Iowa

NASA Astrophysics Data System (ADS)

Prueger, J. H.; Hatfield, J. L.; Kustas, W. P.

2003-12-01

Evaporation from production corn-soybean surfaces is often assumed to be uniform across a regional extent such as the Upper Midwest in the U.S.; however, there are few direct measurements of the spatial and temporal variation of evaporation to support this assumption. During a soil moisture remote sensing study in the summer of 2002 (SMEX02), fourteen energy balance stations complete with net radiometers, soil heat flux plates, a three-dimensional sonic anemometer, and fast response CO2-H2O sensors (eddy covariance) were deployed across an 25-kilometer corn-soybean production watershed in central Iowa south of Ames, Iowa. Data were collected beginning in mid-May through August and summarized into half-hourly and daily intervals. Two intercomparisons of all eddy covariance systems were conducted, one prior to the SMEX02 study (May 2002) over an alfalfa field and one after the study over a grass surface in August (2002). The coefficient of variation among the eddy covariance instruments was less than 7%. Latent heat flux values among corn and soybean fields that were greater than 7% were considered to be real differences in evaporation among fields. Diurnal differences in net radiation and latent heat fluxes were evident among both corn and soybean fields and when seasonal totals were evaluated the differences persisted. Variation in latent heat flux among corn and soybeans was attributed to soil type, water availability and spatial variation of precipitation across the watershed. The results from fourteen eddy covariance stations provide a measure of the spatial variation in latent heat flux across a region that is considered to be relatively homogenous. This information will aid in evaluating regional evaporation models.

The role of soil drainage class in carbon dioxide exchange and decomposition in boreal black spruce (Picea mariana) forest stands

USGS Publications Warehouse

Wickland, K.P.; Neff, J.C.; Harden, J.W.

2010-01-01

Black spruce (Picea mariana (Mill.) B.S.P.) forest stands range from well drained to poorly drained, typically contain large amounts of soil organic carbon (SOC), and are often underlain by permafrost. To better understand the role of soil drainage class in carbon dioxide (CO2) exchange and decomposition, we measured soil respiration and net CO2 fluxes, litter decomposition and litterfall rates, and SOC stocks above permafrost in three Alaska black spruce forest stands characterized as well drained (WD), moderately drained (MD), and poorly drained (PD). Soil respiration and net CO2 fluxes were not significantly different among sites, although the relation between soil respiration rate and temperature varied with site (Qw: WD > MD > PD). Annual estimated soil respiration, litter decomposition, and groundcover photosynthesis were greatest at PD. These results suggest that soil temperature and moisture conditions in shallow organic horizon soils at PD were more favorable for decomposition compared with the better drained sites. SOC stocks, however, increase from WD to MD to PD such that surface decomposition and C storage are diametric. Greater groundcover vegetation productivity, protection of deep SOC by permafrost and anoxic conditions, and differences in fire return interval and (or) severity at PD counteract the relatively high near-surface decomposition rates, resulting in high net C accumulation.

Effect of mosaic representation of vegetation in land surface schemes on simulated energy and carbon balances

NASA Astrophysics Data System (ADS)

Li, R.; Arora, V. K.

2012-01-01

Energy and carbon balance implications of representing vegetation using a composite or mosaic approach in a land surface scheme are investigated. In the composite approach the attributes of different plant functional types (PFTs) present in a grid cell are aggregated in some fashion for energy and water balance calculations. The resulting physical environmental conditions (including net radiation, soil moisture and soil temperature) are common to all PFTs and affect their ecosystem processes. In the mosaic approach energy and water balance calculations are performed separately for each PFT tile using its own vegetation attributes, so each PFT "sees" different physical environmental conditions and its carbon balance evolves somewhat differently from that in the composite approach. Simulations are performed at selected boreal, temperate and tropical locations to illustrate the differences caused by using the composite versus mosaic approaches of representing vegetation. These idealized simulations use 50% fractional coverage for each of the two dominant PFTs in a grid cell. Differences in simulated grid averaged primary energy fluxes at selected sites are generally less than 5% between the two approaches. Simulated grid-averaged carbon fluxes and pool sizes at these sites can, however, differ by as much as 46%. Simulation results suggest that differences in carbon balance between the two approaches arise primarily through differences in net radiation which directly affects net primary productivity, and thus leaf area index and vegetation biomass.

Comparisons of a Quantum Annealing and Classical Computer Neural Net Approach for Inferring Global Annual CO2 Fluxes over Land

NASA Astrophysics Data System (ADS)

Halem, M.; Radov, A.; Singh, D.

2017-12-01

Investigations of mid to high latitude atmospheric CO2 show growing amplitudes in seasonal variations over the past several decades. Recent high-resolution satellite measurements of CO2 concentration are now available for three years from the Orbiting Carbon Observatory-2. The Atmospheric Radiation Measurement (ARM) program of DOE has been making long-term CO2-flux measurements (in addition to CO2 concentration and an array of other meteorological quantities) at several towers and mobile sites located around the globe at half-hour frequencies. Recent papers have shown CO2 fluxes inferred by assimilating CO2 observations into ecosystem models are largely inconsistent with station observations. An investigation of how the biosphere has reacted to changes in atmospheric CO2 is essential to our understanding of potential climate-vegetation feedbacks. Thus, new approaches for calculating CO2-flux for assimilation into land surface models are necessary for improving the prediction of annual carbon uptake. In this study, we calculate and compare the predicted CO2 fluxes results employing a Feed Forward Backward Propagation Neural Network model on two architectures, (i) an IBM Minsky Computer node and (ii) a hybrid version of the ARC D-Wave quantum annealing computer. We compare the neural net results of predictions of CO2 flux from ARM station data for three different DOE ecosystem sites; an arid plains near Oklahoma City, a northern arctic site at Barrows AL, and a tropical rainforest site in the Amazon. Training times and predictive results for the calculating annual CO2 flux for the two architectures for each of the three sites are presented. Comparative results of predictions as measured by RMSE and MAE are discussed. Plots and correlations of observed vs predicted CO2 flux are also presented for all three sites. We show the estimated training times for quantum and classical calculations when extended to calculating global annual Carbon Uptake over land. We also examine the efficiency, dependability and resilience of the quantum neural net approach relative to classical computer systems in predicting annual CO2 flux globally.

Development and testing of instrumentation for ship-based UAV measurements of ocean surface processes and the marine atmospheric boundary layer

NASA Astrophysics Data System (ADS)

Reineman, B. D.; Lenain, L.; Statom, N.; Melville, W. K.

2012-12-01

We have developed instrumentation packages for unmanned aerial vehicles (UAVs) to measure ocean surface processes along with momentum fluxes and latent, sensible, and radiative heat fluxes in the marine atmospheric boundary layer (MABL). The packages have been flown over land on BAE Manta C1s and over water on Boeing-Insitu ScanEagles. The low altitude required for accurate surface flux measurements (< 30 m) is below the typical safety limit of manned research aircraft; however, with advances in laser altimeters, small-aircraft flight control, and real-time kinematic differential GPS, low-altitude flight is now within the capability of small UAV platforms. Fast-response turbulence, hygrometer, and temperature probes permit turbulent flux measurements, and short- and long-wave radiometers allow the determination of net radiation, surface temperature, and albedo. Onboard laser altimetry and high-resolution visible and infrared video permit observations of surface waves and fine-scale (O(10) cm) ocean surface temperature structure. Flight tests of payloads aboard ScanEagle UAVs were conducted in April 2012 at the Naval Surface Warfare Center Dahlgren Division (Dahlgren, VA), where measurements of water vapor, heat, and momentum fluxes were made from low-altitude (31-m) UAV flights over water (Potomac River). ScanEagles are capable of ship-based launch and recovery, which can extend the reach of research vessels and enable scientific measurements out to ranges of O(10-100) km and altitudes up to 5 km. UAV-based atmospheric and surface observations can complement observations of surface and subsurface phenomena made from a research vessel and avoid the well-known problems of vessel interference in MABL measurements. We present a description of the instrumentation, summarize results from flight tests, and discuss potential applications of these UAVs for ship-based MABL studies.

Spatial variability of shortwave radiative fluxes in the context of snowmelt

NASA Astrophysics Data System (ADS)

Pinker, Rachel T.; Ma, Yingtao; Hinkelman, Laura; Lundquist, Jessica

2014-05-01

Snow-covered mountain ranges are a major source of water supply for run-off and groundwater recharge. Snowmelt supplies as much as 75% of surface water in basins of the western United States. Factors that affect the rate of snow melt include incoming shortwave and longwave radiation, surface albedo, snow emissivity, snow surface temperature, sensible and latent heat fluxes, ground heat flux, and energy transferred to the snowpack from deposited snow or rain. The net radiation generally makes up about 80% of the energy balance and is dominated by the shortwave radiation. Complex terrain poses a great challenge for obtaining the needed information on radiative fluxes from satellites due to elevation issues, spatially-variable cloud cover, rapidly changing surface conditions during snow fall and snow melt, lack of high quality ground truth for evaluation of the satellite based estimates, as well as scale issues between the ground observations and the satellite footprint. In this study we utilize observations of high spatial resolution (5-km) as available from the Moderate Resolution Imaging Spectro-radiometer (MODIS) to derive surface shortwave radiative fluxes in complex terrain, with attention to the impact of slopes on the amount of radiation received. The methodology developed has been applied to several water years (January to July during 2003, 2004, 2005 and 2009) over the western part of the United States, and the available information was used to derive metrics on spatial and temporal variability in the shortwave fluxes. It is planned to apply the findings from this study for testing improvements in Snow Water Equivalent (SWE) estimates.

Pairing FLUXNET sites to validate model representations of land-use/land-cover change

NASA Astrophysics Data System (ADS)

Chen, Liang; Dirmeyer, Paul A.; Guo, Zhichang; Schultz, Natalie M.

2018-01-01

Land surface energy and water fluxes play an important role in land-atmosphere interactions, especially for the climatic feedback effects driven by land-use/land-cover change (LULCC). These have long been documented in model-based studies, but the performance of land surface models in representing LULCC-induced responses has not been investigated well. In this study, measurements from proximate paired (open versus forest) flux tower sites are used to represent observed deforestation-induced changes in surface fluxes, which are compared with simulations from the Community Land Model (CLM) and the Noah Multi-Parameterization (Noah-MP) land model. Point-scale simulations suggest the CLM can represent the observed diurnal and seasonal changes in net radiation (Rnet) and ground heat flux (G), but difficulties remain in the energy partitioning between latent (LE) and sensible (H) heat flux. The CLM does not capture the observed decreased daytime LE, and overestimates the increased H during summer. These deficiencies are mainly associated with models' greater biases over forest land-cover types and the parameterization of soil evaporation. Global gridded simulations with the CLM show uncertainties in the estimation of LE and H at the grid level for regional and global simulations. Noah-MP exhibits a similar ability to simulate the surface flux changes, but with larger biases in H, G, and Rnet change during late winter and early spring, which are related to a deficiency in estimating albedo. Differences in meteorological conditions between paired sites is not a factor in these results. Attention needs to be devoted to improving the representation of surface heat flux processes in land models to increase confidence in LULCC simulations.

Adaptation of an urban land surface model to a tropical suburban area: Offline evaluation, sensitivity analysis, and optimization of TEB/ISBA (SURFEX)

NASA Astrophysics Data System (ADS)

Harshan, Suraj

The main objective of the present thesis is the improvement of the TEB/ISBA (SURFEX) urban land surface model (ULSM) through comprehensive evaluation, sensitivity analysis, and optimization experiments using energy balance and radiative and air temperature data observed during 11 months at a tropical sub-urban site in Singapore. Overall the performance of the model is satisfactory, with a small underestimation of net radiation and an overestimation of sensible heat flux. Weaknesses in predicting the latent heat flux are apparent with smaller model values during daytime and the model also significantly underpredicts both the daytime peak and nighttime storage heat. Surface temperatures of all facets are generally overpredicted. Significant variation exists in the model behaviour between dry and wet seasons. The vegetation parametrization used in the model is inadequate to represent the moisture dynamics, producing unrealistically low latent heat fluxes during a particularly dry period. The comprehensive evaluation of the USLM shows the need for accurate estimation of input parameter values for present site. Since obtaining many of these parameters through empirical methods is not feasible, the present study employed a two step approach aimed at providing information about the most sensitive parameters and an optimized parameter set from model calibration. Two well established sensitivity analysis methods (global: Sobol and local: Morris) and a state-of-the-art multiobjective evolutionary algorithm (Borg) were employed for sensitivity analysis and parameter estimation. Experiments were carried out for three different weather periods. The analysis indicates that roof related parameters are the most important ones in controlling the behaviour of the sensible heat flux and net radiation flux, with roof and road albedo as the most influential parameters. Soil moisture initialization parameters are important in controlling the latent heat flux. The built (town) fraction has a significant influence on all fluxes considered. Comparison between the Sobol and Morris methods shows similar sensitivities, indicating the robustness of the present analysis and that the Morris method can be employed as a computationally cheaper alternative of Sobol's method. Optimization as well as the sensitivity experiments for the three periods (dry, wet and mixed), show a noticeable difference in parameter sensitivity and parameter convergence, indicating inadequacies in model formulation. Existence of a significant proportion of less sensitive parameters might be indicating an over-parametrized model. Borg MOEA showed great promise in optimizing the input parameters set. The optimized model modified using the site specific values for thermal roughness length parametrization shows an improvement in the performances of outgoing longwave radiation flux, overall surface temperature, heat storage flux and sensible heat flux.

Characteristics of the Surface Turbulent Flux and the Components of Radiation Balance over the Grasslands in the Southeastern Tibetan Plateau

NASA Astrophysics Data System (ADS)

Li, H.; Xiao, Z.; Wei, J.

2016-12-01

Characteristics of the Surface Turbulent Flux and the Components of Radiation Balance over the Grasslands in the Southeastern Tibetan PlateauHongyi Li 1, Ziniu Xiao 2 and Junhong Wei31 China Meteorological Administration Training Centre, Beijing, China2 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China 3Theory of Atmospheric Dynamics and Climate, Institute for Atmospheric and Environmental Sciences, Goethe University of Frankfurt, Campus Riedberg, GermanyAbstract:Based on the field observation data over the grasslands in the southeastern Tibetan Plateau and the observational datasets in Nyingchi weather station for the period from May 20 to July 9, 2013, the variation characteristics of the basic meteorological elements in Nyingchi weather station, the surface turbulent fluxes and the components of radiation balance over the grasslands, as well as their relationships, are analyzed in this paper. The results show that in Nyingchi weather station, the daily variations of relative humidity and average total cloud cover are consistent with that of precipitation, but that those of daily average air temperature, daily average ground temperature, daily average wind speed and daily sunshine duration have an opposite change to that of precipitation. During the observation period, latent heat exchange is greater than sensible heat exchange, and latent heat flux is significantly higher when there is rainfall, but sensible heat flux and soil heat flux are lower. The daily variation of the total solar radiation (DR) is synchronous with that of sensible heat flux, and the daily variations of reflective solar radiation (UR), long wave radiation by earth (ULR), net radiation (Rn) and surface albedo are consistent with DR, but that of the long wave radiation by atmosphere (DLR) has an opposite change. The diurnal variations of sensible heat flux, latent heat flux, soil heat flux and the components of surface radiation balance over the grasslands are characterized by higher values at noon and lower values in the morning and evening. Keywords: surface turbulent flux, components of radiation balance, grasslands, southeastern Tibetan Plateau

The Net Carbon Flux due to Deforestation and Forest Re-Growth in the Brazilian Amazon: Analysis using a Process-Based Model

NASA Technical Reports Server (NTRS)

Hirsch, A. I.; Little, W. S.; Houghton, R. A.; Scott, N. A.; White, J. D.

2004-01-01

We developed a process-based model of forest growth, carbon cycling, and land cover dynamics named CARLUC (for CARbon and Land Use Change) to estimate the size of terrestrial carbon pools in terra firme (non-flooded) forests across the Brazilian Legal Amazon and the net flux of carbon resulting from forest disturbance and forest recovery from disturbance. Our goal in building the model was to construct a relatively simple ecosystem model that would respond to soil and climatic heterogeneity that allows us to study of the impact of Amazonian deforestation, selective logging, and accidental fire on the global carbon cycle. This paper focuses on the net flux caused by deforestation and forest re-growth over the period from 1970-1998. We calculate that the net flux to the atmosphere during this period reached a maximum of approx. 0.35 PgC/yr (1PgC = 1 x 10(exp I5) gC) in 1990, with a cumulative release of approx. 7 PgC from 1970- 1998. The net flux is higher than predicted by an earlier study by a total of 1 PgC over the period 1989-1 998 mainly because CARLUC predicts relatively high mature forest carbon storage compared to the datasets used in the earlier study. Incorporating the dynamics of litter and soil carbon pools into the model increases the cumulative net flux by approx. 1 PgC from 1970-1998, while different assumptions about land cover dynamics only caused small changes. The uncertainty of the net flux, calculated with a Monte-Carlo approach, is roughly 35% of the mean value (1 SD).

Updating the lake-atmosphere gas transfer velocity with impacts on the role of lake ecosystems in global carbon cycling

NASA Astrophysics Data System (ADS)

Heiskanen, J. J.; Mammarella, I.; Haapanala, S.; Vesala, T.; Pumpanen, J. S.; Ojala, A.

2013-12-01

Currently, the global estimate for the amount of carbon bound in terrestrial ecosystems is 3.0 × 0.9 Pg C y-1 [Le Quéré et al., 2009]. Lakes are not explicitly included in currently used global carbon models [Randall et al., 2007] but it has been estimated that the global net CO2 flux from lakes to the atmosphere range from 0.07 to 0.15 Pg C y-1 [Cole et al., 2007], corresponding to 2.3-5.0% of the total average terrestrial net uptake of carbon. These lake flux estimates may be considerably biased [MacIntyre et al., 2010], since although the data pertain to about 5000 lakes throughout the world [Sobek and Tranvik, 2005], the estimates are not from direct flux measurements. Instead, they are based on surface-water CO2 partial pressure in combination with the gas transfer velocity, k. The uncertainty in the global net CO2 flux is mostly due to the uncertainties in k, which can vary considerably. Cole and Caraco (1998) measured a range of 1.4 to 4.8 cm h-1 for k, but again, these values are not based on direct flux measurements of CO2. The most widely used empirical models of k have wind speed as the only explaining variable. However, the gas transfer velocity is also known to depend on turbulence in the surface water [MacIntyre et al., 2010], which in turn depends mostly on penetrative water convection at low wind conditions [MacIntyre et al., 2010; MacIntyre et al., 2001] - the conditions often prevailing in lakes [Schladow et al., 2002]. We formulated an improved model for k with heat flux parameterization in addition to a wind-speed parameter, determined from an analysis of 4 months (August - November 2011) of continuous high-frequency data in a typical small boreal lake in southern Finland. The CO2 flux from the lake to the atmosphere, atmospheric partial pressure of CO2, and latent and sensible heat were measured with the EC technique installed on a platform. Ancillary measurements included surface-water CO2 concentration and temperature, and net longwave and shortwave radiation. The modeled average k for the whole period, 9.5 cm h-1, was near to the measured average, 8.7 cm h-1. We used 24-hour averages when comparing the results. The new model for k had an R2 value of 0.66 when its performance was compared to the measured gas transfer velocity. Even though this is a lot higher value than when comparing the measured k with a widely used model for k (Cole and Caraco 1998, R2=0.29), the new model could not predict all the sudden changes in k and still roughly one third of the variation was left unexplained. This might be due to the environmental factors omitted by the model, e.g. surfactants. As a result, we showed that the current estimate of the global net CO2 flux from lakes to the atmosphere triples from 0.07-0.15 Pg C y-1 to 0.23-0.48 Pg C y-1 when the average k by Cole and Caraco (1998) is replaced with the new k. This corresponds to 7.5-16.0% of the total CO2 bound in terrestrial ecosystems compared with the current estimates of 2.3-5.0%. The new parameterization of k, assuming that it represents lakes in general, thus shows that the role of lakes in the global carbon cycle has been heavily underestimated and emphasizes the explicit inclusion of lakes in global carbon models.

Tropical Dynamics Process Studies and Numerical Methods

DTIC Science & Technology

2011-06-16

model. Model input and output arc defined in the Table below. Variable Description Ih Latent heat flux (W/ mA2 ) sh Sensible heat flux (W/ mA2 ) lwo...Net longwave flux (W/ mA2 ) swo Net shortwave flux (W/ mA2 ) 11 Wind speed (m/s) us Atmospheric friction velocity tb Bulk temperature (deg C) dtwo Warm

Multiple constraint analysis of regional land-surface carbon flux

Treesearch

D.P. Turner; M. Göckede; B.E. Law; W.D. Ritts; W.B. Cohen; Z. Yang; T. Hudiburg; R. Kennedy; M. Duane

2011-01-01

We applied and compared bottom-up (process model-based) and top-down (atmospheric inversion-based) scaling approaches to evaluate the spatial and temporal patterns of net ecosystem production (NEP) over a 2.5 × 105 km2 area (the state of Oregon) in the western United States. Both approaches indicated a carbon sink over this...

Towards Global Simulation of Irrigation in a Land Surface Model: Multiple Cropping and Rice Paddy in Southeast Asia

NASA Technical Reports Server (NTRS)

Beaudoing, Hiroko Kato; Rodell, Matthew; Ozdogan, Mutlu

2010-01-01

Agricultural land use significantly influences the surface water and energy balances. Effects of irrigation on land surface states and fluxes include repartitioning of latent and sensible heat fluxes, an increase in net radiation, and an increase in soil moisture and runoff. We are working on representing irrigation practices in continental- to global-scale land surface simulation in NASA's Global Land Data Assimilation System (GLDAS). Because agricultural practices across the nations are diverse, and complex, we are attempting to capture the first-order reality of the regional practices before achieving a global implementation. This study focuses on two issues in Southeast Asia: multiple cropping and rice paddy irrigation systems. We first characterize agricultural practices in the region (i.e., crop types, growing seasons, and irrigation) using the Global data set of monthly irrigated and rainfed crop areas around the year 2000 (MIRCA2000) dataset. Rice paddy extent is identified using remote sensing products. Whether irrigated or rainfed, flooded fields need to be represented and treated explicitly. By incorporating these properties and processes into a physically based land surface model, we are able to quantify the impacts on the simulated states and fluxes.

Estimation of Regional Evapotranspiration Using Remotely Sensed Land Surface Temperature. Part 2: Application of Equilibrium Evaporation Model to Estimate Evapotranspiration by Remote Sensing Technique. [Japan

NASA Technical Reports Server (NTRS)

Kotoda, K.; Nakagawa, S.; Kai, K.; Yoshino, M. M.; Takeda, K.; Seki, K.

1985-01-01

In a humid region like Japan, it seems that the radiation term in the energy balance equation plays a more important role for evapotranspiration then does the vapor pressure difference between the surface and lower atmospheric boundary layer. A Priestley-Taylor type equation (equilibrium evaporation model) is used to estimate evapotranspiration. Net radiation, soil heat flux, and surface temperature data are obtained. Only temperature data obtained by remotely sensed techniques are used.

MetaFluxNet: the management of metabolic reaction information and quantitative metabolic flux analysis.

PubMed

Lee, Dong-Yup; Yun, Hongsoek; Park, Sunwon; Lee, Sang Yup

2003-11-01

MetaFluxNet is a program package for managing information on the metabolic reaction network and for quantitatively analyzing metabolic fluxes in an interactive and customized way. It allows users to interpret and examine metabolic behavior in response to genetic and/or environmental modifications. As a result, quantitative in silico simulations of metabolic pathways can be carried out to understand the metabolic status and to design the metabolic engineering strategies. The main features of the program include a well-developed model construction environment, user-friendly interface for metabolic flux analysis (MFA), comparative MFA of strains having different genotypes under various environmental conditions, and automated pathway layout creation. http://mbel.kaist.ac.kr/ A manual for MetaFluxNet is available as PDF file.

A heat budget for the Stratus mooring in the southeast Pacific

NASA Astrophysics Data System (ADS)

Holte, J.; Straneo, F.; Weller, R. A.; Farrar, J. T.

2012-12-01

The surface layer of the southeast Pacific Ocean (SEP) requires an input of fresh, cold water to balance evaporation and heat gain from incoming solar radiation. Numerous processes contribute to closing the SEP's upper-ocean heat budget, including gyre circulation, Ekman transport and pumping, vertical mixing, and horizontal eddy heat flux divergence. However, there is little consensus on which processes are most important, as many modeling and observational studies have reported conflicting results. To examine how the SEP maintains relatively cool surface temperatures despite such strong surface forcing, we calculate a heat budget for the upper 250 m of the Stratus mooring. The Stratus mooring, deployed at 85(^o)W 20(^o)S since 2000, is in the center of the stratus cloud region. The surface buoy measures meteorological conditions and air-sea fluxes; the mooring line is heavily instrumented, measuring temperature, salinity, and velocity at approximately 15 to 20 depth levels. Our heat budget covers 2004 - 2010. The net air-sea heat flux over this period is 32 W m(^{-2}), approximately 2/3 of the flux over earlier periods. We use Argo profiles, relatively abundant in the region since 2004, to calculate horizontal temperature gradients. These gradients, coupled with the mooring velocity record, are used to estimate the advective heat flux. We find that the cool advective heat flux largely compensates the air-sea heat flux at the mooring; in our calculation this term includes the mean gyre circulation, horizontal Ekman transport, and some contribution from eddies. The passage of numerous eddies is evident in the mooring velocity record, but with the available data we cannot separate the eddy heat flux divergence from the mean heat advection. Vertical mixing and Ekman pumping across the base of the layer are both small.

Analysis of longwave radiation for the Earth-atmosphere system

NASA Technical Reports Server (NTRS)

Tiwari, S. N.; Venuru, C. S.; Subramanian, S. V.

1983-01-01

Accurate radiative transfer models are used to determine the upwelling atmospheric radiance and net radiative flux in the entire longwave spectral range. The validity of the quasi-random band model is established by comparing the results of this model with those of line-by-line formulations and with available theoretical and experimental results. Existing radiative transfer models and computer codes are modified to include various surface and atmospheric effects (surface reflection, nonequilibrium radiation, and cloud effects). The program is used to evaluate the radiative flux in clear atmosphere, provide sensitivity analysis of upwelling radiance in the presence of clouds, and determine the effects of various climatological parameters on the upwelling radiation and anisotropic function. Homogeneous and nonhomogeneous gas emissivities can also be evaluated under different conditions.

Solar Spectral Radiative Forcing Due to Dust Aerosol During the Puerto Rico Dust Experiment

NASA Technical Reports Server (NTRS)

Pilewskie, P.; Bergstrom, R.; Rabbette, M.; Livingston, J.; Russell, P.; Gore, Warren J. (Technical Monitor)

2000-01-01

During the Puerto Rico Dust Experiment (PRIDE) upwelling and downwelling solar spectral irradiance was measured on board the SPAWAR Navajo and downwelling solar spectral flux was measured at a surface site using the NASA Ames Solar Spectral Flux Radiometer. These data will be used to determine the net solar radiative forcing of dust aerosol and to quantify the solar spectral radiative energy budget in the presence of elevated aerosol loading. We will assess the variability in spectral irradiance using formal principal component analysis procedures and relate the radiative variability to aerosol microphysical properties. Finally, we will characterize the sea surface reflectance to improve aerosol optical depth retrievals from the AVHRR satellite and to validate SeaWiFS ocean color products.

ENSO related SST anomalies and relation with surface heat fluxes over south Pacific and Atlantic

NASA Astrophysics Data System (ADS)

Chatterjee, S.; Nuncio, M.; Satheesan, K.

2017-07-01

The role of surface heat fluxes in Southern Pacific and Atlantic Ocean SST anomalies associated with El Nino Southern Oscillation (ENSO) is studied using observation and ocean reanalysis products. A prominent dipole structure in SST anomaly is found with a positive (negative) anomaly center over south Pacific (65S-45S, 120W-70W) and negative (positive) one over south Atlantic (50S-30S, 30W-0E) during austral summer (DJF) of El Nino (LaNina). During late austral spring-early summer (OND) of El Nino (LaNina), anomalous northerly (southerly) meridional moisture transport and a positive (negative) sea level pressure anomaly induces a suppressed (enhanced) latent heat flux from the ocean surface over south Pacific. This in turn results in a shallower than normal mixed layer depth which further helps in development of the SST anomaly. Mixed layer thins further due to anomalous shortwave radiation during summer and a well developed SST anomaly evolves. The south Atlantic pole exhibits exactly opposite characteristics at the same time. The contribution from the surface heat fluxes to mixed layer temperature change is found to be dominant over the advective processes over both the basins. Net surface heat fluxes anomaly is also found to be maximum during late austral spring-early summer period, with latent heat flux having a major contribution to it. The anomalous latent heat fluxes between atmosphere and ocean surface play important role in the growth of observed summertime SST anomaly. Sea-surface height also shows similar out-of-phase signatures over the two basins and are well correlated with the ENSO related SST anomalies. It is also observed that the magnitude of ENSO related anomalies over the southern ocean are weaker in LaNina years than in El Nino years, suggesting an intensified tropics-high latitude tele-connection during warm phases of ENSO.

Measurements and Modeling of Turbulent Fluxes during Persistent Cold Air Pool Events in Salt Lake Valley, Utah

NASA Astrophysics Data System (ADS)

Ivey, C. E.; Sun, X.; Holmes, H.

2017-12-01

Land surface processes are important in meteorology and climate research since they control the partitioning of surface energy and water exchange at the earth's surface. The surface layer is coupled to the planetary boundary layer (PBL) by surface fluxes, which serve as sinks or sources of energy, moisture, momentum, and atmospheric pollutants. Quantifying the surface heat and momentum fluxes at the land-atmosphere interface, especially for different surface land cover types, is important because they can further influence the atmospheric dynamics, vertical mixing, and transport processes that impact local, regional, and global climate. A cold air pool (CAP) forms when a topographic depression (i.e., valley) fills with cold air, where the air in the stagnant layer is colder than the air aloft. Insufficient surface heating, which is not able to sufficiently erode the temperature inversion that forms during the nighttime stable boundary layer, can lead to the formation of persistent CAPs during wintertime. These persistent CAPs can last for days, or even weeks, and are associated with increased air pollution concentrations. Thus, realistic simulations of the land-atmosphere exchange are meaningful to achieve improved predictions of the accumulation, transport, and dispersion of air pollution concentrations. The focus of this presentation is on observations and modeling results using turbulence data collected in Salt Lake Valley, Utah during the 2010-2011 wintertime Persistent Cold Air Pool Study (PCAPS). Turbulent fluxes and the surface energy balance over seven land use types are quantified. The urban site has an energy balance ratio (EBR) larger than one (1.276). Negative Bowen ratio (-0.070) is found at the cropland site. In addition to turbulence observations, half-hourly WRF simulated net radiation, latent heat, sensible heat, ground heat fluxes during one persistent CAP event are evaluated using the PCAPS observations. The results show that sensible and latent heat fluxes during the CAP event are overestimated. The sensitivity of WRF results to large-scale forcing datasets, PBL schemes and land surface models (LSMs) are also investigated. The optimal WRF configuration for simulating surface turbulent fluxes and atmospheric mixing during CAP events is determined.

Influence of Soil Heterogeneity on Mesoscale Land Surface Fluxes During Washita '92

NASA Technical Reports Server (NTRS)

Jasinski, Michael F.; Jin, Hao

1998-01-01

The influence of soil heterogeneity on the partitioning of mesoscale land surface energy fluxes at diurnal time scales is investigated over a 10(exp 6) sq km domain centered on the Little Washita Basin, Oklahoma, for the period June 10 - 18, 1992. The sensitivity study is carried out using MM5/PLACE, the Penn State/NCAR MM5 model enhanced with the Parameterization for Land-Atmosphere-Cloud Exchange or PLACE. PLACE is a one-dimensional land surface model possessing detailed plant and soil water physics algorithms, multiple soil layers, and the capacity to model subgrid heterogeneity. A series of 12-hour simulations were conducted with identical atmospheric initialization and land surface characterization but with different initial soil moisture and texture. A comparison then was made of the simulated land surface energy flux fields, the partitioning of net radiation into latent and sensible heat, and the soil moisture fields. Results indicate that heterogeneity in both soil moisture and texture affects the spatial distribution and partitioning of mesoscale energy balance. Spatial averaging results in an overprediction of latent heat flux, and an underestimation of sensible heat flux. In addition to the primary focus on the partitioning of the land surface energy, the modeling effort provided an opportunity to examine the issue of initializing the soil moisture fields for coupled three-dimensional models. For the present case, the initial soil moisture and temperature were determined from off-line modeling using PLACE at each grid box, driven with a combination of observed and assimilated data fields.

Tropical Warm Pool Surface Heat Budgets and Temperature: Contrasts Between 1997-98 El Nino and 1998-99 La Nina

NASA Technical Reports Server (NTRS)

Chou, Shu-Hsien; Chou, Ming-Dah; Chan, Pui-King; Lin, Po-Hsiung; Wang, Kung-Hwa

2003-01-01

Seasonal and interannual variations of the net surface heating F(sub NET) and sea surface temperature tendency (T(sub s)/dt) in the tropical eastern Indian and western Pacific Oceans are studied. The surface heat fluxes are derived from the Special Sensor Microwave/Imager and Japanese Geostationary Meteorological Satellite radiance measurements for the period October 1997-September 2000. It is found that the magnitude of solar heating is lager than that of evaporative cooling, but the spatial variation of the latter is significantly large than the former. As a result, the spatial variations of seasonal and interannual variability of F(sub NET), follow closely that of evaporative cooling. Seasonal variations of F(sub NET) and T(sub s)/dt are significantly correlated, except for the equatorial western Pacific. The high correlation is primarily attributable to high correlation between seasonal cycles of solar heating and T(sub s)/dt. The change of F(sub NET) between 1997-98 El Nino and 1998-99 La Nina is significantly larger in the tropical eastern Indian Ocean than tropical western Pacific. For the former region, the reduced evaporative cooling arising from weakened winds during the El Nino is generally associated with enhanced solar heating due to decreased cloudiness, and thus increases the interannual variability of F(sub NET). For the latter region, the reduced evaporative cooling due to weakened winds is generally associated with but exceeds the reduced solar heating arising from increased cloudiness, and vise versa. Thus the interannual variability of F(sub NET) is reduced due to this offsetting effect. Interannual variations of F(sub NET) and T(sub s)/dt have very low correlation. This is most likely related to interannual variability of ocean dynamics, which includes the variations of solar radiation penetrating through oceanic mixed layer, upwelling of cold thermocline water, Indonesian throughflow for transporting heat from the Pacific to Indian Ocean, and interhemispheric transport in the Indian Ocean.

Modelling carbon fluxes of forest and grassland ecosystems in Western Europe using the CARAIB dynamic vegetation model: evaluation against eddy covariance data.

NASA Astrophysics Data System (ADS)

Henrot, Alexandra-Jane; François, Louis; Dury, Marie; Hambuckers, Alain; Jacquemin, Ingrid; Minet, Julien; Tychon, Bernard; Heinesch, Bernard; Horemans, Joanna; Deckmyn, Gaby

2015-04-01

Eddy covariance measurements are an essential resource to understand how ecosystem carbon fluxes react in response to climate change, and to help to evaluate and validate the performance of land surface and vegetation models at regional and global scale. In the framework of the MASC project (« Modelling and Assessing Surface Change impacts on Belgian and Western European climate »), vegetation dynamics and carbon fluxes of forest and grassland ecosystems simulated by the CARAIB dynamic vegetation model (Dury et al., iForest - Biogeosciences and Forestry, 4:82-99, 2011) are evaluated and validated by comparison of the model predictions with eddy covariance data. Here carbon fluxes (e.g. net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (RECO)) and evapotranspiration (ET) simulated with the CARAIB model are compared with the fluxes measured at several eddy covariance flux tower sites in Belgium and Western Europe, chosen from the FLUXNET global network (http://fluxnet.ornl.gov/). CARAIB is forced either with surface atmospheric variables derived from the global CRU climatology, or with in situ meteorological data. Several tree (e.g. Pinus sylvestris, Fagus sylvatica, Picea abies) and grass species (e.g. Poaceae, Asteraceae) are simulated, depending on the species encountered on the studied sites. The aim of our work is to assess the model ability to reproduce the daily, seasonal and interannual variablility of carbon fluxes and the carbon dynamics of forest and grassland ecosystems in Belgium and Western Europe.

Recent Carbon Cycle Dynamics in an Ombrotrophic Peatland: Implications From Warming and eCO2 Treatments and the Role of Vegetation Layers in the Flux of CO2 and CH4

NASA Astrophysics Data System (ADS)

Hanson, P. J.; Phillips, J. R.; Nettles, W. R., IV; Heiderman, R.

2017-12-01

Following 2 years of sustained whole-ecosystem warming treatments spanning a range from 0 to +9 °C (SPRUCE experiment), the net fluxes of CO2 and CH4 from a raised-bog peatland in northern Minnesota show increased emissions of both gases from the community of woody ericaceous shrubs, forbs and Sphagnum moss. Increased emissions for CO2 and CH4 are primarily driven by sustaining temperature conditions for metabolic activity throughout the growing season. Seasonal temperature relationships for each gas suggest that warming affected growth and metabolic processes in a consistent manner across a wide range of temperature treatments. Elevated CO2 treatments (eCO2) have not yet shown anticipated increases in the input and processing of recent carbon. Quantitative annual estimates of the amount of net C and greenhouse gas flux increases will be calculated and presented for all treatments. A mid-season deconstruction of the contribution of vegetation layers to net ecosystem exchange of C and community respiration processes was also completed for replicate ambient shrub communities. The deconstruction data demonstrate the fractional contribution of wood shrubs, forbs/sedges and moss to the community to the flux of C and provide further evidence that the current C cycle of the bog is driven primarily by surface phenomenon fed be recently fixed C. These results should be considered early results from the SPRUCE experiment anticipated to operate through 2025. Affiliated studies will add mechanisms to these observations and long-term cumulative effects may differ.

Spatiotemporal dynamics of carbon dioxide and methane fluxes from agricultural and restored wetlands in the California Delta

NASA Astrophysics Data System (ADS)

Hatala, Jaclyn Anne

The Sacramento-San Joaquin Delta in California was drained for agriculture and human settlement over a century ago, resulting in extreme rates of soil subsidence and release of CO2 to the atmosphere from peat oxidation. Because of this century-long ecosystem carbon imbalance where heterotrophic respiration exceeded net primary productivity, most of the land surface in the Delta is now up to 8 meters below sea level. To potentially reverse this trend of chronic carbon loss from Delta ecosystems, land managers have begun converting drained lands back to flooded ecosystems, but at the cost of increased production of CH4, a much more potent greenhouse gas than CO2. To evaluate the impacts of inundation on the biosphere-atmophere exchange of CO2 and CH4 in the Delta, I first measured and analyzed net fluxes of CO2 and CH4 for two continuous years with the eddy covariance technique in a drained peatland pasture and a recently re-flooded rice paddy. This analysis demonstrated that the drained pasture was a consistent large source of CO2 and small source of CH 4, whereas the rice paddy was a mild sink for CO2 and a mild source of CH4. However more importantly, this first analysis revealed nuanced complexities for measuring and interpreting patterns in CO2 and CH4 fluxes through time and space. CO2 and CH4 fluxes are inextricably linked in flooded ecosystems, as plant carbon serves as the primary substrate for the production of CH4 and wetland plants also provide the primary transport pathway of CH4 flux to the atmosphere. At the spatially homogeneous rice paddy during the summer growing season, I investigated rapid temporal coupling between CO2 and CH4 fluxes. Through wavelet Granger-causality analysis, I demonstrated that daily fluctuations in growing season gross ecosystem productivity (photosynthesis) exert a stronger control than temperature on the diurnal pattern in CH4 flux from rice. At a spatially heterogeneous restored wetland site, I analyzed the spatial coupling between net CO2 and CH4 fluxes by characterizing two-dimensional patterns of emergent vegetation within eddy covariance flux footprints. I combined net CO2 and CH4 fluxes from three eddy flux towers with high-resolution remote sensing imagery classified for emergent vegetation and an analytical 2-D flux footprint model to assess the impact of vegetation fractal pattern and abundance on the measured flux. Both emergent vegetation abundance and fractal complexity are important metrics for constraining variability within CO2 and CH4 flux in this complex landscape. Scaling between carbon flux measurements at individual sites and regional scales depends on the connection to remote sensing metrics that can be broadly applied. In the final chapter of this dissertation, I analyzed a long term dataset of hyperspectral ground reflectance measurements collected within the flux tower footprints of three structurally similar yet functionally diverse ecosystems: an annual grassland, a degraded pepperweed pasture, and a rice paddy. The normalized difference vegetation index (NDVI) was highly correlated with landscape-scale photosynthesis across all sites, however this work also revealed new potential spectral indices with high correlation to both net and partitioned CO2 fluxes. This analysis within this dissertation serves as a framework for considering the impacts of temporal and spatial heterogeneity on measured landscape-scale fluxes of CO2 and CH4. Scaling measurements through time and space is especially critical for interpreting fluxes of trace gases with a high degree of temporal heterogeneity, like CH4 and N 2O, from landscapes that have a high degree of spatial heterogeneity, like wetlands. This work articulates a strong mechanistic connection between CO2 and CH4 fluxes in wetland ecosystems, and provides important management considerations for implementing and monitoring inundated land-use conversion as an effective carbon management strategy in the California Delta.

