CERES Monthly Gridded Single Satellite TOA and Surfaces/Clouds (SFC) data in HDF (CER_SFC_Terra-FM1-MODIS_Edition2B)

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A. (Principal Investigator)

The Monthly Gridded TOA/Surface Fluxes and Clouds (SFC) product contains a month of space and time averaged Clouds and the Earth's Radiant Energy System (CERES) data for a single scanner instrument. The SFC is also produced for combinations of scanner instruments. All instantaneous shortwave, longwave, and window fluxes at the Top-of-the-Atmosphere (TOA) and surface from the CERES SSF product for a month are sorted by 1-degree spatial regions and by the local hour of observation. The mean of the instantaneous fluxes for a given region-hour bin is determined and recorded on the SFC along with other flux statistics and scene information. These average fluxes are given for both clear-sky and total-sky scenes. The regional cloud properties are column averaged and are included on the SFC. [Location=GLOBAL] [Temporal_Coverage: Start_Date=1998-01-01; Stop_Date=2003-10-31] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=100] [Data_Resolution: Latitude_Resolution=1 degree; Longitude_Resolution=1 degree; Horizontal_Resolution_Range=100 km - < 250 km or approximately 1 degree - < 2.5 degrees; Temporal_Resolution=1 hour; Temporal_Resolution_Range=Hourly - < Daily].

CERES Monthly Gridded Single Satellite TOA and Surfaces/Clouds (SFC) data in HDF (CER_SFC_Aqua-FM3-MODIS_Edition2A)

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A. (Principal Investigator)

The Monthly Gridded TOA/Surface Fluxes and Clouds (SFC) product contains a month of space and time averaged Clouds and the Earth's Radiant Energy System (CERES) data for a single scanner instrument. The SFC is also produced for combinations of scanner instruments. All instantaneous shortwave, longwave, and window fluxes at the Top-of-the-Atmosphere (TOA) and surface from the CERES SSF product for a month are sorted by 1-degree spatial regions and by the local hour of observation. The mean of the instantaneous fluxes for a given region-hour bin is determined and recorded on the SFC along with other flux statistics and scene information. These average fluxes are given for both clear-sky and total-sky scenes. The regional cloud properties are column averaged and are included on the SFC. [Location=GLOBAL] [Temporal_Coverage: Start_Date=1998-01-01; Stop_Date=2005-12-31] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=100] [Data_Resolution: Latitude_Resolution=1 degree; Longitude_Resolution=1 degree; Horizontal_Resolution_Range=100 km - < 250 km or approximately 1 degree - < 2.5 degrees; Temporal_Resolution=1 hour; Temporal_Resolution_Range=Hourly - < Daily].

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.;

CERES Monthly TOA and SRB Averages (SRBAVG) data in HDF-EOS Grid (CER_SRBAVG_Terra-FM2-MODIS_Edition2C)

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A. (Principal Investigator)

The Monthly TOA/Surface Averages (SRBAVG) product contains a month of space and time averaged Clouds and the Earth's Radiant Energy System (CERES) data for a single scanner instrument. The SRBAVG is also produced for combinations of scanner instruments. The monthly average regional flux is estimated using diurnal models and the 1-degree regional fluxes at the hour of observation from the CERES SFC product. A second set of monthly average fluxes are estimated using concurrent diurnal information from geostationary satellites. These fluxes are given for both clear-sky and total-sky scenes and are spatially averaged from 1-degree regions to 1-degree zonal averages and a global average. For each region, the SRBAVG also contains hourly average fluxes for the month and an overall monthly average. The cloud properties from SFC are column averaged and are included on the SRBAVG. [Location=GLOBAL] [Temporal_Coverage: Start_Date=1998-02-01; Stop_Date=2003-02-28] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180] [Data_Resolution: Latitude_Resolution=1 degree; Longitude_Resolution=1 degree; Horizontal_Resolution_Range=100 km - < 250 km or approximately 1 degree - < 2.5 degrees; Temporal_Resolution=1 month; Temporal_Resolution_Range=Monthly - < Annual].

CERES Monthly TOA and SRB Averages (SRBAVG) data in HDF-EOS Grid (CER_SRBAVG_TRMM-PFM-VIRS_Edition2B)

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A. (Principal Investigator)

The Monthly TOA/Surface Averages (SRBAVG) product contains a month of space and time averaged Clouds and the Earth's Radiant Energy System (CERES) data for a single scanner instrument. The SRBAVG is also produced for combinations of scanner instruments. The monthly average regional flux is estimated using diurnal models and the 1-degree regional fluxes at the hour of observation from the CERES SFC product. A second set of monthly average fluxes are estimated using concurrent diurnal information from geostationary satellites. These fluxes are given for both clear-sky and total-sky scenes and are spatially averaged from 1-degree regions to 1-degree zonal averages and a global average. For each region, the SRBAVG also contains hourly average fluxes for the month and an overall monthly average. The cloud properties from SFC are column averaged and are included on the SRBAVG. [Location=GLOBAL] [Temporal_Coverage: Start_Date=1998-02-01; Stop_Date=2000-03-31] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180] [Data_Resolution: Latitude_Resolution=1 degree; Longitude_Resolution=1 degree; Horizontal_Resolution_Range=100 km - < 250 km or approximately 1 degree - < 2.5 degrees; Temporal_Resolution=1 month; Temporal_Resolution_Range=Monthly - < Annual].

CERES Monthly TOA and SRB Averages (SRBAVG) data in HDF-EOS Grid (CER_SRBAVG_Terra-FM1-MODIS_Edition2C)

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A. (Principal Investigator)

The Monthly TOA/Surface Averages (SRBAVG) product contains a month of space and time averaged Clouds and the Earth's Radiant Energy System (CERES) data for a single scanner instrument. The SRBAVG is also produced for combinations of scanner instruments. The monthly average regional flux is estimated using diurnal models and the 1-degree regional fluxes at the hour of observation from the CERES SFC product. A second set of monthly average fluxes are estimated using concurrent diurnal information from geostationary satellites. These fluxes are given for both clear-sky and total-sky scenes and are spatially averaged from 1-degree regions to 1-degree zonal averages and a global average. For each region, the SRBAVG also contains hourly average fluxes for the month and an overall monthly average. The cloud properties from SFC are column averaged and are included on the SRBAVG. [Location=GLOBAL] [Temporal_Coverage: Start_Date=1998-02-01; Stop_Date=2003-02-28] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180] [Data_Resolution: Latitude_Resolution=1 degree; Longitude_Resolution=1 degree; Horizontal_Resolution_Range=100 km - < 250 km or approximately 1 degree - < 2.5 degrees; Temporal_Resolution=1 month; Temporal_Resolution_Range=Monthly - < Annual].

CERES Monthly TOA and SRB Averages (SRBAVG) data in HDF-EOS Grid (CER_SRBAVG_Terra-FM1-MODIS_Edition2D)

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A. (Principal Investigator)

The Monthly TOA/Surface Averages (SRBAVG) product contains a month of space and time averaged Clouds and the Earth's Radiant Energy System (CERES) data for a single scanner instrument. The SRBAVG is also produced for combinations of scanner instruments. The monthly average regional flux is estimated using diurnal models and the 1-degree regional fluxes at the hour of observation from the CERES SFC product. A second set of monthly average fluxes are estimated using concurrent diurnal information from geostationary satellites. These fluxes are given for both clear-sky and total-sky scenes and are spatially averaged from 1-degree regions to 1-degree zonal averages and a global average. For each region, the SRBAVG also contains hourly average fluxes for the month and an overall monthly average. The cloud properties from SFC are column averaged and are included on the SRBAVG. [Location=GLOBAL] [Temporal_Coverage: Start_Date=1998-02-01; Stop_Date=2004-05-31] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180] [Data_Resolution: Latitude_Resolution=1 degree; Longitude_Resolution=1 degree; Horizontal_Resolution_Range=100 km - < 250 km or approximately 1 degree - < 2.5 degrees; Temporal_Resolution=1 month; Temporal_Resolution_Range=Monthly - < Annual].

Influence of wind speed averaging on estimates of dimethylsulfide emission fluxes

DOE PAGES

Chapman, E. G.; Shaw, W. J.; Easter, R. C.; ...