Direct and indirect effects of atmospheric conditions and soil moisture on surface energy partitioning revealed by a prolonged drought at a temperate forest site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gu, Lianhong; Meyers, T. P.; Pallardy, Stephen G.

2006-01-01

The purpose of this paper is to examine the mechanism that controls the variation of surface energy partitioning between latent and sensible heat fluxes at a temperate deciduous forest site in central Missouri, USA. Taking advantage of multiple micrometeorological and ecophysiological measurements and a prolonged drought in the middle of the 2005 growing season at this site, we studied how soil moisture, atmospheric vapor pressure deficit (VPD), and net radiation affected surface energy partitioning. We stratified these factors to minimize potential confounding effects of correlation among them. We found that all three factors had direct effects on surface energy partitioning,more » but more important, all three factors also had crucial indirect effects. The direct effect of soil moisture was characterized by a rapid decrease in Bowen ratio with increasing soil moisture when the soil was dry and by insensitivity of Bowen ratio to variations in soil moisture when the soil was wet. However, the rate of decrease in Bowen ratio when the soil was dry and the level of soil moisture above which Bowen ratio became insensitive to changes in soil moisture depended on atmospheric conditions. The direct effect of increased net radiation was to increase Bowen ratio. The direct effect of VPD was very nonlinear: Increased VPD decreased Bowen ratio at low VPD but increased Bowen ratio at high VPD. The indirect effects were much more complicated. Reduced soil moisture weakened the influence of VPD but enhanced the influence of net adiation on surface energy partitioning. Soil moisture also controlled how net radiation influenced the relationship between surface energy partitioning and VPD and how VPD affected the relationship between surface energy partitioning and net radiation. Furthermore, both increased VPD and increased net radiation enhanced the sensitivity of Bowen ratio to changes in soil moisture and the effect of drought on surface energy partitioning. The direct and indirect effects of atmospheric conditions and soil moisture on surface energy partitioning identified in this paper provide a target for testing atmospheric general circulation models in their representation of land-atmosphere coupling.« less

Anthropogenic Disturbance of Montane Meadows May Cause Substantial Loss of Soil Carbon to the Atmosphere

NASA Astrophysics Data System (ADS)

Reed, C. C.; Sullivan, B. W.; Hart, S. C.; Drew, M.; Merrill, A.

2016-12-01

High-elevation meadows are biological hotspots that contain high densities of soil carbon (C). The capacity of these ecosystems to sequester C depends on a combination of high primary productivity, seasonally low temperatures, and anaerobic soil conditions associated with water tables at or near the soil surface. However, anthropogenic disturbances in many montane meadows in California's Sierra Nevada have lowered water tables, decreased primary productivity, and created aerobic soil conditions - changes that may alter the balance of greenhouse gas (GHG) emissions and reverse meadows from a net C sink to a net source. Recently, C policy in California has spurred interest in the potential of hydrologic restoration to increase C sequestration in meadows. However, soil C pools and fluxes in degraded meadows must be quantified before the impacts of restoration can accurately be assessed. In this study, we measured soil C stocks in surface soil (1 m) and annual soil GHG fluxes (carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)) in three degraded, northern Sierra Nevada meadows. In a parallel laboratory incubation, we manipulated meadow soil water content to determine target goals for restoration of anaerobic conditions. Our results suggest that degraded meadows contain large reservoirs of existing C, but that this C may be vulnerable to decomposition under current conditions. Soil CO2 fluxes ranged from 26.7-33.1 Mg of CO2 ha-1 y-1, roughly equivalent to the amount of C sequestered annually by 70 acres of U.S. forests. These high rates of soil respiration, combined with low primary productivity, resulted in substantial losses of soil C with implications for climate change, ecosystem function, and restoration. Soils from these meadows were a net source of N2O and a net sink of CH4, but these fluxes were 4 orders of magnitude smaller than CO2. Also, we found substantial GHG emissions persist in these organic soils at peak soil moisture, suggesting that restoration may need to sustain soil water holding capacities in excess of 115%, and possibly 200%, for anaerobic soil conditions to return. These findings highlight the need to conserve properly functioning meadows and provide target conditions for optimal restoration of degraded meadows.

Intercomparisons of Prognostic, Diagnostic, and Inversion Modeling Approaches for Estimation of Net Ecosystem Exchange over the Pacific Northwest Region

NASA Astrophysics Data System (ADS)

Turner, D. P.; Jacobson, A. R.; Nemani, R. R.

2013-12-01

The recent development of large spatially-explicit datasets for multiple variables relevant to monitoring terrestrial carbon flux offers the opportunity to estimate the terrestrial land flux using several alternative, potentially complimentary, approaches. Here we developed and compared regional estimates of net ecosystem exchange (NEE) over the Pacific Northwest region of the U.S. using three approaches. In the prognostic modeling approach, the process-based Biome-BGC model was driven by distributed meteorological station data and was informed by Landsat-based coverages of forest stand age and disturbance regime. In the diagnostic modeling approach, the quasi-mechanistic CFLUX model estimated net ecosystem production (NEP) by upscaling eddy covariance flux tower observations. The model was driven by distributed climate data and MODIS FPAR (the fraction of incident PAR that is absorbed by the vegetation canopy). It was informed by coarse resolution (1 km) data about forest stand age. In both the prognostic and diagnostic modeling approaches, emissions estimates for biomass burning, harvested products, and river/stream evasion were added to model-based NEP to get NEE. The inversion model (CarbonTracker) relied on observations of atmospheric CO2 concentration to optimize prior surface carbon flux estimates. The Pacific Northwest is heterogeneous with respect to land cover and forest management, and repeated surveys of forest inventory plots support the presence of a strong regional carbon sink. The diagnostic model suggested a stronger carbon sink than the prognostic model, and a much larger sink that the inversion model. The introduction of Landsat data on disturbance history served to reduce uncertainty with respect to regional NEE in the diagnostic and prognostic modeling approaches. The FPAR data was particularly helpful in capturing the seasonality of the carbon flux using the diagnostic modeling approach. The inversion approach took advantage of a global network of CO2 observation stations, but had difficulty resolving regional fluxes such as that in the PNW given the still sparse nature of the CO2 measurement network.

Modelling the impact of soil Carbonic Anhydrase on the net ecosystem exchange of OCS at Harvard forest using the MuSICA model

NASA Astrophysics Data System (ADS)

Launois, Thomas; Ogée, Jérôme; Commane, Roisin; Wehr, Rchard; Meredith, Laura; Munger, Bill; Nelson, David; Saleska, Scott; Wofsy, Steve; Zahniser, Mark; Wingate, Lisa

2016-04-01

The exchange of CO2 between the terrestrial biosphere and the atmosphere is driven by photosynthetic uptake and respiratory loss, two fluxes currently estimated with considerable uncertainty at large scales. Model predictions indicate that these biosphere fluxes will be modified in the future as CO2 concentrations and temperatures increase; however, it still unclear to what extent. To address this challenge there is a need for better constraints on land surface model parameterisations. Additional atmospheric tracers of large-scale CO2 fluxes have been identified as potential candidates for this task. In particular carbonyl sulphide (OCS) has been proposed as a complementary tracer of gross photosynthesis over land, since OCS uptake by plants is dominated by carbonic anhydrase (CA) activity, an enzyme abundant in leaves that catalyses CO2 hydration during photosynthesis. However, although the mass budget at the ecosystem is dominated by the flux of OCS into leaves, some OCS is also exchanged between the atmosphere and the soil and this component of the budget requires constraining. In this study, we adapted the process-based isotope-enabled model MuSICA (Multi-layer Simulator of the Interactions between a vegetation Canopy and the Atmosphere) to include the transport, reaction, diffusion and production of OCS within a forested ecosystem. This model was combined with 3 years (2011-2013) of in situ measurements of OCS atmospheric concentration profiles and fluxes at the Harvard Forest (Massachussets, USA) to test hypotheses on the mechanisms responsible for CA-driven uptake by leaves and soils as well as possible OCS emissions during litter decomposition. Model simulations over the three years captured well the impact of diurnally and seasonally varying environmental conditions on the net ecosystem OCS flux. A sensitivity analysis on soil CA activity and soil OCS emission rates was also performed to quantify their impact on the vertical profiles of OCS inside the canopy and the net OCS exchange with the atmosphere.

Improving Global Net Surface Heat Flux with Ocean Reanalysis

NASA Astrophysics Data System (ADS)

Carton, J.; Chepurin, G. A.; Chen, L.; Grodsky, S.

2017-12-01

This project addresses the current level of uncertainty in surface heat flux estimates. Time mean surface heat flux estimates provided by atmospheric reanalyses differ by 10-30W/m2. They are generally unbalanced globally, and have been shown by ocean simulation studies to be incompatible with ocean temperature and velocity measurements. Here a method is presented 1) to identify the spatial and temporal structure of the underlying errors and 2) to reduce them by exploiting hydrographic observations and the analysis increments produced by an ocean reanalysis using sequential data assimilation. The method is applied to fluxes computed from daily state variables obtained from three widely used reanalyses: MERRA2, ERA-Interim, and JRA-55, during an eight year period 2007-2014. For each of these seasonal heat flux errors/corrections are obtained. In a second set of experiments the heat fluxes are corrected and the ocean reanalysis experiments are repeated. This second round of experiments shows that the time mean error in the corrected fluxes is reduced to within ±5W/m2 over the interior subtropical and midlatitude oceans, with the most significant changes occuring over the Southern Ocean. The global heat flux imbalance of each reanalysis is reduced to within a few W/m2 with this single correction. Encouragingly, the corrected forms of the three sets of fluxes are also shown to converge. In the final discussion we present experiments beginning with a modified form of the ERA-Int reanalysis, produced by the DAKKAR program, in which state variables have been individually corrected based on independent measurements. Finally, we discuss the separation of flux error from model error.

Ten years of multiple data stream assimilation with the ORCHIDEE land surface model to improve regional to global simulated carbon budgets: synthesis and perspectives on directions for the future

NASA Astrophysics Data System (ADS)

Peylin, P. P.; Bacour, C.; MacBean, N.; Maignan, F.; Bastrikov, V.; Chevallier, F.

2017-12-01

Predicting the fate of carbon stocks and their sensitivity to climate change and land use/management strongly relies on our ability to accurately model net and gross carbon fluxes. However, simulated carbon and water fluxes remain subject to large uncertainties, partly because of unknown or poorly calibrated parameters. Over the past ten years, the carbon cycle data assimilation system at the Laboratoire des Sciences du Climat et de l'Environnement has investigated the benefit of assimilating multiple carbon cycle data streams into the ORCHIDEE LSM, the land surface component of the Institut Pierre Simon Laplace Earth System Model. These datasets have included FLUXNET eddy covariance data (net CO2 flux and latent heat flux) to constrain hourly to seasonal time-scale carbon cycle processes, remote sensing of the vegetation activity (MODIS NDVI) to constrain the leaf phenology, biomass data to constrain "slow" (yearly to decadal) processes of carbon allocation, and atmospheric CO2 concentrations to provide overall large scale constraints on the land carbon sink. Furthermore, we have investigated technical issues related to multiple data stream assimilation and choice of optimization algorithm. This has provided a wide-ranging perspective on the challenges we face in constraining model parameters and thus better quantifying, and reducing, model uncertainty in projections of the future global carbon sink. We review our past studies in terms of the impact of the optimization on key characteristics of the carbon cycle, e.g. the partition of the northern latitudes vs tropical land carbon sink, and compare to the classic atmospheric flux inversion approach. Throughout, we discuss our work in context of the abovementioned challenges, and propose solutions for the community going forward, including the potential of new observations such as atmospheric COS concentrations and satellite-derived Solar Induced Fluorescence to constrain the gross carbon fluxes of the ORCHIDEE model.

Plants, microorganisms, and soil temperatures contribute to a decrease in methane fluxes on a drained Arctic floodplain.

PubMed

Kwon, Min Jung; Beulig, Felix; Ilie, Iulia; Wildner, Marcus; Küsel, Kirsten; Merbold, Lutz; Mahecha, Miguel D; Zimov, Nikita; Zimov, Sergey A; Heimann, Martin; Schuur, Edward A G; Kostka, Joel E; Kolle, Olaf; Hilke, Ines; Göckede, Mathias

2017-06-01

As surface temperatures are expected to rise in the future, ice-rich permafrost may thaw, altering soil topography and hydrology and creating a mosaic of wet and dry soil surfaces in the Arctic. Arctic wetlands are large sources of CH 4 , and investigating effects of soil hydrology on CH 4 fluxes is of great importance for predicting ecosystem feedback in response to climate change. In this study, we investigate how a decade-long drying manipulation on an Arctic floodplain influences CH 4 -associated microorganisms, soil thermal regimes, and plant communities. Moreover, we examine how these drainage-induced changes may then modify CH 4 fluxes in the growing and nongrowing seasons. This study shows that drainage substantially lowered the abundance of methanogens along with methanotrophic bacteria, which may have reduced CH 4 cycling. Soil temperatures of the drained areas were lower in deep, anoxic soil layers (below 30 cm), but higher in oxic topsoil layers (0-15 cm) compared to the control wet areas. This pattern of soil temperatures may have reduced the rates of methanogenesis while elevating those of CH 4 oxidation, thereby decreasing net CH 4 fluxes. The abundance of Eriophorum angustifolium, an aerenchymatous plant species, diminished significantly in the drained areas. Due to this decrease, a higher fraction of CH 4 was alternatively emitted to the atmosphere by diffusion, possibly increasing the potential for CH 4 oxidation and leading to a decrease in net CH 4 fluxes compared to a control site. Drainage lowered CH 4 fluxes by a factor of 20 during the growing season, with postdrainage changes in microbial communities, soil temperatures, and plant communities also contributing to this reduction. In contrast, we observed CH 4 emissions increased by 10% in the drained areas during the nongrowing season, although this difference was insignificant given the small magnitudes of fluxes. This study showed that long-term drainage considerably reduced CH 4 fluxes through modified ecosystem properties. © 2016 John Wiley & Sons Ltd.

Bacterial Flux by Net Precipitation from the Phyllosphere to the Forest Floor.

NASA Astrophysics Data System (ADS)

Pound, P.; Van Stan, J. T., II; Moore, L. D.; Bittar, T.

2016-12-01

Transport pathways of microbes between ecosystem spheres (atmosphere, phyllosphere, and pedosphere) represent major fluxes in nutrient cycles and have the potential to significantly affect microbial ecological processes. We quantified a previously unexamined microbial flux from the phyllosphere to the pedosphere during rainfall and found it to be substantial. Net rainfall bacterial fluxes for throughfall and stemflow were quantified using flow cytometry and a quantitative Polymerase Chain Reaction (qPCR) assay for a Quercus virginiana (Mill., southern live oak) forest with heavy epiphyte cover of Tillandsia usneoides (L., Spanish moss) and Pleopeltis polypodiodes (L., resurrection fern) in coastal Georgia (Southeast USA). Total net precipitation flux of bacteria was 15 quadrillion cells year-1 ha-1, which (assuming a bacterial cell mass of 1 pg) is approximately 15 kg of bacterial biomass supply per year. Stemflow generation was low in this stand (rarely exceeded 10 L storm-1) yet still delivered half the annual net precipitation flux due to high bacterial concentration. The role of this previously unquantified bacterial flux in the forest floor has also been under studied, yet it may be significant by contributing functional community members (if living) or labile lysates (if dead).

Modeling of microclimatic characteristics of highland area

NASA Astrophysics Data System (ADS)

Sitdikova, Iuliia; Rusin, Igor

2013-04-01

Microclimatic characteristics of highlands may vary considerably over distances of a few meters depending on slope and aspect. There is a problem of estimation of components of surface energy balance based on observation of single stations for description of microclimate highlands. The aim of this paper is to develop a method that would restore microclimatic characteristics of terrain, based on observations of the single station, by physical extrapolation. The input parameters to obtain the microclimatic characteristics are as follows: air temperature, relative humidity, and wind speed on two vertical levels, air pressure, surface temperature, direct and diffused solar radiation and surface albedo. The recent version of the Meteorological Radiation Model (MRM) has been used to calculate a solar radiation over the area and to estimate an influence of cloudiness amounts. The height, slope and aspect were accounted at each point with using a digital elevation model. Have been supposed that air temperature and specific humidity vary with altitude only. Net radiation was calculated at all points of the area. Supposed that the difference between the surface temperature and the air temperature is a linear function of net radiation. The empirical coefficient, which depends on wind speed with adjustment of given area. Latent and sensible fluxes are calculated by using the modified Bowen ratio, which varies on the area. Method was tested on field research in Krasnodar region (RF). The meteorological observations were made every three hour on actinometric and gradient sites. The editional gradient site with different orientation of the slope was organized from 400 meters of the main site. Topographic survey of area was made 1x1,3 km in size for a digital elevation model constructing. At all points of the area of radiation and heat balance were calculated. The results of researches are the maps of surface temperature, net radiation, latent and sensible fluxes. The calculations showed that the average value of components of heat balance by area differ significantly from the data observed on meteorological station.

Accuracy assessment of a net radiation and temperature index snowmelt model using ground observations of snow water equivalent in an alpine basin

NASA Astrophysics Data System (ADS)

Molotch, N. P.; Painter, T. H.; Bales, R. C.; Dozier, J.

2003-04-01

In this study, an accumulated net radiation / accumulated degree-day index snowmelt model was coupled with remotely sensed snow covered area (SCA) data to simulate snow cover depletion and reconstruct maximum snow water equivalent (SWE) in the 19.1-km2 Tokopah Basin of the Sierra Nevada, California. Simple net radiation snowmelt models are attractive for operational snowmelt runoff forecasts as they are computationally inexpensive and have low input requirements relative to physically based energy balance models. The objective of this research was to assess the accuracy of a simple net radiation snowmelt model in a topographically heterogeneous alpine environment. Previous applications of net radiation / temperature index snowmelt models have not been evaluated in alpine terrain with intensive field observations of SWE. Solar radiation data from two meteorological stations were distributed using the topographic radiation model TOPORAD. Relative humidity and temperature data were distributed based on the lapse rate calculated between three meteorological stations within the basin. Fractional SCA data from the Landsat Enhanced Thematic Mapper (5 acquisitions) and the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) (2 acquisitions) were used to derive daily SCA using a linear regression between acquisition dates. Grain size data from AVIRIS (4 acquisitions) were used to infer snow surface albedo and interpolated linearly with time to derive daily albedo values. Modeled daily snowmelt rates for each 30-m pixel were scaled by the SCA and integrated over the snowmelt season to obtain estimates of maximum SWE accumulation. Snow surveys consisting of an average of 335 depth measurements and 53 density measurements during April, May and June, 1997 were interpolated using a regression tree / co-krig model, with independent variables of average incoming solar radiation, elevation, slope and maximum upwind slope. The basin was clustered into 7 elevation / average-solar-radiation zones for SWE accuracy assessment. Model simulations did a poor job at estimating the spatial distribution of SWE. Basin clusters where the solar radiative flux dominated the melt flux were simulated more accurately than those dominated by the turbulent fluxes or the longwave radiative flux.

Baseline and Projected Future Carbon Stocks and Fluxes in the Hawaiian Islands

NASA Astrophysics Data System (ADS)

Selmants, P. C.; Sleeter, B. M.; Giardina, C. P.; Zhu, Z.; Asner, G. P.

2016-12-01

Hawaii is characterized by steep climatic gradients and heterogeneous land cover within a small geographic area, presenting a model tropical system to capture ecosystem carbon dynamics across a wide range of climate, soil, and land use conditions. However, ecosystem carbon balance is poorly understood on a statewide level, and the potential for climate and land use change to affect carbon dynamics in Hawaii has not been formally assessed. We estimated current baseline and projected future ecosystem carbon stocks and fluxes on the seven main Hawaiian Islands using a combination of remote sensing, published plot-level data, and simulation modeling. Total ecosystem carbon storage during the baseline period was estimated at 258 TgC, with 70% stored as soil organic carbon, 25% as live biomass and 5% as surface detritus, and gross primary production was estimated at 20 TgC y-1. Net ecosystem carbon balance, which incorporated carbon losses from freshwater aquatic fluxes to nearshore waters and wildland fire emissions, was estimated as 0.34 TgC y-1 during the baseline period, offsetting 7% of anthropogenic emissions. We used a state and transition simulation model to estimate the response of ecosystem carbon stocks and fluxes to potential changes in climate, land use, and wildfire over a 50-year projection period (2012-2061). Total ecosystem carbon storage was projected to increase by 5% by the year 2061, but net ecosystem carbon balance was projected to decline by 35% due to climate change induced reductions in statewide net primary production and increased carbon losses from land use and land cover change. Our analysis indicates that the State of Hawaii would remain a net carbon sink overall, primarily because of ecosystem carbon sequestration on Hawaii Island, but predicted changes in climate and land use on Kauai and Oahu would convert these islands to net carbon sources. The Hawaii carbon assessment is part of a larger effort by the U.S. Geological Survey to assess the carbon sequestration potential of ecosystems across the United States and should provide valuable information for setting research and policy priorities for sustainable carbon management strategies aimed at offsetting anthropogenic carbon emissions.

Earth observation based assessment of the water production and water consumption of Nile Basin agro-ecosystems

USGS Publications Warehouse

Bastiaanssen, Wim G.M.; Karimi, Poolad; Rebelo, Lisa-Maria; Duan, Zheng; Senay, Gabriel; Muthuwatte, Lal; Smakhtin, Vladimir

2014-01-01

The increasing competition for water resources requires a better understanding of flows, fluxes, stocks, and the services and benefits related to water consumption. This paper explains how public domain Earth Observation data based on Moderate Resolution Imaging Spectroradiometer (MODIS), Second Generation Meteosat (MSG), Tropical Rainfall Measurement Mission (TRMM) and various altimeter measurements can be used to estimate net water production (rainfall (P) > evapotranspiration (ET)) and net water consumption (ET > P) of Nile Basin agro-ecosystems. Rainfall data from TRMM and the Famine Early Warning System Network (FEWS-NET) RainFall Estimates (RFE) products were used in conjunction with actual evapotranspiration from the Operational Simplified Surface Energy Balance (SSEBop) and ETLook models. Water flows laterally between net water production and net water consumption areas as a result of runoff and withdrawals. This lateral flow between the 15 sub-basins of the Nile was estimated, and partitioned into stream flow and non-stream flow using the discharge data. A series of essential water metrics necessary for successful integrated water management are explained and computed. Net water withdrawal estimates (natural and humanly instigated) were assumed to be the difference between net rainfall (Pnet) and actual evapotranspiration (ET) and some first estimates of withdrawals—without flow meters—are provided. Groundwater-dependent ecosystems withdraw large volumes of groundwater, which exceed water withdrawals for the irrigation sector. There is a strong need for the development of more open-access Earth Observation databases, especially for information related to actual ET. The fluxes, flows and storage changes presented form the basis for a global framework to describe monthly and annual water accounts in ungauged river basins.

Validation of the Martilli's Urban Boundary Layer Scheme with measurements from two mid-latitude European cities

NASA Astrophysics Data System (ADS)

Hamdi, R.; Schayes, G.

2005-07-01

The Martilli's urban parameterization scheme is improved and implemented in a mesoscale model in order to take into account the typical effects of a real city on the air temperature near the ground and on the surface exchange fluxes. The mesoscale model is run on a single column using atmospheric data and radiation recorded above roof level as forcing. Here, the authors validate the Martilli's urban boundary layer scheme using measurements from two mid-latitude European cities: Basel, Switzerland and Marseilles, France. For Basel, the model performance is evaluated with observations of canyon temperature, surface radiation, and energy balance fluxes obtained during the Basel urban boundary layer experiment (BUBBLE). The results show that the urban parameterization scheme is able to reproduce the generation of the Urban Heat Island (UHI) effect over urban area and represents correctly most of the behavior of the fluxes typical of the city center of Basel, including the large heat uptake by the urban fabric and the positive sensible heat flux at night. For Marseilles, the model performance is evaluated with observations of surface temperature, canyon temperature, surface radiation, and energy balance fluxes collected during the field experiments to constrain models of atmospheric pollution and transport of emissions (ESCOMPTE) and its urban boundary layer (UBL) campaign. At both urban sites, vegetation cover is less than 20%, therefore, particular attention was directed to the ability of the Martilli's urban boundary layer scheme to reproduce the observations for the Marseilles city center, where the urban parameters and the synoptic forcing are totally different from Basel. Evaluation of the model with wall, road, and roof surface temperatures gave good results. The model correctly simulates the net radiation, canyon temperature, and the partitioning between the turbulent and storage heat fluxes.

Validation of Martilli's urban boundary layer scheme with measurements from two mid-latitude European cities

NASA Astrophysics Data System (ADS)

Hamdi, R.; Schayes, G.

2007-08-01

Martilli's urban parameterization scheme is improved and implemented in a mesoscale model in order to take into account the typical effects of a real city on the air temperature near the ground and on the surface exchange fluxes. The mesoscale model is run on a single column using atmospheric data and radiation recorded above roof level as forcing. Here, the authors validate Martilli's urban boundary layer scheme using measurements from two mid-latitude European cities: Basel, Switzerland and Marseilles, France. For Basel, the model performance is evaluated with observations of canyon temperature, surface radiation, and energy balance fluxes obtained during the Basel urban boundary layer experiment (BUBBLE). The results show that the urban parameterization scheme represents correctly most of the behavior of the fluxes typical of the city center of Basel, including the large heat uptake by the urban fabric and the positive sensible heat flux at night. For Marseilles, the model performance is evaluated with observations of surface temperature, canyon temperature, surface radiation, and energy balance fluxes collected during the field experiments to constrain models of atmospheric pollution and transport of emissions (ESCOMPTE) and its urban boundary layer (UBL) campaign. At both urban sites, vegetation cover is less than 20%, therefore, particular attention was directed to the ability of Martilli's urban boundary layer scheme to reproduce the observations for the Marseilles city center, where the urban parameters and the synoptic forcing are totally different from Basel. Evaluation of the model with wall, road, and roof surface temperatures gave good results. The model correctly simulates the net radiation, canyon temperature, and the partitioning between the turbulent and storage heat fluxes.

Removal of terrestrial DOC in aquatic ecosystems of a temperate river network

USGS Publications Warehouse

Wollheim, W.M.; Stewart, R. J.; Aiken, George R.; Butler, Kenna D.; Morse, Nathaniel B.; Salisbury, J.

2015-01-01

Surface waters play a potentially important role in the global carbon balance. Dissolved organic carbon (DOC) fluxes are a major transfer of terrestrial carbon to river systems, and the fate of DOC in aquatic systems is poorly constrained. We used a unique combination of spatially distributed sampling of three DOC fractions throughout a river network and modeling to quantify the net removal of terrestrial DOC during a summer base flow period. We found that aquatic reactivity of terrestrial DOC leading to net loss is low, closer to conservative chloride than to reactive nitrogen. Net removal occurred mainly from the hydrophobic organic acid fraction, while hydrophilic and transphilic acids showed no net change, indicating that partitioning of bulk DOC into different fractions is critical for understanding terrestrial DOC removal. These findings suggest that river systems may have only a modest ability to alter the amounts of terrestrial DOC delivered to coastal zones.

RCCM2-BATS model over tropical South America: Applications to tropical deforestation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hahmann, A.N.; Dickinson, R.E.

A multiyear simulation of the global climate uses a revised version of the National Center for Atmospheric Research (NCAR) Community Climate Model Version 2 (CCM2) coupled to the Biosphere-Atmosphere Transfer Scheme (BATS). It is compared with global and rain gauge precipitation climatologies to evaluate precipitation fields and European Centre for Medium-Range Forecasts analyses to evaluate the atmospheric circulation. The near-surface climate is compared with data from Amazonian field campaigns. The model simulation of the South American climate agrees closely with the observational record and is much improved from past simulations with previous versions of the NCAR Community Climate model overmore » this portion of the Tropics. The model is then used to study the local and regional response to tropical deforestation over Amazonia. In addition to the standard deforestation forcing, consisting mainly of increased albedo and decreased roughness length, two additional sensitivity experiments were conducted to assess the individual contributions from these forcings to the deforestation changes. The standard deforestation simulation shows slight increases in annually averaged surface temperature (+1{degrees}C) and reductions in annually averaged precipitation and evaporation (-363 and -149 mm yr{sup -1}, respectively). As expected, increases in surface albedo over Amazonia produce a reduction in net downward solar radiation at the surface and consequently a reduction in net surface radiation and surface latent heat flux. The roughness decrease, on the other hand, reduces the surface latent heat fluxes through decreases in the surface drag coefficient. The regional changes in moisture convergence and precipitation during the Amazonian wet season display a shift in the area of maximum precipitation rather than an overall decrease over the deforested area. 45 refs., 16 figs., 4 tabs.« less

Predicting the severity of spurious “double ITCZ” problem in CMIP5 coupled models from AMIP simulations [Tropical versus extratropical origins of the spurious 'double ITCZ' in coupled climate models

DOE PAGES

Xiang, Baoqiang; Zhao, Ming; Held, Isaac M.; ...

2017-02-13

The severity of the double Intertropical Convergence Zone (DI) problem in climate models can be measured by a tropical precipitation asymmetry index (PAI), indicating whether tropical precipitation favors the Northern Hemisphere or the Southern Hemisphere. Examination of 19 Coupled Model Intercomparison Project phase 5 models reveals that the PAI is tightly linked to the tropical sea surface temperature (SST) bias. As one of the factors determining the SST bias, the asymmetry of tropical net surface heat flux in Atmospheric Model Intercomparison Project (AMIP) simulations is identified as a skillful predictor of the PAI change from an AMIP to a coupledmore » simulation, with an intermodel correlation of 0.90. Using tropical top-of-atmosphere (TOA) fluxes, the correlations are lower but still strong. However, the extratropical asymmetries of surface and TOA fluxes in AMIP simulations cannot serve as useful predictors of the PAI change. Furthermore, this study suggests that the largest source of the DI bias is from the tropics and from atmospheric models.« less

Effect of Climate Extremes, Seasonal Change, and Agronomic Practices on Measured Evapotranspiration and CO2 Exchange in Sacramento-San Joaquin River Delta Alfalfa Fields

NASA Astrophysics Data System (ADS)

Clay, J.; Kent, E. R.; Leinfelder-Miles, M.; Paw U, K. T.; Little, C.; Lambert, J. J.

2017-12-01

Evapotranspiration and CO2 exchange was measured in five alfalfa fields in the Sacramento-San Joaquin River Delta region from 2016 to 2017 using eddy covariance and surface renewal methods. Seasonal changes of evapotranspiration and CO2 fluxes were compared between 2016, a drought year, and 2017, a high rainfall year. Additionally, changes in evapotranspiration and CO2 flux were investigated across various agronomic considerations, such as irrigation methods (border-check flood and sub-surface), stand life, and herbicide programs. Components of the energy balance, including net radiation, latent heat, ground heat flux, and sensible heat, were evaluated considering correlations to wind speed measured by three sonic anemometers, irrigation frequency, and crop cutting cycle. Comparisons between two different types of radiometers were also carried out. Under drought conditions, we observed higher amounts of evapotranspiration in a field having a stand life of less than two years of age compared to older stands, and in a sub-surface irrigated field compared to flood irrigated fields.

Can land degradation drive differences in the C exchange of two similar semiarid ecosystems?

NASA Astrophysics Data System (ADS)

López-Ballesteros, Ana; Oyonarte, Cecilio; Kowalski, Andrew S.; Serrano-Ortiz, Penélope; Sánchez-Cañete, Enrique P.; Rosario Moya, M.; Domingo, Francisco

2018-01-01

Currently, drylands occupy more than one-third of the global terrestrial surface and are recognized as areas vulnerable to land degradation. The concept of land degradation stems from the loss of an ecosystem's biological productivity due to long-term loss of natural vegetation or depletion of soil nutrients. Drylands' key role in the global carbon (C) balance has been recently demonstrated, but the effects of land degradation on C sequestration by these ecosystems still need to be investigated. In the present study, we compared net C and water vapor fluxes, together with satellite, meteorological and vadose zone (CO2, water content and temperature) measurements, between two nearby (˜ 23 km) experimental sites representing natural (i.e., site of reference) and degraded grazed semiarid grasslands. We utilized data acquired over 6 years from two eddy covariance stations located in southeastern Spain with highly variable precipitation magnitude and distribution. Results show a striking difference in the annual C balances with an average net CO2 exchange of 196 ± 40 (C release) and -23 ± 2 g C m-2 yr-1 (C fixation) for the degraded and natural sites, respectively. At the seasonal scale, differing patterns in net CO2 fluxes were detected over both growing and dry seasons. As expected, during the growing seasons, greater net C uptake over longer periods was observed at the natural site. However, a much greater net C release, probably derived from subterranean ventilation, was measured at the degraded site during drought periods. After subtracting the nonbiological CO2 flux from net CO2 exchange, flux partitioning results point out that, during the 6 years of study, gross primary production, ecosystem respiration and water use efficiency were, on average, 9, 2 and 10 times higher, respectively, at the natural site versus the degraded site. We also tested differences in all monitored meteorological and soil variables and CO2 at 1.50 m belowground was the variable showing the greatest intersite difference, with ˜ 1000 ppm higher at the degraded site. Thus, we believe that subterranean ventilation of this vadose zone CO2, previously observed at both sites, partly drives the differences in C dynamics between them, especially during the dry season. It may be due to enhanced subsoil-atmosphere interconnectivity at the degraded site.

Drivers of surface moisture flux variations in northern terrestrial regions

NASA Astrophysics Data System (ADS)

Fischer, R.; Walsh, J. E.

2017-12-01

The wetness of the high-latitude land surface is strongly dependent on the difference between precipitation (P) and evapotranspiration (ET). Variations of ET over daily, seasonal and interannual timescales are poorly documented, as are their relationships to key drivers. A combination of regional climate model output and eddy covariance measurements from five flux tower sites in Alaska are used to test the hypothesis that temperature is the key driver of ET in tundra regions underlain by permafrost, while precipitation plays a greater role in boreal forest areas. At the tundra sites, both the flux tower data and the model simulations show that daily and warm-season totals of ET are largely temperature driven, although daily ET also shows a negative correlation with P. At the boreal forest sites, P is the main driver of year-to-year variations of the seasonally integrated net moisture flux, although ET does not correlate strongly with either P or T. A short period of negative P-ET typically occurs during the warm season in the flux tower data. The model depicts a stronger hydrologic cycle (larger P, larger ET) relative to the measurements at all the sites.

Interannual variability of Net Ecosystem CO2 Exchange and its component fluxes in a subalpine Mediterranean ecosystem (SE Spain)

NASA Astrophysics Data System (ADS)

Chamizo, Sonia; Serrano-Ortiz, Penélope; Sánchez-Cañete, Enrique P.; Domingo, Francisco; Arnau-Rosalén, Eva; Oyonarte, Cecilio; Pérez-Priego, Óscar; López-Ballesteros, Ana; Kowalski, Andrew S.

2015-04-01

Recent decades under climate change have seen increasing interest in quantifying the carbon (C) balance of different terrestrial ecosystems, and their behavior as sources or sinks of C. Both CO2 exchange between terrestrial ecosystems and the atmosphere and identification of its drivers are key to understanding land-surface feedbacks to climate change. The eddy covariance (EC) technique allows measurements of net ecosystem C exchange (NEE) from short to long time scales. In addition, flux partitioning models can extract the components of net CO2 fluxes, including both biological processes of photosynthesis or gross primary production (GPP) and respiration (Reco), and also abiotic drivers like subsoil CO2 ventilation (VE), which is of particular relevance in semiarid environments. The importance of abiotic processes together with the strong interannual variability of precipitation, which strongly affects CO2 fluxes, complicates the accurate characterization of the C balance in semiarid landscapes. In this study, we examine 10 years of interannual variability of NEE and its components at a subalpine karstic plateau, El Llano de los Juanes, in the Sierra de Gádor (Almería, SE Spain). Results show annual NEE ranging from 55 g C m-2 (net emission) to -54 g C m-2 (net uptake). Among C flux components, GPP was the greatest contributing 42-57% of summed component magnitudes, while contributions by Reco and VE ranged from 27 to 46% and from 3 to 18%, respectively. Annual precipitation during the studied period exhibited high interannual variability, ranging from 210 mm to 1374 mm. Annual precipitation explained 50% of the variance in Reco, 59% of that in GPP, and 56% for VE. While Reco and GPP were positively correlated with annual precipitation (correlation coefficient, R, of 0.71 and 0.77, respectively), VE showed negative correlation with this driver (R = -0.74). During the driest year (2004-2005), annual GPP and Reco reached their lowest values, while contribution of VE to annual NEE reached its highest value. There were also positive correlations with annual evapotranspiration (R = 0.71 for Reco and 0.64 for GPP), which explained 51% and 42% of the variance in Reco and GPP, respectively. Despite the variability in CO2 fluxes depending on the year, we can conclude that this ecosystem is approximately carbon neutral over a decade. Our results highlight the importance of considering interannual variability in CO2 fluxes, and also the need to account for abiotic contributions to the C balance in semiarid ecosystems, especially during dry years, to better predict the roles of these ecosystems in the global C balance.

Technical note: 3-hourly temporal downscaling of monthly global terrestrial biosphere model net ecosystem exchange

DOE PAGES

Fisher, Joshua B.; Sikka, Munish; Huntzinger, Deborah N.; ...

2016-07-29

Here, the land surface provides a boundary condition to atmospheric forward and flux inversion models. These models require prior estimates of CO 2 fluxes at relatively high temporal resolutions (e.g., 3-hourly) because of the high frequency of atmospheric mixing and wind heterogeneity. However, land surface model CO 2 fluxes are often provided at monthly time steps, typically because the land surface modeling community focuses more on time steps associated with plant phenology (e.g., seasonal) than on sub-daily phenomena. Here, we describe a new dataset created from 15 global land surface models and 4 ensemble products in the Multi-scale Synthesis andmore » Terrestrial Model Intercomparison Project (MsTMIP), temporally downscaled from monthly to 3-hourly output. We provide 3-hourly output for each individual model over 7 years (2004–2010), as well as an ensemble mean, a weighted ensemble mean, and the multi-model standard deviation. Output is provided in three different spatial resolutions for user preferences: 0.5° × 0.5°, 2.0° × 2.5°, and 4.0° × 5.0° (latitude × longitude).« less

Regional surface soil heat flux estimate from multiple remote sensing data in a temperate and semiarid basin

NASA Astrophysics Data System (ADS)

Li, Nana; Jia, Li; Lu, Jing; Menenti, Massimo; Zhou, Jie

2017-01-01

The regional surface soil heat flux (G0) estimation is very important for the large-scale land surface process modeling. However, most of the regional G0 estimation methods are based on the empirical relationship between G0 and the net radiation flux. A physical model based on harmonic analysis was improved (referred to as "HM model") and applied over the Heihe River Basin northwest China with multiple remote sensing data, e.g., FY-2C, AMSR-E, and MODIS, and soil map data. The sensitivity analysis of the model was studied as well. The results show that the improved model describes the variation of G0 well. Land surface temperature (LST) and thermal inertia (Γ) are the two key input variables to the HM model. Compared with in situ G0, there are some differences, mainly due to the differences between remote-sensed LST and the in situ LST. The sensitivity analysis shows that the errors from -7 to -0.5 K in LST amplitude and from -300 to 300 J m-2 K-1 s-0.5 in Γ will cause about 20% errors, which are acceptable for G0 estimation.

Energy Balance and Evapotranspiration in a High Mountain Area during Summer.

NASA Astrophysics Data System (ADS)

Konzelmann, T.; Calanca, P.; Müller, G.; Menzel, L.; Lang, H.

1997-07-01

A meteorological experiment was carried out in summer 1995 at two representative sites above and below the timberline in the Dischma Valley, near Davos, Switzerland. The study aimed at investigating the characteristics of the surface energy balance and of the evapotranspiration in a high alpine environment during the vegetation period. At both sites, net radiation is the only energy source. It amounts to about 80 W m2 at the lower and 100 W m2 at the upper sites, respectively. Since the albedo and the longwave radiation budget do not differ significantly, net radiation was found to be linearly dependent on global radiation. The latent heat flux associated with evapotranspiration represents the most important energy sink, averaging to 70 W m2 at the lower and 63 W m2 at the upper locations. It is therefore of comparable magnitude, despite a larger energy availability at the upper site. This is due to a significantly larger Bowen ratio at this upper location. On the other hand, the diurnal course of the Bowen ratio is at both sites such that the latent heat flux can be expressed as a linear function of net or global radiation. For a better characterization, the actual evapotranspiration was compared to Penman's parameterization, which represents the potential limit for saturated surface conditions. The comparison shows that, even during wet periods, evapotranspiration is regulated by the moisture conditions in the soil and the physiological behavior of vegetation.