2002-12-03

The effect of various wind-speed-averaging periods on calculated DMS emission fluxes is quantitatively assessed. Here, a global climate model and an emission flux module were run in stand-alone mode for a full year. Twenty-minute instantaneous surface wind speeds and related variables generated by the climate model were archived, and corresponding 1-hour-, 6-hour-, daily-, and monthly-averaged quantities calculated. These various time-averaged, model-derived quantities were used as inputs in the emission flux module, and DMS emissions were calculated using two expressions for the mass transfer velocity commonly used in atmospheric models. Results indicate that the time period selected for averaging wind speedsmore » can affect the magnitude of calculated DMS emission fluxes. A number of individual marine cells within the global grid show DMS emissions fluxes that are 10-60% higher when emissions are calculated using 20-minute instantaneous model time step winds rather than monthly-averaged wind speeds, and at some locations the differences exceed 200%. Many of these cells are located in the southern hemisphere where anthropogenic sulfur emissions are low and changes in oceanic DMS emissions may significantly affect calculated aerosol concentrations and aerosol radiative forcing.« less

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.

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.

Evaluation of energy fluxes in the NCEP climate forecast system version 2.0 (CFSv2)

NASA Astrophysics Data System (ADS)

Rai, Archana; Saha, Subodh Kumar

2018-01-01

The energy fluxes at the surface and top of the atmosphere (TOA) from a long free run by the NCEP climate forecast system version 2.0 (CFSv2) are validated against several observation and reanalysis datasets. This study focuses on the annual mean energy fluxes and tries to link it with the systematic cold biases in the 2 m air temperature, particularly over the land regions. The imbalance in the long term mean global averaged energy fluxes are also evaluated. The global averaged imbalance at the surface and at the TOA is found to be 0.37 and 6.43 Wm-2, respectively. It is shown that CFSv2 overestimates the land surface albedo, particularly over the snow region, which in turn contributes to the cold biases in 2 m air temperature. On the other hand, surface albedo is highly underestimated over the coastal region around Antarctica and that may have contributed to the warm bias over that oceanic region. This study highlights the need for improvements in the parameterization of snow/sea-ice albedo scheme for a realistic simulation of surface temperature and that may have implications on the global energy imbalance in the model.

Enhancing surface methane fluxes from an oligotrophic lake: exploring the microbubble hypothesis.

PubMed

McGinnis, Daniel F; Kirillin, Georgiy; Tang, Kam W; Flury, Sabine; Bodmer, Pascal; Engelhardt, Christof; Casper, Peter; Grossart, Hans-Peter

2015-01-20

Exchange of the greenhouse gases carbon dioxide (CO2) and methane (CH4) across inland water surfaces is an important component of the terrestrial carbon (C) balance. We investigated the fluxes of these two gases across the surface of oligotrophic Lake Stechlin using a floating chamber approach. The normalized gas transfer rate for CH4 (k600,CH4) was on average 2.5 times higher than that for CO2 (k600,CO2) and consequently higher than Fickian transport. Because of its low solubility relative to CO2, the enhanced CH4 flux is possibly explained by the presence of microbubbles in the lake’s surface layer. These microbubbles may originate from atmospheric bubble entrainment or gas supersaturation (i.e., O2) or both. Irrespective of the source, we determined that an average of 145 L m(–2) d(–1) of gas is required to exit the surface layer via microbubbles to produce the observed elevated k600,CH4. As k600 values are used to estimate CH4 pathways in aquatic systems, the presence of microbubbles could alter the resulting CH4 and perhaps C balances. These microbubbles will also affect the surface fluxes of other sparingly soluble gases in inland waters, including O2 and N2.

Mass fluxes of organic pollutants between groundwater, streambed sediments and surface water

NASA Astrophysics Data System (ADS)

Schirmer, Mario; Kalbus, Edda; Schmidt, Christian

2010-05-01

Rivers and groundwater are commonly hydraulically connected and thus also pollutants migrate between one and the other. Particularly in small lowland streams, pollutant transport by discharging groundwater can deteriorate the surface water quality. Moreover, in urban and industrial areas streambed sediments are often polluted with a variety of organic and inorganic substances. For planning measures to improve surface water quality or to mitigate pollutant migration, it is an essential prerequisite to understand pollutant pathways and mass fluxes between the stream, the streambed sediment and the connected aquifer. We present methodological approaches and results of a study conducted at a small man-made stream located in the industrial area of Bitterfeld-Wolfen, Germany. This site is characterized by a diffuse groundwater contamination with a variety of aliphatic and aromatic organic substances. The underlying approach of this study was to quantify the mass fluxes between the aquifer, the streambed and the stream by combining high-resolution with integral monitoring approaches. Magnitudes and pattern of water fluxes were obtained by mapping streambed temperatures. The method was applied to a reach of 280 m in length. The mass fluxes from the aquifer towards the stream were estimated by combining the water fluxes with representative, average pollutant concentrations. The concentrations were obtained from an integral pumping test with four simultaneously pumped wells operated for the period of five days. For monochlorobenzene (MCB), the main groundwater pollutant at the site, the resulting average mass flux from the aquifer towards the stream was estimated to 724 µg/m²/d. Mass flux calculations with average aqueous concentrations of MCB in the streambed were found to be higher than those originating from the aquifer. Consequently, the streambed sediments represent a secondary pollutant source for the surface water. Pollutant concentrations in the streambed were lower at locations with high groundwater discharge and vice versa. Hence, the spatial heterogeneity of water fluxes must be considered when mass fluxes between surface water and streambed sediments are assessed. River restoration could improve the structural state of rivers and may thus result in an enhanced biodegradation of organic pollutants in the streambed. However, before any physical measure is applied a profound knowledge of pollutant concentration and pathways is required in order to avoid mobilization of sediment-bound pollutants.

On Averaging Timescales for the Surface Energy Budget Closure Problem

NASA Astrophysics Data System (ADS)

Grachev, A. A.; Fairall, C. W.; Persson, O. P. G.; Uttal, T.; Blomquist, B.; McCaffrey, K.

2017-12-01

An accurate determination of the surface energy budget (SEB) and all SEB components at the air-surface interface is of obvious relevance for the numerical modelling of the coupled atmosphere-land/ocean/snow system over different spatial and temporal scales, including climate modelling, weather forecasting, environmental impact studies, and many other applications. This study analyzes and discusses comprehensive measurements of the SEB and the surface energy fluxes (turbulent, radiative, and ground heat) made over different underlying surfaces based on the data collected during several field campaigns. Hourly-averaged, multiyear data sets collected at two terrestrial long-term research observatories located near the coast of the Arctic Ocean at Eureka (Canadian Archipelago) and Tiksi (East Siberia) and half-hourly averaged fluxes collected during a year-long field campaign (Wind Forecast Improvement Project 2, WFIP 2) at the Columbia River Gorge (Oregon) in areas of complex terrain. Our direct measurements of energy balance show that the sum of the turbulent sensible and latent heat fluxes systematically underestimate the available energy at half-hourly and hourly time scales by around 20-30% at these sites. This imbalance of the surface energy budget is comparable to other terrestrial sites. Surface energy balance closure is a formulation of the conservation of energy principle (the first law of thermodynamics). The lack of energy balance closure at hourly time scales is a fundamental and pervasive problem in micrometeorology and may be caused by inaccurate estimates of the energy storage terms in soils, air and biomass in the layer below the measurement height and above the heat flux plates. However, the residual energy imbalance is significantly reduced at daily and monthly timescales. Increasing the averaging time to daily scales substantially reduces the storage terms because energy locally entering the soil, air column, and vegetation in the morning is released in the afternoon and evening.

Reporting central tendencies of chamber measured surface emission and oxidation.

PubMed

Abichou, Tarek; Clark, Jeremy; Chanton, Jeffery

2011-05-01

Methane emissions, concentrations, and oxidation were measured on eleven MSW landfills in eleven states spanning from California to Pennsylvania during the three year study. The flux measurements were performed using a static chamber technique. Initial concentration samples were collected immediately after placement of the flux chamber. Oxidation of the emitted methane was evaluated using stable isotope techniques. When reporting overall surface emissions and percent oxidation for a landfill cover, central tendencies are typically used to report "averages" of the collected data. The objective of this study was to determine the best way to determine and report central tendencies. Results showed that 89% of the data sets of collected surface flux have lognormal distributions, 83% of the surface concentration data sets are also lognormal. Sixty seven percent (67%) of the isotope measured percent oxidation data sets are normally distributed. The distribution of data for all eleven landfills provides insight of the central tendencies of emissions, concentrations, and percent oxidation. When reporting the "average" measurement for both flux and concentration data collected at the surface of a landfill, statistical analyses provided insight supporting the use of the geometric mean. But the arithmetic mean can accurately represent the percent oxidation, as measured with the stable isotope technique. We examined correlations between surface CH(4) emissions and surface air CH(4) concentrations. Correlation of the concentration and flux values using the geometric mean proved to be a good fit (R(2)=0.86), indicating that surface scans are a good way of identifying locations of high emissions. Copyright © 2010 Elsevier Ltd. All rights reserved.