Thermal Properties and Energy Fluxes in Pre-monsoon Season of 2016 at the Ponkar Debris-Covered Glacier, Manang, Nepal Himalaya

NASA Astrophysics Data System (ADS)

Chand, M. B.; Kayastha, R. B.; Armstrong, R. L.

2016-12-01

Himalayan glaciers are characterized by the presence of extensive debris cover in ablation areas. It is essential to understand the thermal properties and assess the effect of debris in glacier ice melt rate in debris-covered glaciers. Meteorological conditions are recorded on the lower ablation zone of the debris-covered Ponkar Glacier, Bhimthang, Manang, Nepal during pre-monsoon season of 2016. Debris temperature at different depths is monitored for winter and pre-monsoon season to estimate the effective heat conduction. Similarly, melt under the debris is also measured for pre-monsoon season. The incoming and outgoing shortwave radiations are measured at 2 m above the surface and other variables including air temperature, humidity, wind speed, and precipitation are used to estimate surface energy balance. Energy flux is dominated by net shortwave radiation as the foremost source of melting, where contribution of net longwave radiation, sensible, latent, and conductive heat flux is low. The daily average temperature gradients of the debris layer from surface to 30 cm below for winter and pre-monsoon seasons are 0.04 oC cm-1 and 0.23 oC cm-1, respectively. Debris thermal conductivities are 0.30 W m-1 K-1 and 1.69 W m-1 K-1 for the winter and pre-monsoon season, respectively. The higher value of conductivity during pre-monsoon season is due to the higher air temperature and increased precipitation compared to the winter months. The daily mean measured ice melt under a debris layer of 11-20 cm ranges from 0.6 to 1.1 cm. Estimation of melt at a few points can be used to estimate the general melting pattern for the glacier surface, which can be improved by using the spatial distribution of debris thickness and surface temperature.

On the freshwater budget in the eastern tropical Atlantic during the development of the cold tongue

NASA Astrophysics Data System (ADS)

Schlundt, Michael; Krahmann, Gerd; Brandt, Peter; Karstensen, Johannes

2013-04-01

The most striking sea surface temperature (SST) phenomenon in the tropical Atlantic is the seasonal appearance of the Atlantic Cold Tongue (ACT). Onset, duration, spatial extent and strength of cooling are subject to significant interannual variability. The ACT onset is also associated with remarkable changes in upper ocean salinity. To examine the different contributions to these changes we here focus on and present a mixed layer freshwater budget in the eastern tropical Atlantic. Our investigation is based on an exceptionally large set of observations during the onset of the ACT in late boreal spring/ early boreal summer 2011: more than 5400 CTD-profiles acquired by seven gliders running simultaneously to two research cruises, 180 ship based CTD-profiles, time series data from the PIRATA buoy array as well as measurements from the Argo float program are used to derive mixed layer depth, lateral and vertical salinity gradients. To derive turbulent mixing and inferred diapycnal salt flux, microstructure observations are taken into account. Furthermore satellite measurements of sea surface salinity (SSS) by the SMOS mission and of SST by the TMI radiometer as well as atmospheric reanalysis data and the OSCAR project products are implemented. Freshwater budget terms were calculated for different sub-regions. These sub-regions are chosen using pre-defined thresholds in SSS, SST or mixed layer depth. Overall the freshwater budget is dominated by the net surface freshwater flux and horizontal advection by strong zonal currents. Other terms, like entrainment and diapycnal mixing are found to be regionally important. In particular, the observed increase in salinity in the near-equatorial region during ACT onset is found to be the result of the northward migration of the ITCZ associated with reduced net surface freshwater flux at the equator as well as mixing of salty subsurface waters into the surface mixed layer.

Global Intercomparison of 12 Land Surface Heat Flux Estimates

NASA Technical Reports Server (NTRS)

Jimenez, C.; Prigent, C.; Mueller, B.; Seneviratne, S. I.; McCabe, M. F.; Wood, E. F.; Rossow, W. B.; Balsamo, G.; Betts, A. K.; Dirmeyer, P. A.;

Estimated Annual Net Change in Soil Carbon per US County, 1990-2004

DOE Data Explorer

West, Tristram O.; Brandt, Craig C.; Wilson, Bradly S.; Hellwinckel, Chap M.; Tyler, Donald D.; Marland, Gregg; De La Torre Ugarte, Daniel D.; Larson, James A.; Nelson, Richard G.

2008-01-01

These data represent the estimated net change (Megagram per year) in soil carbon due to changes in the crop type and tillage intensity. Estimated accumulation of soil carbon under Conservation Reserve Program (CRP)lands is included in these estimates. Negative values represent a net flux from the atmosphere to the soil; positive values represent a net flux from the soil to the atmosphere. As such, soil carbon sequestration is represented here as a negative value.

Surface Heat Balance Analysis of Tainan City on March 6, 2001 Using ASTER and Formosat-2 Data

PubMed Central

Kato, Soushi; Yamaguchi, Yasushi; Liu, Cheng-Chien; Sun, Chen-Yi

2008-01-01

The urban heat island phenomenon occurs as a mixed result of anthropogenic heat discharge, decreased vegetation, and increased artificial impervious surfaces. To clarify the contribution of each factor to the urban heat island, it is necessary to evaluate the surface heat balance. Satellite remote sensing data of Tainan City, Taiwan, obtained from Terra ASTER and Formosat-2 were used to estimate surface heat balance in this study. ASTER data is suitable for analyzing heat balance because of the wide spectral range. We used Formosat-2 multispectral data to classify the land surface, which was used to interpolate some surface parameters for estimating heat fluxes. Because of the high spatial resolution of the Formosat-2 image, more roads, open spaces and small vegetation areas could be distinguished from buildings in urban areas; however, misclassifications of land cover in such areas using ASTER data would overestimate the sensible heat flux. On the other hand, the small vegetated areas detected from the Formosat-2 image slightly increased the estimation of latent heat flux. As a result, the storage heat flux derived from Formosat-2 is higher than that derived from ASTER data in most areas. From these results, we can conclude that the higher resolution land coverage map increases accuracy of the heat balance analysis. Storage heat flux occupies about 60 to 80% of the net radiation in most of the artificial surface areas in spite of their usages. Because of the homogeneity of the building roof materials, there is no contrast between the storage heat flux in business and residential areas. In sparsely vegetated urban areas, more heat is stored and latent heat is smaller than that in the forested suburbs. This result implies that density of vegetation has a significant influence in decreasing temperatures. PMID:27873856

Spatialization of instantaneous and daily average net radiation and soil heat flux in the territory of Itaparica, Northeast Brazil

NASA Astrophysics Data System (ADS)

Lopes, Helio L.; Silva, Bernardo B.; Teixeira, Antônio H. C.; Accioly, Luciano J. O.

2012-09-01

This work has as aim to quantify the energy changes between atmosphere and surface by modeling both net radiation and soil heat flux related to land use and cover. The methodology took into account modeling and mapping of physical and biophysical parameters using MODIS images and SEBAL algorithm in an area of native vegetation and irrigated crops. The results showed that there are variations in the values of the estimated parameters for different land cover types and mainly in caatinga cover. The dense caatinga presents mean values of soil heat flux (Go) of 124.9 Wm-2 while sparse caatinga with incidence of erosion, present average value of 132.6 Wm-2. For irrigated plots cultivated with banana, coconut, and papaya the mean Go values were 103.8, 98.6, 113.9 Wm-2, respectively. With regard to the instantaneous net radiation (Rn), dense caatinga presented mean value of 626.1 Wm-2, while sparse caatinga a mean value of 575.2 Wm-2. Irrigated areas cultivated with banana, coconut, and papaya presented Rn of 658.1, 647.4 and 617.9 W m-2 respectively. Applying daily mean net radiation (RnDAve) it was found that dense caatinga had a mean value of 417.1 W m-2, while sparse caatinga had a mean value of 379.9 W m-2. For the irrigated crops of banana, coconut and papaya the RnDAve values were 430.9, 431.3 and 411.6 W m-2, respectively. Sinusoidal model can be applied to determine the maximum and RnDAve considering the diverse classes of LULC; however, there is a need to compare the results with field data for validation of this model.

Comparison of 37 months global net radiation flux derived from PICARD-BOS over the same period observations of CERES and ARGO

NASA Astrophysics Data System (ADS)

Zhu, Ping; Wild, Martin

2016-04-01

The absolute level of the global net radiation flux (NRF) is fixed at the level of [0.5-1.0] Wm-2 based on the ocean heat content measurements [1]. The space derived global NRF is at the same order of magnitude than the ocean [2]. Considering the atmosphere has a negligible effects on the global NRF determination, the surface global NRF is consistent with the values determined from space [3]. Instead of studying the absolute level of the global NRF, we focus on the interannual variation of global net radiation flux, which were derived from the PICARD-BOS experiment and its comparison with values over the same period but obtained from the NASA-CERES system and inferred from the ocean heat content survey by ARGO network. [1] Allan, Richard P., Chunlei Liu, Norman G. Loeb, Matthew D. Palmer, Malcolm Roberts, Doug Smith, and Pier-Luigi Vidale (2014), Changes in global net radiative imbalance 1985-2012, Geophysical Research Letters, 41 (no.15), 5588-5597. [2] Loeb, Norman G., John M. Lyman, Gregory C. Johnson, Richard P. Allan, David R. Doelling, Takmeng Wong, Brian J. Soden, and Graeme L. Stephens (2012), Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty, Nature Geoscience, 5 (no.2), 110-113. [3] Wild, Martin, Doris Folini, Maria Z. Hakuba, Christoph Schar, Sonia I. Seneviratne, Seiji Kato, David Rutan, Christof Ammann, Eric F. Wood, and Gert Konig-Langlo (2015), the energy balance over land and oceans: an assessment based on direct observations and CMIP5 climate models, Climate Dynamics, 44 (no.11-12), 3393-3429.

Surface Energy Balance System (SEBS) Handbook

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, DR

2011-02-14

A Surface Energy Balance System (SEBS) has been installed collocated with each deployed ECOR system at the Southern Great Plains (SGP), North Slope of Alaska (NSA), Tropical Western Pacific (TWP), ARM Mobile Facility 1 (AMF1), and ARM Mobile Facility 2 (AMF2). The surface energy balance system consists of upwelling and downwelling solar and infrared radiometers within one net radiometer, a wetness sensor, and soil measurements. The SEBS measurements allow the comparison of ECOR sensible and latent heat fluxes with the energy balance determined from the SEBS and provide information on wetting of the sensors for data quality purposes.

Ionic requirements of proximal tubular sodium transport. I. Bicarbonate and chloride.

PubMed

Green, R; Giebisch, G

1975-11-01

Simultaneous perfusion of peritubular capillaries and proximal convoluted tubules was used to study the effect of varying transepithelial ionic gradients on ionic fluxes. Results show that net sodium influx and volume flux was one-third of normal when bicarbonate was absent, no chloride gradient existed, and glucose and amino acids were absent. Addition of bicarbonate to the luminal fluid did not restore the flux to normal, but peritubular bicarbonate did restore it. A chloride gradient imposed when no bicarbonate was present could only increase the fluxes slightly, but his flux was significant even after cyanide had poisoned transport. Reversing the chloride concentration gradient decreased the net sodium and volume fluxes whether bicarbonate was present or not. Glucose had no effect on fluxes, but substitution of Na by choline abolished them entirely. It is concluded that sodium is actively transported, that a chloride concentration gradient from lumen to plasma could account for up to 20% of net transport, and that peritubular bicarbonate is necessary for normal rates of sodium and fluid absorption.

Comparison Of Landscape-level Carbon Flux Estimates from Budgeting The Planetary Boundary Layer And Footprinting On Remote Sensing Images

NASA Astrophysics Data System (ADS)

Chen, B.; Chen, J. M.; Mo, G.

2006-12-01

Carbon balance estimation at the landscape/regional scale is a challenge because of the heterogeneity of the land surface and the nonlinearity inherent in ecophysiological processes. Two methodologies, a simple atmospheric boundary-layer budgeting method and an integrated modeling method, were explored and compared in this study. Studies of the atmospheric boundary-layer (ABL) budget of CO2 have the potential to provide information on carbon balance of the land surface on a regional scale. Indeed, the surface area of integration by the ABL moving through a tower in one day was estimated to be ~104 km2. Two novel methodologies to retrieve the landscape/regional carbon balance information captured by the CO2 concentration measurements are explored and compared in this study: boundary-layer budgeting and remote sensing-based footprint integration. We investigated four boreal continental sites in this study. Boundary-layer budgeting: By assuming the horizontal advection is negligible, the regional surface net flux (representative of an upwind area ~105 km2) can be calculated as, Fc=(Cm-CFT)ù+dC/dt*zi, where ù is the mean vertical velocity, zi is the mean ABL height, and and are the biweekly mean mixing ratio of CO2 in the ABL and the free troposphere, respectively. ù is from the NCEP (National Centers for Environmental Prediction) reanalysis data, while zi was simulated by an one-dimensional ABL model. The CO2 flux in the upwind area of the tower was also estimated based on ecosystem modeling using remote sensing measurements. Remote sensing-based footprint integration: The total regional flux captured by the sensor on a tower (mixing ratio) is the weighted sum of the upwind footprint source areas (Ømega), Fc= Σ FiWi, where Fi and Wi are the CO2 flux and its weighting factor for each pixel, respectively. Fiis calculated using an ecosystem model (BEPS: Boreal Ecosystem Productivity Simulator). Wiis comparative contribution factor of footprint function for each pixel within the whole footprint area as, Wi= fi/Σ fi, while the footprint function fi (the pixel i with x,y coordinates; x and y are along and the cross daily mean wind direction, respectively) is computed using a concentration footprint model as, fi(x,y,zm-z0)=Dy(x,y)Dz(x,zm)/U(x) Where Dy and Dz are the crosswind and vertical concentration distribution function, respectively and U(x) is the effective speed of plume advection. They are dependant on standard surface-layer scaling parameters and based on an analytical solution of Eulerian theory. Methodology comparison: The regional fluxes estimated using these two methods matched well. These regional net CO2 flux estimates were also comparable to local-scale measurements by eddy covariance techniques. The calculated upwind regional CO2 flux shows considerable seasonal and inter-annual variations. Annual regional flux was sensitive to air temperature in boreal regions and the temperature-sensitivities were region dependent. Larger fluxes are found in the warmer growing seasons and warmer years in the boreal forest regions.

Coral-algae metabolism and diurnal changes in the CO2-carbonate system of bulk sea water.

PubMed

Jokiel, Paul L; Jury, Christopher P; Rodgers, Ku'ulei S

2014-01-01

Precise measurements were conducted in continuous flow seawater mesocosms located in full sunlight that compared metabolic response of coral, coral-macroalgae and macroalgae systems over a diurnal cycle. Irradiance controlled net photosynthesis (P net), which in turn drove net calcification (G net), and altered pH. P net exerted the dominant control on [CO3 (2-)] and aragonite saturation state (Ωarag) over the diel cycle. Dark calcification rate decreased after sunset, reaching zero near midnight followed by an increasing rate that peaked at 03:00 h. Changes in Ωarag and pH lagged behind G net throughout the daily cycle by two or more hours. The flux rate P net was the primary driver of calcification. Daytime coral metabolism rapidly removes dissolved inorganic carbon (DIC) from the bulk seawater and photosynthesis provides the energy that drives G net while increasing the bulk water pH. These relationships result in a correlation between G net and Ωarag, with Ωarag as the dependent variable. High rates of H(+) efflux continued for several hours following mid-day peak G net suggesting that corals have difficulty in shedding waste protons as described by the Proton Flux Hypothesis. DIC flux (uptake) followed P net and G net and dropped off rapidly following peak P net and peak G net indicating that corals can cope more effectively with the problem of limited DIC supply compared to the problem of eliminating H(+). Over a 24 h period the plot of total alkalinity (AT ) versus DIC as well as the plot of G net versus Ωarag revealed a circular hysteresis pattern over the diel cycle in the coral and coral-algae mesocosms, but not the macroalgae mesocosm. Presence of macroalgae did not change G net of the corals, but altered the relationship between Ωarag and G net. Predictive models of how future global changes will effect coral growth that are based on oceanic Ωarag must include the influence of future localized P net on G net and changes in rate of reef carbonate dissolution. The correlation between Ωarag and G net over the diel cycle is simply the response of the CO2-carbonate system to increased pH as photosynthesis shifts the equilibria and increases the [CO3 (2-)] relative to the other DIC components of [HCO3 (-)] and [CO2]. Therefore Ωarag closely tracked pH as an effect of changes in P net, which also drove changes in G net. Measurements of DIC flux and H(+) flux are far more useful than concentrations in describing coral metabolism dynamics. Coral reefs are systems that exist in constant disequilibrium with the water column.

Characterizing near-surface CO2 conditions before injection - Perspectives from a CCS project in the Illinois Basin, USA

USGS Publications Warehouse

Locke, R.A.; Krapac, I.G.; Lewicki, J.L.; Curtis-Robinson, E.

2011-01-01

The Midwest Geological Sequestration Consortium is conducting a large-scale carbon capture and storage (CCS) project in Decatur, Illinois, USA to demonstrate the ability of a deep saline formation to store one million tonnes of carbon dioxide (CO2) from an ethanol facility. Beginning in early 2011, CO2 will be injected at a rate of 1,000 tonnes/day for three years into the Mount Simon Sandstone at a depth of approximately 2,100 meters. An extensive Monitoring, Verification, and Accounting (MVA) program has been undertaken for the Illinois Basin Decatur Project (IBDP) and is focused on the 0.65 km2 project site. Goals include establishing baseline conditions to evaluate potential impacts from CO2 injection, demonstrating that project activities are protective of human health and the environment, and providing an accurate accounting of stored CO2. MVA efforts are being conducted pre-, during, and post- CO2 injection. Soil and net CO2 flux monitoring has been conducted for more than one year to characterize near-surface CO2 conditions. More than 2,200 soil CO2 flux measurements have been manually collected from a network of 118 soil rings since June 2009. Three ring types have been evaluated to determine which type may be the most effective in detecting potential CO 2 leakage. Bare soil, shallow-depth rings were driven 8 cm into the ground and were prepared to minimize surface vegetation in and near the rings. Bare soil, deep-depth rings were prepared similarly, but were driven 46 cm. Natural-vegetation, shallow-depth rings were driven 8 cm and are most representative of typical vegetation conditions. Bare-soil, shallow-depth rings had the smallest observed mean flux (1.78 ??mol m-2 s-1) versus natural-vegetation, shallow-depth rings (3.38 ??mol m-2 s-1). Current data suggest bare ring types would be more sensitive to small CO2 leak signatures than natural ring types because of higher signal to noise ratios. An eddy covariance (EC) system has been in use since June 2009. Baseline data from EC monitoring is being used to characterize pre-injection conditions, and may then be used to detect changes in net exchange CO2 fluxes (Fc) that could be the result of CO2 leakage into the near-surface environment during or following injection. When injection at IBDP begins, soil and net CO2 monitoring efforts will have established a baseline of near-surface conditions that will be important to help demonstrate the effectiveness of storage activities. ?? 2011 Published by Elsevier Ltd.

Impact of gyro-motion and sheath acceleration on the flux distribution on rough surfaces

NASA Astrophysics Data System (ADS)

Schmid, K.; Mayer, M.; Adelhelm, C.; Balden, M.; Lindig, S.; ASDEX Upgrade Team

2010-10-01

As was already observed experimentally, the erosion of tungsten (W) coated graphite (C) tiles in ASDEX-Upgrade (AUG) exhibits regular erosion patterns on the micrometre rough surfaces whose origin is not fully understood: surfaces inclined towards the magnetic field direction show strong net W erosion while surfaces facing away from the magnetic field are shadowed from erosion and may even exhibit net W deposition. This paper presents a model which explains the observed erosion/deposition pattern. It is based on the calculation of ion trajectories dropping through the plasma sheath region to the rough surface with combined magnetic and electrical fields. The surface topography used in the calculations is taken from atomic force microscope measurement of real AUG tiles. The calculated erosion patterns are directly compared with secondary electron microscopy images of the erosion zones from the same location. The erosion on surfaces inclined towards the magnetic field is due to ions from the bulk plasma which enter the sheath gyrating along the magnetic field lines, while the deposition of W on surfaces facing away from the magnetic field is due to promptly re-deposited W that is ionized still within the magnetic pre-sheath.

Carbon dioxide and energy fluxes over a large shallow lake in China

NASA Astrophysics Data System (ADS)

Zhao, Xiaosong

2017-04-01

The turbulent exchange of carbon dioxide and energy between water and atmosphere over lakes differ from those over vegetated surfaces due to high heat capacity of water and different water ecological environment. For a shallow lake, the underlying surface generally changes between water covered and land covered with water level fluctuation, which significantly influences carbon dioxide and energy fluxes. Continuous measurement of the carbon dioxide (CO2), latent (LE) and sensible (H) heat fluxes was made using the eddy covariance method over the Poyang Lake, the largest fresh lake in China, from August 2013 to December 2015. Results indicated that the surface energy budget has a strong seasonal pattern, with peaks in LE and H observed in early August and September. There was 10 days delay between the net radiation and the latent heat flux. More net radiation (Rn) was allocated to the LE rather than H through the year, with monthly mean LE/Rn of 0.65 and H/Rn of 0.11, which caused Bowen ratio was 0.15 in water-covered period, lower than that in land-covered period. The water heat storage experienced shifting from heat storage to heat release, with maximum heat storage in July and maximum heat release in September. The water heat advection was account for 4% to 10% of Rn and peaked in June. The annual evaporation is 875 mm, 893 mm and 1019 mm in 2013 (from August 2013 to July 2014), 2014 and 2015, which was account for approximately 57% of precipitation in the three years. The large lake acted as a CO2 source in inundating period and a CO2 sink in exposure period. The energy fluxes were controlled by environmental factors with timescale dependence. On daily scale, the LE and H were highly correlated with product of wind speed and vapor pressure deficit (UVPD) or wind speed (U) in the water-covered period, and with Rn in the land-covered period. Monthly LE, H and annual H were controlled by Rn, while annual LE was primarily dependent on water depth. Annual CO2 budget was regulated by duration of inundating period.

Gas hydrate decomposition recorded by authigenic barite at pockmark sites of the northern Congo Fan

NASA Astrophysics Data System (ADS)

Kasten, Sabine; Nöthen, Kerstin; Hensen, Christian; Spieß, Volkhard; Blumenberg, Martin; Schneider, Ralph R.

2012-12-01

The geochemical cycling of barium was investigated in sediments of pockmarks of the northern Congo Fan, characterized by surface and subsurface gas hydrates, chemosynthetic fauna, and authigenic carbonates. Two gravity cores retrieved from the so-called Hydrate Hole and Worm Hole pockmarks were examined using high-resolution pore-water and solid-phase analyses. The results indicate that, although gas hydrates in the study area are stable with respect to pressure and temperature, they are and have been subject to dissolution due to methane-undersaturated pore waters. The process significantly driving dissolution is the anaerobic oxidation of methane (AOM) above the shallowest hydrate-bearing sediment layer. It is suggested that episodic seep events temporarily increase the upward flux of methane, and induce hydrate formation close to the sediment surface. AOM establishes at a sediment depth where the upward flux of methane from the uppermost hydrate layer counterbalances the downward flux of seawater sulfate. After seepage ceases, AOM continues to consume methane at the sulfate/methane transition (SMT) above the hydrates, thereby driving the progressive dissolution of the hydrates "from above". As a result the SMT migrates downward, leaving behind enrichments of authigenic barite and carbonates that typically precipitate at this biogeochemical reaction front. Calculation of the time needed to produce the observed solid-phase barium enrichments above the present-day depths of the SMT served to track the net downward migration of the SMT and to estimate the total time of hydrate dissolution in the recovered sediments. Methane fluxes were higher, and the SMT was located closer to the sediment surface in the past at both sites. Active seepage and hydrate formation are inferred to have occurred only a few thousands of years ago at the Hydrate Hole site. By contrast, AOM-driven hydrate dissolution as a consequence of an overall net decrease in upward methane flux seems to have persisted for a considerably longer time at the Worm Hole site, amounting to a few tens of thousands of years.

Modeling the radiative effects of biomass burning aerosols on carbon fluxes in the Amazon region

NASA Astrophysics Data System (ADS)

Moreira, Demerval S.; Longo, Karla M.; Freitas, Saulo R.; Yamasoe, Marcia A.; Mercado, Lina M.; Rosário, Nilton E.; Gloor, Emauel; Viana, Rosane S. M.; Miller, John B.; Gatti, Luciana V.; Wiedemann, Kenia T.; Domingues, Lucas K. G.; Correia, Caio C. S.

2017-12-01

Every year, a dense smoke haze covers a large portion of South America originating from fires in the Amazon Basin and central parts of Brazil during the dry biomass burning season between August and October. Over a large portion of South America, the average aerosol optical depth at 550 nm exceeds 1.0 during the fire season, while the background value during the rainy season is below 0.2. Biomass burning aerosol particles increase scattering and absorption of the incident solar radiation. The regional-scale aerosol layer reduces the amount of solar energy reaching the surface, cools the near-surface air, and increases the diffuse radiation fraction over a large disturbed area of the Amazon rainforest. These factors affect the energy and CO2 fluxes at the surface. In this work, we applied a fully integrated atmospheric model to assess the impact of biomass burning aerosols in CO2 fluxes in the Amazon region during 2010. We address the effects of the attenuation of global solar radiation and the enhancement of the diffuse solar radiation flux inside the vegetation canopy. Our results indicate that biomass burning aerosols led to increases of about 27 % in the gross primary productivity of Amazonia and 10 % in plant respiration as well as a decline in soil respiration of 3 %. Consequently, in our model Amazonia became a net carbon sink; net ecosystem exchange during September 2010 dropped from +101 to -104 TgC when the aerosol effects are considered, mainly due to the aerosol diffuse radiation effect. For the forest biome, our results point to a dominance of the diffuse radiation effect on CO2 fluxes, reaching a balance of 50-50 % between the diffuse and direct aerosol effects for high aerosol loads. For C3 grasses and savanna (cerrado), as expected, the contribution of the diffuse radiation effect is much lower, tending to zero with the increase in aerosol load. Taking all biomes together, our model shows the Amazon during the dry season, in the presence of high biomass burning aerosol loads, changing from being a source to being a sink of CO2 to the atmosphere.

Surface-atmosphere exchange of ammonia over peatland using QCL-based eddy-covariance measurements and inferential modeling

NASA Astrophysics Data System (ADS)

Zöll, Undine; Brümmer, Christian; Schrader, Frederik; Ammann, Christof; Ibrom, Andreas; Flechard, Christophe R.; Nelson, David D.; Zahniser, Mark; Kutsch, Werner L.

2016-09-01

Recent advances in laser spectrometry offer new opportunities to investigate ecosystem-atmosphere exchange of environmentally relevant trace gases. In this study, we demonstrate the applicability of a quantum cascade laser (QCL) absorption spectrometer to continuously measure ammonia concentrations at high time resolution and thus to quantify the net exchange between a seminatural peatland ecosystem and the atmosphere based on the eddy-covariance approach. Changing diurnal patterns of both ammonia concentration and fluxes were found during different periods of the campaign. We observed a clear tipping point in early spring with decreasing ammonia deposition velocities and increasingly bidirectional fluxes that occurred after the switch from dormant vegetation to CO2 uptake but was triggered by a significant weather change. While several biophysical parameters such as temperature, radiation, and surface wetness were identified to partially regulate ammonia exchange at the site, the seasonal concentration pattern was clearly dominated by agricultural practices in the surrounding area. Comparing the results of a compensation point model with our measurement-based flux estimates showed considerable differences in some periods of the campaign due to overestimation of non-stomatal resistances caused by low acid ratios. The total cumulative campaign exchange of ammonia after 9 weeks, however, differed only in a 6 % deviation with 911 and 857 g NH3-N ha-1 deposition being found by measurements and modeling, respectively. Extrapolating our findings to an entire year, ammonia deposition was lower than reported by Hurkuck et al. (2014) for the same site in previous years using denuder systems. This was likely due to a better representation of the emission component in the net signal of eddy-covariance fluxes as well as better adapted site-specific parameters in the model. Our study not only stresses the importance of high-quality measurements for studying and assessing land surface-atmosphere interactions but also demonstrates the potential of QCL spectrometers for continuous observation of reactive nitrogen species as important additional instruments within long-term monitoring research infrastructures such as ICOS or NEON at sites with strong nearby ammonia sources leading to relatively high mean background concentrations and fluxes.

The Dependence of Heat and Gas Transfer Velocities on Wind-Generated and Mechanically Generated Aqueous-Phase Turbulence

NASA Astrophysics Data System (ADS)

Liang, H.; Mukto, M.; Loewen, M.; Zappa, C.; Litchendorf, T.; Asher, W.; Jessup, A.

2006-12-01

The air-sea flux, F, of a sparingly soluble nonreactive gas can be expressed as F = kG( CS-CW), where kG is the gas transfer velocity, CS is the concentration of gas that would be expected in the water if the system were in Henry`s Gas Law equilibrium, and CW is the actual concentration of the gas in the water. An analogous relationship for the net heat flux can also be written using the heat transfer velocity, kH, and the bulk-skin temperature difference in the aqueous phase. Hydrodynamical models of gas and heat exchange based on surface renewal theory predict that kG and kH will scale as the square root of the inverse of a timescale of the turbulence. Furthermore, if surface renewal provides an accurate conceptual model for both transfer processes, then both kG and kH should behave identically as turbulence conditions change. Here we report on recent laboratory experiments in which we measured turbulence, heat fluxes, kG, and kH in a 0.5 m by 0.5 m by 1 m deep tank in the presence of turbulence generated mechanically using a random synthetic jet array. The turbulence tank was embedded in a small wind tunnel so that kG and kH could be studied as a function of the mechanically generated turbulence but also turbulence generated by wind stress. Net heat transfer velocities were measured using Active Controlled Flux Technique and estimated from measurements of the latent and sensible heat fluxes combined with direct measurements of the bulk-skin temperature difference. Gas transfer velocities were determined by measuring the evasion rates of sulfur hexafluoride and helium. The length and velocity scales of the aqueous-phase turbulence were measured using a Digital Particle-Image Velocimetry system. These combined data sets are used to study how kG and kH depend on system turbulence, whether this dependence is consonant with that predicted using surface renewal, and whether there is a quantitative difference between mechanically generated turbulence and turbulence generated by the wind stress insofar as air-water exchange is concerned.

Water cycle research associated with the CaPE hydrometeorology project (CHymP

NASA Technical Reports Server (NTRS)

Duchon, Claude E.

1993-01-01

One outgrowth of the Convection and Precipitation/Electrification (CaPE) experiment that took place in central Florida during July and August 1991 was the creation of the CaPE Hydrometeorology Project (CHymP). The principal goal of this project is to investigate the daily water cycle of the CaPE experimental area by analyzing the numerous land and atmosphere in situ and remotely sensed data sets that were generated during the 40-days of observations. The water cycle comprises the atmospheric branch. In turn, the atmospheric branch comprises precipitation leaving the base of the atmospheric volume under study, evaporation and transpiration entering the base, the net horizontal fluxes of water vapor and cloud water through the volume and the conversion of water vapor to cloud water and vice-versa. The sum of these components results in a time rate of change in the water and liquid water (or ice) content of the atmospheric volume. The components of the land branch are precipitation input to and evaporation and transpiration output from the surface, net horizontal fluxes of surface and subsurface water, the sum of which results in a time rate of change in surface and subsurface water mass. The objective of CHymP is to estimate these components in order to determine the daily water budget for a selected area within the CaPE domain. This work began in earnest in the summer of 1992 and continues. Even estimating all the budget components for one day is a complex and time consuming task. The discussions below provides a short summary of the rainfall quality assessment procedures followed by a plan for estimating the horizontal moisture flux.

Global Evolution of an Accretion Disk with a Net Vertical Field: Coronal Accretion, Flux Transport, and Disk Winds

NASA Astrophysics Data System (ADS)

Zhu, Zhaohuan; Stone, James M.

2018-04-01

We report results from global ideal MHD simulations that study thin accretion disks (with thermal scale height H/R = 0.1 and 0.05) threaded by net vertical magnetic fields. Our computations span three orders of magnitude in radius, extend all the way to the pole, and are evolved for more than 1000 innermost orbits. We find that (1) inward accretion occurs mostly in the upper magnetically dominated regions of the disk at z ∼ R, similar to predictions from some previous analytical work and the “coronal accretion” flows found in GRMHD simulations. (2) A quasi-static global field geometry is established in which flux transport by inflows at the surface is balanced by turbulent diffusion. The resulting field is strongly pinched inwards at the surface. A steady-state advection–diffusion model, with a turbulent magnetic Prandtl number of order unity, reproduces this geometry well. (3) Weak unsteady disk winds are launched beyond the disk corona with the Alfvén radius R A /R 0 ∼ 3. Although the surface inflow is filamentary and the wind is episodic, we show that the time-averaged properties are well-described by steady-wind theory. Even with strong fields, β 0 = 103 at the midplane initially, only 5% of the angular momentum transport is driven by the wind, and the wind mass flux from the inner decade of the radius is only ∼0.4% of the mass accretion rate. (4) Within the disk, most of the accretion is driven by the Rϕ stress from the MRI and global magnetic fields. Our simulations have many applications to astrophysical accretion systems.

Imposing strong constraints on tropical terrestrial CO2 fluxes using passenger aircraft based measurements

NASA Astrophysics Data System (ADS)

Niwa, Y.; Machida, T.; Sawa, Y.; Matsueda, H.; Schuck, T. J.; Brenninkmeijer, C. A.; Imasu, R.; Satoh, M.

2011-12-01

Better understanding of the global and regional carbon budget is needed to perform a reliable prediction of future climate with an earth system model. However, the reliability of CO2 source/sink estimation by inverse modeling, which is one of the promising methods to estimate regional carbon budget, is limited because of sparse observational data coverage. Very few observational data are available in tropics. Therefore, especially the reconstruction of tropical terrestrial fluxes has considerable uncertainties. In this study, regional CO2 fluxes for 2006-2008 are estimated by inverse modeling using the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) in addition to the surface measurement dataset of GLOBALVIEW-CO2. CONTRAIL is a recently established CO2 measurement network using in-situ measurement instruments on board commercial aircraft. Five CONTRAIL aircraft travel back and forth between Japan and many areas: Europe, North America, Southeast Asia, South Asia, and Australia. The Bayesian synthesis approach is used to estimate monthly fluxes for 42 regions using NICAM-TM simulations with existing CO2 flux datasets and monthly mean observational data. It is demonstrated that the aircraft data have great impact on estimated tropical terrestrial fluxes. By adding the aircraft data to the surface data, the analyzed uncertainty of tropical fluxes has been reduced by 15 % and more than 30 % uncertainty reduction rate is found in Southeast and South Asia. Specifically, for annual net CO2 fluxes, nearly neutral fluxes of Indonesia, which is estimated using the surface dataset alone, turn to positive fluxes, i.e. carbon sources. In Indonesia, a remarkable carbon release during the severe drought period of October-December in 2006 is estimated, which suggests that biosphere respiration or biomass burning was larger than the prior fluxes. Comparison of the optimized atmospheric CO2 with independent aircraft measurements of CARIBIC tends to validate results of the inversion system. It is expected that the use of instantaneous observational data with more sophisticated inversion methods will provide more accurate estimation of surface CO2 fluxes.

CO/sub 2/ fluxes in the tropical Atlantic during FOCAL cruises

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrie, C.; Oudot, C.; Genthon, C.

1986-10-15

CO/sub 2/ partial pressures in the atmosphere and in surface seawater have been measured in the equatorial Atlantic Ocean during Programme Francais Ocean-Climat en Atlantique Equatorial cruises extending from July 1982 to August 1984 along the 4/degree/W, 22/degree/W, and 35/degree/W meridians. Gas transfer coefficients based on recently reported field data combined with information deduced from wind tunnel experiments are used to compute the CO/sub 2/ fluxes. The global mean net flux between 5/degree/N and 5/degree/S is equal to 1.05 mmol m/sup /minus/2/ d/sup /minus/1/ and is from the ocean to the atmosphere. The escape of CO/sub 2/ increases strongly frommore » the east to the west and is always lower in the north than in the south. The importance of wind speed, pCO/sub 2/ in atmosphere, PCO/sub 2/ in surface seawater, and temperature on the flux variability is discussed. The relative influence of the equatorial upwelling on one hand and of the advection and warming of surface waters on the other hand is studied in order to explain high partial pressure in seawater. 59 refs., 15 figs., 5 tabs.« less

Electricity resonance-induced fast transport of water through nanochannels.

PubMed

Kou, Jianlong; Lu, Hangjun; Wu, Fengmin; Fan, Jintu; Yao, Jun

2014-09-10

We performed molecular dynamics simulations to study water permeation through a single-walled carbon nanotube with electrical interference. It was found that the water net flux across the nanochannel is greatly affected by the external electrical interference, with the maximal net flux occurred at an electrical interference frequency of 16670 GHz being about nine times as high as the net flux at the low or high frequency range of (<1000 GHz or >80,000 GHz). The above phenomena can be attributed to the breakage of hydrogen bonds as the electrical interference frequency approaches to the inherent resonant frequency of hydrogen bonds. The new mechanism of regulating water flux across nanochannels revealed in this study provides an insight into the water transportation through biological water channels and has tremendous potential in the design of high-flux nanofluidic systems.

Up-scaling mineral-aqueous interfacial processes that govern isotope and trace element partitioning during calcite growth

NASA Astrophysics Data System (ADS)

Lammers, L. N.

2014-12-01

The dependence of the isotopic and trace element composition of calcium carbonate minerals on growth conditions including temperature, pH, and salinity is widely used to infer paleoclimate conditions. These inferences rely heavily on phenomenological observations of biogenic and inorganic precipitation both in and ex situ, where only limited variability in solution conditions can be explored. Ionic fluxes between the mineral surface and aqueous growth solution govern the net uptake of both stoichiometric and trace species during calcification, so developing a mechanistic understanding of the reactions governing these fluxes is critical to refine existing proxies and to develop new ones. The micro-scale mechanisms of calcite precipitation from aqueous solution have been extensively studied, and net ionic uptake post-nucleation is known to occur primarily at monomolecular kink sites along step edges at the mineral surface. In this talk, I will present a theoretical framework that uses the quasi-elementary ion attachment and detachment reactions governing ion uptake at kink sites to simultaneously model bulk mineral growth kinetics and tracer partitioning during calcite precipitation. Several distinct processes occur during ion uptake at kink sites that can influence the distribution of trace species, directly impacting the composition of various carbonate paleoproxies including δ44Ca, δ18O, Sr/Ca and Mg/Ca. The distribution of these trace species will be shown to depend on (1) the relative rates of ion desolvation during attachment to kink sites, (2) the relative rates of bond breaking during detachment from kink sites, and (3) the equilibrium partitioning of trace aqueous species. This model accounts for the impact of solution conditions on net ion fluxes and surface speciation, which in turn controls the population of kink sites available for direct ion exchange with the aqueous phase. The impacts of solution variables including pH, temperature and salinity can be treated independently, which unlike traditional partitioning studies allows the impacts of these parameters to be deconvolved. The type of theoretical framework discussed here can be readily extended to explicitly account for each of the major solution composition variables that are implicated in paleoproxy composition.

Annual sediment flux estimates in a tidal strait using surrogate measurements

USGS Publications Warehouse

Ganju, N.K.; Schoellhamer, D.H.

2006-01-01

Annual suspended-sediment flux estimates through Carquinez Strait (the seaward boundary of Suisun Bay, California) are provided based on surrogate measurements for advective, dispersive, and Stokes drift flux. The surrogates are landward watershed discharge, suspended-sediment concentration at one location in the Strait, and the longitudinal salinity gradient. The first two surrogates substitute for tidally averaged discharge and velocity-weighted suspended-sediment concentration in the Strait, thereby providing advective flux estimates, while Stokes drift is estimated with suspended-sediment concentration alone. Dispersive flux is estimated using the product of longitudinal salinity gradient and the root-mean-square value of velocity-weighted suspended-sediment concentration as an added surrogate variable. Cross-sectional measurements validated the use of surrogates during the monitoring period. During high freshwater flow advective and dispersive flux were in the seaward direction, while landward dispersive flux dominated and advective flux approached zero during low freshwater flow. Stokes drift flux was consistently in the landward direction. Wetter than average years led to net export from Suisun Bay, while dry years led to net sediment import. Relatively low watershed sediment fluxes to Suisun Bay contribute to net export during the wet season, while gravitational circulation in Carquinez Strait and higher suspended-sediment concentrations in San Pablo Bay (seaward end of Carquinez Strait) are responsible for the net import of sediment during the dry season. Annual predictions of suspended-sediment fluxes, using these methods, will allow for a sediment budget for Suisun Bay, which has implications for marsh restoration and nutrient/contaminant transport. These methods also provide a general framework for estimating sediment fluxes in estuarine environments, where temporal and spatial variability of transport are large. ?? 2006 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seco, Roger; Karl, Thomas; Guenther, Alex B.