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.

Evaporation of Liquid Droplet in Nano and Micro Scales from Statistical Rate Theory.

PubMed

Duan, Fei; He, Bin; Wei, Tao

2015-04-01

The statistical rate theory (SRT) is applied to predict the average evaporation flux of liquid droplet after the approach is validated in the sessile droplet experiments of the water and heavy water. The steady-state experiments show a temperature discontinuity at the evaporating interface. The average evaporation flux is evaluated by individually changing the measurement at a liquid-vapor interface, including the interfacial liquid temperature, the interfacial vapor temperature, the vapor-phase pressure, and the droplet size. The parameter study shows that a higher temperature jump would reduce the average evaporation flux. The average evaporation flux can significantly be influenced by the interfacial liquid temperature and the vapor-phase pressure. The variation can switch the evaporation into condensation. The evaporation flux is found to remain relative constant if the droplet is larger than a micro scale, while the smaller diameters in nano scale can produce a much higher evaporation flux. In addition, a smaller diameter of droplets with the same liquid volume has a larger surface area. It is suggested that the evaporation rate increases dramatically as the droplet shrinks into nano size.

Analysis of the surface heat balance over the world ocean

NASA Technical Reports Server (NTRS)

Esbensen, S. K.

1981-01-01

It is possible to estimate long term monthly mean latent and sensible heat fluxes over the ocean to within or approximately 20% relative accuracy of the bulk aerodynamic formulas, by using observations of the monthly mean surface wind speed and the monthly mean sea air temperature and humidity differences. It is possible to make an estimate of the fluxes on a month to month basis from monthly averaged surface data.

A comparison of cellulosic fuel yields and separated soil-surface CO2 fluxes in maize and prairie biofuel cropping systems

NASA Astrophysics Data System (ADS)

Nichols, Virginia A.

It has been suggested that strategic incorporation of perennial vegetation into agricultural landscapes could provide ecosystem services while maintaining agricultural productivity. To evaluate potential use of prairie as a Midwestern cellulosic feedstock, we investigated theoretical cellulosic fuel yields, as well as soil-surface carbon dioxide emissions of prairie-based biofuel systems as compared to maize-based systems on fertile soils in Boone County, IA, USA. Investigated systems were: a maize-soybean rotation grown for grain only, continuous maize grown for grain and stover both with and without a winter rye cover crop, and a 31-species reconstructed prairie grown with and without spring nitrogen fertilization for fall-harvested biomass. From 2009-2013, the highest producing system was N-fertilized prairie, averaging 10.4 Mg ha -1 yr-1 above-ground biomass with average harvest removals of 7.8 Mg ha-1 yr-1. The unfertilized prairie produced 7.4 Mg ha-1 yr-1, averaging harvests of 5.3 Mg ha-1 yr-1. Lowest cellulosic biomass harvests were realized from continuous maize systems, averaging 3.5 Mg ha -1 yr-1 when grown with, and 3.7 Mg ha-1 yr-1 when grown without a winter rye cover crop, respectively. Un-fertilized prairie biomass and maize stover had equivalent dietary conversion ratios at 330 g ethanol kg-1 dry biomass, but N-fertilized prairie was lower at 315. Over four years prairie systems averaged 1287 L cellulosic ethanol ha-1 yr-1 more than maize systems, with fertilization increasing prairie ethanol production by 865 L ha-1 yr-1. Harvested biomass accounted for >90% of ethanol yield variation. A major hurdle in carbon cycling studies is the separation of the soil-surface CO2 flux into its respective components. From 2012-2013 we used a shading method to separate soil-surface CO2 resulting from oxidation of soil organic matter and CO2 derived from live-root activity in three systems: unfertilized prairie, N-fertilized prairie, and continuous maize. Contrary to our hypothesis, total growing-season root CO2 flux was not proportional to end-of-season root biomass of cropping systems; unfertilized prairie contained nearly twice the root biomass of N-fertilized prairie, but the two systems' total root CO2 fluxes were not significantly different in either year. We found that the total growing-season flux of both root- and organic matter-derived CO 2 was higher in the prairie systems compared to the maize system. However, on a percentage basis, the prairies' soil-surface CO2 flux from May-September averaged 29% root-derived while from mid-June through September the maize averaged 22% root-derived. The percentage of the total CO2 flux that was root-derived in a given system varied from year to year, indicating there is no set relationship for a given cropping system.

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.

Methane emissions from tundra environments in the Yukon-Kuskokwin Delta, Alaska

NASA Technical Reports Server (NTRS)

Bartlett, Karen B.; Crill, Patrick M.; Sass, Ronald L.; Harriss, Robert C.; Dise, Nancy B.

1992-01-01

This paper reports CH4 flux to the atmosphere from a variety of tundra environments near Bethel, Alaska during the summer months of 1988. Emissions from wet meadow tundra averaged 144 +/- 31 mg/sq m/d and ranged from 15.6 to 426 mg/sq m/d varying with soil moisture and temperature. Flux from the drier upland tundra was about two orders of magnitude lower and averaged 2.3 +/- 1.1 mg/sq m/d. Tundra lakes emit CH4 from the open water surface as well as from fringing aquatic vegetation; the presence of vegetation significantly enhanced flux over open water rates. Calculated diffusive fluxes from open water varied with lake size, the large lakes emitting 3.8 mg/sq m/d and small lakes emitting an average of 77 mg/sq m/d. An updated estimate of global emissions from tundra indicates an annual fluxes of approximately 11 +/- 3 Tg CH4.

Simulating 3-D radiative transfer effects over the Sierra Nevada Mountains using WRF

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

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

2012-01-01

A surface solar radiation parameterization based on deviations between 3-D and conventional plane-parallel radiative transfer models has been incorporated into the Weather Research and Forecasting (WRF) model to understand the solar insolation over mountain/snow areas and to investigate the impact of the spatial and temporal distribution and variation of surface solar fluxes on land-surface processes. Using the Sierra-Nevada in the western United States as a testbed, we show that mountain effect could produce up to -50 to + 50 W m -2 deviations in the surface solar fluxes over the mountain areas, resulting in a temperature increase of up tomore » 1 °C on the sunny side. Upward surface sensible and latent heat fluxes are modulated accordingly to compensate for the change in surface solar fluxes. Snow water equivalent and surface albedo both show decreases on the sunny side of the mountains, indicating more snowmelt and hence reduced snow albedo associated with more solar insolation due to mountain effect. Soil moisture increases on the sunny side of the mountains due to enhanced snowmelt, while decreases on the shaded side. Substantial differences are found in the morning hours from 8–10 a.m. and in the afternoon around 3–5 p.m., while differences around noon and in the early morning and late afternoon are comparatively smaller. Variation in the surface energy balance can also affect atmospheric processes, such as cloud fields, through the modulation of vertical thermal structure. Negative changes of up to -40 g m -2 are found in the cloud water path, associated with reductions in the surface insolation over the cloud region. The day-averaged deviations in the surface solar flux are positive over the mountain areas and negative in the valleys, with a range between -12~12 W m -2. Changes in sensible and latent heat fluxes and surface skin temperature follow the solar insolation pattern. Differences in the domain-averaged diurnal variation over the Sierras show that the mountain area receives more solar insolation during early morning and late afternoon, resulting in enhanced upward sensible heat and latent heat fluxes from the surface and a corresponding increase in surface skin temperature. During the middle of the day, however, the surface insolation and heat fluxes show negative changes, indicating a cooling effect. Hence overall, the diurnal variations of surface temperature and surface fluxes in the Sierra-Nevada are reduced through the interactions of radiative transfer and mountains. Finally, the hourly differences of the surface solar insolation in higher elevated regions, however, show smaller magnitude in negative changes during the middle of the day and possibly more solar fluxes received during the whole day.« less

Plasma-material interaction in electrothermal and electromagnetic launchers

NASA Astrophysics Data System (ADS)

Bourham, M. A.; Gilligan, J. G.; Hankins, O. E.

1993-07-01

Various material surfaces have been exposed to high heat fluxes from 2 to 80 GW/sq m over 100 microsec duration using the electrothermal launcher, SIRENS. The vapor shield is effective in reducing the heat to the ablating surface, and the energy transmission factor through the vapor shield decreases as the incident heat flux increases. Results show good agreement with code predictions. Visible light emission spectra have been observed both in-bore and from the muzzle flash of the barrel, and from the flash of the source. Measurements of visible emission from the source indicate time averaged temperatures of 1 to 3 eV, and about 1 to 2 eV along the axis of the device, which agree with the theory and experimental measurements of the average heat flux and plasma conductivity.