Considerable amounts and varieties of biogenic volatile organic compounds (BVOCs) are exchanged between vegeta-tion and the surrounding air. These BVOCs play key ecological and atmospheric roles that must be adequately repre-sented for accurately modeling the coupled biosphere–atmosphere–climate earth system. One key uncertainty in existing models is the response of BVOC fluxes to an important global change process: drought. We describe the diur-nal and seasonal variation in isoprene, monoterpene, and methanol fluxes from a temperate forest ecosystem before, during, and after an extreme 2012 drought event in the Ozark region of the central USA. BVOC fluxes were domi-nated by isoprene, whichmore » attained high emission rates of up to 35.4 mg m -2h -1 at midday. Methanol fluxes were characterized by net deposition in the morning, changing to a net emission flux through the rest of the daylight hours. Net flux of CO 2 reached its seasonal maximum approximately a month earlier than isoprenoid fluxes, which high-lights the differential response of photosynthesis and isoprenoid emissions to progressing drought conditions. Never-theless, both processes were strongly suppressed under extreme drought, although isoprene fluxes remained relatively high compared to reported fluxes from other ecosystems. Methanol exchange was less affected by drought throughout the season, conflrming the complex processes driving biogenic methanol fluxes. The fraction of daytime (7–17 h) assimilated carbon released back to the atmosphere combining the three BVOCs measured was 2% of gross primary productivity (GPP) and 4.9% of net ecosystem exchange (NEE) on average for our whole measurement cam-paign, while exceeding 5% of GPP and 10% of NEE just before the strongest drought phase. The MEGANv2.1 model correctly predicted diurnal variations in fluxes driven mainly by light and temperature, although further research is needed to address model BVOC fluxes during drought events.« less

Analysis of uncertainties in GOSAT-inferred regional CO2 fluxes

NASA Astrophysics Data System (ADS)

Ishizawa, M.; Shirai, T.; Maksyutov, S. S.; Yoshida, Y.; Morino, I.; Inoue, M.; Nakatsuru, T.; Uchino, O.; Mabuchi, K.

2016-12-01

Satellite-based CO2 measurements have potential for improving our understanding global carbon cycle because of more spatiotemporal coverage than those from ground-based observations. Since the Greenhouse gases Observing Satellite (GOSAT) was launched in January 2009, it has been measuring the column-average dry air-mole function of CO2 (XCO2) from the space. To utilize the GOSAT XCO2 for better CO2 flux estimates, several challenges should be overcome. Systematic errors (biases) in XCO2 retrievals are a major factor which leads to large differences among inverted CO2 fluxes. Temporally variable data coverage and density are also taken into account when interpreting the estimated surface fluxes. In this study, we employ an atmospheric inverse model to investigate the impacts of retrievals biases and temporally varying global distribution of GOSAT XCO2 on surface CO2 flux estimates. Inversions are performed for 2009-2013, with several subsets of the 5-year record of GOSAT XCO2 (v2.21) and its bias-corrected XCO2. GOSAT XCO2 data consist of three types: H-gain for vegetated lands, M-gain for bright surfaces (desert areas), and sun-glint for ocean surface. The results show that the global spatial distributions of estimated CO2 fluxes depend on the subset of XCO2 used. M-gain XCO2 results in unrealistically high CO2 emissions in and around the Middle East, including the neighboring ocean regions. On the other hand, M-gain XCO2 causes compensating unrealistic uptakes far beyond M-gain regions in low latitudes, also partially contributing on the summer uptake in Europe. The joint inversions with both surface measurements and GOSAT XCO2 data obtain larger flux gradient between the northern extra-tropics and the tropics than the inversion with surface measurements only for the first 2 years. Recently, these North-South gradients seem to be gradually reducing as the tropics become a weaker source or turn into a sink, while the net emission strength in East Asia is increasing. The 5-year XCO2 data allows us detailed analysis of uncertainties in GOSAT-inferred fluxes and assessment of GOSAT XCO2 biases.

Temporal variation of VOC fluxes measured with PTR-TOF above a boreal forest

NASA Astrophysics Data System (ADS)

Schallhart, Simon; Rantala, Pekka; Kajos, Maija K.; Aalto, Juho; Mammarella, Ivan; Ruuskanen, Taina M.; Kulmala, Markku

2018-01-01

Between April and June 2013 fluxes of volatile organic compounds (VOCs) were measured in a Scots pine and Norway spruce forest using the eddy covariance (EC) method with a proton transfer reaction time-of-flight (PTR-TOF) mass spectrometer. The observations were performed above a boreal forest at the SMEAR II site in southern Finland.We found a total of 25 different compounds with exchange and investigated their seasonal variations from spring to summer. The majority of the net VOC flux was comprised of methanol, monoterpenes, acetone and butene + butanol. The butene + butanol emissions were concluded to not originate from the forest and, therefore, be anthropogenic. The VOC exchange followed a seasonal trend and the emissions increased from spring to summer. Only three compounds were emitted during the snowmelt while in summer emissions of some 19 VOCs were observed. During the measurement period in April, the emissions were dominated by butene + butanol, while during the start of the growing season and in summer, methanol was the most emitted compound. The main source of methanol was likely the growth of new biomass. During a 21-day period in June, the net VOC flux was 2.1 nmol m-2 s-1. This is on the lower end of PTR-TOF flux measurements from other ecosystems, which range from 2 to 10 nmol m-2 s-1. The EC flux results were compared with surface layer profile measurements, using a proton transfer reaction quadrupole mass spectrometer, which is permanently installed at the SMEAR II site. For the major compounds, the fluxes measured with the two different methods agreed well.

Turbulent flow and scalar transport in a large wind farm

NASA Astrophysics Data System (ADS)

Porte-Agel, F.; Markfort, C. D.; Zhang, W.

2012-12-01

Wind energy is one of the fastest growing sources of renewable energy world-wide, and it is expected that many more large-scale wind farms will be built and cover a significant portion of land and ocean surfaces. By extracting kinetic energy from the atmospheric boundary layer and converting it to electricity, wind farms may affect the transport of momentum, heat, moisture and trace gases (e.g. CO_2) between the atmosphere and the land surface locally and globally. Understanding wind farm-atmosphere interaction is complicated by the effects of turbine array configuration, wind farm size, land-surface characteristics, and atmospheric thermal stability. A wind farm of finite length may be modeled as an added roughness or as a canopy in large-scale weather and climate models. However, it is not clear which analogy is physically more appropriate. Also, surface scalar flux is affected by wind farms and needs to be properly parameterized in meso-scale and/or high-resolution numerical models. Experiments involving model wind farms, with perfectly aligned and staggered configurations, having the same turbine distribution density, were conducted in a thermally-controlled boundary-layer wind tunnel. A neutrally stratified turbulent boundary layer was developed with a surface heat source. Measurements of the turbulent flow and fluxes over and through the wind farm were made using a custom x-wire/cold-wire anemometer; and surface scalar flux was measured with an array of surface-mounted heat flux sensors far within the quasi-developed region of the wind-farm. The turbulence statistics exhibit similar properties to those of canopy-type flows, but retain some characteristics of surface-layer flows in a limited region above the wind farms as well. The flow equilibrates faster and the overall momentum absorption is higher for the staggered compared to the aligned farm, which is consistent with canopy scaling and leads to a larger effective roughness. Although the overall surface heat flux change produced by the wind farms is found to be small, with a net reduction of 4% for the staggered wind farm and nearly zero change for the aligned wind farm, the highly heterogeneous spatial distribution of the surface heat flux, dependent on wind farm layout, is significant. This comprehensive first wind-tunnel dataset on turbulent flow and scalar transport in wind farms will be further used to develop and validate new parameterizations of surface fluxes in numerical models.

Ecosystem-scale VOC fluxes during an extreme drought in a ...

EPA Pesticide Factsheets

Considerable amounts and varieties of biogenic volatile organic compounds (BVOCs) are exchanged between vegetation and the surrounding air. These BVOCs play key ecological and atmospheric roles that must be adequately represented for accurately modeling the coupled biosphere-atmosphere-climate Earth system. One key uncertainty in existing models is the response of BVOC fluxes to an important global change process: drought. We describe the diurnal and seasonal variation in isoprene, monoterpene and methanol fluxes from a temperate forest ecosystem before, during, and after an extreme 2012 drought event in the Ozark region of the central USA. BVOC fluxes were dominated by isoprene, which attained high emission rates of up to 35.4 mg m-2 h-1 at midday. Methanol fluxes were characterized by net deposition in the morning, changing to a net emission flux through the rest of the daylight hours. Net flux of CO2 reached its seasonal maximum approximately a month earlier than isoprenoid fluxes, which highlights the differential response of photosynthesis and isoprenoid emissions to progressing drought conditions. Nevertheless, both processes were strongly suppressed under extreme drought, although isoprene fluxes remained relatively high compared to reported fluxes from other ecosystems. Methanol exchange was less affected by drought throughout the season, confirming the complex processes driving biogenic methanol fluxes. The fraction of daytime (7-17 h) assimilated carbo

Galileo Net Flux Radiometer Report 1997

NASA Technical Reports Server (NTRS)

Tomasko, Martin G.

1997-01-01

On 7 December 1995, the Galileo probe entered Jupiter's atmosphere. The Net Flux Radiometer (NFR) on board the probe, measured upward and downward fluxes in the visible and infrared. At the University of Arizona, we have analyzed the data from the two visible-light channels, as well as the solar contributions to the thermal channels. The results are being prepared for submission to JGR in early September.

An ecosystem-scale perspective of the net land methanol flux. Synthesis of micrometeorological flux measurements

DOE PAGES

Wohlfahrt, G.; Amelynck, C.; Ammann, C.; ...

2015-07-09

Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants as the major source and the reaction with OH as the major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates, reflecting uncertainties in the approaches used to model and the empirical data used to separately constrain these terms. Here we compiled micrometeorological methanol flux data from eight different study sites and reviewed the corresponding literature in order to provide a first cross-site synthesis ofmore » the terrestrial ecosystem-scale methanol exchange and present an independent data-driven view of the land–atmosphere methanol exchange. Our study shows that the controls of plant growth on production, and thus the methanol emission magnitude, as well as stomatal conductance on the hourly methanol emission variability, established at the leaf level, hold across sites at the ecosystem level. Unequivocal evidence for bi-directional methanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the formation of surface wetness. Methanol may adsorb to or dissolve in this surface water and eventually be chemically or biologically removed from it. Management activities in agriculture and forestry are shown to increase local methanol emission by orders of magnitude; however, they are neglected at present in global budgets. While contemporary net land methanol budgets are overall consistent with the grand mean of the micrometeorological methanol flux measurements, we caution that the present approach of simulating methanol emission and deposition separately is prone to opposing systematic errors and does not allow for full advantage to be taken of the rich information content of micrometeorological flux measurements.« less

Controlling factors of evaporation and CO2 flux over an open water lake in southeastern margin of Tibetan Plateau

NASA Astrophysics Data System (ADS)

Du, Q.; Liu, H.; Liu, Y.; Wang, L.; Xu, L.

2017-12-01

Erhai lake is located in the southeastern margin of Tibetan Plateau. Based on the 4 years measurement over Erhai lake with eddy covariance technique (EC) from 2012 to 2015, the diurnal and seasonal variations of latent and sensible heat and CO2 fluxes, and their controlling factors over different time scales were analyzed. The diurnal average LE ranged from 31 to 171 Wm-2, while Hs ranged from -31 to 21 Wm-2. Bowen ratio was larger during January and May and smaller during June and October. The lake continued storing heat during January and June, and releasing heat since July. The diurnal average CO2 fluxes during nighttime were higher than the daytime, and carbon uptake was almost observed during the midday time of the day for the whole study period. The annual carbon budget fluctuated from 117.5 to 161.7 g C m-2 a-1, while annual total evaporation (ET) from 1120.8 to 1228.5 mm for the four-years period. The Erhai Lake behaved as a net carbon source over the whole period but carbon uptake was observed during the middle time of each year. The difference between water surface and air temperature (DeltaT) and the product of DeltaT and wind speed were the main controlling factors for Hs from halfhourly to monthly scale. There was significant relationship between wind speed, the product of wind speed and vapor pressure deficit (VPD) and LE on halfhourly and daily scales. The total cloud amount and net radiation (Rn) had a large effect on monthly variation of LE. Photosynthetic active radiation (PAR) and wind speed was mainly responsible for the variation of halfhourly and daily CO2 fluxes, respectively. The total cloud amount was the most important factors controlling for annual total ET. The annual rainfall, water surface temperature was observed to be negatively related with annual CO2 fluxes.

An ecosystem-scale perspective of the net land methanol flux: synthesis of micrometeorological flux measurements

PubMed Central

Wohlfahrt, G.; Amelynck, C.; Ammann, C.; Arneth, A.; Bamberger, I.; Goldstein, A. H.; Gu, L.; Guenther, A.; Hansel, A.; Heinesch, B.; Holst, T.; Hörtnagl, L.; Karl, T.; Laffineur, Q.; Neftel, A.; McKinney, K.; Munger, J. W.; Pallardy, S. G.; Schade, G. W.; Seco, R.; Schoon, N.

2015-01-01

Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants as the major source and the reaction with OH as the major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates reflecting uncertainties in the approaches used to model, and the empirical data used to separately constrain these terms. Here we compiled micrometeorological methanol flux data from eight different study sites and reviewed the corresponding literature in order to provide a first cross-site synthesis of the terrestrial ecosystem-scale methanol exchange and present an independent data-driven view of the land–atmosphere methanol exchange. Our study shows that the controls of plant growth on the production, and thus the methanol emission magnitude, and stomatal conductance on the hourly methanol emission variability, established at the leaf level, hold across sites at the ecosystem-level. Unequivocal evidence for bi-directional methanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the formation of surface wetness. Methanol may adsorb to or dissolve in this surface water and eventually be chemically or biologically removed from it. Management activities in agriculture and forestry are shown to increase local methanol emission by orders of magnitude; they are however neglected at present in global budgets. While contemporary net land methanol budgets are overall consistent with the grand mean of the micrometeorological methanol flux measurements, we caution that the present approach of simulating methanol emission and deposition separately is prone to opposing systematic errors and does not allow taking full advantage of the rich information content of micrometeorological flux measurements. PMID:25983744

Climate-driven uncertainties in modeling terrestrial gross primary production: a site level to global-scale analysis.

PubMed

Barman, Rahul; Jain, Atul K; Liang, Miaoling

2014-05-01

We used a land surface model to quantify the causes and extents of biases in terrestrial gross primary production (GPP) due to the use of meteorological reanalysis datasets. We first calibrated the model using meteorology and eddy covariance data from 25 flux tower sites ranging from the tropics to the northern high latitudes and subsequently repeated the site simulations using two reanalysis datasets: NCEP/NCAR and CRUNCEP. The results show that at most sites, the reanalysis-driven GPP bias was significantly positive with respect to the observed meteorology-driven simulations. Notably, the absolute GPP bias was highest at the tropical evergreen tree sites, averaging up to ca. 0.45 kg C m(-2)  yr(-1) across sites (ca. 15% of site level GPP). At the northern mid-/high-latitude broadleaf deciduous and the needleleaf evergreen tree sites, the corresponding annual GPP biases were up to 20%. For the nontree sites, average annual biases of up to ca. 20-30% were simulated within savanna, grassland, and shrubland vegetation types. At the tree sites, the biases in short-wave radiation and humidity strongly influenced the GPP biases, while the nontree sites were more affected by biases in factors controlling water stress (precipitation, humidity, and air temperature). In this study, we also discuss the influence of seasonal patterns of meteorological biases on GPP. Finally, using model simulations for the global land surface, we discuss the potential impacts of site-level reanalysis-driven biases on the global estimates of GPP. In a broader context, our results can have important consequences on other terrestrial ecosystem fluxes (e.g., net primary production, net ecosystem production, energy/water fluxes) and reservoirs (e.g., soil carbon stocks). In a complementary study (Barman et al., ), we extend the present analysis for latent and sensible heat fluxes, thus consistently integrating the analysis of climate-driven uncertainties in carbon, energy, and water fluxes using a single modeling framework. © 2013 John Wiley & Sons Ltd.

Impact of anthropogenic atmospheric nitrogen and sulfur deposition on ocean acidification and the inorganic carbon system.

PubMed

Doney, Scott C; Mahowald, Natalie; Lima, Ivan; Feely, Richard A; Mackenzie, Fred T; Lamarque, Jean-Francois; Rasch, Phil J

2007-09-11

Fossil fuel combustion and agriculture result in atmospheric deposition of 0.8 Tmol/yr reactive sulfur and 2.7 Tmol/yr nitrogen to the coastal and open ocean near major source regions in North America, Europe, and South and East Asia. Atmospheric inputs of dissociation products of strong acids (HNO(3) and H2SO(4)) and bases (NH(3)) alter surface seawater alkalinity, pH, and inorganic carbon storage. We quantify the biogeochemical impacts by using atmosphere and ocean models. The direct acid/base flux to the ocean is predominately acidic (reducing total alkalinity) in the temperate Northern Hemisphere and alkaline in the tropics because of ammonia inputs. However, because most of the excess ammonia is nitrified to nitrate (NO(3)(-)) in the upper ocean, the effective net atmospheric input is acidic almost everywhere. The decrease in surface alkalinity drives a net air-sea efflux of CO(2), reducing surface dissolved inorganic carbon (DIC); the alkalinity and DIC changes mostly offset each other, and the decline in surface pH is small. Additional impacts arise from nitrogen fertilization, leading to elevated primary production and biological DIC drawdown that reverses in some places the sign of the surface pH and air-sea CO(2) flux perturbations. On a global scale, the alterations in surface water chemistry from anthropogenic nitrogen and sulfur deposition are a few percent of the acidification and DIC increases due to the oceanic uptake of anthropogenic CO(2). However, the impacts are more substantial in coastal waters, where the ecosystem responses to ocean acidification could have the most severe implications for mankind.

Global radiative adjustment after a collapse of the Atlantic meridional overturning circulation

NASA Astrophysics Data System (ADS)

Drijfhout, Sybren S.

2015-10-01

The transient climate response to a collapse of the Atlantic meridional overturning circulation (AMOC) is analysed from the difference between two ensembles of climate model simulations with ECHAM5/MPI-OM, one with hosing and the other without hosing. The primary effect of the collapse is to redistribute heat over the two hemispheres. However, Northern Hemisphere sea ice increase in response to the AMOC collapse induces a hemisphere-wide cooling, amplified by atmospheric feedbacks, in particular water vapour. The Southern Hemisphere warming is governed by slower processes. After 25 years the global cooling peaks. Thereafter, the response is characterised by a gradual readjustment of global mean temperature. During the AMOC collapse a downward radiation anomaly arises at the top of the atmosphere (TOA), heating the earth's surface. The net downward radiation anomaly at TOA arises from reduced longwave emission by the atmosphere, overcompensating the increased net upward anomalies in shortwave and longwave radiation at the surface. This radiation anomaly is associated with net ocean heat uptake: cooling of the overlying atmosphere results from reduced ocean heat release through the increase of sea-ice cover in the North Atlantic. The change in energy flow arises from the reduction in latent and sensible heat flux, which dominate the surface radiation budget. Similar experiments with a climate model of intermediate complexity reveal a stronger shortwave response that acts to reduce the net downward radiation anomaly at TOA. The net shortwave and longwave radiation anomalies at TOA always decrease during the first 100 years after the AMOC collapse, but in the intermediate complexity model this is associated with a sign change after 90 years when the net radiation anomaly at TOA becomes upward, accompanied by net ocean heat loss. After several hundred years the longwave and shortwave anomalies increase again, while the net residual at TOA remains small. This radiative adjustment is associated with the transition to a colder climate.

Measuring and modeling near surface reflected and emitted radiation fluxes at the FIFE site

NASA Technical Reports Server (NTRS)

Blad, Blaine L.; Norman, John M.; Walter-Shea, Elizabeth; Starks, Patrick; Vining, Roel; Hays, Cynthia

1988-01-01

Research was conducted during the four Intensive Field Campaigns (IFC) of the FIFE project in 1987. The research was done on a tall grass prairie with specific measurement sites on and near the Konza Prairie in Kansas. Measurements were made to help meet the following objectives: determination of the variability in reflected and emitted radiation fluxes in selected spectral wavebands as a function of topography and vegetative community; development of techniques to account for slope and sun angle effects on the radiation fluxes; estimation of shortwave albedo and net radiation fluxes using the reflected and emitted spectral measurements described; estimation of leaf and canopy spectral properties from calculated normalized differences coupled with off-nadir measurements using inversion techniques; estimation of plant water status at several locations with indices utilizing plant temperature and other environmental parameters; and determination of relationships between estimated plant water status and measured soil water content. Results are discussed.

Growth and etching characteristics of (001) β-Ga2O3 by plasma-assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Oshima, Yuichi; Ahmadi, Elaheh; Kaun, Stephen; Wu, Feng; Speck, James S.

2018-01-01

We investigated the homoepitaxial growth and etching characteristics of (001) β-Ga2O3 by plasma-assisted molecular beam epitaxy. The growth rate of β-Ga2O3 increased with increasing Ga-flux, reaching a clear plateau of 56 nm h-1, and then decreased at higher Ga-flux. The growth rate decreased from 56 to 42 nm h-1 when the substrate temperature was increased from 750 °C to 800 °C. The growth rate was negative (net etching) when only Ga-flux was supplied. The etching rate proportionally increased with increasing the Ga-flux, reaching 84 nm h-1. The etching was enhanced at higher temperatures. It was found that Ga-etching of (001) β-Ga2O3 substrates prior to the homoepitaxial growth markedly improved the surface roughness of the film.

Small spatial variability in methane emission measured from a wet patterned boreal bog

NASA Astrophysics Data System (ADS)

Korrensalo, Aino; Männistö, Elisa; Alekseychik, Pavel; Mammarella, Ivan; Rinne, Janne; Vesala, Timo; Tuittila, Eeva-Stiina

2018-03-01

We measured methane fluxes of a patterned bog situated in Siikaneva in southern Finland from six different plant community types in three growing seasons (2012-2014) using the static chamber method with chamber exposure of 35 min. A mixed-effects model was applied to quantify the effect of the controlling factors on the methane flux. The plant community types differed from each other in their water level, species composition, total leaf area (LAITOT) and leaf area of aerenchymatous plant species (LAIAER). Methane emissions ranged from -309 to 1254 mg m-2 d-1. Although methane fluxes increased with increasing peat temperature, LAITOT and LAIAER, they had no correlation with water table or with plant community type. The only exception was higher fluxes from hummocks and high lawns than from high hummocks and bare peat surfaces in 2013 and from bare peat surfaces than from high hummocks in 2014. Chamber fluxes upscaled to ecosystem level for the peak season were of the same magnitude as the fluxes measured with the eddy covariance (EC) technique. In 2012 and in August 2014 there was a good agreement between the two methods; in 2013 and in July 2014, the chamber fluxes were higher than the EC fluxes. Net fluxes to soil, indicating higher methane oxidation than production, were detected every year and in all community types. Our results underline the importance of both LAIAER and LAITOT in controlling methane fluxes and indicate the need for automatized chambers to reliably capture localized events to support the more robust EC method.

Seasonal variations in methane fluxes in response to summer warming and leaf litter addition in a subarctic heath ecosystem

NASA Astrophysics Data System (ADS)

Pedersen, Emily Pickering; Elberling, Bo; Michelsen, Anders

2017-08-01

Methane (CH4) is a powerful greenhouse gas controlled by both biotic and abiotic processes. Few studies have investigated CH4 fluxes in subarctic heath ecosystems, and climate change-induced shifts in CH4 flux and the overall carbon budget are therefore largely unknown. Hence, there is an urgent need for long-term in situ experiments allowing for the study of ecosystem processes over time scales relevant to environmental change. Here we present in situ CH4 and CO2 flux measurements from a wet heath ecosystem in northern Sweden subjected to 16 years of manipulations, including summer warming with open-top chambers, birch leaf litter addition, and the combination thereof. Throughout the snow-free season, the ecosystem was a net sink of CH4 and CO2 (CH4 -0.27 mg C m-2 d-1; net ecosystem exchange -1827 mg C m-2 d-1), with highest CH4 uptake rates (-0.70 mg C m-2 d-1) during fall. Warming enhanced net CO2 flux, while net CH4 flux was governed by soil moisture. Litter addition and the combination with warming significantly increased CH4 uptake rates, explained by a pronounced soil drying effect of up to 32% relative to ambient conditions. Both warming and litter addition also increased the seasonal average concentration of dissolved organic carbon in the soil. The site was a carbon sink with a net uptake of 60 g C m-2 over the snow-free season. However, warming reduced net carbon uptake by 77%, suggesting that this ecosystem type might shift from snow-free season sink to source with increasing summer temperatures.

The Energy Budget of the Polar Atmosphere in MERRA

NASA Technical Reports Server (NTRS)

Cullather, Richard I.; Bosilovich, Michael G.

2010-01-01

Components of the atmospheric energy budget from the Modern Era Retrospective-analysis for Research and Applications (MERRA) are evaluated in polar regions for the period 1979-2005 and compared with previous estimates, in situ observations, and contemporary reanalyses. Closure of the energy budget is reflected by the analysis increments term, which results from virtual enthalpy and latent heating contributions and averages -11 W/sq m over the north polar cap and -22 W/sq m over the south polar cap. Total energy tendency and energy convergence terms from MERRA agree closely with previous study for northern high latitudes but convergence exceeds previous estimates for the south polar cap by 46 percent. Discrepancies with the Southern Hemisphere transport are largest in autumn and may be related to differences in topography with earlier reanalyses. For the Arctic, differences between MERRA and other sources in TOA and surface radiative fluxes maximize in May. These differences are concurrent with the largest discrepancies between MERRA parameterized and observed surface albedo. For May, in situ observations of the upwelling shortwave flux in the Arctic are 80 W/sq m larger than MERRA, while the MERRA downwelling longwave flux is underestimated by 12 W/sq m throughout the year. Over grounded ice sheets, the annual mean net surface energy flux in MERRA is erroneously non-zero. Contemporary reanalyses from the Climate Forecast Center (CFSR) and the Interim Re-Analyses of the European Centre for Medium Range Weather Forecasts (ERA-I) are found to have better surface parameterizations, however these collections are also found to have significant discrepancies with observed surface and TOA energy fluxes. Discrepancies among available reanalyses underscore the challenge of reproducing credible estimates of the atmospheric energy budget in polar regions.

Evaluation of NASA's Carbon Monitoring System (CMS) Flux Pilot: Terrestrial CO2 Fluxes

NASA Astrophysics Data System (ADS)

Fisher, J. B.; Polhamus, A.; Bowman, K. W.; Collatz, G. J.; Potter, C. S.; Lee, M.; Liu, J.; Jung, M.; Reichstein, M.

2011-12-01

NASA's Carbon Monitoring System (CMS) flux pilot project combines NASA's Earth System models in land, ocean and atmosphere to track surface CO2 fluxes. The system is constrained by atmospheric measurements of XCO2 from the Japanese GOSAT satellite, giving a "big picture" view of total CO2 in Earth's atmosphere. Combining two land models (CASA-Ames and CASA-GFED), two ocean models (ECCO2 and NOBM) and two atmospheric chemistry and inversion models (GEOS-5 and GEOS-Chem), the system brings together the stand-alone component models of the Earth System, all of which are run diagnostically constrained by a multitude of other remotely sensed data. Here, we evaluate the biospheric land surface CO2 fluxes (i.e., net ecosystem exchange, NEE) as estimated from the atmospheric flux inversion. We compare against the prior bottom-up estimates (e.g., the CASA models) as well. Our evaluation dataset is the independently derived global wall-to-wall MPI-BGC product, which uses a machine learning algorithm and model tree ensemble to "scale-up" a network of in situ CO2 flux measurements from 253 globally-distributed sites in the FLUXNET network. The measurements are based on the eddy covariance method, which uses observations of co-varying fluxes of CO2 (and water and energy) from instruments on towers extending above ecosystem canopies; the towers integrate fluxes over large spatial areas (~1 km2). We present global maps of CO2 fluxes and differences between products, summaries of fluxes by TRANSCOM region, country, latitude, and biome type, and assess the time series, including timing of minimum and maximum fluxes. This evaluation shows both where the CMS is performing well, and where improvements should be directed in further work.

Assessing the influence of historic net and gross land changes on the carbon fluxes of Europe.

PubMed

Fuchs, Richard; Schulp, Catharina J E; Hengeveld, Geerten M; Verburg, Peter H; Clevers, Jan G P W; Schelhaas, Mart-Jan; Herold, Martin

2016-07-01

Legacy effects of land cover/use on carbon fluxes require considering both present and past land cover/use change dynamics. To assess past land use dynamics, model-based reconstructions of historic land cover/use are needed. Most historic reconstructions consider only the net area difference between two time steps (net changes) instead of accounting for all area gains and losses (gross changes). Studies about the impact of gross and net land change accounting methods on the carbon balance are still lacking. In this study, we assessed historic changes in carbon in soils for five land cover/use types and of carbon in above-ground biomass of forests. The assessment focused on Europe for the period 1950 to 2010 with decadal time steps at 1-km spatial resolution using a bookkeeping approach. To assess the implications of gross land change data, we also used net land changes for comparison. Main contributors to carbon sequestration between 1950 and 2010 were afforestation and cropland abandonment leading to 14.6 PgC sequestered carbon (of which 7.6 PgC was in forest biomass). Sequestration was highest for old-growth forest areas. A sequestration dip was reached during the 1970s due to changes in forest management practices. Main contributors to carbon emissions were deforestation (1.7 PgC) and stable cropland areas on peaty soils (0.8 PgC). In total, net fluxes summed up to 203 TgC yr(-1) (98 TgC yr(-1) in forest biomass and 105 TgC yr(-1) in soils). For areas that were subject to land changes in both reconstructions (35% of total area), the differences in carbon fluxes were about 68%. Overall for Europe the difference between accounting for either gross or net land changes led to 7% difference (up to 11% per decade) in carbon fluxes with systematically higher fluxes for gross land change data. © 2015 John Wiley & Sons Ltd.

Coupled carbon-water exchange of the Amazon rain forest, II. Comparison of predicted and observed seasonal exchange of energy, CO2, isoprene and ozone at a remote site in Rondônia

NASA Astrophysics Data System (ADS)

Simon, E.; Meixner, F. X.; Rummel, U.; Ganzeveld, L.; Ammann, C.; Kesselmeier, J.

2005-10-01

A one-dimensional multi-layer scheme describing the coupled exchange of energy and CO2, the emission of isoprene and the dry deposition of ozone is applied to a rain forest canopy in southwest Amazonia. The model was constrained using mean diel cycles of micrometeorological quantities observed during two periods in the wet and dry season 1999. Calculated net fluxes and concentration profiles for both seasonal periods are compared to observations made at two nearby towers.

The modeled day- and nighttime thermal stratification of the canopy layer is consistent with observations in dense canopies. The observed and modeled net fluxes above and H2O and CO2 concentration profiles within the canopy show a good agreement. The predicted net carbon sink decreases from 2.5 t C ha-1 yr-1 for wet season conditions to 1 t C ha-1 yr-1 for dry season conditions, whereas observed and modeled midday Bowen ratio increases from 0.5 to 0.8. The evaluation results confirmed a seasonal variability of leaf physiological parameters, as already suggested in a companion study. The calculated midday canopy net flux of isoprene increased from 7.1 mg C m-2 h-1 during the wet season to 11.4 mg C m-2 h-1 during the late dry season. Applying a constant emission capacity in all canopy layers, resulted in a disagreement between observed and simulated profiles of isoprene concentrations, suggesting a smaller emission capacity of shade adapted leaves and deposition to the soil or leaf surfaces. Assuming a strong light acclimation of emission capacity, equivalent to a 66% reduction of the standard emission factor for leaves in the lower canopy, resulted in a better agreement of observed and modeled concentration profiles and a 30% reduction of the canopy net flux compared to model calculations with a constant emission factor. The mean calculated ozone flux for dry season conditions at noontime was ≍12 n mol m-2 s-1, agreeing well with observed values. The corresponding deposition velocity increased from 0.8 cm s-1 to >1.6 cm s-1 in the wet season, which can not be explained by increased stomatal uptake. Considering reasonable physiological changes in stomatal regulation, the modeled value was not larger than 1.05 cm s-1. Instead, the observed fluxes could be explained with the model by decreasing the cuticular resistance to ozone deposition from 5000 to 1000 s m-1.

Geothermal flux through palagonitized tephra, Surtsey, Iceland - The Surtsey temperature-data-relay experiment via Landsat-1

NASA Technical Reports Server (NTRS)

Friedman, J. D.; Preble, D. M.; Jakobsson, S.

1976-01-01

The net geothermal flux through palagonitized basaltic tephra rims of the Surtur I and Surtur II craters at Surtsey, Iceland, in 1972, is estimated at 780 plus or minus 325 microcal/sq cm/s, indicating a decline since 1969 when a flux of 1500 microcal/sq cm/s was estimated. Heat flux in this range characterizes the postvolcanic environment on Surtsey in which the subaerial polagonitization of basaltic tephra is associated with mass transfer of hydrothermal vapor, either of meteoric or sea-water origin, only a few years after cessation of eruptive activity. The flux estimation is the result of the Surtsey data-relay experiment via Landsat-1 which was carried out in several phases. Temperature data were transmitted for a 38-day period in November and December 1972. A near-surface vertical gradient of 69.4 C/m was obtained, suggesting a mixed mechanism of heat transfer, partitioned between conduction and convection.

Understory vegetation mediates permafrost active layer dynamics and carbon dioxide fluxes in open-canopy larch forests of northeastern Siberia.

PubMed

Loranty, Michael M; Berner, Logan T; Taber, Eric D; Kropp, Heather; Natali, Susan M; Alexander, Heather D; Davydov, Sergey P; Zimov, Nikita S

2018-01-01

Arctic ecosystems are characterized by a broad range of plant functional types that are highly heterogeneous at small (~1-2 m) spatial scales. Climatic changes can impact vegetation distribution directly, and also indirectly via impacts on disturbance regimes. Consequent changes in vegetation structure and function have implications for surface energy dynamics that may alter permafrost thermal dynamics, and are therefore of interest in the context of permafrost related climate feedbacks. In this study we examine small-scale heterogeneity in soil thermal properties and ecosystem carbon and water fluxes associated with varying understory vegetation in open-canopy larch forests in northeastern Siberia. We found that lichen mats comprise 16% of understory vegetation cover on average in open canopy larch forests, and lichen abundance was inversely related to canopy cover. Relative to adjacent areas dominated by shrubs and moss, lichen mats had 2-3 times deeper permafrost thaw depths and surface soils warmer by 1-2°C in summer and less than 1°C in autumn. Despite deeper thaw depths, ecosystem respiration did not differ across vegetation types, indicating that autotrophic respiration likely dominates areas with shrubs and moss. Summertime net ecosystem exchange of CO2 was negative (i.e. net uptake) in areas with high shrub cover, while positive (i.e. net loss) in lichen mats and areas with less shrub cover. Our results highlight relationships between vegetation and soil thermal dynamics in permafrost ecosystems, and underscore the necessity of considering both vegetation and permafrost dynamics in shaping carbon cycling in permafrost ecosystems.

Flux agreement above a Scots pine plantation

NASA Astrophysics Data System (ADS)

Gay, L. W.; Vogt, R.; Bernhofer, Ch.; Blanford, J. H.

1996-03-01

The surface energy exchange of 12m high Scots pine plantation at Hartheim, Germany, was measured with a variety of methods during a 11-day period of fine weather in mid-May 1992. Net radiation and rate of thermal storage were measured with conventional net radiometers, soil heat flux discs and temperature-based storage models. The turbulent fluxes discussed in this report were obtained with an interchanging Bowen ratio energy budget system (BREB, at 14 m), two one-propeller eddy correlation systems (OPEC systems 1 and 2 at 17m), a 1-dimensional sonic eddy correlation system (SEC system 3) at 15 m, all on one “low” tower, and a 3-dimensional sonic eddy correlation system (SEC system 22) at 22 m on the “high” tower that was about 46 m distant. All systems measured sensible and latent heat (H and LE) directly, except for OPEC systems 1 and 2 which estimated LE as a residual term in the surface energy balance. Closure of turbulent fluxes from the two SEC systems was around 80% for daytime and 30% for night, with closure of 1-dimensional SEC system 3 exceeding that of 3-dimensional SEC system 22. The night measurements of turbulent fluxes contained considerable uncertainty, especially with the BREB system where measured gradients often yielded erroneous fluxes due to problems inherent in the method (i.e., computational instability as Bowen's ratio approaches -1). Also, both eddy correlation system designs (OPEC and SEC) appeared to underestimate |H| during stable conditions at night. In addition, both sonic systems (1- and 3-dimensional) underestimated |LE| during stable conditions. The underestimate of |H| at night generated residual estimates of OPEC LE containing a “phantom dew” error that erroneously decreased daily LE totals by about 10 percent. These special night problems are circumvented here by comparing results for daytime periods only, rather than for full days. To summarize, turbulent fluxes on the low tower from OPEC system 2 and the adjacent SEC system 3 were in reasonable agreement, while the BREB system appeared to overestimate H and underestimate LE; H and LE measured by SEC system 22 on the high tower were lower than from OPEC and SEC3 on the low tower. The turbulent flux measurements tended to converge, but the data exhibit unexplained differences between days, between systems, and between locations.

Ecosystem Modeling of Biological Processes to Global Budgets

NASA Technical Reports Server (NTRS)

Christopher, Potter S.; Condon, Estelle (Technical Monitor)

2000-01-01

From an ecological perspective, the search for life on distant planets begins from several key assumptions. The first of these is that, viewed from a remote location in space, the signature of life on a distant planet will be the result of net gas exchange of organisms with their environment. On the basis of extensive biogeochemical measurements and biogenic trace gas fluxes in modem Earth environments, it is probable that certain groups of organisms both produce and consume the same trace gas(es) within a single bioprofile of Solid (porous) substrate or surface water. The net gas exchange rate with the atmosphere measured at the living surface is frequently the result of competing metabolic reactions, which may carried out by different functional groups of organisms located at dissimilar 'climatic' or chemical microsites within the same bioprofile. Biogenic gases produced at one (deep) level of a bioprofile may be consumed by another functional group of organisms located closer to the level of surface exchange with the atmosphere. A second key assumption is that the net biogenic fluxes of atmospheric gases on Earth can be used to infer relative abundance and functional composition of the major organisms on a distant planet. Examples of this principle include the presence of methanogenic microorganisms abundant today in freshwater ecosystems worldwide, which are major source of atmospheric methane and its seasonal variability in Earth's atmosphere. A third assumption is that scaling up biogenic gas fluxes from a single biological community to the planetary level requires flux measurements at the whole ecosystem level. This implies that measurements of biogenic gas exchange with the global atmosphere cannot be easily inferred from measurements of gas production rates of single organisms, which may have been isolated in some manner from the setting of their native ecosystem. Hence, the unit of biological organization used in modern Earth Science for scaling up to biosphere effects on atmospheric composition is the ecosystem level. These assumptions are the foundation for developing modern emission budgets for biogenic gases such as carbon dioxide, methane, carbon monoxide, isoprene, nitrous and nitric oxide, and ammonia. Such emission budgets commonly include information on seasonal flux patterns, typical diurnal profiles, and spatial resolution of at least one degree latitude/longitude for the globe. On the basis of these budgets, it is possible to compute 'base emission rates' for the major biogenic trace gases from both terrestrial and ocean sources, which may be useful benchmarks for defining the gas production rates of organisms, especially those from early Earth history, which are required to generate a detectable signal on a global atmosphere. This type of analysis is also the starting point for evaluation of the 'biological processes to global gas budget' extrapolation procedure described above for early Earth ecosystems.

Air-sea interaction over the Indian Ocean due to variations in the Indonesian throughflow

NASA Astrophysics Data System (ADS)

Wajsowicz, R. C.