Flux canceling in three-dimensional radiative magnetohydrodynamic simulations

NASA Astrophysics Data System (ADS)

Thaler, Irina; Spruit, H. C.

2017-05-01

We aim to study the processes involved in the disappearance of magnetic flux between regions of opposite polarity on the solar surface using realistic three-dimensional (3D) magnetohydrodynamic (MHD) simulations. "Retraction" below the surface driven by magnetic forces is found to be a very effective mechanism of flux canceling of opposite polarities. The speed at which flux disappears increases strongly with initial mean flux density. In agreement with existing inferences from observations we suggest that this is a key process of flux disappearance within active complexes. Intrinsic kG strength concentrations connect the surface to deeper layers by magnetic forces, and therefore the influence of deeper layers on the flux canceling process is studied. We do this by comparing simulations extending to different depths. For average flux densities of 50 G, and on length scales on the order of 3 Mm in the horizontal and 10 Mm in depth, deeper layers appear to have only a mild influence on the effective rate of diffusion.

Aerodynamic Surface Stress Intermittency and Conditionally Averaged Turbulence Statistics

NASA Astrophysics Data System (ADS)

Anderson, W.

2015-12-01

Aeolian erosion of dry, flat, semi-arid landscapes is induced (and sustained) by kinetic energy fluxes in the aloft atmospheric surface layer. During saltation -- the mechanism responsible for surface fluxes of dust and sediment -- briefly suspended sediment grains undergo a ballistic trajectory before impacting and `splashing' smaller-diameter (dust) particles vertically. Conceptual models typically indicate that sediment flux, q (via saltation or drift), scales with imposed aerodynamic (basal) stress raised to some exponent, n, where n > 1. Since basal stress (in fully rough, inertia-dominated flows) scales with the incoming velocity squared, u^2, it follows that q ~ u^2n (where u is some relevant component of the above flow field, u(x,t)). Thus, even small (turbulent) deviations of u from its time-averaged value may play an enormously important role in aeolian activity on flat, dry landscapes. The importance of this argument is further augmented given that turbulence in the atmospheric surface layer exhibits maximum Reynolds stresses in the fluid immediately above the landscape. In order to illustrate the importance of surface stress intermittency, we have used conditional averaging predicated on aerodynamic surface stress during large-eddy simulation of atmospheric boundary layer flow over a flat landscape with momentum roughness length appropriate for the Llano Estacado in west Texas (a flat agricultural region that is notorious for dust transport). By using data from a field campaign to measure diurnal variability of aeolian activity and prevailing winds on the Llano Estacado, we have retrieved the threshold friction velocity (which can be used to compute threshold surface stress under the geostrophic balance with the Monin-Obukhov similarity theory). This averaging procedure provides an ensemble-mean visualization of flow structures responsible for erosion `events'. Preliminary evidence indicates that surface stress peaks are associated with the passage of inclined, high-momentum regions flanked by adjacent low-momentum regions. We will characterize geometric attributes of such structures and explore streamwise and vertical vorticity distribution within the conditionally averaged flow field.

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.

Importance of ocean mesoscale variability for air-sea interactions in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Putrasahan, D. A.; Kamenkovich, I.; Le Hénaff, M.; Kirtman, B. P.

2017-06-01

Mesoscale variability of currents in the Gulf of Mexico (GoM) can affect oceanic heat advection and air-sea heat exchanges, which can influence climate extremes over North America. This study is aimed at understanding the influence of the oceanic mesoscale variability on the lower atmosphere and air-sea heat exchanges. The study contrasts global climate model (GCM) with 0.1° ocean resolution (high resolution; HR) with its low-resolution counterpart (1° ocean resolution with the same 0.5° atmosphere resolution; LR). The LR simulation is relevant to current generation of GCMs that are still unable to resolve the oceanic mesoscale. Similar to observations, HR exhibits positive correlation between sea surface temperature (SST) and surface turbulent heat flux anomalies, while LR has negative correlation. For HR, we decompose lateral advective heat fluxes in the upper ocean into mean (slowly varying) and mesoscale-eddy (fast fluctuations) components. We find that the eddy flux divergence/convergence dominates the lateral advection and correlates well with the SST anomalies and air-sea latent heat exchanges. This result suggests that oceanic mesoscale advection supports warm SST anomalies that in turn feed surface heat flux. We identify anticyclonic warm-core circulation patterns (associated Loop Current and rings) which have an average diameter of 350 km. These warm anomalies are sustained by eddy heat flux convergence at submonthly time scales and have an identifiable imprint on surface turbulent heat flux, atmospheric circulation, and convective precipitation in the northwest portion of an averaged anticyclone.

Aerosol-Induced Radiative Flux Changes Off the United States Mid-Atlantic Coast: Comparison of Values Calculated from Sunphotometer and In Situ Data with Those Measured by Airborne Pyranometer

NASA Technical Reports Server (NTRS)

Russell, P. B.; Livingston, J. M.; Hignett, P.; Kinne, S.; Wong, J.; Chien, A.; Bergstrom, R.; Durkee, P.; Hobbs, P. V.

2000-01-01

The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) measured a variety of aerosol radiative effects (including flux changes) while simultaneously measuring the chemical, physical, and optical properties of the responsible aerosol particles. Here we use TARFOX-determined aerosol and surface properties to compute shortwave radiative flux changes for a variety of aerosol situations, with midvisible optical depths ranging from 0.06 to 0.55. We calculate flux changes by several techniques with varying degrees of sophistication, in part to investigate the sensitivity of results to computational approach. We then compare computed flux changes to those determined from aircraft measurements. Calculations using several approaches yield downward and upward flux changes that agree with measurements. The agreement demonstrates closure (i.e. consistency) among the TARFOX-derived aerosol properties, modeling techniques, and radiative flux measurements. Agreement between calculated and measured downward flux changes is best when the aerosols are modeled as moderately absorbing (midvisible single-scattering albedos between about 0.89 and 0.93), in accord with independent measurements of the TARPOX aerosol. The calculated values for instantaneous daytime upwelling flux changes are in the range +14 to +48 W/sq m for midvisible optical depths between 0.2 and 0.55. These values are about 30 to 100 times the global-average direct forcing expected for the global-average sulfate aerosol optical depth of 0.04. The reasons for the larger flux changes in TARFOX include the relatively large optical depths and the focus on cloud-free, daytime conditions over the dark ocean surface. These are the conditions that produce major aerosol radiative forcing events and contribute to any global-average climate effect.

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.

Uncertainty in eddy covariance flux estimates resulting from spectral attenuation [Chapter 4

Treesearch

W. J. Massman; R. Clement

2004-01-01

Surface exchange fluxes measured by eddy covariance tend to be underestimated as a result of limitations in sensor design, signal processing methods, and finite flux-averaging periods. But, careful system design, modern instrumentation, and appropriate data processing algorithms can minimize these losses, which, if not too large, can be estimated and corrected using...

Surface energy balance estimates at local and regional scales using optical remote sensing from an aircraft platform and atmospheric data collected over semiarid rangelands

USGS Publications Warehouse

Kustas, William P.; Moran, M.S.; Humes, K.S.; Stannard, D.I.; Pinter, P. J.; Hipps, L.E.; Swiatek, E.; Goodrich, D.C.

1994-01-01

Remotely sensed data in the visible, near-infrared, and thermal-infrared wave bands were collected from a low-flying aircraft during the Monsoon '90 field experiment. Monsoon '90 was a multidisciplinary experiment conducted in a semiarid watershed. It had as one of its objectives the quantification of hydrometeorological fluxes during the “monsoon” or wet season. The remote sensing observations along with micrometeprological and atmospheric boundary layer (ABL) data were used to compute the surface energy balance over a range of spatial scales. The procedure involved averaging multiple pixels along transects flown over the meteorological and flux (METFLUX) stations. Average values of the spectral reflectance and thermal-infrared temperatures were computed for pixels of order 10−1 to 101 km in length and were used with atmospheric data for evaluating net radiation (Rn), soil heat flux (G), and sensible (H) and latent (LE) heat fluxes at these same length scales. The model employs a single-layer resistance approach for estimating H that requires wind speed and air temperature in the ABL and a remotely sensed surface temperature. The values of Rn and G are estimated from remote sensing information together with near-surface observations of air temperature, relative humidity, and solar radiation. Finally, LE is solved as the residual term in the surface energy balance equation. Model calculations were compared to measurements from the METFLUX network for three days having different environmental conditions. Average percent differences for the three days between model and the METFLUX estimates of the local fluxes were about 5% for Rn, 20% for Gand H, and 15% for LE. Larger differences occurred during partly cloudy conditions because of errors in interpreting the remote sensing data and the higher spatial and temporal variation in the energy fluxes. Minor variations in modeled energy fluxes were observed when the pixel size representing the remote sensing inputs changed from 0.2 to 2 km. Regional scale estimates of the surface energy balance using bulk ABL properties for the model parameters and input variables and the 10-km pixel data differed from the METFLUX network averages by about 4% for Rn, 10% for G and H, and 15% for LE. Model sensitivity in calculating the turbulent fluxes H and LE to possible variations in key model parameters (i.e., the roughness lengths for heat and momentum) was found to be fairly significant. Therefore the reliability of the methods for estimating key model parameters and potential errors needs further testing over different ecosystems and environmental conditions.