The effects of the Indonesian throughflow on the upper thermocline circulation and surface heat flux over the Indian Ocean are presented for a 3-D ocean model forced by two different monthly wind-stress climatologies, as they show interesting differences, which could have implications for long-term variability in the Indian and Australasian monsoons. The effects are determined by contrasting a control run with a run in which the throughflow is blocked by an artificial land-bridge across the exit channels into the Indian Ocean. In the model forced by ECMWF wind stresses, there is little impact on the annual mean surface heat flux in the region surrounding the throughflow exit straits, whereas in the model forced by SSM/I-based wind stresses, a modest throughflow of less than 5 ×106 m3s-1 over the upper 300 m induces an extra 10-50 Wm-2 output. In the SSM/I-forced model, there is insignificant penetration of the throughflow into the northern Indian Ocean. However, in the ECMWF-forced model, the throughflow induces a 5-10 Wm-2 reduction in heat input into the ocean, i.e., an effective output, over the Somali Current in the annual mean. These differences are attributed to differences in the strength and direction of the Ekman transport of the ambient flow, and the vertical structure of the transport and temperature anomalies associated with the throughflow. In both models, the throughflow induces a 5-30 Wm-2 increase in net output over a broad swathe of the southern Indian Ocean, and a reduction in heat output of 10-60 Wm-2 in a large L-shaped band around Tasmania. Effective increases in throughflow-induced net output reach up to 40 (60) Wm-2 over the Agulhas Current retroflection in the ECMWF (SSM/I)-forced model. Seasonal variations in the throughflow's effect on the net surface heat flux are attributed to seasonal variations in the ambient circulation of the Indian Ocean, specifically in coastal upwelling along the south Javan, west Australian, and Somalian coasts, and in the depth of convective overturning between 40°S to 50°S, and its sensing of the mean throughflow's thermal anomaly. The seasonal anomalies plus annual mean yield maximum values for the throughflow-induced net surface heat output in boreal summer. Values may exceed 40 Wm-2 in the southern Indian Ocean interior in both models, exceed 60 Wm-2 over the Agulhas retroflection and immediate vicinity of the exit channels in the SSM/I-forced model, and reach 30 Wm-2 over the Somali jet in the ECMWF-forced model.

Horizontal convection with mechanical stirring

NASA Astrophysics Data System (ADS)

Griffiths, Ross; Stewart, Kial; Hughes, Graham

2012-11-01

The effects of turbulent mixing on convective circulation forced by a horizontal gradient of buoyancy at the surface is examined using laboratory experiments in which a salt flux is introduced at the surface, at one end of a box, and a freshwater buoyancy condition is applied over the rest of the surface. Horizontal rods are oscillated and yo-yoed continuously through the water column, providing a diffusivity that can be calibrated. The convection reaches a stationary state having zero net salt flux. We find that for small stirring rates the small but finite volume flux from the dense source is significant and a virtual source correction is required to take this into account. The density stratification and overturning volume transport are consistent with a theoretical model for high Rayleigh numbers: the transport ψ increases with diffusivity κ (ψg ~ gκ 1 / 4) . The results show that vertical mixing in the boundary layer is important, particularly in setting the density of the interior and the overturning rate. However, interior mixing is unimportant, which raises an interesting question over whether abyssal mixing rates in the ocean play any significant role in setting the abyssal ocean density or the transport in the Meridional Overturning Circulation.

Instantaneous and daily values of the surface energy balance over agricultural fields using remote sensing and a reference field in an arid environment

USGS Publications Warehouse

Kustas, William P.; Moran, M.S.; Jackson, R. D.; Gay, L.W.; Duell, L.F.W.; Kunkel, K.E.; Matthias, A.D.

1990-01-01

Remotely sensed surface temperature and reflectance in the visible and near infrared wavebands along with ancilliary meteorological data provide the capability of computing three of the four surface energy balance components (i.e., net radiation, soil heat flux, and sensible heat flux) at different spatial and temporal scales. As a result, under nonadvective conditions, this enables the estimation of the remaining term (i.e., the latent heat flux). One of the practical applications with this approach is to produce evapotranspiration (ET) maps for agricultural regions which consist of an array of fields containing different crops at varying stages of growth and soil moisture conditions. Such a situation exists in the semiarid southwest at the University of Arizona Maricopa Agricultural Center, south of Phoenix. For one day (14 June 1987), surface temperature and reflectance measurements from an aircraft 150 m above ground level (agl) were acquired over fields from zero to nearly full cover at four times between 1000 MST and 1130 MST. The diurnal pattern of the surface energy balance was measured over four fields, which included alfalfa at 60% cover, furrowed cotton at 20% and 30% cover, and partially plowed what stubble. Instantaneous and daily values of ET were estimated for a representative area around each flux site with an energy balance model that relies on a reference ET. This reference value was determined with remotely sensed data and several meteorological inputs. The reference ET was adjusted to account for the different surface conditions in the other fields using only remotely sensed variables. A comparison with the flux measurements suggests the model has difficulties with partial canopy conditions, especially related to the estimation of the sensible heat flux. The resulting errors for instantaneous ET were on the order of 100 W m-2 and for daily values of order 2 mm day-1. These findings suggest future research should involve development of methods to account for the variability of meteorological parameters brought about by changes in surface conditions and improvements in the modeling of sensible heat transfer across the surface-atmosphere interface for partial canopy conditions using remote sensing information. ?? 1990.

Statistical partitioning of a three-year time series of direct urban net CO2 flux measurements into biogenic and anthropogenic components

NASA Astrophysics Data System (ADS)

Menzer, Olaf; McFadden, Joseph P.

2017-12-01

Eddy covariance flux measurements are increasingly used to quantify the net carbon dioxide exchange (FC) in urban areas. FC represents the sum of anthropogenic emissions, biogenic carbon release from plant and soil respiration, and carbon uptake by plant photosynthesis. When FC is measured in natural ecosystems, partitioning into respiration and photosynthesis is a well-established procedure. In contrast, few studies have partitioned FC at urban flux tower sites due to the difficulty of accounting for the temporal and spatial variability of the multiple sources and sinks. Here, we partitioned a three-year time series of flux measurements from a suburban neighborhood of Minneapolis-Saint Paul, Minnesota, USA. We segregated FC into one subset that captured fluxes from a residential neighborhood and into another subset that covered a golf course. For both land use types we modeled anthropogenic flux components based on winter data and extrapolated them to the growing season, to estimate gross primary production (GPP) and ecosystem respiration (Reco) at half-hourly, daily, monthly and annual scales. During the growing season, GPP had the largest magnitude (up to - 9.83 g C m-2 d-1) of any component CO2 flux, biogenic or anthropogenic, and both GPP and Reco were more dynamic seasonally than anthropogenic fluxes. Owing to the balancing of Reco against GPP, and the limitations of the growing season in a cold temperate climate zone, the net biogenic flux was only 1.5%-4.5% of the anthropogenic flux in the dominant residential land use type, and between 25%-31% of the anthropogenic flux in highly managed greenspace. Still, the vegetation sink at our site was stronger than net anthropogenic emissions on 16-20 days over the residential area and on 66-91 days over the recreational area. The reported carbon flux sums and dynamics are a critical step toward developing models of urban CO2 fluxes within and across cities that differ in vegetation cover.

Ecosystem-scale volatile organic compound fluxes during an extreme drought in a broadleaf temperate forest of the Missouri Ozarks (central USA)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seco, Roger; Karl, Thomas; Guenther, Alex

Considerable amounts and varieties of biogenic volatile organic compounds (BVOCs) are exchanged between vegetation and the surrounding air. These BVOCs play key ecological and atmospheric roles that must be adequately represented for accurately modeling the coupled biosphere–atmosphere–climate earth system. One key uncertainty in existing models is the response of BVOC fluxes to an important global change process: drought. Here, we describe the diurnal and seasonal variation in isoprene, monoterpene, and methanol fluxes from a temperate forest ecosystem before, during, and after an extreme 2012 drought event in the Ozark region of the central USA. BVOC fluxes were dominated by isoprene,more » which attained high emission rates of up to 35.4 mg m 2 h 1 at midday. Methanol fluxes were characterized by net deposition in the morning, changing to a net emission flux through the rest of the daylight hours. Net flux of CO 2 reached its seasonal maximum approximately a month earlier than isoprenoid fluxes, which highlights the differential response of photosynthesis and isoprenoid emissions to progressing drought conditions. Nevertheless, both processes were strongly suppressed under extreme drought, although isoprene fluxes remained relatively high compared to reported fluxes from other ecosystems. Methanol exchange was less affected by drought throughout the season, confirming the complex processes driving biogenic methanol fluxes. The fraction of daytime (7–17 h) assimilated carbon released back to the atmosphere combining the three BVOCs measured was 2% of gross primary productivity (GPP) and 4.9% of net ecosystem exchange (NEE) on average for our whole measurement campaign, while exceeding 5% of GPP and 10% of NEE just before the strongest drought phase. In conclusion, the MEGANv2.1 model correctly predicted diurnal variations in fluxes driven mainly by light and temperature, although further research is needed to address model BVOC fluxes during drought events.« less

Ecosystem-scale volatile organic compound fluxes during an extreme drought in a broadleaf temperate forest of the Missouri Ozarks (central USA).

PubMed

Seco, Roger; Karl, Thomas; Guenther, Alex; Hosman, Kevin P; Pallardy, Stephen G; Gu, Lianhong; Geron, Chris; Harley, Peter; Kim, Saewung

2015-10-01

Considerable amounts and varieties of biogenic volatile organic compounds (BVOCs) are exchanged between vegetation and the surrounding air. These BVOCs play key ecological and atmospheric roles that must be adequately represented for accurately modeling the coupled biosphere-atmosphere-climate earth system. One key uncertainty in existing models is the response of BVOC fluxes to an important global change process: drought. We describe the diurnal and seasonal variation in isoprene, monoterpene, and methanol fluxes from a temperate forest ecosystem before, during, and after an extreme 2012 drought event in the Ozark region of the central USA. BVOC fluxes were dominated by isoprene, which attained high emission rates of up to 35.4 mg m(-2)  h(-1) at midday. Methanol fluxes were characterized by net deposition in the morning, changing to a net emission flux through the rest of the daylight hours. Net flux of CO2 reached its seasonal maximum approximately a month earlier than isoprenoid fluxes, which highlights the differential response of photosynthesis and isoprenoid emissions to progressing drought conditions. Nevertheless, both processes were strongly suppressed under extreme drought, although isoprene fluxes remained relatively high compared to reported fluxes from other ecosystems. Methanol exchange was less affected by drought throughout the season, confirming the complex processes driving biogenic methanol fluxes. The fraction of daytime (7-17 h) assimilated carbon released back to the atmosphere combining the three BVOCs measured was 2% of gross primary productivity (GPP) and 4.9% of net ecosystem exchange (NEE) on average for our whole measurement campaign, while exceeding 5% of GPP and 10% of NEE just before the strongest drought phase. The meganv2.1 model correctly predicted diurnal variations in fluxes driven mainly by light and temperature, although further research is needed to address model BVOC fluxes during drought events. © 2015 John Wiley & Sons Ltd.

Ecosystem-scale volatile organic compound fluxes during an extreme drought in a broadleaf temperate forest of the Missouri Ozarks (central USA)

DOE PAGES

Seco, Roger; Karl, Thomas; Guenther, Alex; ...

2015-07-07

Considerable amounts and varieties of biogenic volatile organic compounds (BVOCs) are exchanged between vegetation and the surrounding air. These BVOCs play key ecological and atmospheric roles that must be adequately represented for accurately modeling the coupled biosphere–atmosphere–climate earth system. One key uncertainty in existing models is the response of BVOC fluxes to an important global change process: drought. Here, we describe the diurnal and seasonal variation in isoprene, monoterpene, and methanol fluxes from a temperate forest ecosystem before, during, and after an extreme 2012 drought event in the Ozark region of the central USA. BVOC fluxes were dominated by isoprene,more » which attained high emission rates of up to 35.4 mg m 2 h 1 at midday. Methanol fluxes were characterized by net deposition in the morning, changing to a net emission flux through the rest of the daylight hours. Net flux of CO 2 reached its seasonal maximum approximately a month earlier than isoprenoid fluxes, which highlights the differential response of photosynthesis and isoprenoid emissions to progressing drought conditions. Nevertheless, both processes were strongly suppressed under extreme drought, although isoprene fluxes remained relatively high compared to reported fluxes from other ecosystems. Methanol exchange was less affected by drought throughout the season, confirming the complex processes driving biogenic methanol fluxes. The fraction of daytime (7–17 h) assimilated carbon released back to the atmosphere combining the three BVOCs measured was 2% of gross primary productivity (GPP) and 4.9% of net ecosystem exchange (NEE) on average for our whole measurement campaign, while exceeding 5% of GPP and 10% of NEE just before the strongest drought phase. In conclusion, the MEGANv2.1 model correctly predicted diurnal variations in fluxes driven mainly by light and temperature, although further research is needed to address model BVOC fluxes during drought events.« less

Hydrologic support of carbon dioxide flux revealed by whole-lake carbon budgets

USGS Publications Warehouse

Stets, E.G.; Striegl, Robert G.; Aiken, G.R.; Rosenberry, D.O.; Winter, T.C.

2009-01-01

Freshwater lakes are an important component of the global carbon cycle through both organic carbon (OC) sequestration and carbon dioxide (CO 2) emission. Most lakes have a net annual loss of CO2 to the atmosphere and substantial current evidence suggests that biologic mineralization of allochthonous OC maintains this flux. Because net CO 2 flux to the atmosphere implies net mineralization of OC within the lake ecosystem, it is also commonly assumed that net annual CO2 emission indicates negative net ecosystem production (NEP). We explored the relationship between atmospheric CO2 emission and NEP in two lakes known to have contrasting hydrologie characteristics and net CO2 emission. We calculated NEP for calendar year 2004 using whole-lake OC and inorganic carbon (IC) budgets, NEPoc and NEPIC, respectively, and compared the resulting values to measured annual CO 2 flux from the lakes. In both lakes, NEPIc and NEP Ic were positive, indicating net autotrophy. Therefore CO2 emission from these lakes was apparently not supported by mineralization of allochthonous organic material. In both lakes, hydrologie CO2 inputs, as well as CO2 evolved from netcalcite precipitation, could account for the net CO2 emission. NEP calculated from diel CO2 measurements was also affected by hydrologie inputs of CO2. These results indicate that CO2 emission and positive NEP may coincide in lakes, especially in carbonate terrain, and that all potential geologic, biogeochemical, and hydrologie sources of CO2 need to be accounted for when using CO2 concentrations to infer lake NEP. Copyright 2009 by the American Geophysical Union.

A Decadal Inversion of CO2 Using the Global Eulerian-Lagrangian Coupled Atmospheric Model (GELCA): Sensitivity to the Ground-Based Observation Network

NASA Technical Reports Server (NTRS)

Shirai, T.; Ishizawa, M.; Zhuravlev, R.; Ganshin, A.; Belikov, D.; Saito, M.; Oda, T.; Valsala, V.; Gomez-Pelaez, A. J.; Langenfelds, R.;

Storm-induced inner-continental shelf circulation and sediment transport: Long Bay, South Carolina

USGS Publications Warehouse

Warner, John C.; Armstrong, Brandy N.; Sylvester, Charlene S.; Voulgaris, George; Nelson, Tim; Schwab, William C.; Denny, Jane F.

2012-01-01

Long Bay is a sediment-starved, arcuate embayment located along the US East Coast connecting both South and North Carolina. In this region the rates and pathways of sediment transport are important because they determine the availability of sediments for beach nourishment, seafloor habitat, and navigation. The impact of storms on sediment transport magnitude and direction were investigated during the period October 2003–April 2004 using bottom mounted flow meters, acoustic backscatter sensors and rotary sonars deployed at eight sites offshore of Myrtle Beach, SC, to measure currents, water levels, surface waves, salinity, temperature, suspended sediment concentrations, and bedform morphology. Measurements identify that sediment mobility is caused by waves and wind driven currents from three predominant types of storm patterns that pass through this region: (1) cold fronts, (2) warm fronts and (3) low-pressure storms. The passage of a cold front is accompanied by a rapid change in wind direction from primarily northeastward to southwestward. The passage of a warm front is accompanied by an opposite change in wind direction from mainly southwestward to northeastward. Low-pressure systems passing offshore are accompanied by a change in wind direction from southwestward to southeastward as the offshore storm moves from south to north.During the passage of cold fronts more sediment is transported when winds are northeastward and directed onshore than when the winds are directed offshore, creating a net sediment flux to the north–east. Likewise, even though the warm front has an opposite wind pattern, net sediment flux is typically to the north–east due to the larger fetch when the winds are northeastward and directed onshore. During the passage of low-pressure systems strong winds, waves, and currents to the south are sustained creating a net sediment flux southwestward. During the 3-month deployment a total of 8 cold fronts, 10 warm fronts, and 10 low-pressure systems drove a net sediment flux southwestward. Analysis of a 12-year data record from a local buoy shows an average of 41 cold fronts, 32 warm fronts, and 26 low-pressure systems per year. The culmination of these events would yield a cumulative net inner-continental shelf transport to the south–west, a trend that is further verified by sediment textural analysis and bedform morphology on the inner-continental shelf.

Annual and Seasonal Variability of Net Heat Budget in the Northern Indian Ocean

NASA Astrophysics Data System (ADS)

Pinker, Rachel T.; Bentamy, Abderrahim; Chen, Wen; Kumar, M. R. Ramesh; Mathew, Simi; Venkatesan, Ramasamy

2017-04-01

In this study we investigate the spatial and temporal features of the net heat budget over the Northern Indian Ocean (focusing on the Arabian Sea and the Bay of Bengal), using satellite and numerical model estimates. The main objective is to characterize the annual, seasonal, and inter-annual patterns over this basin of climatic significance. To assess the temporal variability, several turbulent and radiative fluxes are used The turbulent fluxes are based on information from the Institut Français pout la Recherche et l'Exploitation de la MER (IFREMER V3), the Hamburg Ocean-Atmosphere Parameters from Satellite (HOAPS V3), the SEAFLUX V1, the Japanese Ocean Flux Data sets with Use of Remote Sensing Observations (J-OFURO V2), the Objective Analysis Fluxes (OAFlux V2), the European Center for Medium Weather Forecasts (ECMWF), the ERA Interim, the National centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis, CFSR, and the National Aeronautics Space Administration (NASA) Modern Era Retrospective Analysis for Research and Application (MERRA). The radiative fluxes, both shortwave and longwave, include those produced at the University of Maryland (UMD) as well as those derived from several of the above mentioned numerical models. An attempt will be made to evaluate the various fluxes against buoy observations such as those from the RAMA array. The National Institute of Ocean Technology, Chennai, India under its Ocean Observation Program has deployed a series of OMNI Buoys both in the Arabian Sea and the Bay of Bengal. These buoys are equipped with sensors to measure the radiation as well as other parameters. Comparison has been done with the OMNI observations and good agreement has been found with the current set-up of the instrument at a 3 m level. We found significant differences between the various products at specific locations. The ultimate objective is to investigates the sources of the differences in terms of atmospheric variables (surface winds, air temperature and humidity), oceanic variables (sea surface temperature, sea state), and on bulk parametrizations.

New constraints on Northern Hemisphere growing season net flux

NASA Astrophysics Data System (ADS)

Yang, Z.; Washenfelder, R. A.; Keppel-Aleks, G.; Krakauer, N. Y.; Randerson, J. T.; Tans, P. P.; Sweeney, C.; Wennberg, P. O.

2007-06-01

Observations of the column-averaged dry molar mixing ratio of CO2 above both Park Falls, Wisconsin and Kitt Peak, Arizona, together with partial columns derived from aircraft profiles over Eurasia and North America are used to estimate the seasonal integral of net ecosystem exchange (NEE) between the atmosphere and the terrestrial biosphere in the Northern Hemisphere. We find that NEE is ~25% larger than predicted by the Carnegie Ames Stanford Approach (CASA) model. We show that the estimates of NEE may have been biased low by too weak vertical mixing in the transport models used to infer seasonal changes in Northern Hemisphere CO2 mass from the surface measurements of CO2 mixing ratio.

Surface Water and Energy Budgets for Sub-Saharan Africa in GFDL Coupled Climate Model

NASA Astrophysics Data System (ADS)

Tian, D.; Wood, E. F.; Vecchi, G. A.; Jia, L.; Pan, M.

2015-12-01

This study compare surface water and energy budget variables from the Geophysical Fluid Dynamics Laboratory (GFDL) FLOR models with the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR), Princeton University Global Meteorological Forcing Dataset (PGF), and PGF-driven Variable Infiltration Capacity (VIC) model outputs, as well as available observations over the sub-Saharan Africa. The comparison was made for four configurations of the FLOR models that included FLOR phase 1 (FLOR-p1) and phase 2 (FLOR-p2) and two phases of flux adjusted versions (FLOR-FA-p1 and FLOR-FA-p2). Compared to p1, simulated atmospheric states in p2 were nudged to the Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis. The seasonal cycle and annual mean of major surface water (precipitation, evapotranspiration, runoff, and change of storage) and energy variables (sensible heat, ground heat, latent heat, net solar radiation, net longwave radiation, and skin temperature) over a 34-yr period during 1981-2014 were compared in different regions in sub-Saharan Africa (West Africa, East Africa, and Southern Africa). In addition to evaluating the means in three sub-regions, empirical orthogonal functions (EOFs) analyses were conducted to compare both spatial and temporal characteristics of water and energy budget variables from four versions of GFDL FLOR, NCEP CFSR, PGF, and VIC outputs. This presentation will show how well each coupled climate model represented land surface physics and reproduced spatiotemporal characteristics of surface water and energy budget variables. We discuss what caused differences in surface water and energy budgets in land surface components of coupled climate model, climate reanalysis, and reanalysis driven land surface model. The comparisons will reveal whether flux adjustment and nudging would improve depiction of the surface water and energy budgets in coupled climate models.

Calcium transport in turtle bladder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabatini, S.; Kurtzman, N.A.

1987-12-01

Unidirectional {sup 45}Ca fluxes were measured in the turtle bladder under open-circuit and short-circuit conditions. In the open-circuited state net calcium flux (J{sup net}{sub Ca}) was secretory (serosa to mucosa). Ouabain reversed J{sup net}{sub Ca} to an absorptive flux. Amiloride reduced both fluxes such that J{sup net}{sub Ca} was not significantly different from zero. Removal of mucosal sodium caused net calcium absorption; removal of serosal sodium caused calcium secretion. When bladders were short circuited, J{sup net}{sub Ca} decreased to approximately one-third of control value but remained secretory. When ouabain was added under short-circuit conditions, J{sup net}{sub Ca} was similar inmore » magnitude and direction to ouabain under open-circuited conditions (i.e., absorptive). Tissue {sup 45}Ca content was {approx equal}30-fold lower when the isotope was placed in the mucosal bath, suggesting that the apical membrane is the resistance barrier to calcium transport. The results obtained in this study are best explained by postulating a Ca{sup 2+}-ATPase on the serosa of the turtle bladder epithelium and a sodium-calcium antiporter on the mucosa. In this model, the energy for calcium movement would be supplied, in large part, by the Na{sup +}-K{sup +}-ATPase. By increasing cell sodium, ouabain would decrease the activity of the mucosal sodium-calcium exchanger (or reverse it), uncovering active calcium transport across the serosa.« less

Idealized Cloud-System Resolving Modeling for Tropical Convection Studies

NASA Astrophysics Data System (ADS)

Anber, Usama M.

A three-dimensional limited-domain Cloud-Resolving Model (CRM) is used in idealized settings to study the interaction between tropical convection and the large scale dynamics. The model domain is doubly periodic and the large-scale circulation is parameterized using the Weak Temperature Gradient (WTG) Approximation and Damped Gravity Wave (DGW) methods. The model simulations fall into two main categories: simulations with a prescribed radiative cooling profile, and others in which radiative cooling profile interacts with clouds and water vapor. For experiments with a prescribed radiative cooling profile, radiative heating is taken constant in the vertical in the troposphere. First, the effect of turbulent surface fluxes and radiative cooling on tropical deep convection is studied. In the precipitating equilibria, an increment in surface fluxes produces a greater increase in precipitation than an equal increment in column-integrated radiative heating. The gross moist stability remains close to constant over a wide range of forcings. With dry initial conditions, the system exhibits hysteresis, and maintains a dry state with for a wide range of net energy inputs to the atmospheric column under WTG. However, for the same forcings the system admits a rainy state when initialized with moist conditions, and thus multiple equilibria exist under WTG. When the net forcing is increased enough that simulations, which begin dry, eventually develop precipitation. DGW, on the other hand, does not have the tendency to develop multiple equilibria under the same conditions. The effect of vertical wind shear on tropical deep convection is also studied. The strength and depth of the shear layer are varied as control parameters. Surface fluxes are prescribed. For weak wind shear, time-averaged rainfall decreases with shear and convection remains disorganized. For larger wind shear, rainfall increases with shear, as convection becomes organized into linear mesoscale systems. This non-monotonic dependence of rainfall on shear is observed when the imposed surface fluxes are moderate. For larger surface fluxes, convection in the unsheared basic state is already strongly organized, but increasing wind shear still leads to increasing rainfall. In addition to surface rainfall, the impacts of shear on the parameterized large-scale vertical velocity, convective mass fluxes, cloud fraction, and momentum transport are also discussed. For experiments with interactive radiative cooling profile, the effect of cloud-radiation interaction on cumulus ensemble is examined in sheared and unsheared environments with both fixed and interactive sea surface temperature (SST). For fixed SST, interactive radiation, when compared to simulations in which radiative profile has the same magnitude and vertical shape but does not interact with clouds or water vapor, is found to suppress mean precipitation by inducing strong descent in the lower troposphere, increasing the gross moist stability. For interactive SST, using a slab ocean mixed layer, there exists a shear strength above which the system becomes unstable and develops oscillatory behavior. Oscillations have periods of wet precipitating states followed by periods of dry non-precipitating states. The frequencies of oscillations are intraseasonal to subseasonal, depending on the mixed layer depth. Finally, the model is coupled to a land surface model with fully interactive radiation and surface fluxes to study the diurnal and seasonal radiation and water cycles in the Amazon basin. The model successfully captures the afternoon precipitation and cloud cover peak and the greater latent heat flux in the dry season for the first time; two major biases in GCMs with implications for correct estimates of evaporation and gross primary production in the Amazon. One of the key findings is that the fog layer near the surface in the west season is crucial for determining the surface energy budget and precipitation. This suggests that features on the diurnal time scale can significantly impact climate on the seasonal time scale.

Sensitivity Analysis of Flux Determination in Heart by H2 18O -provided Labeling Using a Dynamic Isotopologue Model of Energy Transfer Pathways

PubMed Central

Schryer, David W.; Peterson, Pearu; Illaste, Ardo; Vendelin, Marko

2012-01-01

To characterize intracellular energy transfer in the heart, two organ-level methods have frequently been employed: inversion and saturation transfer, and dynamic labeling. Creatine kinase (CK) fluxes obtained by following oxygen labeling have been considerably smaller than the fluxes determined by saturation transfer. It has been proposed that dynamic labeling determines net flux through CK shuttle, whereas saturation transfer measures total unidirectional flux. However, to our knowledge, no sensitivity analysis of flux determination by oxygen labeling has been performed, limiting our ability to compare flux distributions predicted by different methods. Here we analyze oxygen labeling in a physiological heart phosphotransfer network with active CK and adenylate kinase (AdK) shuttles and establish which fluxes determine the labeling state. A mathematical model consisting of a system of ordinary differential equations was composed describing enrichment in each phosphoryl group and inorganic phosphate. By varying flux distributions in the model and calculating the labeling, we analyzed labeling sensitivity to different fluxes in the heart. We observed that the labeling state is predominantly sensitive to total unidirectional CK and AdK fluxes and not to net fluxes. We conclude that measuring dynamic incorporation of into the high-energy phosphotransfer network in heart does not permit unambiguous determination of energetic fluxes with a higher magnitude than the ATP synthase rate when the bidirectionality of fluxes is taken into account. Our analysis suggests that the flux distributions obtained using dynamic labeling, after removing the net flux assumption, are comparable with those from inversion and saturation transfer. PMID:23236266

Chloride cycling in two forested lake watersheds in the west-central Adirondack Mountains, New York, U.S.A.

USGS Publications Warehouse

Peters, N.E.

1991-01-01

The chemistry of precipitation, throughfall, soil water, ground water, and surface water was evaluated in two forested lake-watersheds over a 4-yr period to assess factors controlling C1- cycling. Results indicate that C1- cycling in these watersheds is more complex than the generally held view of the rapid transport of atmospherically derived C1- through the ecosystem. The annual throughfall Cl- flux for individual species in the northern hardwood forest was 2 to 5 times that of precipitation (56 eq ha-1), whereas the Na+ throughfall flux, in general, was similar to the precipitation flux. Concentrations of soil-water Cl- sampled from ceramic tension lysimeters at 20 cm below land surface generally exceeded the Na+ concentrations and averaged 31 ??eq L-1, the highest of any waters sampled in the watersheds, except throughfall under red spruce which averaged 34 ??eq L-1. Chloride was concentrated prior to storms and mobilized rapidly during storms as suggested by increases in streamwater Cl- concentrations with increasing flow. Major sources of Cl- in both watersheds are the forest floor and hornblende weathering in the soils and till. In the Panther Lake watershed, which contains mainly thick deposits of till( > 3 m), hornblende weathering results in a net Cl- flux 3 times greater than that in the Woods Lake watershed, which contains mainly thin deposits of till. The estimated accumulation rate of Cl- in the biomass of the two watersheds was comparable to the precipitation Cl- flux.The chemistry of precipitation, throughfall, soil water, ground water, and surface water was evaluated in two forested lake-watersheds over a 4-yr period to assess factors controlling Cl- cycling. Results indicate that Cl- cycling in these watersheds is more complex than the generally held view of the rapid transport of atmospherically derived Cl- through the excosystem. The annual throughfall Cl- flux for individual species in the northern hardwood forest was 2 to 5 times that of precipitation (56 eq ha-1), whereas the Na+ throughfall flux, in general, was similar to the precipitation flux. Concentrations of soil-water Cl- sampled from ceramic tension lysimeters at 20 cm below land surface generally exceeded the Na+ concentrations and averaged 31 ??eq L-1, the highest of any waters sampled in the watersheds, except throughfall under red spruce which averaged 34 ??eq L-1. Chloride was concentrated prior to storms and mobilized rapidly during storms as suggested by increases in streamwater Cl- concentrations with increasing flow. Major sources of Cl- in both watersheds are the forest floor and hornblende weathering in the soils and till. In the Panther Lake watershed, which contains mainly thick deposits of till (> 3 m), hornblende weathering results in a net Cl- flux 3 times greater than that in the Woods Lake watershed, which contains mainly thin deposits of till. The estimated accumulation rate of Cl- in the biomass of the two watersheds was comparable to the precipitation Cl- flux.

[Characteristics of CO2 flux before and in the heating period at urban complex underlying surface area].

PubMed

Jia, Qing-yu; Zhou, Guang-sheng; Wang, Yu; Liu, Xiao-mei

2010-04-01

Urban areas were significant contributors to global carbon dioxide emissions. The eddy covariance (EC) was used to measure carbon dioxide (CO2) concentration and flux data at urban area in Shenyang. This research analyzed the characteristics of atmospheric CO2 concentration and flux in October 2008 to November 2008 period before and in the heating period. The results showed that the daily variation of CO2 concentration was two-peak curve. The first peak time appeared as same as sunrise time, while the second peak time impacted by vehicles and heating. The result of CO2 flux showed that urban atmospheric CO2 was net emissions, vegetation photosynthesis absorbed CO2 of traffic, the CO2 flux peak appeared at 17:15-18:15 in the heating period, CO2 emission increased 29.37 g x (m2 x d)(-1) in the heating period than that before the heating period; there was corresponding relationship between CO2 flux and the time when temperature peak and sensible heating flux (Hc) turn positive. The results also indicated that atmospheric CO2 concentration and its flux were affected seriously by both wind direction and carbon sources.

Heat flux variations over sea ice observed at the coastal area of the Sejong Station, Antarctica

NASA Astrophysics Data System (ADS)

Park, Sang-Jong; Choi, Tae-Jin; Kim, Seong-Joong

2013-08-01

This study presents variations of sensible heat flux and latent heat flux over sea ice observed in 2011 from the 10-m flux tower located at the coast of the Sejong Station on King George Island, Antarctica. A period from July to September was selected as a sea ice period based on daily record of sea state and hourly photos looking at the Marian Cove in front of the Sejong Station. For the sea ice period, mean sensible heat flux is about -11 Wm-2, latent heat flux is about +2 W m-2, net radiation is -12 W m-2, and residual energy is -3 W m-2 with clear diurnal variations. Estimated mean values of surface exchange coefficients for momentum, heat and moisture are 5.15 × 10-3, 1.19 × 10-3, and 1.87 × 10-3, respectively. The observed exchange coefficients of heat shows clear diurnal variations while those of momentum and moisture do not show diurnal variation. The parameterized exchange coefficients of heat and moisture produces heat fluxes which compare well with the observed diurnal variations of heat fluxes.

Climatological mean and decadal change in surface ocean pCO 2, and net sea-air CO 2 flux over the global oceans

NASA Astrophysics Data System (ADS)

Takahashi, Taro; Sutherland, Stewart C.; Wanninkhof, Rik; Sweeney, Colm; Feely, Richard A.; Chipman, David W.; Hales, Burke; Friederich, Gernot; Chavez, Francisco; Sabine, Christopher; Watson, Andrew; Bakker, Dorothee C. E.; Schuster, Ute; Metzl, Nicolas; Yoshikawa-Inoue, Hisayuki; Ishii, Masao; Midorikawa, Takashi; Nojiri, Yukihiro; Körtzinger, Arne; Steinhoff, Tobias; Hoppema, Mario; Olafsson, Jon; Arnarson, Thorarinn S.; Tilbrook, Bronte; Johannessen, Truls; Olsen, Are; Bellerby, Richard; Wong, C. S.; Delille, Bruno; Bates, N. R.; de Baar, Hein J. W.

2009-04-01

A climatological mean distribution for the surface water pCO 2 over the global oceans in non-El Niño conditions has been constructed with spatial resolution of 4° (latitude) ×5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO 2 obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper [Takahashi et al., 2002. Global sea-air CO 2 flux based on climatological surface ocean pCO 2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601-1622]. A time-trend analysis using deseasonalized surface water pCO 2 data in portions of the North Atlantic, North and South Pacific and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO 2 over these oceanic areas has increased on average at a mean rate of 1.5 μatm y -1 with basin-specific rates varying between 1.2±0.5 and 2.1±0.4 μatm y -1. A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Niño periods in the equatorial Pacific and those made in coastal zones are excluded from the database. Seasonal changes in the surface water pCO 2 and the sea-air pCO 2 difference over four climatic zones in the Atlantic, Pacific, Indian and Southern Oceans are presented. Over the Southern Ocean seasonal ice zone, the seasonality is complex. Although it cannot be thoroughly documented due to the limited extent of observations, seasonal changes in pCO 2 are approximated by using the data for under-ice waters during austral winter and those for the marginal ice and ice-free zones. The net air-sea CO 2 flux is estimated using the sea-air pCO 2 difference and the air-sea gas transfer rate that is parameterized as a function of (wind speed) 2 with a scaling factor of 0.26. This is estimated by inverting the bomb 14C data using Ocean General Circulation models and the 1979-2005 NCEP-DOE AMIP-II Reanalysis (R-2) wind speed data. The equatorial Pacific (14°N-14°S) is the major source for atmospheric CO 2, emitting about +0.48 Pg-C y -1, and the temperate oceans between 14° and 50° in the both hemispheres are the major sink zones with an uptake flux of -0.70 Pg-C y -1 for the northern and -1.05 Pg-C y -1 for the southern zone. The high-latitude North Atlantic, including the Nordic Seas and portion of the Arctic Sea, is the most intense CO 2 sink area on the basis of per unit area, with a mean of -2.5 tons-C month -1 km -2. This is due to the combination of the low pCO 2 in seawater and high gas exchange rates. In the ice-free zone of the Southern Ocean (50°-62°S), the mean annual flux is small (-0.06 Pg-C y -1) because of a cancellation of the summer uptake CO 2 flux with the winter release of CO 2 caused by deepwater upwelling. The annual mean for the contemporary net CO 2 uptake flux over the global oceans is estimated to be -1.6±0.9 Pg-C y -1, which includes an undersampling correction to the direct estimate of -1.4±0.7 Pg-C y -1. Taking the pre-industrial steady-state ocean source of 0.4±0.2 Pg-C y -1 into account, the total ocean uptake flux including the anthropogenic CO 2 is estimated to be -2.0±1.0 Pg-C y -1 in 2000.

Combining tower mixing ratio and community model data to estimate regional-scale net ecosystem carbon exchange by boundary layer inversion over four flux towers in the United States

Treesearch

Xueri Dang; Chun-Ta Lai; David Y. Hollinger; Andrew J. Schauer; Jingfeng Xiao; J. William Munger; Clenton Owensby; James R. Ehleringer

2011-01-01

We evaluated an idealized boundary layer (BL) model with simple parameterizations using vertical transport information from community model outputs (NCAR/NCEP Reanalysis and ECMWF Interim Analysis) to estimate regional-scale net CO2 fluxes from 2002 to 2007 at three forest and one grassland flux sites in the United States. The BL modeling...

Multidecadal-scale adjustment of the ocean mixed layer heat budget in the tropics: examining ocean reanalyses

NASA Astrophysics Data System (ADS)

Cook, Kerry H.; Vizy, Edward K.; Sun, Xiaoming

2018-03-01

Distributions of ocean mixed layer temperature trends and trends in the net heat flux from the atmosphere differ, indicating the important role of the transport of heat within the ocean for determining temperature trends. Annual-mean, linear trends in the components of the tropical ocean mixed layer heat budget for 1980-2015 are diagnosed in 4 ocean reanalyses to improve our physical understanding of multidecadal-scale SST trends. The well-known temperature trend in the tropical Pacific, with cooling in the east and warming in the west, is reproduced in each reanalysis with high statistical significance. Cooling in the east is associated with negative trends in the net heat flux from the atmosphere and enhanced equatorial upwelling related to a strengthening of the subtropical cells. Negative trends in the net heat flux also occur in the western tropical Pacific, but advective warming associated with a strengthening and shoaling of the equatorial undercurrent overwhelms these negative trends. The strengthening of the equatorial undercurrent is consistent with enhanced easterly wind stress, which is applied to the ocean reanalyses, and differential sea level trends that enhance the negative zonal height gradient across the Pacific. The Pacific North Equatorial countercurrent is also strengthening in all 4 reanalyses in association with a strengthening of the sea level trough at 10°N in the central and eastern Pacific. All 4 ocean reanalyses produce warming of 0.1-0.3 K/decade in the North Atlantic with statistical significance levels ranging from below 90-99%. The Atlantic is similar to the Pacific in having the equatorial undercurrent strengthening, but indications of shoaling are less consistent in the reanalyses and the North Equatorial Countercurrent in the Atlantic is not strengthening. Large-scale ocean mixed layer warming trends in the Indian Ocean in the reanalyses are interrupted by some regional cooling close to the equator. Net surface heat flux trends are mostly negative, indicating increasing heat fluxes from the ocean to the atmosphere. Wind stress trends applied to the ocean reanalyses are weak, but trends in the Indian Ocean equatorial undercurrent are strong. Since the Indian monsoon climate introduces strong seasonality, the annual analysis may not be adequate for studying physical processes in this ocean basin.

Turbulence measurements using tethered balloon instrumentation during FIRE 1987

NASA Technical Reports Server (NTRS)

Hignett, Phillip

1990-01-01

As part of the surface-based observations conducted on San Nicolas Island, the U.K. Meteorological Office operated a set of turbulence probes attached to a balloon tether cable. Typically six probes were used, each capable of measuring momentum, heat, and humidity fluxes. Two probes were fitted with net radiometers, one positioned above cloud and the other below; a third probe carried a Lyman-alpha hygrometer fitted with a pre-heater for the measurement of total water content. Some preliminary results are presented from the 14th July describing the variation in structure of the cloudy boundary layer during the daytime. This day was characterized by a complete cloud cover, an inversion height of approximately 600 m. and north-westerly winds of approximately 6 m.s(-1). As an illustration the equivalent potential temperature derived from a profile ascent made between approximately 0830 and 0930 (PDT) is shown. The data has been smoothed to a height resolution of about 4 metres. At this time the cloud base was approximately 200 m. and very light drizzle was reaching the surface. The vertical velocity variance and potential temperature flux for two periods are shown; the first (shown by full lines) immediately follows the profile and the second (shown by dashed lines) is central around 1400 (PDT). The data have been normalized by their maximum values in the first period. Cloud base has now risen to approximately 300 m. There is a marked variation during the morning, particularly in sigma w. The net radiative flux above cloud top has by now reached its maximum value.