The impact of using area-averaged land surface properties —topography, vegetation condition, soil wetness—in calculations of intermediate scale (approximately 10 km 2) surface-atmosphere heat and moisture fluxes

NASA Astrophysics Data System (ADS)

Sellers, Piers J.; Heiser, Mark D.; Hall, Forrest G.; Verma, Shashi B.; Desjardins, Raymond L.; Schuepp, Peter M.; Ian MacPherson, J.

1997-03-01

It is commonly assumed that biophysically based soil-vegetation-atmosphere transfer (SVAT) models are scale-invariant with respect to the initial boundary conditions of topography, vegetation condition and soil moisture. In practice, SVAT models that have been developed and tested at the local scale (a few meters or a few tens of meters) are applied almost unmodified within general circulation models (GCMs) of the atmosphere, which have grid areas of 50-500 km 2. This study, which draws much of its substantive material from the papers of Sellers et al. (1992c, J. Geophys. Res., 97(D17): 19033-19060) and Sellers et al. (1995, J. Geophys. Res., 100(D12): 25607-25629), explores the validity of doing this. The work makes use of the FIFE-89 data set which was collected over a 2 km × 15 km grassland area in Kansas. The site was characterized by high variability in soil moisture and vegetation condition during the late growing season of 1989. The area also has moderate topography. The 2 km × 15 km 'testbed' area was divided into 68 × 501 pixels of 30 m × 30 m spatial resolution, each of which could be assigned topographic, vegetation condition and soil moisture parameters from satellite and in situ observations gathered in FIFE-89. One or more of these surface fields was area-averaged in a series of simulation runs to determine the impact of using large-area means of these initial or boundary conditions on the area-integrated (aggregated) surface fluxes. The results of the study can be summarized as follows: 1. analyses and some of the simulations indicated that the relationships describing the effects of moderate topography on the surface radiation budget are near-linear and thus largely scale-invariant. The relationships linking the simple ratio vegetation index ( SR), the canopy conductance parameter (▽ F) and the canopy transpiration flux are also near-linear and similarly scale-invariant to first order. Because of this, it appears that simple area-averaging operations can be applied to these fields with relatively little impact on the calculated surface heat flux. 2. The relationships linking surface and root-zone soil wetness to the soil surface and canopy transpiration rates are non-linear. However, simulation results and observations indicate that soil moisture variability decreases significantly as an area dries out, which partially cancels out the effects of these non-linear functions.In conclusion, it appears that simple averages of topographic slope and vegetation parameters can be used to calculate surface energy and heat fluxes over a wide range of spatial scales, from a few meters up to many kilometers at least for grassland sites and areas with moderate topography. Although the relationships between soil moisture and evapotranspiration are non-linear for intermediate soil wetnesses, the dynamics of soil drying act to progressively reduce soil moisture variability and thus the impacts of these non-linearities on the area-averaged surface fluxes. These findings indicate that we may be able to use mean values of topography, vegetation condition and soil moisture to calculate the surface-atmosphere fluxes of energy, heat and moisture at larger length scales, to within an acceptable accuracy for climate modeling work. However, further tests over areas with different vegetation types, soils and more extreme topography are required to improve our confidence in this approach.

The NASA Carbon Airborne Flux Experiment (CARAFE): instrumentation and methodology

NASA Astrophysics Data System (ADS)

Wolfe, Glenn M.; Kawa, S. Randy; Hanisco, Thomas F.; Hannun, Reem A.; Newman, Paul A.; Swanson, Andrew; Bailey, Steve; Barrick, John; Thornhill, K. Lee; Diskin, Glenn; DiGangi, Josh; Nowak, John B.; Sorenson, Carl; Bland, Geoffrey; Yungel, James K.; Swenson, Craig A.

2018-03-01

The exchange of trace gases between the Earth's surface and atmosphere strongly influences atmospheric composition. Airborne eddy covariance can quantify surface fluxes at local to regional scales (1-1000 km), potentially helping to bridge gaps between top-down and bottom-up flux estimates and offering novel insights into biophysical and biogeochemical processes. The NASA Carbon Airborne Flux Experiment (CARAFE) utilizes the NASA C-23 Sherpa aircraft with a suite of commercial and custom instrumentation to acquire fluxes of carbon dioxide, methane, sensible heat, and latent heat at high spatial resolution. Key components of the CARAFE payload are described, including the meteorological, greenhouse gas, water vapor, and surface imaging systems. Continuous wavelet transforms deliver spatially resolved fluxes along aircraft flight tracks. Flux analysis methodology is discussed in depth, with special emphasis on quantification of uncertainties. Typical uncertainties in derived surface fluxes are 40-90 % for a nominal resolution of 2 km or 16-35 % when averaged over a full leg (typically 30-40 km). CARAFE has successfully flown two missions in the eastern US in 2016 and 2017, quantifying fluxes over forest, cropland, wetlands, and water. Preliminary results from these campaigns are presented to highlight the performance of this system.

Estimating regional CO2 and CH4 fluxes using GOSAT XCO2 and XCH4 observations

NASA Astrophysics Data System (ADS)

Fraser, A. C.; Palmer, P. I.; Feng, L.; Parker, R.; Boesch, H.; Cogan, A. J.

2012-12-01

We infer regional monthly surface flux estimates for CO2 and CH4, June 2009-December 2010, from proxy dry-air column-averaged mole fractions of CO2 and CH4 from the Greenhouse gases Observing SATellite (GOSAT) using an ensemble Kalman Filter combined with the GEOS-Chem chemistry transport model. We compare these flux estimates with estimates inferred from in situ surface mole fraction measurements and from combining in situ and GOSAT measurements in order to quantify the added value of GOSAT data above the conventional surface measurement network. We find that the error reduction, a measure of how much the posterior fluxes are being informed by the assimilated data, at least doubles when GOSAT measurements are used versus the surface only inversions, with the exception of regions that are well covered by the surface network at the spatial and temporal resolution of our flux estimation calculation. We have incorporated a new online bias correction scheme to account for GOSAT biases. We report global and regional flux estimates inferred from GOSAT and/or in situ measurements. While the global posterior fluxes from GOSAT and in situ measurements agree, we find significant differences in the regional fluxes, particularly over the tropics. We evaluate the posterior fluxes by comparing them against independent surface mole fraction, column, and aircraft measurements using the GEOS-Chem model as an intermediary.

Calculation of surface temperature and surface fluxes in the GLAS GOM

NASA Technical Reports Server (NTRS)

Sud, Y. C.; Abeles, J. A.

1981-01-01

Because the GLAS model's surface fluxes of sensible and latent heat exhibit strong 2 delta t oscillations at the individual grid points as well as in the zonal hemispheric averages and because a basic weakness of the GLAS model lower evaporation over oceans and higher evaporation over land in a typical monthly simulation, the GLAS model PBL parameterization was changed to calculate the mixed layer temperature gradient by solution of a quadratic equation for a stable PBL and by a curve fit relation for an unstable PBL. The new fluxes without any 2 delta t oscillation. Also, the geographical distributions of the surface fluxes are improved. The parameterization presented is incorporated into the new GLAS climate model. Some results which compare the evaporation over land and ocean between old and new calculations are appended.

The Use of CASES-97 Observations to Assess and Parameterize the Impact of Land-Surface Heterogeneity on Area-Average Surface Heat Fluxes for Large-Scale Coupled Atmosphere-Hydrology Models

NASA Technical Reports Server (NTRS)

Chen, Fei; Yates, David; LeMone, Margaret

2001-01-01

To understand the effects of land-surface heterogeneity and the interactions between the land-surface and the planetary boundary layer at different scales, we develop a multiscale data set. This data set, based on the Cooperative Atmosphere-Surface Exchange Study (CASES97) observations, includes atmospheric, surface, and sub-surface observations obtained from a dense observation network covering a large region on the order of 100 km. We use this data set to drive three land-surface models (LSMs) to generate multi-scale (with three resolutions of 1, 5, and 10 kilometers) gridded surface heat flux maps for the CASES area. Upon validating these flux maps with measurements from surface station and aircraft, we utilize them to investigate several approaches for estimating the area-integrated surface heat flux for the CASES97 domain of 71x74 square kilometers, which is crucial for land surface model development/validation and area water and energy budget studies. This research is aimed at understanding the relative contribution of random turbulence versus organized mesoscale circulations to the area-integrated surface flux at the scale of 100 kilometers, and identifying the most important effective parameters for characterizing the subgrid-scale variability for large-scale atmosphere-hydrology models.

The spontaneous concentration of magnetic field in the photosphere of the sun

NASA Technical Reports Server (NTRS)

Parker, E. N.

1981-01-01

The basic physics of magnetic flux tubes in the solar photosphere is reviewed, with areas still open to conjecture pointed out. The question of the concentration of individual small flux tubes to levels of 1-2 kilogauss, when the average solar surface magnetic field is on the order of 10 gauss, by processes of twisting and the formation of flux ropes made up of tubes wound around each other is considered together with the effects of turbulence on the flux tube. Mechanisms for tube compression by the evacuation of the gas contained within a flux tube are then examined, and the possibility of field concentration through the cooling of the gas within the tube in a superadiabatic process is suggested. Attention is then given to possible mechanisms serving to maintain the concentration of flux tubes far below the surface of the sun which gives rise to sunspots and pores as the flux tree emerges through the surface.

Seasonal Clear-Sky Flux and Cloud Radiative Effect Anomalies in the Arctic Atmospheric Column Associated with the Arctic Oscillation and Arctic Dipole

NASA Technical Reports Server (NTRS)

Hegyi, Bradley M.; Taylor, Patrick C.

2017-01-01

The impact of the Arctic Oscillation (AO) and Arctic Dipole (AD) on the radiative flux into the Arctic mean atmospheric column is quantified. 3-month-averaged AO and AD indices are regressed with corresponding surface and top-of-atmosphere (TOA) fluxes from the CERES-SFC and CERES-TOA EBAF datasets over the period 2000-2014. An increase in clear-sky fluxes into the Arctic mean atmospheric column during fall is the largest net flux anomaly associated with AO, primarily driven by a positive net longwave flux anomaly (i.e. increase of net flux into the atmospheric column) at the surface. A decrease in the Arctic mean atmospheric column cloud radiative effect during winter and spring is the largest flux anomaly associated with AD, primarily driven by a change in the longwave cloud radiative effect at the surface. These prominent responses to AO and AD are widely distributed across the ice-covered Arctic, suggesting that the physical process or processes that bring about the flux change associated with AO and AD are distributed throughout the Arctic.

How well do we understand the Earth's radiation budget and the role of clouds? Selected results of the GEWEX radiation flux assessment

NASA Astrophysics Data System (ADS)

Raschke, E.; Kinne, S.

2013-05-01

Multi-year average radiative flux maps of three satellite data-sets (CERES, ISSCP and GEWEX-SRB) are compared to each other and to typical values by global modeling (median values of results of 20 climate models of the 4th IPCC Assessment). Diversity assessments address radiative flux products and at the top of the atmosphere (TOA) and the surface, with particular attention to impacts by clouds. Involving both data from surface and TOA special attention is given to the vertical radiation flux divergence and on the infrared Greenhouse effect, which are rarely shown in literature.

Methane flux from Minnesota Peatlands

NASA Astrophysics Data System (ADS)

Crill, P. M.; Bartlett, K. B.; Harriss, R. C.; Gorham, E.; Verry, E. S.; Sebacher, D. I.; Madzar, L.; Sanner, W.

1988-12-01

Northern (>40°N) wetlands have been suggested as the largest natural source of methane (CH4) to the troposphere. To refine our estimates of source strengths from this region and to investigate climatic controls on the process, fluxes were measured from a variety of Minnesota peatlands during May, June, and August 1986. Sites included forested and unforested ombrotrophic bogs and minerotrophic fens in and near the U.S. Department of Agriculture Marcell Experimental Forest and the Red Lake peatlands. Late spring and summer fluxes ranged from 11 to 866 mg CH4 m-2 d-1, averaging 207 mg CH4 m-2 d-1 overall. At Marcell Forest, forested bogs and fen sites had lower fluxes (averages of 77 ± 21 mg CH4 m-2 d-1 and 142 ± 19 mg CH4 m-2 d-1) than open bogs (average of 294 ± 30 mg CH4 m-2 d-1). In the Red Lake peatland, circumneutral fens, with standing water above the peat surface, produced more methane than acid bog sites in which the water table was beneath the moss surface (325 ± 31 and 102 ± 13 mg CH4 m-2 d-1, respectively). Peat temperature was an important control. Methane flux increased in response to increasing soil temperature. For example, the open bog in the Marcell Forest with the highest CH4 flux exhibited a 74-fold increase in flux over a three-fold increase in temperature. We estimate that the methane flux from all peatlands north of 40° may be on the order of 70 to 90 Tg/yr though estimates of this sort are plagued by uncertainties in the areal extent of peatlands, length of the CH4 producing season, and the spatial and temporal variability of the flux.

Nonequilibrium thermodynamics and the transport phenomena in magnetically confined plasmas

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

Balescu, R.

1987-09-01

The neoclassical theory of transport in magnetically confined plasmas is reviewed. The emphasis is laid on a set of relationships existing among the banana transport coefficients. The surface-averaged entropy production in such plasmas is evaluated. It is shown that neoclassical effects emerge from the entropy production due to parallel transport processes. The Pfirsch-Schlueter effect can be clearly interpreted as due to spatial fluctuations of parallel fluxes on a magnetic surface: the corresponding entropy production is the measure of these fluctuations. The banana fluxes can be formulated in a quasithermodynamic form in which the average entropy production is a bilinear formmore » in the parallel fluxes and the conjugate generalized stresses. A formulation as a quadratic form in the thermodynamic forces is also possible, but leads to anomalies, which are discussed in some detail.« less

Improved Statistical Model Of 10.7-cm Solar Radiation

NASA Technical Reports Server (NTRS)

Vedder, John D.; Tabor, Jill L.

1993-01-01

Improved mathematical model simulates short-term fluctuations of flux of 10.7-cm-wavelength solar radiation during 91-day averaging period. Called "F10.7 flux", important as measure of solar activity and because it is highly correlated with ultraviolet radiation causing fluctuations in heating and density of upper atmosphere. F10.7 flux easily measureable at surface of Earth.

Spatial Interpretation of Tower, Chamber and Modelled Terrestrial Fluxes in a Tropical Forest Plantation

NASA Astrophysics Data System (ADS)

Whidden, E.; Roulet, N.

2003-04-01

Interpretation of a site average terrestrial flux may be complicated in the presence of inhomogeneities. Inhomogeneity may invalidate the basic assumptions of aerodynamic flux measurement. Chamber measurement may miss or misinterpret important temporal or spatial anomalies. Models may smooth over important nonlinearities depending on the scale of application. Although inhomogeneity is usually seen as a design problem, many sites have spatial variance that may have a large impact on net flux, and in many cases a large homogeneous surface is unrealistic. The sensitivity and validity of a site average flux are investigated in the presence of an inhomogeneous site. Directional differences are used to evaluate the validity of aerodynamic methods and the computation of a site average tower flux. Empirical and modelling methods are used to interpret the spatial controls on flux. An ecosystem model, Ecosys, is used to assess spatial length scales appropriate to the ecophysiologic controls. A diffusion model is used to compare tower, chamber, and model data, by spatially weighting contributions within the tower footprint. Diffusion model weighting is also used to improve tower flux estimates by producing footprint averaged ecological parameters (soil moisture, soil temperature, etc.). Although uncertainty remains in the validity of measurement methods and the accuracy of diffusion models, a detailed spatial interpretation is required at an inhomogeneous site. Flux estimation between methods improves with spatial interpretation, showing the importance to an estimation of a site average flux. Small-scale temporal and spatial anomalies may be relatively unimportant to overall flux, but accounting for medium-scale differences in ecophysiological controls is necessary. A combination of measurements and modelling can be used to define the appropriate time and length scales of significant non-linearity due to inhomogeneity.

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.