Improved assessment of gross and net primary productivity of Canada's landmass

NASA Astrophysics Data System (ADS)

Gonsamo, Alemu; Chen, Jing M.; Price, David T.; Kurz, Werner A.; Liu, Jane; Boisvenue, Céline; Hember, Robbie A.; Wu, Chaoyang; Chang, Kuo-Hsien

2013-12-01

assess Canada's gross primary productivity (GPP) and net primary productivity (NPP) using boreal ecosystem productivity simulator (BEPS) at 250 m spatial resolution with improved input parameter and driver fields and phenology and nutrient release parameterization schemes. BEPS is a process-based two-leaf enzyme kinetic terrestrial ecosystem model designed to simulate energy, water, and carbon (C) fluxes using spatial data sets of meteorology, remotely sensed land surface variables, soil properties, and photosynthesis and respiration rate parameters. Two improved key land surface variables, leaf area index (LAI) and land cover type, are derived at 250 m from Moderate Resolution Imaging Spectroradiometer sensor. For diagnostic error assessment, we use nine forest flux tower sites where all measured C flux, meteorology, and ancillary data sets are available. The errors due to input drivers and parameters are then independently corrected for Canada-wide GPP and NPP simulations. The optimized LAI use, for example, reduced the absolute bias in GPP from 20.7% to 1.1% for hourly BEPS simulations. Following the error diagnostics and corrections, daily GPP and NPP are simulated over Canada at 250 m spatial resolution, the highest resolution simulation yet for the country or any other comparable region. Total NPP (GPP) for Canada's land area was 1.27 (2.68) Pg C for 2008, with forests contributing 1.02 (2.2) Pg C. The annual comparisons between measured and simulated GPP show that the mean differences are not statistically significant (p > 0.05, paired t test). The main BEPS simulation error sources are from the driver fields.

Influence of increasing active-layer depth and continued permafrost degradation on carbon, water and energy fluxes over two forested permafrost landscapes in the Taiga Plains, NWT, Canada

NASA Astrophysics Data System (ADS)

Sonnentag, O.; Baltzer, J.; Chasmer, L. E.; Detto, M.; Marsh, P.; Quinton, W. L.

2012-12-01

Recent research suggests an increase in active-layer depth (ALD) in the continuous permafrost zone and degradation of the discontinuous permafrost zone into seasonally frozen. Increasing ALD and continued permafrost degradation will have far-reaching consequences for northern ecosystems including altered regional hydrology and the exposure of additional soil organic carbon (C) to microbial decomposition. These changes might cause positive or negative net feedbacks to the climate system by altering important land surface properties and/or by releasing stored soil organic C to the atmosphere as CO2 and/or CH4. Knowledge gaps exist regarding the links between increasing ALD and/or permafrost degradation, regional hydrology, vegetation composition and structure, land surface properties, and CO2 and CH4 sink-source strengths. The goal of our interdisciplinary project is to shed light on these links by providing a mechanistic understanding of permafrost-thawing consequences for hydrological, ecophysiological and biogeochemical processes at two forested permafrost landscapes in the Taiga Plains, NWT, Canada: Scotty Creek and Havikpak Creek in the discontinuous and in the continuous permafrost zones, respectively (Fig.). The sites will be equipped with identical sets of instrumentation (start: 2013), to measure landscape-scale net exchanges of CO2, CH4, water and energy with the eddy covariance technique. These measurements will be complemented by repeated surveys of surface and frost table topography and vegetation, by land cover-type specific fluxes of CO2 and CH4 measured with a static chamber technique, and by remote sensing-based footprint analysis. With this research we will address the following questions: What is the net effect of permafrost thawing-induced biophysical and biogeochemical feedbacks to the climate system? How do these two different types of feedback differ between the discontinuous and continuous permafrost zones? Is the decrease (increase) in net CO2 (CH4) exchange measured over mostly tundra sites in the continuous permafrost zone generalizable to forested landscapes in both the discontinuous and continuous permafrost zones? With this contribution, we report on the project status, present its objectives and hypotheses, and outline its timeline and sampling design.

The role of vegetation in the CO2 flux from a tropical urban neighbourhood

NASA Astrophysics Data System (ADS)

Velasco, E.; Roth, M.; Tan, S. H.; Quak, M.; Nabarro, S. D. A.; Norford, L.

2013-03-01

Urban surfaces are usually net sources of CO2. Vegetation can potentially have an important role in reducing the CO2 emitted by anthropogenic activities in cities, particularly when vegetation is extensive and/or evergreen. Negative daytime CO2 fluxes, for example have been observed during the growing season at suburban sites characterized by abundant vegetation and low population density. A direct and accurate estimation of carbon uptake by urban vegetation is difficult due to the particular characteristics of the urban ecosystem and high variability in tree distribution and species. Here, we investigate the role of urban vegetation in the CO2 flux from a residential neighbourhood in Singapore using two different approaches. CO2 fluxes measured directly by eddy covariance are compared with emissions estimated from emissions factors and activity data. The latter includes contributions from vehicular traffic, household combustion, soil respiration and human breathing. The difference between estimated emissions and measured fluxes should approximate the biogenic flux. In addition, a tree survey was conducted to estimate the annual CO2 sequestration using allometric equations and an alternative model of the metabolic theory of ecology for tropical forests. Palm trees, banana plants and turfgrass were also included in the survey with their annual CO2 uptake obtained from published growth rates. Both approaches agree within 2% and suggest that vegetation captures 8% of the total emitted CO2 in the residential neighbourhood studied. A net uptake of 1.4 ton km-2 day-1 (510 ton km-2 yr-1 ) was estimated from the difference between the daily CO2 uptake by photosynthesis (3.95 ton km-2 ) and release by respiration (2.55 ton km-2). The study shows the importance of urban vegetation at the local scale for climate change mitigation in the tropics.

Variation of energy and carbon fluxes from a restored temperate freshwater wetland and implications for carbon market verification protocols

USGS Publications Warehouse

Anderson, Frank; Bergamaschi, Brian; Sturtevant, Cove; Knox, Sarah; Hastings, Lauren; Windham-Myers, Lisamarie; Detto, Matteo; Hestir, Erin L.; Drexler, Judith; Miller, Robin L.; Matthes, Jaclyn; Verfaillie, Joseph; Baldocchi, Dennis; Snyder, Richard L.; Fujii, Roger

2016-01-01

Temperate freshwater wetlands are among the most productive terrestrial ecosystems, stimulating interest in using restored wetlands as biological carbon sequestration projects for greenhouse gas reduction programs. In this study, we used the eddy covariance technique to measure surface energy carbon fluxes from a constructed, impounded freshwater wetland during two annual periods that were 8 years apart: 2002–2003 and 2010–2011. During 2010–2011, we measured methane (CH4) fluxes to quantify the annual atmospheric carbon mass balance and its concomitant influence on global warming potential (GWP). Peak growing season fluxes of latent heat and carbon dioxide (CO2) were greater in 2002–2003 compared to 2010–2011. In 2002, the daily net ecosystem exchange reached as low as −10.6 g C m−2 d−1, which was greater than 3 times the magnitude observed in 2010 (−2.9 g C m−2 d−1). CH4 fluxes during 2010–2011 were positive throughout the year and followed a strong seasonal pattern, ranging from 38.1 mg C m−2 d−1 in the winter to 375.9 mg C m−2 d−1 during the summer. The results of this study suggest that the wetland had reduced gross ecosystem productivity in 2010–2011, likely due to the increase in dead plant biomass (standing litter) that inhibited the generation of new vegetation growth. In 2010–2011, there was a net positive GWP (675.3 g C m−2 yr−1), and when these values are evaluated as a sustained flux, the wetland will not reach radiative balance even after 500 years.

FLUXNET to MODIS: Connecting the dots to capture heterogenious biosphere metabolism

NASA Astrophysics Data System (ADS)

Woods, K. D.; Schwalm, C.; Huntzinger, D. N.; Massey, R.; Poulter, B.; Kolb, T.

2015-12-01

Eddy co-variance flux towers provide our most widely distributed network of direct observations for land-atmosphere carbon exchange. Carbon flux sensitivity analysis is a method that uses in situ networks to understand how ecosystems respond to changes in climatic variables. Flux towers concurrently observe key ecosystem metabolic processes (e..g. gross primary productivity) and micrometeorological variation, but only over small footprints. Remotely sensed vegetation indices from MODIS offer continuous observations of the vegetated land surface, but are less direct, as they are based on light use efficiency algorithms, and not on the ground observations. The marriage of these two data products offers an opportunity to validate remotely sensed indices with in situ observations and translate information derived from tower sites to globally gridded products. Here we provide correlations between Enhanced Vegetation Index (EVI), Leaf Area Index (LAI) and MODIS gross primary production with FLUXNET derived estimates of gross primary production, respiration and net ecosystem exchange. We demonstrate remotely sensed vegetation products which have been transformed to gridded estimates of terrestrial biosphere metabolism on a regional-to-global scale. We demonstrate anomalies in gross primary production, respiration, and net ecosystem exchange as predicted by both MODIS-carbon flux sensitivities and meteorological driver-carbon flux sensitivities. We apply these sensitivities to recent extreme climatic events and demonstrate both our ability to capture changes in biosphere metabolism, and differences in the calculation of carbon flux anomalies based on method. The quantification of co-variation in these two methods of observation is important as it informs both how remotely sensed vegetation indices are correlated with on the ground tower observations, and with what certainty we can expand these observations and relationships.

Snow Never Falls on Satellite Radiometers: A Compelling Alternative to Ground Observations

NASA Astrophysics Data System (ADS)

Hinkelman, L. M.; Lapo, K. E.; Cristea, N. C.; Lundquist, J. D.

2014-12-01

Snowmelt is an important source of surface water for ecosystems, river flow, drinking water, and production of hydroelectric power. Thus accurate modeling of snow accumulation and melt is needed to improve our understanding of the impact of climate change on mountain snowpack and for use in water resource forecasting and management decisions. One of the largest potential sources of uncertainty in modeling mountain snow is the net radiative flux. This is because while net irradiance makes up the majority of the surface energy balance, it is one of the most difficult forcings to measure at remote mountain locations. Here we investigate the use of irradiances derived from satellite measurements in the place of surface observations. NASA's Clouds and the Earth's Radiant Energy System (CERES) SYN satellite product provides longwave and shortwave irradiances at the ground on three-hourly temporal and one degree spatial resolution.Although the low resolution of these data is a drawback, their availability over the entire globe for the full period of March 2000 through December 2010 (and beyond, as processing continues) makes them an attractive option for use in modeling. We first assessed the accuracy of the SYN downwelling solar and longwave fluxes by comparison to measurements at NOAA's Surface Radiation Network (SURFRAD) reference stations and at remote mountain stations. The performance of several snow models of varying complexity when using SYN irradiances as forcing data was then evaluated. Simulated snow water equivalent and runoff from cases using SYN data fell in the range of those from simulations forced with irradiances from higher quality surface observations or more highly-regarded empirical methods. We therefore judge the SYN irradiances to be suitable for use in snowmelt modeling and preferable to in situ measurements of questionable quality.

Comparing Multiple Evapotranspiration-calculating Methods, Including Eddy Covariance and Surface Renewal, Using Empirical Measurements from Alfalfa Fields in the Sacramento-San Joaquin River Delta

NASA Astrophysics Data System (ADS)

Clay, J.; Kent, E. R.; Leinfelder-Miles, M.; Lambert, J. J.; Little, C.; Paw U, K. T.; Snyder, R. L.

2016-12-01

Eddy covariance and surface renewal measurements were used to estimate evapotranspiration (ET) over a variety of crop fields in the Sacramento-San Joaquin River Delta during the 2016 growing season. However, comparing and evaluating multiple measurement systems and methods for determining ET was focused upon at a single alfalfa site. The eddy covariance systems included two systems for direct measurement of latent heat flux: one using a separate sonic anemometer and an open path infrared gas analyzer and another using a combined system (Campbell Scientific IRGASON). For these methods, eddy covariance was used with measurements from the Campbell Scientific CSAT3, the LI-COR 7500a, the Campbell Scientific IRGASON, and an additional R.M. Young sonic anemometer. In addition to those direct measures, the surface renewal approach included several energy balance residual methods in which net radiation, ground heat flux, and sensible heat flux (H) were measured. H was measured using several systems and different methods, including using multiple fast-response thermocouple measurements and using the temperatures measured by the sonic anemometers. The energy available for ET was then calculated as the residual of the surface energy balance equation. Differences in ET values were analyzed between the eddy covariance and surface renewal methods, using the IRGASON-derived values of ET as the standard for accuracy.

Relating hyporheic fluxes, residence times, and redox-sensitive biogeochemical processes upstream of beaver dams

USGS Publications Warehouse

Briggs, Martin A.; Lautz, Laura; Hare, Danielle K.

2013-01-01

¨hler number seemed to overestimate the actual transition as indicated by multiple secondary electron acceptors, illustrating the gradient nature of anaerobic transition. Temporal flux variability in low-flux morphologies generated a much greater range in hyporheic redox conditions compared to high-flux zones, and chemical responses to changing flux rates were consistent with those predicted from the empirical relationship between redox condition and residence time. The Raz tracer revealed that hyporheic flow paths have strong net aerobic respiration, particularly at higher residence time, but this reactive exchange did not affect the net stream signal at the reach scale.

The connection from the Sun to Planets and the Galaxy by QFT

NASA Astrophysics Data System (ADS)

Chen, Shao-Guang

I deduce the new gravitational formula from the variance in mass of QFT and GR (H05-0029-08, E15-0039 -08, E14-0032-08, D31-0054-10) in the partial differential: f (QFT) = f (GR) = delta∂ (m v)/delta∂ t = f _{P} + f _{C} , f _{P} = m delta∂ v / delta∂ t = - ( G m M /r (2) ) r / r, f _{C} = v delta∂ m / delta∂ t = - ( G mM / r (2) ) v / c (1), f (QFT) is the quasi-Casimir pressure of net virtual neutrinos nuν _{0} flux (after counteract contrary direction nuν _{0}). f (GR) is equivalent to Einstein’s equation as a new version of GR. GR can be inferred from Eq.(1) thereby from QFT, but QFT cannot be inferred from Eq.(1) or GR. f (QFT) is essential but f (GR) is phenomenological. Eq.(1) is obtained just by to absorb the essence of corpuscule collided gravitation origin ism proposed by Fatio in 1690 and 1920 Majorana’s experiment concept about gravitational shield effect again fuse with QFT. Its core content is that the gravity produced by particles collide cannot linear addition, i.e., Eq.(1) with the adding nonlinearity caused by the variable mass to replace the nonlinearity of Einstein’s equation and the nonlinear gravitation problems can be solved using the classical gradual approximation of alone f _{P} and alone f _{C}. Such as the calculation of advance of the perihelion of QFT, let the gravitational potential U = - G M /r which is just the distribution density of net nuν _{0} flux. From SR we again get Eq.(1): f (QFT) = f _{P} + f _{C}, f _{P} = - m ( delta∂ U / delta∂ r) r / r, f _{C} = - m ( delta∂U / delta∂ r) v / c , U = (1 - betaβ (2) )V, V is the Newtonian gravitational potential. f_{ P} correspond the change rate of three-dimensional momentum p, f_{C} correspond the change rate of fourth dimensional momentum i m c which show directly as a dissipative force of mass change. In my paper ‘To cross the great gap between the modern physics and classic physics, China Science &Technology Overview 129 85-91(2011)’ with the measuring value of one-way velocity of light (H05-0020-08) to replace the infinity value of light speed measured by Galileo in 1607, thereby the mass m in NM will become variable m. Or else, the energy of electron in accelerator should not larger than 0.51Mev which conflict with the experimental fact. According to the variable mass and the definition of force we again get Eq.(1) from NM without hypothesis, i.e., NM is generalized in which Galileo coordinates transformation and the action at a distance will be of no effect. Eq.(1) has more reliable experimental base and generalized NM may be applied to the high-speed and the microscopic conditions. Because of the result of a test of GR with use of a hydrogen-maser frequency standard in a spacecraft launched nearly vertically upward to 10000 km (R. F. C. Vessot et.al., Phys. Rev. Lett. 45, 2081 (1980)), the isotropy of one-way velocity of light had been validated at the 1*10 (-10) level (D2.4-0030-12, H0.1-0009-12, H0.2-0008-12). Again from the Lorentz transformation (H01-0006-08) and the uncertainty principle (H05-0036-10) deduced from the metrical results of Doppler effects, SR and QM, thereby QFT and GR, all become the inferential theorems from generalized NM. Eq.(1) is as a bridge to join the modern physics and classical physics. In my paper ‘Basal electric and magnetic fields of celestial bodies come from positive-negative charge separation caused by gravitation of quasi-Casimir pressure in weak interaction’ (D31-0054-10): According to QFT the gravitation is the statistic average pressure collided by net virtual neutrinos nuν _{0} flux, the net nuν _{0} flux can press a part freedom electrons in plasma of ionosphere into the surface of celestial bodies, the static electric force of redundant positive ions prevents electrons further falling and till reach the equilibrium of stable spatial charge distribution, which is just the cause of the geomagnetic field and the geo-electric field. In the solar surface plasma add the negative charge from ionosphere electrons again rotate, thereby come into being the solar basal magnetic field. The solar surface plasma with additional electrons get the dynamic balance between the upwards force of stable positive charge distribution in the solar upside gas and the downwards force of the vacuum net nuν _{0} flux pressure (solar gravity). When the Jupiter enter into the connecting line of Sun and the center of Galaxy, the pressure (solar gravity) observed from earth will weaken because of the Jupiter stop (shield) the most net nuν _{0} flux which shoot to Sun from the center of Galaxy. The dynamic balance of forces on the solar surface plasma at once is broken and the plasma will upwards eject as the solar wind with redundant negative charge, at the same time, the solar surface remain a cavity as a sunspot whorl with the positive charge relative to around plasma. The whorl caused by that the reaction of plasma eject front and upwards with the different velocity at different latitude of solar rotation, leads to the cavity around in the downwards and backwards helix movement. The solar rotation more slow, when the cavity is filled by around plasma in the reverse turn direction and return to small negative charge, the Jupiter at front had been produced a new cavity. Thereby we had observe the sunspot pair with different directions whorl and different magnetic polarity. Jupiter possess half mass of all planets in solar system, its action to stop net nuν _{0} flux is primary, then Jupiter’s period of 11.8 sidereal years accord basically with the period of sunspot eruptions. From the Sun to the Jupiter again to the Galaxy to be connected by the vacuum net virtual neutrinos nuν _{0} flux of QFT, its distribution density is just the gravitational potential U = - G M /r of QFT. Foregoing analysis is only an example, using the net nuν _{0} flux and U we research and dispose the connection from the Sun to Planets and the Galaxy should obtain many testable results by observation.

Eddy Correlation Flux Measurement System Handbook

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, D. R.

2016-01-01

The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat, and carbon dioxide (CO2) (and methane at one Southern Great Plains extended facility (SGP EF) and the North Slope of Alaska Central Facility (NSA CF). The fluxes are obtained with the eddy covariance technique, which involves correlation of the vertical wind component with the horizontal wind component, the air temperature, the water vapor density, and the CO2 concentration. The instruments used are: • a fast-response, three-dimensional (3D) wind sensor (sonic anemometer) to obtain the orthogonal wind componentsmore » and the speed of sound (SOS) (used to derive the air temperature) • an open-path infrared gas analyzer (IRGA) to obtain the water vapor density and the CO2 concentration, and • an open-path infrared gas analyzer (IRGA) to obtain methane density and methane flux at one SGP EF and at the NSA CF. The ECOR systems are deployed at the locations where other methods for surface flux measurements (e.g., energy balance Bowen ratio [EBBR] systems) are difficult to employ, primarily at the north edge of a field of crops. A Surface Energy Balance System (SEBS) has been installed collocated with each deployed ECOR system in SGP, NSA, Tropical Western Pacific (TWP), ARM Mobile Facility 1 (AMF1), and ARM Mobile Facility 2 (AMF2). The surface energy balance system consists of upwelling and downwelling solar and infrared radiometers within one net radiometer, a wetness sensor, and soil measurements. The SEBS measurements allow the comparison of ECOR sensible and latent heat fluxes with the energy balance determined from the SEBS and provide information on wetting of the sensors for data quality purposes. The SEBS at one SGP and one NSA site also support upwelling and downwelling PAR measurements to qualify those two locations as Ameriflux sites.« less

Water and CO2 Exchange for Different Land Use in Pampa Biome in Southern Brazil

NASA Astrophysics Data System (ADS)

Roberti, D. R.; de Moraes, O. L. L.; Diaz, M.; Tatsch, J. D.; Acevedo, O. C.; Zimermann, H. R.; Rubert, G. C.; Acosta, R.; Campos Velho, H. F.

2015-12-01

The Pampa is the newest and most unknown Brazilian Biome. It is located in the Southern portion of the country, as well as part of Argentina and the entire Uruguay, and is formed principally by natural grasslands that have been used for centuries for grazing livestock. In recent decades it has gone through a process of intense land use change and degradation, with the replacement of natural vegetation by rice paddy crops, soybean and exotic forests. Recent studies show that the Pampa has only 36% of its original vegetation in Brazil. Research on carbon and greenhouse gas emissions in Pampa Biome are recent. It is known that the Pampa natural areas contain high stocks of soil organic carbon, and therefore their conservation is relevant for climate change mitigation. However, the net exchange of carbon and water between the surface and the atmosphere are unknown. To fill this gap, a flux tower network, SULFLUX - www.ufsm.br/sulfux, was created. Currently, SULFLUX comprises three flux towers in the Pampa biome, two of them being over natural vegetation and the other one over a rice paddy. The flux towers are nearly 100 km apart from each other. We examine the effects of climate on carbon fluxes of through the year 2014. Analysis of temporal variability in water and CO2 fluxes are examined at daily to annual scales. Overall, regional variability in climatic drivers, land use and soil proprieties appears to have a greater effect on evapotranspiration than on net carbon exchange.

Does temperature nudging overwhelm aerosol radiative ...

EPA Pesticide Factsheets

For over two decades, data assimilation (popularly known as nudging) methods have been used for improving regional weather and climate simulations by reducing model biases in meteorological parameters and processes. Similar practice is also popular in many regional integrated meteorology-air quality models that include aerosol direct and indirect effects. However in such multi-modeling systems, temperature changes due to nudging can compete with temperature changes induced by radiatively active & hygroscopic short-lived tracers leading to interesting dilemmas: From weather and climate prediction’s (retrospective or future) point of view when nudging is continuously applied, is there any real added benefit of using such complex and computationally expensive regional integrated modeling systems? What are the relative sizes of these two competing forces? To address these intriguing questions, we convert temperature changes due to nudging into radiative fluxes (referred to as the pseudo radiative forcing, PRF) at the surface and troposphere, and compare the net PRF with the reported aerosol radiative forcing. Results indicate that the PRF at surface dominates PRF at top of the atmosphere (i.e., the net). Also, the net PRF is about 2-4 times larger than estimated aerosol radiative forcing at regional scales while it is significantly larger at local scales. These results also show large surface forcing errors at many polluted urban sites. Thus, operational c

Three-dimensional variations of atmospheric CO2: aircraft measurements and multi-transport model simulations

NASA Astrophysics Data System (ADS)

Niwa, Y.; Patra, P. K.; Sawa, Y.; Machida, T.; Matsueda, H.; Belikov, D.; Maki, T.; Ikegami, M.; Imasu, R.; Maksyutov, S.; Oda, T.; Satoh, M.; Takigawa, M.

2011-04-01

Numerical simulation and validation of three-dimensional structure of atmospheric carbon dioxide (CO2) is necessary for quantification of transport model uncertainty and its role on surface flux estimation by inverse modeling. Simulations of atmospheric CO2 were performed using four transport models and two sets of surface fluxes compared with an aircraft measurement dataset of Comprehensive Observation Network for Trace gases by AIrLiner (CONTRAIL), covering various latitudes, longitudes, and heights. Under this transport model intercomparison project, spatiotemporal variations of CO2 concentration for 2006-2007 were analyzed with a three-dimensional perspective. Results show that the models reasonably simulated vertical profiles and seasonal variations not only over northern latitude areas but also over the tropics and southern latitudes. From CONTRAIL measurements and model simulations, intrusion of northern CO2 in to the Southern Hemisphere, through the upper troposphere, was confirmed. Furthermore, models well simulated the vertical propagation of seasonal variation in the northern free-troposphere. However, significant model-observation discrepancies were found in Asian regions, which are attributable to uncertainty of the surface CO2 flux data. The models consistently underestimated the north-tropics mean gradient of CO2 both in the free-troposphere and marine boundary layer during boreal summer. This result suggests that the north-tropics contrast of annual mean net non-fossil CO2 flux should be greater than 2.7 Pg C yr-1 for 2007.

Empirical prediction of net splanchnic release of ketogenic nutrients, acetate, butyrate and β-hydroxybutyrate in ruminants: a meta-analysis.

PubMed

Loncke, C; Nozière, P; Bahloul, L; Vernet, J; Lapierre, H; Sauvant, D; Ortigues-Marty, I

2015-03-01

For energy feeding systems for ruminants to evolve towards a nutrient-based system, dietary energy supply has to be determined in terms of amount and nature of nutrients. The objective of this study was to establish response equations of the net hepatic flux and net splanchnic release of acetate, butyrate and β-hydroxybutyrate to changes in diet and animal profiles. A meta-analysis was applied on published data compiled from the FLuxes of nutrients across Organs and tissues in Ruminant Animals database, which pools the results from international publications on net splanchnic nutrient fluxes measured in multi-catheterized ruminants. Prediction variables were identified from current knowledge on digestion, hepatic and other tissue metabolism. Subsequently, physiological and other, more integrative, predictors were obtained. Models were established for intakes up to 41 g dry matter per kg BW per day and diets containing up to 70 g concentrate per 100 g dry matter. Models predicted the net hepatic fluxes or net splanchnic release of each nutrient from its net portal appearance and the animal profile. Corrections were applied to account for incomplete hepatic recovery of the blood flow marker, para-aminohippuric acid. Changes in net splanchnic release (mmol/kg BW per hour) could then be predicted by combining the previously published net portal appearance models and the present net hepatic fluxes models. The net splanchnic release of acetate and butyrate were thus predicted from the intake of ruminally fermented organic matter (RfOM) and the nature of RfOM (acetate: residual mean square error (RMSE)=0.18; butyrate: RMSE=0.01). The net splanchnic release of β-hydroxybutyrate was predicted from RfOM intake and the energy balance of the animals (RMSE=0.035), or from the net portal appearance of butyrate and the energy balance of the animals (RMSE=0.050). Models obtained were independent of ruminant species, and presented low interfering factors on the residuals, least square means or individual slopes. The model equations highlighted the importance of considering the physiological state of animals when predicting splanchnic metabolism. This work showed that it is possible to use simple predictors to accurately predict the amount and nature of ketogenic nutrients released towards peripheral tissues in both sheep and cattle at different physiological status. These results provide deeper insight into biological processes and will contribute to the development of improved tools for dietary formulation.

Suspended sediment fluxes in a tidal wetland: Measurement, controlling factors, and error analysis

USGS Publications Warehouse

Ganju, N.K.; Schoellhamer, D.H.; Bergamaschi, B.A.

2005-01-01

Suspended sediment fluxes to and from tidal wetlands are of increasing concern because of habitat restoration efforts, wetland sustainability as sea level rises, and potential contaminant accumulation. We measured water and sediment fluxes through two channels on Browns Island, at the landward end of San Francisco Bay, United States, to determine the factors that control sediment fluxes on and off the island. In situ instrumentation was deployed between October 10 and November 13, 2003. Acoustic Doppler current profilers and the index velocity method were employed to calculate water fluxes. Suspended sediment concentrations (SSC) were determined with optical sensors and cross-sectional water sampling. All procedures were analyzed for their contribution to total error in the flux measurement. The inability to close the water balance and determination of constituent concentration were identified as the main sources of error; total error was 27% for net sediment flux. The water budget for the island was computed with an unaccounted input of 0.20 m 3 s-1 (22% of mean inflow), after considering channel flow, change in water storage, evapotranspiration, and precipitation. The net imbalance may be a combination of groundwater seepage, overland flow, and flow through minor channels. Change of island water storage, caused by local variations in water surface elevation, dominated the tidalty averaged water flux. These variations were mainly caused by wind and barometric pressure change, which alter regional water levels throughout the Sacramento-San Joaquin River Delta. Peak instantaneous ebb flow was 35% greater than peak flood flow, indicating an ebb-dominant system, though dominance varied with the spring-neap cycle. SSC were controlled by wind-wave resuspension adjacent to the island and local tidal currents that mobilized sediment from the channel bed. During neap tides sediment was imported onto the island but during spring tides sediment was exported because the main channel became ebb dominant Over the 34-d monitoring period 14,000 kg of suspended sediment were imported through the two channels. The water imbalance may affect the sediment balance if the unmeasured water transport pathways are capable of transporting large amounts of sediment. We estimate a maximum of 2,800 kg of sediment may have been exported through unmeasured pathways, giving a minimum net import of 11,200 kg. Sediment flux measurements provide insight on tidal to fortnightly marsh sedimentation processes, especially in complex systems where sedimentation is spatially and temporally variable. ?? 2005 Estuarine Research Federation.

Estimation of Regional Net CO2 Exchange over the Southern Great Plains

NASA Astrophysics Data System (ADS)

Biraud, S. C.; Riley, W. J.; Fischer, M. L.; Torn, M. S.; Cooley, H. S.

2004-12-01

Estimating spatially distributed ecosystem CO2 exchange is an important component of the North American Carbon Program. We describe here a methodology to estimate Net Ecosystem Exchange (NEE) over the Southern Great Plains, using: (1) data from the Department Of Energy's Atmospheric Radiation Measurement (ARM) sites in Oklahoma and Kansas; (2) meteorological forcing data from the Mesonet facilities; (3) soil and vegetation types from 1 km resolution USGS databases; (4) vegetation status (e.g., LAI) from 1 km satellite measurements of surface reflectance (MODIS); (5) a tested land-surface model; and (6) a coupled land-surface and meteorological model (MM5/ISOLSM). This framework allows us to simulate regional surface fluxes in addition to ABL and free troposphere concentrations of CO2 at a continental scale with fine-scale nested grids centered on the ARM central facility. We use the offline land-surface and coupled models to estimate regional NEE, and compare predictions to measurements from the 9 Extended Facility sites with eddy correlation measurements. Site level comparisons to portable ECOR measurements in several crop types are also presented. Our approach also allows us to extend bottom-up estimates to periods and areas where meteorological forcing data are unavailable.

Evaluating the effects of historical land cover change on summertime weather and climate in New Jersey

NASA Astrophysics Data System (ADS)

Wichansky, Paul Stuart

The 19th-century agrarian landscape of New Jersey (NJ) and the surrounding region has been extensively transformed to the present-day land cover by urbanization, reforestation, and localized areas of deforestation. This study used a mesoscale atmospheric numerical model to investigate the sensitivity of the warm season climate of NJ to these land cover changes. Reconstructed 1880s-era and present-day land cover datasets were used as surface boundary conditions for a set of simulations performed with the Regional Atmospheric Modeling System (RAMS). Three-member ensembles with historical and present-day land cover were compared to examine the sensitivity of surface air and dewpoint temperatures, rainfall, the individual components of the surface energy budget, horizontal and vertical winds, and the vertical profiles of temperature and humidity to these land cover changes. Mean temperatures for the present-day landscape were 0.3-0.6°C warmer than for the historical landscape over a considerable portion of NJ and the surrounding region, with daily maximum temperatures at least 1.0°C warmer over some of the highly urbanized locations. Reforested regions in the present-day landscape, however, showed a slight cooling. Surface warming was generally associated with repartitioning of net radiation from latent to sensible heat flux, and conversely for cooling. Reduced evapotranspiration from much of the present-day land surface led to dewpoint temperature decreases of 0.3-0.6°C. While urbanization was accompanied by strong surface albedo decreases and increases in net shortwave radiation, reforestation and potential changes in forest composition have generally increased albedos and also enhanced landscape heterogeneity. The increased deciduousness of forests may have further reduced net downward longwave radiation. These land cover changes have modified boundary-layer dynamics by increasing low-level convergence and upper-level divergence in the interior of NJ, especially where sensible heat fluxes have increased for the present-day landscape, hence enhancing uplift in the mid-troposphere. The mesoscale circulations that developed in the present-day ensemble were also more effective at lifting available moisture to higher levels of the boundary layer, lowering dewpoints near the surface but increasing them aloft. Likewise, the sea breeze in coastal areas of NJ in the present-day ensemble had stronger uplift during the afternoon and enhanced moisture transport to higher levels.

New Constraints on Terrestrial Surface-Atmosphere Fluxes of Gaseous Elemental Mercury Using a Global Database.

PubMed

Agnan, Yannick; Le Dantec, Théo; Moore, Christopher W; Edwards, Grant C; Obrist, Daniel

2016-01-19

Despite 30 years of study, gaseous elemental mercury (Hg(0)) exchange magnitude and controls between terrestrial surfaces and the atmosphere still remain uncertain. We compiled data from 132 studies, including 1290 reported fluxes from more than 200,000 individual measurements, into a database to statistically examine flux magnitudes and controls. We found that fluxes were unevenly distributed, both spatially and temporally, with strong biases toward Hg-enriched sites, daytime and summertime measurements. Fluxes at Hg-enriched sites were positively correlated with substrate concentrations, but this was absent at background sites. Median fluxes over litter- and snow-covered soils were lower than over bare soils, and chamber measurements showed higher emission compared to micrometeorological measurements. Due to low spatial extent, estimated emissions from Hg-enriched areas (217 Mg·a(-1)) were lower than previous estimates. Globally, areas with enhanced atmospheric Hg(0) levels (particularly East Asia) showed an emerging importance of Hg(0) emissions accounting for half of the total global emissions estimated at 607 Mg·a(-1), although with a large uncertainty range (-513 to 1353 Mg·a(-1) [range of 37.5th and 62.5th percentiles]). The largest uncertainties in Hg(0) fluxes stem from forests (-513 to 1353 Mg·a(-1) [range of 37.5th and 62.5th percentiles]), largely driven by a shortage of whole-ecosystem fluxes and uncertain contributions of leaf-atmosphere exchanges, questioning to what degree ecosystems are net sinks or sources of atmospheric Hg(0).

Upper Ocean Response to the Atmospheric Cold Pools Associated With the Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Pei, Suyang; Shinoda, Toshiaki; Soloviev, Alexander; Lien, Ren-Chieh

2018-05-01

Atmospheric cold pools are frequently observed during the Madden-Julian Oscillation events and play an important role in the development and organization of large-scale convection. They are generally associated with heavy precipitation and strong winds, inducing large air-sea fluxes and significant sea surface temperature (SST) fluctuations. This study provides a first detailed investigation of the upper ocean response to the strong cold pools associated with the Madden-Julian Oscillation, based on the analysis of in situ data collected during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign and one-dimensional ocean model simulations validated by the data. During strong cold pools, SST drops rapidly due to the atmospheric cooling in a shoaled mixed layer caused by the enhanced near-surface salinity stratification generated by heavy precipitation. Significant contribution also comes from the component of surface heat flux produced by the cold rain temperature. After the period of heavy rain, while net surface cooling remains, SST gradually recovers due to the enhanced entrainment of warmer waters below the mixed layer.

Surface Energy Balance System (SEBS) Handbook

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, D. R.

2016-01-01

A Surface Energy Balance System (SEBS) has been installed collocated with each deployed Eddy Correlation Flux Measurement System (ECOR) at the Atmospheric Radiation Measurement (ARM) Climate Research Facility’s Southern Great Plains (SGP) site, North Slope of Alaska (NSA) site, first ARM Mobile Facility (AMF1), second ARM Mobile Facility (AMF2), and third ARM Mobile Facility (AMF3) at Oliktok Point (OLI). A SEBS was also deployed with the Tropical Western Pacific (TWP) site, before it was decommissioned. Data from these sites, including the retired TWP, are available in the ARM Data Archive. The SEBS consists of upwelling and downwelling solar and infraredmore » radiometers within one net radiometer, a wetness sensor, and soil measurements. The SEBS measurements allow the comparison of ECOR sensible and latent heat fluxes with the energy balance determined from the SEBS and provide information on wetting of the sensors for data quality purposes.« less

Mapping surface energy balance components by combining landsat thematic mapper and ground-based meteorological data

USGS Publications Warehouse

Moran, M.S.; Jackson, R. D.; Raymond, L.H.; Gay, L.W.; Slater, P.N.

1989-01-01

Surface energy balance components were evaluated by combining satellite-based spectral data with on-site measurements of solar irradiance, air temperature, wind speed, and vapor pressure. Maps of latent heat flux density (??E) and net radiant flux density (Rn) were produced using Landsat Thematic Mapper (TM) data for three dates: 23 July 1985, 5 April 1986, and 24 June 1986. On each date, a Bowen-ratio apparatus, located in a vegetated field, was used to measure ??E and Rn at a point within the field. Estimates of ??E and Rn were also obtained using radiometers aboard an aircraft flown at 150 m above ground level. The TM-based estimates differed from the Bowen-ratio and aircraft-based estimates by less than 12 % over mature fields of cotton, wheat, and alfalfa, where ??E and Rn ranged from 400 to 700 Wm-2. ?? 1989.

Turbulent transports over tundra

NASA Technical Reports Server (NTRS)

Fitzjarrald, David R.; Moore, Kathleen E.

1992-01-01

An extensive period of eddy correlation surface flux measurements was conducted at a site distant from the coast on the western Alaskan tundra. The surface exchange of heat and moisture over tundra during the summer was limited by a strong resistance to transfer from the upper soil layer through the ground cover, with canopy resistances to evaporation observed to be approximately 200 s/m. Though July 1988 was anomalously warm and dry in the region and August was close to normal temperature and rainfall, there was no appreciable difference in the canopy resistance between the periods. During the dry sunny period at the end of July, the observed evaporation rate was 2 mm/d. High canopy resistance led to an approximate equipartition of net radiation between latent and sensible heat, each accounting for 40 percent of the available energy, with heat balance apparently going into soil heat flux.

A Simulation Model of Carbon Cycling and Methane Emissions in Amazon Wetlands

NASA Technical Reports Server (NTRS)

Potter, Christopher; Melack, John; Hess, Laura; Forsberg, Bruce; Novo, Evlyn Moraes; Klooster, Steven

2004-01-01

An integrative carbon study is investigating the hypothesis that measured fluxes of methane from wetlands in the Amazon region can be predicted accurately using a combination of process modeling of ecosystem carbon cycles and remote sensing of regional floodplain dynamics. A new simulation model has been build using the NASA- CASA concept for predicting methane production and emission fluxes in Amazon river and floodplain ecosystems. Numerous innovations area being made to model Amazon wetland ecosystems, including: (1) prediction of wetland net primary production (NPP) as the source for plant litter decomposition and accumulation of sediment organic matter in two major vegetation classes - flooded forests (varzea or igapo) and floating macrophytes, (2) representation of controls on carbon processing and methane evasion at the diffusive boundary layer, through the lake water column, and in wetland sediments as a function of changes in floodplain water level, (3) inclusion of surface emissions controls on wetland methane fluxes, including variations in daily surface temperature and of hydrostatic pressure linked to water level fluctuations. A model design overview and early simulation results are presented.

Flux variance partitioning: a new approach to advance eddy covariance observations for greenhouse gas emissions

USDA-ARS?s Scientific Manuscript database

Eddy covariance (EC) is a well-established, non-intrusive observational technique that has long been used to measure the net carbon balance of numerous ecosystems including crop lands for perennial crops such as orchards and vineyards, and pasturelands. While EC measures net carbon fluxes well, it ...

Estimating photosynthetic 13C discrimination in terrestrial CO2 exchange from canopy to regional scales.

Treesearch

Chun-Ta Lai; James R. Ehleringer; Pieter Tans; Steven C. Wofsy; Shawn P. Urbanski; David Y. Hollinger

2004-01-01

We determined δ13C values associated with canopy gross and net C02 fluxes from four U.S. sites sampled between 2001 and 2002. Annual mean, flux-weighted δ13C values of net ecosystem C02 exchange (NEE) were estimated for four contrasting ecosystems (three...

Gas-particle interactions above a Dutch heathland: I. Surface exchange fluxes of NH3, SO2, HNO3 and HCl

NASA Astrophysics Data System (ADS)

Nemitz, E.; Sutton, M. A.; Wyers, G. P.; Jongejan, P. A. C.

2004-07-01

A field measurement campaign was carried out over a Dutch heathland to investigate the effect of gas-to-particle conversion and ammonium aerosol evaporation on surface/atmosphere fluxes of ammonia and related species. Continuous micrometeorological measurements of the surface exchange of NH3, SO2, HNO3 and HCl were made and are analyzed here with regard to average fluxes, deposition velocities (Vd), canopy resistances (Rc) and canopy compensation point for NH3. Gradients of SO2, HNO3 and HCl were measured with a novel wet-denuder system with online anion chromatography. Measurements of HNO3 and HCl indicate an Rc of 100 to 200 s m-1 during warm daytime periods, probably at least partly due to non-zero acid partial pressures above NH4NO3 and NH4Cl on the leaf surfaces. Although it is likely that this observation is exacerbated by the effect of the evaporation of airborne NH4+ on the gradient measurements, the findings nevertheless add to the growing evidence that HNO3 and HCl are not always deposited at the maximum rate. Ammonia (NH3) fluxes show mainly deposition, with some periods of significant daytime emission. The net exchange could be reproduced both with an Rc model (deposition fluxes only) using resistance parameterizations from former measurements, as well as with the canopy compensation point model, using parameterizations derived from the measurements. The apoplastic ratio of ammonium and hydrogen concentration (Γs=[NH4+]/[H+]) of 1200 estimated from the measurements is large for semi-natural vegetation, but smaller than indicated by previous measurements at this site.

Gas-particle interactions above a Dutch heathland: I. Surface exchange fluxes of NH3, SO2, HNO3 and HCl

NASA Astrophysics Data System (ADS)

Nemitz, E.; Sutton, M. A.; Wyers, G. P.; Jongejan, P. A. C.

2004-03-01

A field measurement campaign was carried out over a Dutch heathland to investigate the effect of gas-to-particle conversion and ammonium aerosol evaporation on surface/atmosphere fluxes of ammonia and related species. Continuous micrometeorological measurements of the surface exchange of NH3, SO2, HNO3 and HCl were made and are analyzed here with regard to average fluxes, deposition velocities (Vd), canopy resistances (Rc) and canopy compensation point for NH3. Gradients of SO2, HNO3 and HCl were measured with a novel wet-denuder system with online anion chromatography. Measurements of HNO3 and HCl indicate an Rc of 100 to 200 s m-1 during warm daytime periods, probably at least partly due to non-zero acid partial pressures above NH4NO3 and NH4Cl on the leaf surfaces. Although it is likely that this observation is exacerbated by the effect of the evaporation of airborne NH4+ on the gradient measurements, the findings nevertheless add to the growing evidence that HNO3 and HCl are not always deposited at the maximum rate. Ammonia (NH3) fluxes show mainly deposition, with some periods of significant daytime emission. The net exchange could be reproduced both with an Rc model (deposition fluxes only) using resistance parameterizations from former measurements, as well as with the canopy compensation point model, using parameterizations derived from the measurements. The apoplastic ratio of ammonium and hydrogen concentration (Γs=[NH4+]/[H+]) of 1200 estimated from the measurements is large for semi- natural vegetation, but smaller than indicated by previous measurements at this site.

Landscape analysis of soil methane flux across complex terrain

NASA Astrophysics Data System (ADS)

Kaiser, Kendra E.; McGlynn, Brian L.; Dore, John E.

2018-05-01

Relationships between methane (CH4) fluxes and environmental conditions have been extensively explored in saturated soils, while research has been less prevalent in aerated soils because of the relatively small magnitudes of CH4 fluxes that occur in dry soils. Our study builds on previous carbon cycle research at Tenderfoot Creek Experimental Forest, Montana, to identify how environmental conditions reflected by topographic metrics can be leveraged to estimate watershed scale CH4 fluxes from point scale measurements. Here, we measured soil CH4 concentrations and fluxes across a range of landscape positions (7 riparian, 25 upland), utilizing topographic and seasonal (29 May-12 September) gradients to examine the relationships between environmental variables, hydrologic dynamics, and CH4 emission and uptake. Riparian areas emitted small fluxes of CH4 throughout the study (median: 0.186 µg CH4-C m-2 h-1) and uplands increased in sink strength with dry-down of the watershed (median: -22.9 µg CH4-C m-2 h-1). Locations with volumetric water content (VWC) below 38 % were methane sinks, and uptake increased with decreasing VWC. Above 43 % VWC, net CH4 efflux occurred, and at intermediate VWC net fluxes were near zero. Riparian sites had near-neutral cumulative seasonal flux, and cumulative uptake of CH4 in the uplands was significantly related to topographic indices. These relationships were used to model the net seasonal CH4 flux of the upper Stringer Creek watershed (-1.75 kg CH4-C ha-1). This spatially distributed estimate was 111 % larger than that obtained by simply extrapolating the mean CH4 flux to the entire watershed area. Our results highlight the importance of quantifying the space-time variability of net CH4 fluxes as predicted by the frequency distribution of landscape positions when assessing watershed scale greenhouse gas balances.

Connections Between the Spring Breakup of the Southern Hemisphere Polar Vortex, Stationary Waves, and Air-sea Roughness

NASA Technical Reports Server (NTRS)

Garfinkel, Chaim I.; Oman, Luke David; Barnes, Elizabeth A.; Waugh, Darryn W.; Hurwitz, Margaret H.; Molod, Andrea M.

2013-01-01

A robust connection between the drag on surface-layer winds and the stratospheric circulation is demonstrated in NASA's Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM). Specifically, an updated parameterization of roughness at the air-sea interface, in which surface roughness is increased for moderate wind speeds (4ms to 20ms), leads to a decrease in model biases in Southern Hemispheric ozone, polar cap temperature, stationary wave heat flux, and springtime vortex breakup. A dynamical mechanism is proposed whereby increased surface roughness leads to improved stationary waves. Increased surface roughness leads to anomalous eddy momentum flux convergence primarily in the Indian Ocean sector (where eddies are strongest climatologically) in September and October. The localization of the eddy momentum flux convergence anomaly in the Indian Ocean sector leads to a zonally asymmetric reduction in zonal wind and, by geostrophy, to a wavenumber-1 stationary wave pattern. This tropospheric stationary wave pattern leads to enhanced upwards wave activity entering the stratosphere. The net effect is an improved Southern Hemisphere vortex: the vortex breaks up earlier in spring (i.e., the spring late-breakup bias is partially ameliorated) yet is no weaker in mid-winter. More than half of the stratospheric biases appear to be related to the surface wind speed biases. As many other chemistry climate models use a similar scheme for their surface layer momentum exchange and have similar biases in the stratosphere, we expect that results from GEOSCCM may be relevant for other climate models.

Short-circuit current and ionic fluxes in the isolated colonic mucosa of Bufo arenarum.

PubMed

Lew, V L

1970-03-01

1. The unidirectional fluxes of (22)Na, (36)Cl and [(14)C]bicarbonate ions were measured in paired portions of the isolated and short-circuited colonic mucosa of Bufo arenarum, separated from its muscular layer. Pharmacological effects as well as effects of changes in the composition of the nutrient solutions on the electrical parameters of membrane activity (potential difference, short-circuit current and total membrane resistance) are described.2. The net fluxes of both Cl and bicarbonate ions were not significantly different from zero in the absence of electrochemical gradients across the membrane.3. The net Na flux from mucosa to serosa represented a variable proportion of the short-circuit current ranging from 62 to 100%.4. The proportion of membranes with high discrepancies between net Na flux and short-circuit current decreased with the duration of captivity of the toads.5. When Na was entirely replaced by choline in the mucosal bathing solution, the short-circuit current dropped by a variable amount within the range of 64 to 98% of its control values in different membranes. This effect was completely reversible. Similar changes in the serosal solution had no effect.6. The short-circuit current and potential difference were very sensitive to the serosal concentration of bicarbonate ions. In different membranes, 60-100% of the short-circuit current was reversibly abolished by bathing the serosal surface with a bicarbonate-free solution. The mucosal bicarbonate level had no effect on either the potential difference or the short-circuit current. 5 mM bicarbonate in the serosal solution restored at least 50% of the short-circuit control value and full recovery was attained by concentrations near 30 mM bicarbonate.7. Anoxia brought the potential difference and short-circuit current reversibly down to zero in about 50 min.8. Ouabain reduced the short-circuit current up to 80% in about 40 min when present in the serosal solution at a concentration of 10(-4)M. At this or lower concentrations the ouabain effect was reversible. Above this level ouabain produced 100% inhibition in 3-4 hr, but this was no longer reversible. Ouabain had no effect on the short-circuit current either when applied to the mucosal surface or in the absence of Na from the mucosal solution.9. Diamox produced a variable inhibition of the short-circuit current of up to 30% only at concentrations above 10 mM.10. Possible mechanisms are discussed for the appearance of the non-Na component of the short-circuit current. A theory concerning its nature is proposed.

Assessment of clear sky radiative fluxes in CMIP5 climate models using surface observations from BSRN

NASA Astrophysics Data System (ADS)

Wild, M.; Hakuba, M. Z.; Folini, D.; Ott, P.; Long, C. N.

2017-12-01

Clear sky fluxes in the latest generation of Global Climate Models (GCM) from CMIP5 still vary largely particularly at the Earth's surface, covering in their global means a range of 16 and 24 Wm-2 in the surface downward clear sky shortwave (SW) and longwave radiation, respectively. We assess these fluxes with monthly clear sky reference climatologies derived from more than 40 Baseline Surface Radiation Network (BSRN) sites based on Long and Ackermann (2000) and Hakuba et al. (2015). The comparison is complicated by the fact that the monthly SW clear sky BSRN reference climatologies are inferred from measurements under true cloud-free conditions, whereas the GCM clear sky fluxes are calculated continuously at every timestep solely by removing the clouds, yet otherwise keeping the prevailing atmospheric composition (e.g. water vapor, temperature, aerosols) during the cloudy conditions. This induces the risk of biases in the GCMs just due to the additional sampling of clear sky fluxes calculated under atmospheric conditions representative for cloudy situations. Thereby, a wet bias may be expected in the GCMs compared to the observational references, which may induce spurious low biases in the downward clear sky SW fluxes. To estimate the magnitude of these spurious biases in the available monthly mean fields from 40 CMIP5 models, we used their respective multi-century control runs, and searched therein for each month and each BSRN station the month with the lowest cloud cover. The deviations of the clear sky fluxes in this month from their long-term means have then be used as indicators of the magnitude of the abovementioned sampling biases and as correction factors for an appropriate comparison with the BSRN climatologies, individually applied for each model and BSRN site. The overall correction is on the order of 2 Wm-2. This revises our best estimate for the global mean surface downward SW clear sky radiation, previously at 249 Wm-2 infered from the GCM clear sky flux fields and their biases compared to the BSRN climatologies, now to 247 Wm-2 including this additional correction. 34 out of 40 CMIP5 GCMs exceed this reference value. With a global mean surface albedo of 13 % and net TOA SW clear sky flux of 287 Wm-2 from CERES-EBAF this results in a global mean clear sky surface and atmospheric SW absorption of 214 and 73 Wm-2, respectively.

Carbon dioxide and methane exchange at a cool-temperate freshwater marsh

NASA Astrophysics Data System (ADS)

Strachan, Ian B.; Nugent, Kelly A.; Crombie, Stephanie; Bonneville, Marie-Claude

2015-06-01

Freshwater marshes have been shown to be strong sinks for carbon dioxide (CO2) on an annual basis relative to other wetland types; however it is likely that these ecosystems are also strong emitters of methane (CH4), reducing their carbon (C) sequestration potential. Multiyear C balances in these ecosystems are necessary therefore to determine their contribution to the global C cycle. Despite this, the number of multiyear studies in marshes is few, with, to the best of our knowledge, only one other Northern marsh C balance reported. This study presents five years of eddy covariance flux measurements of CO2, and four years of warm-season chamber measurements of CH4 at a cool-temperate Typha angustifolia marsh. Annual average cumulative net ecosystem exchange of CO2 (NEE) at the marsh was -224 ± 54 g C m-2 yr-1 (±SD) over the five-year period, ranging from -126 to -284 g C m-2 yr-1. Enhancement of the ecosystem respiration during warmer spring, autumn and winter periods appeared the strongest determinant of annual NEE totals. Warm season fluxes of CH4 from the Typha vegetation (avg. 1.0 ± 1.2 g C m-2 d-1) were significantly higher than fluxes from the water surface (0.5 ± 0.4 g C m-2 d-1) and unvegetated mats (0.2 ± 0.2 g C m-2 d-1). Air temperature was a primary driver of all CH4 fluxes, while water table was not a significant correlate as water levels were always at or above the vegetative mat surfaces. Weighting by the surface cover proportion of water and vegetation yielded a net ecosystem CH4 emission of 127 ± 19 g C m-2 yr-1. Combining CO2 and CH4, the annual C sink at the Mer Bleue marsh was reduced to -97 ± 57 g C m-2 yr-1, illustrating the importance of accounting for CH4 when generating marsh C budgets.

Global shortwave energy budget at the earth's surface from ERBE observations

NASA Technical Reports Server (NTRS)

Breon, Francois-Marie; Frouin, Robert

1994-01-01

A method is proposed to compute the net solar (shortwave) irradiance at the earth's surface from Earth Radiation Budget Experiment (ERBE) data in the S4 format. The S4 data are monthly averaged broadband planetary albedo collected at selected times during the day. Net surface shortwave irradiance is obtained from the shortwave irradiance incident at the top of the atmosphere (known) by subtracting both the shortwave energy flux reflected by the earth-atmosphere system (measured) and the energy flux absorbed by the atmosphere (modeled). Precalculated atmospheric- and surface-dependent functions that characterize scattering and absorption in the atmosphere are used, which makes the method easily applicable and computationally efficient. Four surface types are distinguished, namely, ocean, vegetation, desert, and snow/ice. Over the tropical Pacific Ocean, the estimates based on ERBE data compare well with those obtained from International Satellite Cloud Climatology Project (ISCCP) B3 data. For the 9 months analyzed the linear correlation coefficient and the standard difference between the two datasets are 0.95 and 14 W/sq m (about 6% of the average shortwave irradiance), respectively, and the bias is 15 W/sq m (higher ERBE values). The bias, a strong function of ISCCP satellite viewing zenith angle, is mostly in the ISCCP-based estimates. Over snow/ice, vegetation, and desert no comparison is made with other satellite-based estimates, but theoretical calculations using the discrete ordinate method suggest that over highly reflective surfaces (snow/ice, desert) the model, which accounts crudely for multiple reflection between the surface and clouds, may substantially overestimate the absorbed solar energy flux at the surface, especially when clouds are optically thick. The monthly surface shortwave irradiance fields produced for 1986 exhibit the main features characteristic of the earth's climate. As found in other studies, our values are generally higher than Esbensen and Kushnir's by as much as 80 W/sq m in the tropical oceans. A cloud parameter, defined as the difference between clear-sky and actual irradiances normalized to top-of-atmosphere clear-sky irradiance, is also examined. This parameter, minimally affected by sun zenith angle, is higher in the midlatitude regions of storm tracks than in the intertropical convergence zone (ITCZ), suggesting that, on average, the higher cloud coverage in midlatitudes is more effective at reducing surface shortwave irradiance than opaque, convective, yet sparser clouds in the ITCZ. Surface albedo estimates are realistic, generally not exceeding 0.06 in the ocean, as high as 0.9 in polar regions, and reaching 0.5 in the Sahara and Arabian deserts.

Year-round Regional CO2 Fluxes from Boreal and Tundra Ecosystems in Alaska

NASA Astrophysics Data System (ADS)

Commane, R.; Lindaas, J.; Benmergui, J. S.; Luus, K. A.; Chang, R. Y. W.; Daube, B. C.; Euskirchen, E. S.; Henderson, J.; Karion, A.; Miller, J. B.; Miller, S. M.; Parazoo, N.; Randerson, J. T.; Sweeney, C.; Tans, P. P.; Thoning, K. W.; Veraverbeke, S.; Miller, C. E.; Wofsy, S. C.

2016-12-01

High-latitude ecosystems could release large amounts of carbon dioxide (CO2) to the atmosphere in a warmer climate. We derive temporally and spatially resolved year-round CO2 fluxes in Alaska from a synthesis of airborne and tower CO2 observations in 2012-2014. We find that tundra ecosystems were net sources of atmospheric CO2. We discuss these flux estimates in the context of long-term CO2 measurements at Barrow, AK, to asses the long term trend in carbon fluxes in the Arctic. Many Earth System Models incorrectly simulate net carbon uptake in Alaska presently. Our results imply that annual net emission of CO2 to the atmosphere may have increased markedly in this region of the Arctic in response to warming climate, supporting the view that climate-carbon feedback is strongly positive in the high Arctic.

Predicted net efflux of radiocarbon from the ocean and increase in atmospheric radiocarbon content

NASA Astrophysics Data System (ADS)

Caldeira, Ken; Rau, Greg H.; Duffy, Philip B.

Prior to changes introduced by man, production of radiocarbon (14C) in the stratosphere nearly balanced the flux of 14C from the atmosphere to the ocean and land biosphere, which in turn nearly balanced radioactive decay in these 14C reservoirs. This balance has been altered by land-use changes, fossil-fuel burning, and atmospheric nuclear detonations. Here, we use a model of the global carbon cycle to quantify these radiocarbon fluxes and make predictions about their magnitude in the future. Atmospheric nuclear detonations increased atmospheric 14C content by about 80% by the mid-1960's. Since that time, the 14C content of the atmosphere has been diminishing as this bomb radiocarbon has been entering the oceans and terrestrial biosphere. However, we predict that atmospheric 14C content will reach a minimum and start to increase within the next few years if fossil-fuel burning continues according to a “business-as-usual” scenario, even though fossil fuels are devoid of 14C. This will happen because fossil-fuel carbon diminishes the net flux of 14C from the atmosphere to the oceans and land biosphere, forcing 14C to accumulate in the atmosphere. Furthermore, the net flux of both bomb and natural 14C into the ocean are predicted to continue to slow and then, in the middle of the next century, to reverse, so that there will be a net flux of 14C from the ocean to the atmosphere. The predicted reversal of net 14C fluxes into the ocean is a further example of human impacts on the global carbon cycle.

Annual and latitudinal variations of surface fluxes and meteorological variables at Arctic terrestrial sites

NASA Astrophysics Data System (ADS)

Grachev, Andrey; Uttal, Taneil; Persson, Ola; Konopleva-Akish, Elena; Crepinsek, Sara; Cox, Christopher; Fairall, Christopher; Makshtas, Alexander; Repina, Irina

2016-04-01

This study analyzes and discusses seasonal and latitudinal variations of surface fluxes (turbulent, radiative, and soil ground heat) and other ancillary surface/snow/permafrost data based on in-situ measurements made at two long-term research observatories near the coast of the Arctic Ocean located in Canada and Russia. The hourly averaged data collected at Eureka (Canadian territory of Nunavut) and Tiksi (East Siberia) located at two quite different latitudes (80.0 N and 71.6 N respectively) are analyzed in details to describe the seasons in the Arctic. Although Eureka and Tiksi are located at the different continents and at the different latitudes, the annual course of the surface meteorology and the surface fluxes are qualitatively very similar. The air and soil temperatures display the familiar strong seasonal trend with maximum of measured temperatures in mid-summer and minimum during winter. According to our data, variation in incoming short-wave solar radiation led the seasonal pattern of the air and soil temperatures, and the turbulent fluxes. During the dark Polar nights, air and ground temperatures are strongly controlled by long-wave radiation associated generally with cloud cover. Due to the fact that in average the higher latitudes receive less solar radiation than lower latitudes, a length of the convective atmospheric boundary layer (warm season) is shorter and middle-summer amplitude of the turbulent fluxes is generally less in Eureka than in Tiksi. However, since solar elevation angle at local midnight in the middle of Arctic summer is higher for Eureka as compared to Tiksi, stable stratification and upward turbulent flux for carbon dioxide is generally did not observed at Eureka site during summer seasons. It was found a high correlation between the turbulent fluxes of sensible and latent heat, carbon dioxide and the net solar radiation. A comprehensive evaluation of energy balance closure problem is performed based on the multi-year data sets collected at the Arctic terrestrial sites. The work is supported by the NOAA Climate Program Office, the U.S. National Science Foundation (NSF) with award ARC 11-07428, and by the U.S. Civilian Research & Development Foundation (CRDF) with award RUG1-2976-ST-10.

The HIRLAM fast radiation scheme for mesoscale numerical weather prediction models

NASA Astrophysics Data System (ADS)

Rontu, Laura; Gleeson, Emily; Räisänen, Petri; Pagh Nielsen, Kristian; Savijärvi, Hannu; Hansen Sass, Bent

2017-07-01

This paper provides an overview of the HLRADIA shortwave (SW) and longwave (LW) broadband radiation schemes used in the HIRLAM numerical weather prediction (NWP) model and available in the HARMONIE-AROME mesoscale NWP model. The advantage of broadband, over spectral, schemes is that they can be called more frequently within the model, without compromising on computational efficiency. In mesoscale models fast interactions between clouds and radiation and the surface and radiation can be of greater importance than accounting for the spectral details of clear-sky radiation; thus calling the routines more frequently can be of greater benefit than the deterioration due to loss of spectral details. Fast but physically based radiation parametrizations are expected to be valuable for high-resolution ensemble forecasting, because as well as the speed of their execution, they may provide realistic physical perturbations. Results from single-column diagnostic experiments based on CIRC benchmark cases and an evaluation of 10 years of radiation output from the FMI operational archive of HIRLAM forecasts indicate that HLRADIA performs sufficiently well with respect to the clear-sky downwelling SW and longwave LW fluxes at the surface. In general, HLRADIA tends to overestimate surface fluxes, with the exception of LW fluxes under cold and dry conditions. The most obvious overestimation of the surface SW flux was seen in the cloudy cases in the 10-year comparison; this bias may be related to using a cloud inhomogeneity correction, which was too large. According to the CIRC comparisons, the outgoing LW and SW fluxes at the top of atmosphere are mostly overestimated by HLRADIA and the net LW flux is underestimated above clouds. The absorption of SW radiation by the atmosphere seems to be underestimated and LW absorption seems to be overestimated. Despite these issues, the overall results are satisfying and work on the improvement of HLRADIA for the use in HARMONIE-AROME NWP system is ongoing. In a HARMONIE-AROME 3-D forecast experiment we have shown that the frequency of the call for the radiation parametrization and choice of the parametrization scheme makes a difference to the surface radiation fluxes and changes the spatial distribution of the vertically integrated cloud cover and precipitation.

Free convection in the Matian atmosphere

NASA Technical Reports Server (NTRS)

Clow, G. D.; Haberle, R. M.

1990-01-01

The 'free convective' regime for the Martian atmospheric boundary layer (ABL) was investigated. This state occurs when the mean windspeed at the top of the ABL drops below some critical value U(sub c) and positive buoyant forces are present. Such forces can arise either from vertical temperature or water vapor gradients across the atmospheric surface layer. During free convection, buoyant forces drive narrow plumes that ascend to the inversion height with a return circulation consisting of broad slower-moving downdraughts. Horizontal pressure, temperature, windspeed, and water vapor fluctuations resulting form this circulation pattern can be quite large adjacent to the ground (within the surface layer). The local turbulent fluctuations cause non-zero mean surface stresses, sensible heat fluxes, and latent heat fluxes, even when the mean regional windspeed is zero. Although motions above the surface layer are insensitive to the nature of the surface, the sensible and latent heat fluxes are primarily controlled by processes within the interfacial sublayer immediately adjacent to the ground during free convection. Thus the distinction between aerodynamically smooth and rough airflow within the interfacial sublayer is more important than for the more typical situation where the mean regional windspeed is greater than U(sub c). Buoyant forces associated with water vapor gradients are particularly large on Mars at low pressures and high temperatures when the surface relative humidity is 100 percent, enhancing the likelihood of free convection under these conditions. On this basis, Ingersol postulated the evaporative heat losses from an icy surface on Mars at 237 K and current pressures would exceed the available net radiative flux at the surface, thus prohibiting ice from melting at low atmospheric pressures. Schumann has developed equations describing the horizontal fluctuations and mean vertical gradients occurring during free convection. Schumann's model was generalized to include convection driven by water vapor gradients and to include the effects of circulation above both aerodynamically smooth and rough surfaces.

Uncertainty in predictions of forest carbon dynamics: separating driver error from model error.

PubMed

Spadavecchia, L; Williams, M; Law, B E

2011-07-01

We present an analysis of the relative magnitude and contribution of parameter and driver uncertainty to the confidence intervals on estimates of net carbon fluxes. Model parameters may be difficult or impractical to measure, while driver fields are rarely complete, with data gaps due to sensor failure and sparse observational networks. Parameters are generally derived through some optimization method, while driver fields may be interpolated from available data sources. For this study, we used data from a young ponderosa pine stand at Metolius, Central Oregon, and a simple daily model of coupled carbon and water fluxes (DALEC). An ensemble of acceptable parameterizations was generated using an ensemble Kalman filter and eddy covariance measurements of net C exchange. Geostatistical simulations generated an ensemble of meteorological driving variables for the site, consistent with the spatiotemporal autocorrelations inherent in the observational data from 13 local weather stations. Simulated meteorological data were propagated through the model to derive the uncertainty on the CO2 flux resultant from driver uncertainty typical of spatially extensive modeling studies. Furthermore, the model uncertainty was partitioned between temperature and precipitation. With at least one meteorological station within 25 km of the study site, driver uncertainty was relatively small ( 10% of the total net flux), while parameterization uncertainty was larger, 50% of the total net flux. The largest source of driver uncertainty was due to temperature (8% of the total flux). The combined effect of parameter and driver uncertainty was 57% of the total net flux. However, when the nearest meteorological station was > 100 km from the study site, uncertainty in net ecosystem exchange (NEE) predictions introduced by meteorological drivers increased by 88%. Precipitation estimates were a larger source of bias in NEE estimates than were temperature estimates, although the biases partly compensated for each other. The time scales on which precipitation errors occurred in the simulations were shorter than the temporal scales over which drought developed in the model, so drought events were reasonably simulated. The approach outlined here provides a means to assess the uncertainty and bias introduced by meteorological drivers in regional-scale ecological forecasting.

A joint data assimilation system (Tan-Tracker) to simultaneously estimate surface CO2 fluxes and 3-D atmospheric CO2 concentrations from observations

NASA Astrophysics Data System (ADS)

Tian, X.; Xie, Z.; Liu, Y.; Cai, Z.; Fu, Y.; Zhang, H.; Feng, L.

2014-12-01

We have developed a novel framework ("Tan-Tracker") for assimilating observations of atmospheric CO2 concentrations, based on the POD-based (proper orthogonal decomposition) ensemble four-dimensional variational data assimilation method (PODEn4DVar). The high flexibility and the high computational efficiency of the PODEn4DVar approach allow us to include both the atmospheric CO2 concentrations and the surface CO2 fluxes as part of the large state vector to be simultaneously estimated from assimilation of atmospheric CO2 observations. Compared to most modern top-down flux inversion approaches, where only surface fluxes are considered as control variables, one major advantage of our joint data assimilation system is that, in principle, no assumption on perfect transport models is needed. In addition, the possibility for Tan-Tracker to use a complete dynamic model to consistently describe the time evolution of CO2 surface fluxes (CFs) and the atmospheric CO2 concentrations represents a better use of observation information for recycling the analyses at each assimilation step in order to improve the forecasts for the following assimilations. An experimental Tan-Tracker system has been built based on a complete augmented dynamical model, where (1) the surface atmosphere CO2 exchanges are prescribed by using a persistent forecasting model for the scaling factors of the first-guess net CO2 surface fluxes and (2) the atmospheric CO2 transport is simulated by using the GEOS-Chem three-dimensional global chemistry transport model. Observing system simulation experiments (OSSEs) for assimilating synthetic in situ observations of surface CO2 concentrations are carefully designed to evaluate the effectiveness of the Tan-Tracker system. In particular, detailed comparisons are made with its simplified version (referred to as TT-S) with only CFs taken as the prognostic variables. It is found that our Tan-Tracker system is capable of outperforming TT-S with higher assimilation precision for both CO2 concentrations and CO2 fluxes, mainly due to the simultaneous estimation of CO2 concentrations and CFs in our Tan-Tracker data assimilation system. A experiment for assimilating the real dry-air column CO2 retrievals (XCO2) from the Japanese Greenhouse Gases Observation Satellite (GOSAT) further demonstrates its potential wide applications.

Effect of plasma ion bombardment on the reflectance of Io's trailing and leading hemispheres

NASA Technical Reports Server (NTRS)

Sack, N. J.; Baragiola, R. A.; Johnson, R. E.

1993-01-01

The possible effect of a net difference in the ion bombardment flux to the surface of Io on the ratio of the reflectance spectra is investigated. Io's vapor-deposited surface layers are simulated by a laboratory-produced film of vapor-deposited SO2 with a small admixture (about 3 percent) of H2S and (about 0.1 percent) H2O. It is shown that the reflectance ratio in the UV/visible of the surface bombarded by keV ions to the unbombarded surface is surprisingly similar to the observed ratio of Io's trailing to leading hemispherical reflectance. The changes produced are either structural or involve products of species originally present in the sample.

δ2H isotopic flux partitioning of evapotranspiration over a grass field following a water pulse and subsequent dry down

NASA Astrophysics Data System (ADS)

Good, Stephen P.; Soderberg, Keir; Guan, Kaiyu; King, Elizabeth G.; Scanlon, Todd M.; Caylor, Kelly K.

2014-02-01

The partitioning of surface vapor flux (FET) into evaporation (FE) and transpiration (FT) is theoretically possible because of distinct differences in end-member stable isotope composition. In this study, we combine high-frequency laser spectroscopy with eddy covariance techniques to critically evaluate isotope flux partitioning of FET over a grass field during a 15 day experiment. Following the application of a 30 mm water pulse, green grass coverage at the study site increased from 0 to 10% of ground surface area after 6 days and then began to senesce. Using isotope flux partitioning, transpiration increased as a fraction of total vapor flux from 0% to 40% during the green-up phase, after which this ratio decreased while exhibiting hysteresis with respect to green grass coverage. Daily daytime leaf-level gas exchange measurements compare well with daily isotope flux partitioning averages (RMSE = 0.0018 g m-2 s-1). Overall the average ratio of FT to FET was 29%, where uncertainties in Keeling plot intercepts and transpiration composition resulted in an average of uncertainty of ˜5% in our isotopic partitioning of FET. Flux-variance similarity partitioning was partially consistent with the isotope-based approach, with divergence occurring after rainfall and when the grass was stressed. Over the average diurnal cycle, local meteorological conditions, particularly net radiation and relative humidity, are shown to control partitioning. At longer time scales, green leaf area and available soil water control FT/FET. Finally, we demonstrate the feasibility of combining isotope flux partitioning and flux-variance similarity theory to estimate water use efficiency at the landscape scale.

A method to quantify and value floodplain sediment and nutrient retention ecosystem services

USGS Publications Warehouse

Hopkins, Kristina G.; Noe, Gregory; Franco, Fabiano; Pindilli, Emily J.; Gordon, Stephanie; Metes, Marina J.; Claggett, Peter; Gellis, Allen; Hupp, Cliff R.; Hogan, Dianna

2018-01-01

Floodplains provide critical ecosystem services to local and downstream communities by retaining floodwaters, sediments, and nutrients. The dynamic nature of floodplains is such that these areas can both accumulate sediment and nutrients through deposition, and export material downstream through erosion. Therefore, estimating floodplain sediment and nutrient retention should consider the net flux of both depositional and erosive processes. An ecosystem services framework was used to quantify and value the sediment and nutrient ecosystem service provided by floodplains in the Difficult Run watershed, a small (151 km2) suburban watershed located in the Piedmont of Virginia (USA). A sediment balance was developed for Difficult Run and two nested watersheds. The balance included upland sediment delivery to streams, stream bank flux, floodplain flux, and stream load. Upland sediment delivery was estimated using geospatial datasets and a modified Revised Universal Soil Loss Equation. Predictive models were developed to extrapolate field measurements of the flux of sediment, sediment-bound nitrogen (N), and sediment-bound phosphorus (P) from stream banks and floodplains to 3232 delineated stream segments in the study area. A replacement cost approach was used to estimate the economic value of the sediment and nutrient retention ecosystem service based on estimated net stream bank and floodplain flux of sediment-bound N for all streams in the study area. Results indicated the net fluvial fluxes of sediment, sediment-bound N, and sediment-bound P were −10,439 Mg yr−1 (net export), 57,300 kg-N yr−1(net trapping), and 98 kg-P yr−1(net trapping), respectively. For sediment, floodplain retention was offset by substantial losses from stream bank erosion, particularly in headwater catchments, resulting in a net export of sediment. Nutrient retention in the floodplain exceeded that lost through stream bank erosion resulting in net retention of nutrients (TN and TP). Using a conservative cost estimate of $12.69 (USD) per kilogram of nitrogen, derived from wastewater treatment costs, the estimated annual value for sediment and nutrient retention on Difficult Run floodplains was $727,226 ± 194,220 USD/yr. Values and differences in floodplain nitrogen retention among stream reaches can be used to target areas for floodplain conservation and stream restoration. The methods presented are scalable and transferable to other areas if appropriate datasets are available for validation.

Constraining a land-surface model with multiple observations by application of the MPI-Carbon Cycle Data Assimilation System V1.0

NASA Astrophysics Data System (ADS)

Schürmann, Gregor J.; Kaminski, Thomas; Köstler, Christoph; Carvalhais, Nuno; Voßbeck, Michael; Kattge, Jens; Giering, Ralf; Rödenbeck, Christian; Heimann, Martin; Zaehle, Sönke

2016-09-01

We describe the Max Planck Institute Carbon Cycle Data Assimilation System (MPI-CCDAS) built around the tangent-linear version of the JSBACH land-surface scheme, which is part of the MPI-Earth System Model v1. The simulated phenology and net land carbon balance were constrained by globally distributed observations of the fraction of absorbed photosynthetically active radiation (FAPAR, using the TIP-FAPAR product) and atmospheric CO2 at a global set of monitoring stations for the years 2005 to 2009. When constrained by FAPAR observations alone, the system successfully, and computationally efficiently, improved simulated growing-season average FAPAR, as well as its seasonality in the northern extra-tropics. When constrained by atmospheric CO2 observations alone, global net and gross carbon fluxes were improved, despite a tendency of the system to underestimate tropical productivity. Assimilating both data streams jointly allowed the MPI-CCDAS to match both observations (TIP-FAPAR and atmospheric CO2) equally well as the single data stream assimilation cases, thereby increasing the overall appropriateness of the simulated biosphere dynamics and underlying parameter values. Our study thus demonstrates the value of multiple-data-stream assimilation for the simulation of terrestrial biosphere dynamics. It further highlights the potential role of remote sensing data, here the TIP-FAPAR product, in stabilising the strongly underdetermined atmospheric inversion problem posed by atmospheric transport and CO2 observations alone. Notwithstanding these advances, the constraint of the observations on regional gross and net CO2 flux patterns on the MPI-CCDAS is limited through the coarse-scale parametrisation of the biosphere model. We expect improvement through a refined initialisation strategy and inclusion of further biosphere observations as constraints.

Net ecosystem production: A comprehensive measure of net carbon accumulation by ecosystems

USGS Publications Warehouse

Randerson, J.T.; Chapin, F. S.; Harden, J.W.; Neff, J.C.; Harmon, M.E.

2002-01-01

The conceptual framework used by ecologists and biogeochemists must allow for accurate and clearly defined comparisons of carbon fluxes made with disparate techniques across a spectrum of temporal and spatial scales. Consistent with usage over the past four decades, we define "net ecosystem production" (NEP) as the net carbon accumulation by ecosystems. Past use of this term has been ambiguous, because it has been used conceptually as a measure of carbon accumulation by ecosystems, but it has often been calculated considering only the balance between gross primary production (GPP) and ecosystem respiration. This calculation ignores other carbon fluxes from ecosystems (e.g., leaching of dissolved carbon and losses associated with disturbance). To avoid conceptual ambiguities, we argue that NEP be defined, as in the past, as the net carbon accumulation by ecosystems and that it explicitly incorporate all the carbon fluxes from an ecosystem, including autotrophic respiration, heterotrophic respiration, losses associated with disturbance, dissolved and particulate carbon losses, volatile organic compound emissions, and lateral transfers among ecosystems. Net biome productivity (NBP), which has been proposed to account for carbon loss during episodic disturbance, is equivalent to NEP at regional or global scales. The multi-scale conceptual framework we describe provides continuity between flux measurements made at the scale of soil profiles and chambers, forest inventories, eddy covariance towers, aircraft, and inversions of remote atmospheric flask samples, allowing a direct comparison of NEP estimates made at all temporal and spatial scales.

Intercomparison of Air-Sea Fluxes in the Bay of Bengal

NASA Astrophysics Data System (ADS)

Buckley, J.; Weller, R. A.; Farrar, J. T.; Tandon, A.

2016-02-01

Heat and momentum exchange between the air and sea in the Bay of Bengal is an important driver of atmospheric convection during the Asian Monsoon. Warm sea surface temperatures resulting from salinity stratified shallow mixed layers trigger widespread showers and thunderstorms. In this study, we compare atmospheric reanalysis flux products to air-sea flux values calculated from shipboard observations from four cruises and an air-sea flux mooring in the Bay of Bengal as part of the Air-Sea Interactions in the Northern Indian Ocean (ASIRI) experiment. Comparisons with months of mooring data show that most long timescale reanalysis error arises from the overestimation of longwave and shortwave radiation. Ship observations and select data from the air-sea flux mooring reveals significant errors on shorter timescales (2-4 weeks) which are greatly influenced by errors in shortwave radiation and latent and sensible heat. During these shorter periods, the reanalyses fail to properly show sharp decreases in air temperature, humidity, and shortwave radiation associated with mesoscale convective systems. Simulations with the Price-Weller-Pinkel (PWP) model show upper ocean mixing and deepening mixed layers during these events that effect the long term upper ocean stratification. Mesoscale convective systems associated with cloudy skies and cold and dry air can reduce net heat into the ocean for minutes to a few days, significantly effecting air-sea heat transfer, upper ocean stratification, and ocean surface temperature and salinity.

A Synthesized Model-Observation Approach to Constraining Gross Urban CO2 Fluxes Using 14CO2 and carbonyl sulfide

NASA Astrophysics Data System (ADS)

LaFranchi, B. W.; Campbell, J. E.; Cameron-Smith, P. J.; Bambha, R.; Michelsen, H. A.

2013-12-01

Urbanized regions are responsible for a disproportionately large percentage (30-40%) of global anthropogenic greenhouse gas (GHG) emissions, despite covering only 2% of the Earth's surface area [Satterthwaite, 2008]. As a result, policies enacted at the local level in these urban areas can, in aggregate, have a large global impact, both positive and negative. In order to address the scientific questions that are required to drive these policy decisions, methods are needed that resolve gross CO2 flux components from the net flux. Recent work suggests that the critical knowledge gaps in CO2 surface fluxes could be addressed through the combined analysis of atmospheric carbonyl sulfide (COS) and radiocarbon in atmospheric CO2 (14CO2) [e.g. Campbell et al., 2008; Graven et al., 2009]. The 14CO2 approach relies on mass balance assumptions about atmospheric CO2 and the large differences in 14CO2 abundance between fossil and natural sources of CO2 [Levin et al., 2003]. COS, meanwhile, is a potentially transformative tracer of photosynthesis because its variability in the atmosphere has been found to be influenced primarily by vegetative uptake, scaling linearly will gross primary production (GPP) [Kettle et al., 20027]. Taken together, these two observations provide constraints on two of the three main components of the CO2 budget at the urban scale: photosynthesis and fossil fuel emissions. The third component, respiration, can then be determined by difference if the net flux is known. Here we present a general overview of our synthesized model-observation approach for improving surface flux estimates of CO2 for the upwind fetch of a ~30m tower located in Livermore, CA, USA, a suburb (pop. ~80,000) at the eastern edge of the San Francisco Bay Area. Additionally, we will present initial results from a one week observational intensive, which includes continuous CO2, CH4, CO, SO2, NOx, and O3 observations in addition to measurements of 14CO2 and COS from air samples collected every ~1-3 hours during this time period. References Campbell, J. E., et. al., Science, 322, 1085-1088, 2008. Graven, H. D., et al., Tellus B, 61, 536-546, 2009. Kettle, A. J., et al., J. Geophys. Res.-Atmos., 107, 2002. Levin, I., et al., Geophys. Res. Lett., 30, 2003. Satterthwaite, D., Environment and Urbanization, 20, 539-549, 2008.

Quantifying components of the hydrologic cycle in Virginia using chemical hydrograph separation and multiple regression analysis

USGS Publications Warehouse

Sanford, Ward E.; Nelms, David L.; Pope, Jason P.; Selnick, David L.

2012-01-01

This study by the U.S. Geological Survey, prepared in cooperation with the Virginia Department of Environmental Quality, quantifies the components of the hydrologic cycle across the Commonwealth of Virginia. Long-term, mean fluxes were calculated for precipitation, surface runoff, infiltration, total evapotranspiration (ET), riparian ET, recharge, base flow (or groundwater discharge) and net total outflow. Fluxes of these components were first estimated on a number of real-time-gaged watersheds across Virginia. Specific conductance was used to distinguish and separate surface runoff from base flow. Specific-conductance data were collected every 15 minutes at 75 real-time gages for approximately 18 months between March 2007 and August 2008. Precipitation was estimated for 1971–2000 using PRISM climate data. Precipitation and temperature from the PRISM data were used to develop a regression-based relation to estimate total ET. The proportion of watershed precipitation that becomes surface runoff was related to physiographic province and rock type in a runoff regression equation. Component flux estimates from the watersheds were transferred to flux estimates for counties and independent cities using the ET and runoff regression equations. Only 48 of the 75 watersheds yielded sufficient data, and data from these 48 were used in the final runoff regression equation. The base-flow proportion for the 48 watersheds averaged 72 percent using specific conductance, a value that was substantially higher than the 61 percent average calculated using a graphical-separation technique (the USGS program PART). Final results for the study are presented as component flux estimates for all counties and independent cities in Virginia.