Using Profiles of Water Vapor Flux to Characterize Turbulence in the Convective Boundary Layer

NASA Astrophysics Data System (ADS)

Weber, Kristy Jane

The 2015 Plains Elevated Convection at Night (PECAN) field campaign sought to increase understanding of mechanisms for nocturnal severe weather in the Great Plains of the United States. A collection of instruments from this field campaign, including a water vapor Differential LiDAR (Light Detection Imaging And Ranging) (DIAL) and 449 MHz radar wind profiler were used to measure water vapor flux in regions between 300 m and the convective boundary layer. Methods to properly sample eddies using eddy-covariance were established, where analysis showed that a 90-minute Reynold's averaging period was optimal to sample most eddies. Additionally, a case study was used to demonstrate the additional atmospheric parameters which can be calculated from profiles of water vapor flux, such as the water vapor flux convergence/divergence. Flux footprints calculated at multiple heights within the convective boundary layer also show how a surface based instrument is sampling a completely different source than one taking measurements above 300 m. This result is important, as it shows how measurements above the surface layer will not be expected to match with those taken within a few meters of the surface, especially if average surface features such as land use type and roughness length are significantly different. These calculated water vapor flux profile measurements provide a new tool to analyze boundary layer dynamics during the PECAN field campaign, and their relationships to PECAN's study areas such as mesoscale convective systems (MCSs), nocturnal low-level jets (NLLJs), elevated convective initiation, and the propagation of bores or wavelike features from nocturnal convective systems.

Downward longwave surface radiation from sun-synchronous satellite data - Validation of methodology

NASA Technical Reports Server (NTRS)

Darnell, W. L.; Gupta, S. K.; Staylor, W. F.

1986-01-01

An extensive study has been carried out to validate a satellite technique for estimating downward longwave radiation at the surface. The technique, mostly developed earlier, uses operational sun-synchronous satellite data and a radiative transfer model to provide the surface flux estimates. The satellite-derived fluxes were compared directly with corresponding ground-measured fluxes at four different sites in the United States for a common one-year period. This provided a study of seasonal variations as well as a diversity of meteorological conditions. Dome heating errors in the ground-measured fluxes were also investigated and were corrected prior to the comparisons. Comparison of the monthly averaged fluxes from the satellite and ground sources for all four sites for the entire year showed a correlation coefficient of 0.98 and a standard error of estimate of 10 W/sq m. A brief description of the technique is provided, and the results validating the technique are presented.

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.

A synthesis of methane emissions from 71 northern, temperate, and subtropical wetlands.

PubMed

Turetsky, Merritt R; Kotowska, Agnieszka; Bubier, Jill; Dise, Nancy B; Crill, Patrick; Hornibrook, Ed R C; Minkkinen, Kari; Moore, Tim R; Myers-Smith, Isla H; Nykänen, Hannu; Olefeldt, David; Rinne, Janne; Saarnio, Sanna; Shurpali, Narasinha; Tuittila, Eeva-Stiina; Waddington, J Michael; White, Jeffrey R; Wickland, Kimberly P; Wilmking, Martin

2014-07-01

Wetlands are the largest natural source of atmospheric methane. Here, we assess controls on methane flux using a database of approximately 19 000 instantaneous measurements from 71 wetland sites located across subtropical, temperate, and northern high latitude regions. Our analyses confirm general controls on wetland methane emissions from soil temperature, water table, and vegetation, but also show that these relationships are modified depending on wetland type (bog, fen, or swamp), region (subarctic to temperate), and disturbance. Fen methane flux was more sensitive to vegetation and less sensitive to temperature than bog or swamp fluxes. The optimal water table for methane flux was consistently below the peat surface in bogs, close to the peat surface in poor fens, and above the peat surface in rich fens. However, the largest flux in bogs occurred when dry 30-day averaged antecedent conditions were followed by wet conditions, while in fens and swamps, the largest flux occurred when both 30-day averaged antecedent and current conditions were wet. Drained wetlands exhibited distinct characteristics, e.g. the absence of large flux following wet and warm conditions, suggesting that the same functional relationships between methane flux and environmental conditions cannot be used across pristine and disturbed wetlands. Together, our results suggest that water table and temperature are dominant controls on methane flux in pristine bogs and swamps, while other processes, such as vascular transport in pristine fens, have the potential to partially override the effect of these controls in other wetland types. Because wetland types vary in methane emissions and have distinct controls, these ecosystems need to be considered separately to yield reliable estimates of global wetland methane release. © 2014 John Wiley & Sons Ltd.

A synthesis of methane emissions from 71 northern, temperate, and subtropical wetlands

USGS Publications Warehouse

Turetsky, Merritt R.; Kotowska, Agnieszka; Bubier, Jill; Dise, Nancy B.; Crill, Patrick; Hornibrook, Ed R.C.; Minkkinen, Kari; Moore, Tim R.; Myers-Smith, Isla H.; Nykanen, Hannu; Olefeldt, David; Rinne, Janne; Saarnio, Sanna; Shurpali, Narasinha; Tuittila, Eeva-Stiina; Waddington, J. Michael; White, Jeffrey R.; Wickland, Kimberly P.; Wilmking, Martin

2014-01-01

Wetlands are the largest natural source of atmospheric methane. Here, we assess controls on methane flux using a database of approximately 19 000 instantaneous measurements from 71 wetland sites located across subtropical, temperate, and northern high latitude regions. Our analyses confirm general controls on wetland methane emissions from soil temperature, water table, and vegetation, but also show that these relationships are modified depending on wetland type (bog, fen, or swamp), region (subarctic to temperate), and disturbance. Fen methane flux was more sensitive to vegetation and less sensitive to temperature than bog or swamp fluxes. The optimal water table for methane flux was consistently below the peat surface in bogs, close to the peat surface in poor fens, and above the peat surface in rich fens. However, the largest flux in bogs occurred when dry 30-day averaged antecedent conditions were followed by wet conditions, while in fens and swamps, the largest flux occurred when both 30-day averaged antecedent and current conditions were wet. Drained wetlands exhibited distinct characteristics, e.g. the absence of large flux following wet and warm conditions, suggesting that the same functional relationships between methane flux and environmental conditions cannot be used across pristine and disturbed wetlands. Together, our results suggest that water table and temperature are dominant controls on methane flux in pristine bogs and swamps, while other processes, such as vascular transport in pristine fens, have the potential to partially override the effect of these controls in other wetland types. Because wetland types vary in methane emissions and have distinct controls, these ecosystems need to be considered separately to yield reliable estimates of global wetland methane release.

A Novel A Posteriori Investigation of Scalar Flux Models for Passive Scalar Dispersion in Compressible Boundary Layer Flows

NASA Astrophysics Data System (ADS)

Braman, Kalen; Raman, Venkat

2011-11-01

A novel direct numerical simulation (DNS) based a posteriori technique has been developed to investigate scalar transport modeling error. The methodology is used to test Reynolds-averaged Navier-Stokes turbulent scalar flux models for compressible boundary layer flows. Time-averaged DNS velocity and turbulence fields provide the information necessary to evolve the time-averaged scalar transport equation without requiring the use of turbulence modeling. With this technique, passive dispersion of a scalar from a boundary layer surface in a supersonic flow is studied with scalar flux modeling error isolated from any flowfield modeling errors. Several different scalar flux models are used. It is seen that the simple gradient diffusion model overpredicts scalar dispersion, while anisotropic scalar flux models underpredict dispersion. Further, the use of more complex models does not necessarily guarantee an increase in predictive accuracy, indicating that key physics is missing from existing models. Using comparisons of both a priori and a posteriori scalar flux evaluations with DNS data, the main modeling shortcomings are identified. Results will be presented for different boundary layer conditions.

A second-order Budkyo-type parameterization of landsurface hydrology

NASA Technical Reports Server (NTRS)

Andreou, S. A.; Eagleson, P. S.

1982-01-01

A simple, second order parameterization of the water fluxes at a land surface for use as the appropriate boundary condition in general circulation models of the global atmosphere was developed. The derived parameterization incorporates the high nonlinearities in the relationship between the near surface soil moisture and the evaporation, runoff and percolation fluxes. Based on the one dimensional statistical dynamic derivation of the annual water balance, it makes the transition to short term prediction of the moisture fluxes, through a Taylor expansion around the average annual soil moisture. A comparison of the suggested parameterization is made with other existing techniques and available measurements. A thermodynamic coupling is applied in order to obtain estimations of the surface ground temperature.