The impact of an extreme case of irrigation on the southeastern United States climate

NASA Astrophysics Data System (ADS)

Selman, Christopher; Misra, Vasubandhu

2017-02-01

The impacts of irrigation on southeast United States diurnal climate are investigated using simulations from a regional climate model. An extreme case is assumed, wherein irrigation is set to 100 % of field capacity over the growing season of May through October. Irrigation is applied to the root zone layers of 10-40 and 40-100 cm soil layers only. It is found that in this regime there is a pronounced decrease in monthly averaged temperatures in irrigated regions across all months. In non-irrigated areas a slight warming is simulated. Diurnal maximum temperatures in irrigated areas warm, while diurnal minimum temperatures cool. The daytime warming is attributed to an increase in shortwave flux at the surface owing to diminished low cloud cover. Nighttime and daily mean cooling result as a consequence repartitioning of energy into latent heat flux over sensible heat flux, and of a higher net downward ground heat flux. Excess heat is transported into the deep soil layer, preventing a rapidly intensifying positive feedback loop. Both diurnal and monthly average precipitations are reduced over irrigated areas at a magnitude and spatial pattern similar to one another. Due to the excess moisture availability, evaporation is seen to increase, but this is nearly balanced by a corresponding reduction in sensible heat flux. Concomitant with additional moisture availability is an increase in both transient and stationary moisture flux convergences. However, despite the increase, there is a large-scale stabilization of the atmosphere stemming from a cooled surface.

A thickness-weighted average perspective of force balance in an idealized circumpolar current

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ringler, Todd Darwin; Saenz, Juan Antonio; Wolfram, Jr., Phillip Justin

The exact, three-dimensional thickness-weighted averaged (TWA) Boussinesq equations are used to diagnose eddy-mean flow interaction in an idealized circumpolar current (ICC). The force exerted by mesoscale eddies on the TWA velocity is expressed as the divergence of the Eliassen-Palm flux tensor. Consistent with previous findings, the analysis indicates that the dynamically relevant definition of the ocean surface layer is comprised of the set of buoyancy coordinates that ever reside at the ocean surface at a given horizontal position. The surface layer is found to be a physically distinct object with a diabatic- and force-balance that is largely isolated from themore » underlying adiabatic region in the interior. Within the ICC surface layer, the TWA meridional velocity is southward/northward in the top/bottom half, and has a value near zero at the bottom. In the top half of the surface layer, the zonal forces due to wind stress and meridional advection of potential vorticity act to accelerate the TWA zonal velocity; equilibrium is obtained by eddies decelerating the zonal flow via a downward flux of eastward momentum that increases with depth. In the bottom half of the surface layer, the accelerating force of the wind stress is balanced by the eddy force and meridional advection of potential vorticity. The bottom of the surface layer coincides with the location where the zonal eddy force, meridional advection of potential vorticity and zonal wind stress force are all zero. The net meridional transport, S f, within the surface layer is a small residual of its southward and northward TWA meridional flows. Furthermore, the mean meridional gradient of surface-layer buoyancy is advected by S f to balance the surface buoyancy fluxs.« less

A thickness-weighted average perspective of force balance in an idealized circumpolar current

DOE PAGES

Ringler, Todd Darwin; Saenz, Juan Antonio; Wolfram, Jr., Phillip Justin; ...

2016-11-22

The exact, three-dimensional thickness-weighted averaged (TWA) Boussinesq equations are used to diagnose eddy-mean flow interaction in an idealized circumpolar current (ICC). The force exerted by mesoscale eddies on the TWA velocity is expressed as the divergence of the Eliassen-Palm flux tensor. Consistent with previous findings, the analysis indicates that the dynamically relevant definition of the ocean surface layer is comprised of the set of buoyancy coordinates that ever reside at the ocean surface at a given horizontal position. The surface layer is found to be a physically distinct object with a diabatic- and force-balance that is largely isolated from themore » underlying adiabatic region in the interior. Within the ICC surface layer, the TWA meridional velocity is southward/northward in the top/bottom half, and has a value near zero at the bottom. In the top half of the surface layer, the zonal forces due to wind stress and meridional advection of potential vorticity act to accelerate the TWA zonal velocity; equilibrium is obtained by eddies decelerating the zonal flow via a downward flux of eastward momentum that increases with depth. In the bottom half of the surface layer, the accelerating force of the wind stress is balanced by the eddy force and meridional advection of potential vorticity. The bottom of the surface layer coincides with the location where the zonal eddy force, meridional advection of potential vorticity and zonal wind stress force are all zero. The net meridional transport, S f, within the surface layer is a small residual of its southward and northward TWA meridional flows. Furthermore, the mean meridional gradient of surface-layer buoyancy is advected by S f to balance the surface buoyancy fluxs.« less

Observed Variation in Carbon and Water Exchange Across Crop Types, Seasons, and Years in Un-irrigated Land of the Southern Great Plains

NASA Astrophysics Data System (ADS)

Fischer, M. L.; Billesbach, D. P.; Riley, W. J.; Berry, J. A.; Torn, M. S.

2004-12-01

Accurate prediction of the regional responses of carbon and water fluxes to changing climate, land use, and management requires models that are parameterized and tested against measurements made in multiple land cover types and over seasonal and inter-annual time scales. In particular, modelers predicting fluxes for un-irrigated agriculture are posed with the additional challenge of characterizing the onset and severity of water stress. We report results from three years of an ongoing series of measurement campaigns that quantify the spatial heterogeneity of land surface-atmosphere exchanges of carbon dioxide, water, and energy. Eddy covariance flux measurements were made in pastures and dominant crop types surrounding the US-DOE Atmospheric Radiation Measurement Program central facility near Lamont, Oklahoma (36.605 N, 97.485 W). Ancillary measurements included radiation budget, meteorology, soil moisture and temperature, leaf area index, plant biomass, and plant and soil carbon and nitrogen content. Within a given year, the dominant spatial variation in fluxes of carbon, water, and energy are caused by variations of land cover due to the distinct phenology of winter-spring (winter wheat) versus summer crops (e.g., pasture, sorghum, soybeans). Within crop and yearly variations were smaller. In 2002, variations in net ecosystem carbon exchange (NEE), for three closely spaced winter wheat fields was 10-20%. Variations between years for the same crop types were also large. Net primary production (NPP) of winter wheat in the spring of 2003 versus 2002 increased by a factor of two, while NEE increased by 35%. The large increase in production and NEE are positively correlated with precipitation, integrated over the previous summer-fall periods. We discuss the implications of these results by extracting and comparing factors relevant for parameterization of land surface models and by comparing crop yield with historic variations in yield at the landscape scale.

Effect of decreasing dietary phosphorus supply on net recycling of inorganic phosphate in lactating dairy cows.

PubMed

Puggaard, L; Kristensen, N B; Sehested, J

2011-03-01

Five ruminally cannulated lactating Holstein cows, fitted with permanent indwelling catheters in the mesenteric vein, hepatic vein, portal vein, and an artery were used to study intestinal absorption and net recycling of inorganic phosphate (P(i)) to the gastrointestinal tract. Treatments were low P (LP; 2.4 g of P/kg of DM) and high P (HP; 3.4 g of P/kg of DM). The dietary total P (tP) concentrations were obtained by replacing 0.50% calcium carbonate in the LP diet with 0.50% monocalcium phosphate in the HP diet. Diets were fed for 14 d and cows were sampled on d 14 in each period. Cows were fed restrictively, resulting in equal dry matter intakes as well as milk, fat, and protein yields between treatments. Net P(i) recycling (primarily salivary) was estimated as the difference between net portal plasma flux (net absorption of P(i)) and apparently digested tP (feed - fecal tP difference). Phosphorus intake, apparently digested tP, and fecal tP excretion decreased with LP. An effect of decreased tP intake on net portal plasma flux of P(i) could not be detected. However, despite numerically minute net fluxes across the liver, the net splanchnic flux of P(i) was less in LP compared with that in HP. Though arterial plasma P(i) concentration decreased, net P(i) recycling was not decreased when tP intake was decreased, and recycling of P(i) was maintained at the expense of deposition of P(i) in bones. Data are not consistent with salivary P(i) secretion being the primary regulator of P(i) homeostasis at low tP intakes. On the contrary, maintaining salivary P(i) recycling at low tP intakes indicates that rumen function was prioritized at the expense of bone P reserves. Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

The impact of boundary layer turbulence on snow growth and precipitation: Idealized Large Eddy Simulations

NASA Astrophysics Data System (ADS)

Chu, Xia; Xue, Lulin; Geerts, Bart; Kosović, Branko

2018-05-01

Ice particles and supercooled droplets often co-exist in planetary boundary-layer (PBL) clouds. The question examined in this numerical study is how large turbulent PBL eddies affect snow growth and surface precipitation from mixed-phase PBL clouds. In order to simplify this question, this study assumes an idealized BL with well-developed turbulence but no surface heat fluxes or radiative heat exchanges. Large Eddy Simulations with and without resolved PBL turbulence are compared. This comparison demonstrates that the impact on snow growth in mixed-phase clouds is controlled by two opposing mechanisms, a microphysical and a dynamical one. The cloud microphysical impact of large turbulent eddies is based on the difference in saturation vapor pressure over water and over ice. The net outcome of alternating turbulent up- and downdrafts is snow growth by diffusion and/or accretion (riming). On the other hand, turbulence-induced entrainment and detrainment may suppress snow growth. In the case presented herein, the net effect of these microphysical and dynamical processes is positive, but in general the net effect depends on ambient conditions, in particular the profiles of temperature, humidity, and wind.

Charge tunable thin-film composite membranes by gamma-ray triggered surface polymerization.

PubMed

Reis, Rackel; Duke, Mikel C; Tardy, Blaise L; Oldfield, Daniel; Dagastine, Raymond R; Orbell, John D; Dumée, Ludovic F

2017-06-30

Thin-film composite poly(amide) (PA) membranes have greatly diversified water supplies and food products. However, users would benefit from a control of the electrostatic interactions between the liquid and the net surface charge interface in order to benefit wider application. The ionic selectivity of the 100 nm PA semi-permeable layer is significantly affected by the pH of the solution. In this work, for the first time, a convenient route is presented to configure the surface charge of PA membranes by gamma ray induced surface grafting. This rapid and up-scalable method offers a versatile route for surface grafting by adjusting the irradiation total dose and the monomer concentration. Specifically, thin coatings obtained at low irradiation doses between 1 and 10 kGy and at low monomer concentration of 1 v/v% in methanol/water (1:1) solutions, dramatically altered the net surface charge of the pristine membranes from -25 mV to +45 mV, whilst the isoelectric point of the materials shifted from pH 3 to pH 7. This modification resulted in an improved water flux by over 55%, from 45.9 to up 70 L.m -2 .h -1 , whilst NaCl rejection was found to drop by only 1% compared to pristine membranes.

Net Thermal Radiation in the Atmosphere of Venus

NASA Technical Reports Server (NTRS)

Revercomb, H. E.; Sromovsky, L. A.; Suomi, V. E.; Boese, R. W.

1985-01-01

The four entry probes of the Pioneer Venus mission measured the radiative net flux in the atmosphere of Venus at latitudes of 60 deg. N, 31 deg. S, 27 deg. S, and 4 deg. N. The three higher latitude probes carried instruments (small probe net flux radiometers; SNFR) with external sensors. The measured SNFR net fluxes are too large below the clouds, but an error source and correction scheme have been found (H. E. Revercomb, L. A. Sromovsky, and V. E. Suomi, 1982, Icarus 52, 279-300). The near-equatorial probe carried an infrared radiometer (LIR) which viewed the atmosphere through a window in the probe. The LIR measurements are reasonable in the clouds, but increase to physically unreasonable levels shortly below the clouds. The probable error source and a correction procedure are identified. Three main conclusions can be drawn from comparisons of the four corrected flux profiles with radiative transfer calculations: (1) thermal net fluxes for the sounder probe do not require a reduction in the Mode 3 number density as has been suggested by O.B. Toon, B. Ragent, D. Colburn, J. Blamont, and C. Cot (1964. Icarus 37, 143-160), but the probe measurements as a whole are most consistent with a significantly reduced mode 3 contribution to the cloud opacity; (2) at all probe sites, the fluxes imply that the upper cloud contains a yet undetected source of IR opacity; and (3) beneath the clouds the fluxes at a given altitude increase with latitude, suggesting greater IR cooling below the clouds a( high latitudes and water vapor mixing ratios of about 2-5 x 10(exp -5) near 6 deg., 2-5 x 10(exp -11) near 30 deg., and less than 5 x 10(exp -4 ) near the equator. The suggested latitudinal variation of IR cooling is consistent with descending motions at high latitudes, and it is speculated that it could provide an important additional drive for the general circulation.

Sensitivity of the Tropical Atmosphere Energy Balance to ENSO-Related SST Changes: How Well Can We Quantify Hydrologic and Radiative Responses?

NASA Technical Reports Server (NTRS)

Robertson, Franklin R.; Fitzjarrald, Dan; Sohn, Byung-Ju; Arnold, James E. (Technical Monitor)

2001-01-01

The continuing debate over feedback mechanisms governing tropical sea surface temperatures (SSTs) and tropical climate in general has highlighted the diversity of potential checks and balances within the climate system. Competing feedbacks due to changes in surface evaporation, water vapor, and cloud long- and shortwave radiative properties each may serve critical roles in stabilizing or destabilizing the climate system. It is also intriguing that even those climate variations having origins internal to the climate system-- changes in ocean heat transport for example, apparently require complementary equilibrating effects by changes in atmospheric energy fluxes. Perhaps the best observational evidence of this is the relatively invariant nature of tropically averaged net radiation exiting the top-of-atmosphere (TOA) as measured by broadband satellite sensors over the past two decades. Thus, analyzing how these feedback mechanisms are operating within the context of current interannual variability may offer considerable insight for anticipating future climate change. In this paper we focus on how fresh water and radiative fluxes over the tropical oceans change during ENSO warm and cold events and how these changes affect the tropical energy balance. At present, ENSO remains the most prominent known mode of natural variability at interannual time scales. Although great advances have been made in understanding this phenomenon and realizing prediction skill over the past decade, our ability to document the coupled water and energy changes observationally and to represent them in climate models seems far from settled (Soden, 2000 J Climate). Our analysis makes use a number of data bases, principally those derived from space-based measurements, to explore systematic changes in rainfall, evaporation, and surface and top-of-atmosphere (TOA) radiative fluxes, A reexamination of the Langley 8-Year Surface Radiation Budget data set reveals errors in the surface longwave emission due to use of biased SSTs. Subsequent correction allows subsequent use of this data set along with ERBE TOA fluxes to infer net atmospheric radiative beating. Further analysis of recent rainfall algorithms provides new estimates for precipitation variability in line with interannual evaporation changes inferred from the da Silva, Young, Levitus COADS analysis. The overall results from our analysis suggest an increase (decrease) of the hydrologic cycle during ENSO warm (cold) events at the rate of about 5 Wm-2 per K of SST change. This rate is slightly less than that which would be expected for constant relative humidity over the tropical oceans. Corresponding radiative fluxes seem systematically smaller resulting in a enhanced (suppressed) export of energy from the tropical ocean regions during warm (cold) SST events. Discussion of likely errors due to sampling and measurement strategies are discussed along with their impacts on our conclusions.

Testing a land model in ecosystem functional space via a comparison of observed and modeled ecosystem flux responses to precipitation regimes and associated stresses in a Central U.S. forest: Test Model in Ecosystem Functional Space

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gu, Lianhong; Pallardy, Stephen G.; Yang, Bai

Testing complex land surface models has often proceeded by asking the question: does the model prediction agree with the observation? This approach has yet led to high-performance terrestrial models that meet the challenges of climate and ecological studies. Here we test the Community Land Model (CLM) by asking the question: does the model behave like an ecosystem? We pursue its answer by testing CLM in the ecosystem functional space (EFS) at the Missouri Ozark AmeriFlux (MOFLUX) forest site in the Central U.S., focusing on carbon and water flux responses to precipitation regimes and associated stresses. In the observed EFS, precipitationmore » regimes and associated water and heat stresses controlled seasonal and interannual variations of net ecosystem exchange (NEE) of CO 2 and evapotranspiration in this deciduous forest ecosystem. Such controls were exerted more strongly by precipitation variability than by the total precipitation amount per se. A few simply constructed climate variability indices captured these controls, suggesting a high degree of potential predictability. While the interannual fluctuation in NEE was large, a net carbon sink was maintained even during an extreme drought year. Although CLM predicted seasonal and interanual variations in evapotranspiration reasonably well, its predictions of net carbon uptake were too small across the observed range of climate variability. Also, the model systematically underestimated the sensitivities of NEE and evapotranspiration to climate variability and overestimated the coupling strength between carbon and water fluxes. Its suspected that the modeled and observed trajectories of ecosystem fluxes did not overlap in the EFS and the model did not behave like the ecosystem it attempted to simulate. A definitive conclusion will require comprehensive parameter and structural sensitivity tests in a rigorous mathematical framework. We also suggest that future model improvements should focus on better representation and parameterization of process responses to environmental stresses and on more complete and robust representations of carbon-specific processes so that adequate responses to climate variability and a proper degree of coupling between carbon and water exchanges are captured.« less

Testing a land model in ecosystem functional space via a comparison of observed and modeled ecosystem flux responses to precipitation regimes and associated stresses in a Central U.S. forest: Test Model in Ecosystem Functional Space

DOE PAGES

Gu, Lianhong; Pallardy, Stephen G.; Yang, Bai; ...

2016-07-14

Testing complex land surface models has often proceeded by asking the question: does the model prediction agree with the observation? This approach has yet led to high-performance terrestrial models that meet the challenges of climate and ecological studies. Here we test the Community Land Model (CLM) by asking the question: does the model behave like an ecosystem? We pursue its answer by testing CLM in the ecosystem functional space (EFS) at the Missouri Ozark AmeriFlux (MOFLUX) forest site in the Central U.S., focusing on carbon and water flux responses to precipitation regimes and associated stresses. In the observed EFS, precipitationmore » regimes and associated water and heat stresses controlled seasonal and interannual variations of net ecosystem exchange (NEE) of CO 2 and evapotranspiration in this deciduous forest ecosystem. Such controls were exerted more strongly by precipitation variability than by the total precipitation amount per se. A few simply constructed climate variability indices captured these controls, suggesting a high degree of potential predictability. While the interannual fluctuation in NEE was large, a net carbon sink was maintained even during an extreme drought year. Although CLM predicted seasonal and interanual variations in evapotranspiration reasonably well, its predictions of net carbon uptake were too small across the observed range of climate variability. Also, the model systematically underestimated the sensitivities of NEE and evapotranspiration to climate variability and overestimated the coupling strength between carbon and water fluxes. Its suspected that the modeled and observed trajectories of ecosystem fluxes did not overlap in the EFS and the model did not behave like the ecosystem it attempted to simulate. A definitive conclusion will require comprehensive parameter and structural sensitivity tests in a rigorous mathematical framework. We also suggest that future model improvements should focus on better representation and parameterization of process responses to environmental stresses and on more complete and robust representations of carbon-specific processes so that adequate responses to climate variability and a proper degree of coupling between carbon and water exchanges are captured.« less

Assessing the net impact of long-term drainage disturbance on a permafrost ecosystem through multi-disciplinary observations

NASA Astrophysics Data System (ADS)

Goeckede, Mathias; Kwon, Min Jung; Kittler, Fanny; Burjack, Ina; Heimann, Martin; Zimov, Nikita; Zimov, Sergey

2016-04-01

This study presents findings from a multi-disciplinary disturbance experiment established on the floodplain of the Kolyma River near Chersky, Northeast Siberia. Parts of our site have been artificially drained by ditches since 2004 to study shifts in biogeochemical and biogeophysical ecosystem properties following a sustained lowering of the water table. In particular, we are interested in changes in carbon and energy flux patterns, and resulting effects on the sustainability of the permafrost carbon pool. We conduct a paired experiment with two uniformly instrumented sites representing drained and reference tundra, respectively. Year-round fluxes of carbon (CO2 and CH4) and energy are available from two eddy-covariance towers, supplemented by a comprehensive monitoring of surface layer meteorology. These tower datasets are supplemented by observations targeting microsite flux rates with flux chamber transects, microbial and vegetation community structures, radiocarbon signals, nutrient availability and seasonal dynamics in phenology. Through our multi-disciplinary observations we can document that the drainage triggered a suite of secondary changes in ecosystem properties, including e.g. vegetation structure (more tussocks and shrubs), snow cover regime (earlier buildup, earlier snow melt), soil temperature (warmer soils throughout the year) and thaw depth (reduced). Concerning the energy budget, this results in an intensification of energy transfer to the lower atmosphere, particularly in form of sensible heat. The CO2 exchange between ecosystem and atmosphere is intensified as well, with drainage leading to both higher assimilation (taller vegetation) and respiration (warmer topsoils) rates. Increases in respiration dominate here, thus the net sink strength of the ecosystem for CO2 is reduced as a consequence of lowering the water table. CH4 emissions are reduced by more then 50% following the drainage, since in the disturbed area conditions for both production (dryer soils) and transport (less plant-mediated transport due to shifts in vegetation) have negative impacts on flux rates. Summarizing, drainage results in complex effects with both positive and negative contributions to the net global warming potential of this ecosystem, with the long-term effect most likely leading to a positive feedback with global warming.

Mechanisms Regulating Deep Moist Convection and Sea-Surface Temperatures of the Tropics

NASA Technical Reports Server (NTRS)

Sud, Y. C.; Walker, G. K.; Lau, K. M.

1998-01-01

Despite numerous previous studies, two relationships between deep convection and the sea-surface temperature (SST) of the tropics remain unclear. The first is the cause for the sudden emergence of deep convection at about 28 deg SST, and the second is its proximity to the highest observed SST of about 30 C. Our analysis provides a rational explanation for both by utilizing the Improved Meteorological (IMET) buoy data together with radar rainfall retrievals and atmospheric soundings provided by the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE). The explanation relies on the basic principles of moist convection as enunciated in the Arakawa-Schubert cumulus parameterization. Our analysis shows that an SST range of 28-29 C is necessary for "charging" the atmospheric boundary layer with sufficient moist static energy that can enable the towering convection to reach up to the 200 hPa level. In the IMET buoy data, the changes in surface energy fluxes associated with different rainfall amounts show that the deep convection not only reduces the solar flux into the ocean with a thick cloud cover, but it also generates downdrafts which bring significantly cooler and drier air into the boundary-layer thereby augmenting oceanic cooling by increased sensible and latent heat fluxes. In this way, the ocean seasaws between a net energy absorber for non-raining and a net energy supplier for deep-convective raining conditions. These processes produce a thermostat-like control of the SST. The data also shows that convection over the warm pool is modulated by dynamical influences of large-scale circulation embodying tropical easterly waves (with a 5-day period) and MJOs (with 40-day period); however, the quasi-permanent feature of the vertical profile of moist static energy, which is primarily maintained by the large-scale circulation and thermodynamical forcings, is vital for both the 28 C SST for deep convection and its upper limit at about 30 C.

Retrieving SW fluxes from geostationary narrowband radiances for the NASA-CERES SYN1deg product

NASA Astrophysics Data System (ADS)

Wrenn, F. J., IV; Doelling, D. R.; Liang, L.

2016-12-01

The CERES mission was designed to measure the natural variability of the net TOA flux over long time scales relevant to climate monitoring. To achieve this goal, CERES provides the level-3 SSF1deg, SYN1deg, and EBAF monthly 1° by 1° regional TOA flux. The single satellite (Terra or Aqua) SSF1deg 24-hour shortwave flux is based on one daytime measurements and assumes constant meteorology to model the diurnal change in albedo. To accurately describe regions with a prominent diurnal signal, the SYN1deg Edition4 dataset employs hourly geostationary (GEO) measurements. This improves upon Edition3, which used 3-hourly GEO measurements and with temporal interpolation. The EBAF product combines the temporal stability of the SSF1deg product with the diurnal information from SYN1deg and removes the CERES instrument calibration bias by constraining the net flux balance to the ocean heat storage term. The SYN-1deg product retrieves hourly SW fluxes from GEO measurements. Over regions with large diurnal cycles, such as maritime stratus and land afternoon convective locations, the GEO derived SW fluxes will capture the diurnal flux not observed with Terra or Aqua sun-synchronous satellites. Obtaining fluxes from geostationary satellite radiance is a multistep process. First, most GEO visible imagers lack calibration and must be calibrated to MODIS and VIIRS. Second, the GEO imager visible channel radiances are converted to broadband radiances using empirical and theoretical models. The lack of coincident, collocated, and co-angled GEO and CERES measurements makes building an empirical model difficult. The narrowband to broadband models are a function of surface and cloud conditions, which are difficult to identify due to the inconsistent cloud retrievals between the 16 GEO imagers used in the CERES record. Third, the GEO derived broadband radiances are passed through the CERES angular distribution model (ADM) to convert the radiances to fluxes. Lastly, the GEO derived broadband fluxes are normalized with CERES fluxes in order to preserve the CERES instrument calibration. Validation is performed by comparing the GEO converted fluxes against CERES observations using coincident and collocated data. This work will focus on the GEO visible radiance conversion, validation approach, and Edition4 improvements.

Retrieving SW fluxes from geostationary narrowband radiances for the NASA-CERES SYN1deg product

NASA Astrophysics Data System (ADS)

Wrenn, F. J., IV; Doelling, D. R.; Liang, L.

2017-12-01

The CERES mission was designed to measure the natural variability of the net TOA flux over long time scales relevant to climate monitoring. To achieve this goal, CERES provides the level-3 SSF1deg, SYN1deg, and EBAF monthly 1° by 1° regional TOA flux. The single satellite (Terra or Aqua) SSF1deg 24-hour shortwave flux is based on one daytime measurements and assumes constant meteorology to model the diurnal change in albedo. To accurately describe regions with a prominent diurnal signal, the SYN1deg Edition4 dataset employs hourly geostationary (GEO) measurements. This improves upon Edition3, which used 3-hourly GEO measurements and with temporal interpolation. The EBAF product combines the temporal stability of the SSF1deg product with the diurnal information from SYN1deg and removes the CERES instrument calibration bias by constraining the net flux balance to the ocean heat storage term. The SYN-1deg product retrieves hourly SW fluxes from GEO measurements. Over regions with large diurnal cycles, such as maritime stratus and land afternoon convective locations, the GEO derived SW fluxes will capture the diurnal flux not observed with Terra or Aqua sun-synchronous satellites. Obtaining fluxes from geostationary satellite radiance is a multistep process. First, most GEO visible imagers lack calibration and must be calibrated to MODIS and VIIRS. Second, the GEO imager visible channel radiances are converted to broadband radiances using empirical and theoretical models. The lack of coincident, collocated, and co-angled GEO and CERES measurements makes building an empirical model difficult. The narrowband to broadband models are a function of surface and cloud conditions, which are difficult to identify due to the inconsistent cloud retrievals between the 16 GEO imagers used in the CERES record. Third, the GEO derived broadband radiances are passed through the CERES angular distribution model (ADM) to convert the radiances to fluxes. Lastly, the GEO derived broadband fluxes are normalized with CERES fluxes in order to preserve the CERES instrument calibration. Validation is performed by comparing the GEO converted fluxes against CERES observations using coincident and collocated data. This work will focus on the GEO visible radiance conversion, validation approach, and Edition4 improvements.

Photosynthetic oxygen production in a warmer ocean: the Sargasso Sea as a case study.

PubMed

Richardson, Katherine; Bendtsen, Jørgen

2017-09-13

Photosynthetic O 2 production can be an important source of oxygen in sub-surface ocean waters especially in permanently stratified oligotrophic regions of the ocean where O 2 produced in deep chlorophyll maxima (DCM) is not likely to be outgassed. Today, permanently stratified regions extend across approximately 40% of the global ocean and their extent is expected to increase in a warmer ocean. Thus, predicting future ocean oxygen conditions requires a better understanding of the potential response of photosynthetic oxygen production to a warmer ocean. Based on our own and published observations of water column processes in oligotrophic regions, we develop a one-dimensional water column model describing photosynthetic oxygen production in the Sargasso Sea to quantify the importance of photosynthesis for the downward flux of O 2 and examine how it may be influenced in a warmer ocean. Photosynthesis is driven in the model by vertical mixing of nutrients (including eddy-induced mixing) and diazotrophy and is found to substantially increase the downward O 2 flux relative to physical-chemical processes alone. Warming (2°C) surface waters does not significantly change oxygen production at the DCM. Nor does a 15% increase in re-mineralization rate (assuming Q 10  = 2; 2°C warming) have significant effect on net sub-surface oxygen accumulation. However, changes in the relative production of particulate (POM) and dissolved organic material (DOM) generate relatively large changes in net sub-surface oxygen production. As POM/DOM production is a function of plankton community composition, this implies plankton biodiversity and food web structure may be important factors influencing O 2 production in a warmer ocean.This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'. © 2017 The Author(s).

Photosynthetic oxygen production in a warmer ocean: the Sargasso Sea as a case study

NASA Astrophysics Data System (ADS)

Richardson, Katherine; Bendtsen, Jørgen

2017-08-01

Photosynthetic O2 production can be an important source of oxygen in sub-surface ocean waters especially in permanently stratified oligotrophic regions of the ocean where O2 produced in deep chlorophyll maxima (DCM) is not likely to be outgassed. Today, permanently stratified regions extend across approximately 40% of the global ocean and their extent is expected to increase in a warmer ocean. Thus, predicting future ocean oxygen conditions requires a better understanding of the potential response of photosynthetic oxygen production to a warmer ocean. Based on our own and published observations of water column processes in oligotrophic regions, we develop a one-dimensional water column model describing photosynthetic oxygen production in the Sargasso Sea to quantify the importance of photosynthesis for the downward flux of O2 and examine how it may be influenced in a warmer ocean. Photosynthesis is driven in the model by vertical mixing of nutrients (including eddy-induced mixing) and diazotrophy and is found to substantially increase the downward O2 flux relative to physical-chemical processes alone. Warming (2°C) surface waters does not significantly change oxygen production at the DCM. Nor does a 15% increase in re-mineralization rate (assuming Q10 = 2; 2°C warming) have significant effect on net sub-surface oxygen accumulation. However, changes in the relative production of particulate (POM) and dissolved organic material (DOM) generate relatively large changes in net sub-surface oxygen production. As POM/DOM production is a function of plankton community composition, this implies plankton biodiversity and food web structure may be important factors influencing O2 production in a warmer ocean. This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'.

What are hot and what are not in an urban landscape: quantifying and explaining the land surface temperature pattern in Beijing, China

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuang, Wenhui; Liu, Yue; Dou, Yinyin

Understanding how landscape components affect the urban heat islands is crucial for urban ecological planning and sustainable development. The purpose of this research was to quantify the spatial pattern of land surface temperatures (LSTs) and associated heat fluxes in relation to land-cover types in Beijing, China, using portable infrared thermometers, thermal infrared imagers, and the moderate resolution imaging spectroradiometer. The spatial differences and the relationships between LSTs and the hierarchical landscape structure were analyzed with in situ observations of surface radiation and heat fluxes. Large LST differences were found among various land-use/land-cover types, urban structures, and building materials. Within themore » urban area, the mean LST of urban impervious surfaces was about 6–12°C higher than that of the urban green space. LSTs of built-up areas were on average 3–6°C higher than LSTs of rural areas. The observations for surface radiation and heat fluxes indicated that the differences were caused by different fractions of sensible heat or latent heat flux in net radiation. LSTs decreased with increasing elevation and normalized difference vegetation index. Variations in building materials and urban structure significantly influenced the spatial pattern of LSTs in urban areas. By contrast, elevation and vegetation cover are the major determinants of the LST pattern in rural areas. In summary, to alleviate urban heat island intensity, urban planners and policy makers should pay special attention to the selection of appropriate building materials, the reasonable arrangement of urban structures, and the rational design of landscape components.« less

What are hot and what are not in an urban landscape: quantifying and explaining the land surface temperature pattern in Beijing, China

DOE PAGES

Kuang, Wenhui; Liu, Yue; Dou, Yinyin; ...

2014-12-06

Understanding how landscape components affect the urban heat islands is crucial for urban ecological planning and sustainable development. The purpose of this research was to quantify the spatial pattern of land surface temperatures (LSTs) and associated heat fluxes in relation to land-cover types in Beijing, China, using portable infrared thermometers, thermal infrared imagers, and the moderate resolution imaging spectroradiometer. The spatial differences and the relationships between LSTs and the hierarchical landscape structure were analyzed with in situ observations of surface radiation and heat fluxes. Large LST differences were found among various land-use/land-cover types, urban structures, and building materials. Within themore » urban area, the mean LST of urban impervious surfaces was about 6–12°C higher than that of the urban green space. LSTs of built-up areas were on average 3–6°C higher than LSTs of rural areas. The observations for surface radiation and heat fluxes indicated that the differences were caused by different fractions of sensible heat or latent heat flux in net radiation. LSTs decreased with increasing elevation and normalized difference vegetation index. Variations in building materials and urban structure significantly influenced the spatial pattern of LSTs in urban areas. By contrast, elevation and vegetation cover are the major determinants of the LST pattern in rural areas. In summary, to alleviate urban heat island intensity, urban planners and policy makers should pay special attention to the selection of appropriate building materials, the reasonable arrangement of urban structures, and the rational design of landscape components.« less

Climatology of sediment flux and composition in the subarctic Northeast Pacific Ocean with biogeochemical implications

NASA Astrophysics Data System (ADS)

Timothy, D. A.; Wong, C. S.; Barwell-Clarke, J. E.; Page, J. S.; White, L. A.; Macdonald, R. W.

2013-09-01

Sequentially sampling conical sediment traps were maintained at Ocean Station Papa (OSP; 50°N, 145°W) in the Alaska Gyre from September 1982 to June 2006. The time series began with a single trap at 3800 m and traps were added at 1000 m and 200 m in March 1983 and May 1989, respectively. A trap at 3500-3700 m also was moored 5° north of OSP from May 1990 to August 1992. Total mass, biogenic silica (BSi), calcium carbonate (CaCO3), particulate organic carbon (POC) and particulate nitrogen (PN) were routinely measured. In this paper, we develop climatologies of sediment flux and composition at OSP, describing the characteristic features for comparison to sedimentary conditions globally. We then expand our use of the climatologies to arrive at four main conclusions regarding ecology and geochemistry at OSP. Fluxes of BSi and CaCO3 at 200 m and 1000 m lag by one month the annual cycle of irradiance and arrive at 3800 m ∼16 d later, with maximum export occurring several months later for POC. Next, the annual cycle of BSi flux shows that diatom production in late winter and spring is higher than indicated by spring decline of surface nutrients. We then show that the annual cycle of POC flux implies a net community production of organic carbon (NCPOC) of 3.6-5.3 mol m-2 y-1, double estimates based on mixed layer tracers but similar to estimates unaffected by mixing. NCPOC, combined with a CaCO3:POC production ratio of 0.18 determined from trap fluxes, gives a net community production of CaCO3 (NCPIC) of 0.65-0.95 mol m-2 y-1, in agreement with CaCO3 dissolution in the water column plus abyssal CaCO3 flux. Lastly, the flux climatologies at 1000 m and 3800 m are used to infer particle transformations in the bathypelagic zone including disaggregation and remineralization. Fluxes at 3800 m are best described as the sum of a primary flux sinking rapidly and a slowly-sinking secondary flux. Disaggregation of the primary flux is the likely source of secondary fluxes, with a lithogenic component transported horizontally also reaching the 3800-m traps. A detailed description of the sampling also is provided so future experiments can benefit from the successes and failures encountered at OSP. Fluxes normalized to 2000 m are 2.7, 1.3 and 1.1 times higher than the global averages for BSi, CaCO3 and POC, respectively. The Alaska Gyre is thus a siliceous basin with unusually high calcareous fluxes. Lithogenic fluxes are minor at OSP, making this site ideal to detect dust-fall events. Fluxes of BSi and CaCO3 lag surface solar irradiance by about one month at 200 m and 1000 m, and by another ∼two weeks at 3800 m. POM is preferentially retained and recycled in the mixed layer, with maximum export occurring several months after maximum fluxes of BSi and CaCO3. Export fluxes are episodic at OSP despite perennially low chlorophyll concentrations showing little seasonality. As a result of episodically high fluxes, 40-50% of MARK7 traps with narrow sampling bottles became clogged during deployment at 3800 m. Given the common occurrence of this problem globally, traps with larger bottom orifices should become standard protocol. Sediment traps provide an excellent opportunity to test sedimentary tracers of past ocean conditions. In this regard, POC content at OSP is a poor indicator of mass or POC flux because POC is diluted by BSi and CaCO3 when mass flux is high. The annual cycle of BSi flux and a reanalysis of surface nutrient data show the spring delay in [Si(OH)4] decline, based on mixed-layer nutrient climatology, results from intense mixing in spring rather than delayed diatom growth as previously proposed. The annual cycle of POC flux, normalized to measures of net community production of organic carbon (NCPOC) in summer-fall (Emerson and Stump, 2010), implies an annual NCPOC of 3.6-5.3 mol m-2 y-1. This rate is similar to estimates of new production and of water-column OC remineralization plus deep POC flux, two equivalencies to NCPOC. It is also similar to estimates of export production at OSP made from global modeling, but it is double estimates of NCPOC based on mass balance of mixed-layer tracers. The estimate of NCPOC and a CaCO3:OC export ratio of 0.18 determined from trap data gives a net community production of CaCO3 (NCPIC) of 0.65-0.95 mol m-2 y-1 in agreement with water-column CaCO3 dissolution plus deep CaCO3 flux. The similarity between the CaCO3:POC flux ratio at 50 m and the CaCO3:POC production ratio from bottle incubations (Lipsen et al., 2007) requires that ∼70% of CaCO3 production must dissolve in the euphotic zone to match the rate of POC recycling at OSP. Flux climatologies at 1000 m and 3800 m imply sediments caught at 3800 m include a component sinking rapidly (the primary flux; ∼120-350 m d-1) and another component sinking slowly (the secondary flux; ∼10-20 m d-1). A mass-balance model finds that secondary fluxes contribute ∼40% to the annual mass flux at 3800 m. Based on compositional evidence and on the arrival times at 3800 m, the secondary flux likely derives from disaggregated primary fluxes with an additional lithogenic component transported horizontally to the bathypelagic zone at OSP. Remineralization of BSi, CaCO3, OC and N estimated from decreasing flux with depth in the bathypelagic zone agrees with estimates for the Pacific Ocean based on water-column tracers provided trapping efficiency at 1000 m is 0.6-0.8 and at 3800 m is 1. Alternatively, the estimates based on tracers may include a component of seafloor remineralization. In this case, remineralization in the water column at OSP is at least 30-45% of the remineralization determined by tracers, with the remainder occurring at the seafloor.

Arctic Ocean CO2 uptake: an improved multiyear estimate of the air-sea CO2 flux incorporating chlorophyll a concentrations

NASA Astrophysics Data System (ADS)

Yasunaka, Sayaka; Siswanto, Eko; Olsen, Are; Hoppema, Mario; Watanabe, Eiji; Fransson, Agneta; Chierici, Melissa; Murata, Akihiko; Lauvset, Siv K.; Wanninkhof, Rik; Takahashi, Taro; Kosugi, Naohiro; Omar, Abdirahman M.; van Heuven, Steven; Mathis, Jeremy T.

2018-03-01

We estimated monthly air-sea CO2 fluxes in the Arctic Ocean and its adjacent seas north of 60° N from 1997 to 2014. This was done by mapping partial pressure of CO2 in the surface water (pCO2w) using a self-organizing map (SOM) technique incorporating chlorophyll a concentration (Chl a), sea surface temperature, sea surface salinity, sea ice concentration, atmospheric CO2 mixing ratio, and geographical position. We applied new algorithms for extracting Chl a from satellite remote sensing reflectance with close examination of uncertainty of the obtained Chl a values. The overall relationship between pCO2w and Chl a was negative, whereas the relationship varied among seasons and regions. The addition of Chl a as a parameter in the SOM process enabled us to improve the estimate of pCO2w, particularly via better representation of its decline in spring, which resulted from biologically mediated pCO2w reduction. As a result of the inclusion of Chl a, the uncertainty in the CO2 flux estimate was reduced, with a net annual Arctic Ocean CO2 uptake of 180 ± 130 Tg C yr-1. Seasonal to interannual variation in the CO2 influx was also calculated.