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 Aggregate Description of Semi-Arid Vegetation with Precipitation-Generated Soil Moisture Heterogeneity

NASA Technical Reports Server (NTRS)

White, Cary B.; Houser, Paul R.; Arain, Altaf M.; Yang, Zong-Liang; Syed, Kamran; Shuttleworth, W. James

1997-01-01

Meteorological measurements in the Walnut Gulch catchment in Arizona were used to synthesize a distributed, hourly-average time series of data across a 26.9 by 12.5 km area with a grid resolution of 480 m for a continuous 18-month period which included two seasons of monsoonal rainfall. Coupled surface-atmosphere model runs established the acceptability (for modelling purposes) of assuming uniformity in all meteorological variables other than rainfall. Rainfall was interpolated onto the grid from an array of 82 recording rain gauges. These meteorological data were used as forcing variables for an equivalent array of stand-alone Biosphere-Atmosphere Transfer Scheme (BATS) models to describe the evolution of soil moisture and surface energy fluxes in response to the prevalent, heterogeneous pattern of convective precipitation. The calculated area-average behaviour was compared with that given by a single aggregate BATS simulation forced with area-average meteorological data. Heterogeneous rainfall gives rise to significant but partly compensating differences in the transpiration and the intercepted rainfall components of total evaporation during rain storms. However, the calculated area-average surface energy fluxes given by the two simulations in rain-free conditions with strong heterogeneity in soil moisture were always close to identical, a result which is independent of whether default or site-specific vegetation and soil parameters were used. Because the spatial variability in soil moisture throughout the catchment has the same order of magnitude as the amount of rain failing in a typical convective storm (commonly 10% of the vegetation's root zone saturation) in a semi-arid environment, non-linearitv in the relationship between transpiration and the soil moisture available to the vegetation has limited influence on area-average surface fluxes.

Comparison of methods for the determination of NO-O3-NO2 fluxes and chemical interactions over a bare soil

NASA Astrophysics Data System (ADS)

Stella, P.; Loubet, B.; Laville, P.; Lamaud, E.; Cazaunau, M.; Laufs, S.; Bernard, F.; Grosselin, B.; Mascher, N.; Kurtenbach, R.; Mellouki, A.; Kleffmann, J.; Cellier, P.

2012-06-01

Tropospheric ozone (O3) is a known greenhouse gas responsible for impacts on human and animal health and ecosystem functioning. In addition, O3 plays an important role in tropospheric chemistry, together with nitrogen oxides. The determination of surface-atmosphere exchange fluxes of these trace gases is a prerequisite to establish their atmospheric budget and evaluate their impact onto the biosphere. In this study, O3, nitric oxide (NO) and nitrogen dioxide (NO2) fluxes were measured using the aerodynamic gradient method over a bare soil in an agricultural field. Ozone and NO fluxes were also measured using eddy-covariance and automatic chambers, respectively. The aerodynamic gradient measurement system, composed of fast response sensors, was capable to measure significant differences in NO and O3 mixing ratios between heights. However, due to local advection, NO2 mixing ratios were highly non-stationary and NO2 fluxes were, therefore, not significantly different from zero. The chemical reactions between O3, NO and NO2 led to little ozone flux divergence between the surface and the measurement height (less than 1% of the flux on average), whereas the NO flux divergence was about 10% on average. The use of fast response sensors allowed reducing the flux uncertainty. The aerodynamic gradient and the eddy-covariance methods gave comparable O3 fluxes. The chamber NO fluxes were down to 70% lower than the aerodynamic gradient fluxes, probably because of either the spatial heterogeneity of the soil NO emissions or the perturbation due to the chamber itself.

Residual-Mean Analysis of the Air-Sea Fluxes and Associated Oceanic Meridional Overturning

DTIC Science & Technology

2006-12-01

the adiabatic component of the MOC which is based entirely on the sea surface data . The coordinate system introduced in this study is somewhat...heat capacity of water. The technique utilizes the observational data based on meteorological re- analysis (density flux at the sea surface) and...Figure 8. Annual mean and temporal standard deviation of the zonally-averaged mixed- layer depth. The plotted data are based on Levitus 94 climatology

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.

Influence of the Surface and Cloud Nonuniformities in the Solar Energy Fluxes in the Arctic

NASA Technical Reports Server (NTRS)

Rozwadowska, A.; Cahalan, R. F.; Einaudi, Franco (Technical Monitor)

2000-01-01

Solar energy fluxes reaching the surface and absorbed by it are basic components of the energy balance of the Arctic. They depend mainly on the solar zenith angle, a state of the atmosphere, especially the cloudiness, and the surface albedo. However, they can also be modified by variabilities in the surface albedo and cloud optical thickness. The surface of the Arctic can be highly nonuniform. The surface of the Arctic Ocean, which covers the huge part of the Arctic can be view as a mosaic of sea water, sea ice, snow and, in the melting period, melting ponds. In our paper, results are presented of Monte Carlo simulations of the expected influence of nonuniform cloud structure and nonuniform surface albedo on radiative fluxes at the Arctic surface. In particular, the plane parallel biases in the surface absorptance and atmospheric transmittance are studied. The bias is defined as the difference between the real absorptance or transmittance (i.e. nonuniform conditions) averaged over a given area, and the uniform or plane parallel case with the same mean cloud optical thickness and the same mean surface albedo. The dependence of the biases is analysed with respect to the following: domain averaged values of the cloud optical thickness and surface albedo, scales of their spatial variabilities, correlation between cloud optical thickness and cloud albedo variabilities, cloud height, and the solar zenith angle. Ranges of means and standard deviations of the input parameters typical of Arctic conditions are obtained from the SHEBA experiment.

The Estimation of Surface Latent Heat Flux over the Ocean and its Relationship to Marine Atmospheric Boundary Layer (MABL) Structure

NASA Technical Reports Server (NTRS)

Palm, Stephen P.; Schwemmer, Geary K.; Vandemark, Doug; Evans, Keith; Miller, David O.; Demoz, Belay B.; Starr, David OC. (Technical Monitor)

2001-01-01

A new technique combining active and passive remote sensing instruments for the estimation of surface latent heat flux over the ocean is presented. This synergistic method utilizes aerosol lidar backscatter data, multi-channel infrared radiometer data, and microwave scatterometer data acquired onboard the NASA P-313 research aircraft during an extended field campaign over the Atlantic ocean in support of the Lidar In-space Technology Experiment (LITE) in September of 1994. The 10 meter wind speed derived from scatterometers and lidar-radiometer inferred near-surface moisture are used to obtain an estimate of the surface flux of moisture via a bulk aerodynamic formula. The results are compared with the Special Sensor Microwave Imager (SSM/I) daily average latent heat flux and show reasonable agreement. However, the SSM/I values are biased low by about 15 W/sq m. In addition, the Marine Atmospheric Boundary Layer (MABL) height, entrainment zone thickness and integrated lidar backscatter intensity are computed from the lidar data and compared with the magnitude of the surface fluxes. The results show that the surface latent heat flux is most strongly correlated with entrainment zone depth, MABL height and the integrated MABL lidar backscatter, with corresponding correlation coefficients of 0.39, 0.43 and 0.71, respectively.

The Estimation of Surface Latent Heat Flux Over the Ocean and its Relationship to Marine Atmospheric Boundary Layer (MABL) Structure

NASA Technical Reports Server (NTRS)

Palm, Stephen P.; Miller, David O.; Schwemmer, Geary

2000-01-01

A new technique combining active and passive remote sensing instruments for the estimation of surface latent heat flux over the ocean is presented. This synergistic method uses aerosol lidar backscatter data, multi-channel infrared radiometer data and microwave scatterometer data acquired onboard the NASA P-3B research aircraft during an extended field campaign over the Atlantic ocean in support of the Lidar In-space Technology Experiment (LITE) in September of 1994. The 10 meter wind speed derived from the scatterometers and the lidar-radiometer inferred near-surface moisture are used to obtain an estimate of the surface flux of moisture via bulk aerodynamic formulae. The results are compared with the Special Sensor Microwave Imager (SSM/I) daily average latent heat flux and show reasonable agreement with an rms error and bias of about 50 and 25 W per square meters, respectively. In addition, the MABL height, entrainment zone thickness and integrated lidar backscatter intensity are computed from the lidar data and compared with the magnitude of the surface fluxes. The results show that the surface latent heat flux is most strongly correlated with entrainment zone top, bottom and the integrated MABL lidar backscatter, with corresponding correlation coefficients of 0.62, 0.67 and 0.61, respectively.

Heat balances of the surface mixed layer in the equatorial Atlantic and Indian Ocean during FGGE

NASA Technical Reports Server (NTRS)

Molinari, R. L.

1985-01-01

Surface meteorological and surface and subsurface oceanographic data collected during FGGE in the equatorial Atlantic and Indian Oceans are used to estimate the terms in a heat balance relation for the mixed layer. The first balance tested is between changes in mixed layer temperature (MLT) and surface energy fluxes. Away from regions of low variance in MLT time series and equatorial and coastal upwelling, surface fluxes can account for 75 percent of the variance in the observed time series. Differences between observed and estimated MLTs indicate that on the average, maximum errors in surface flux are of the order of 20 to 30 W/sq m. In the Atlantic, the addition of zonal advection does not significantly improve the estimates. However in regions of equatorial upwelling, the eastern Atlantic vertical mixing and meridional advection can play an important role in the evolution of MLTs.

CERES Fast Longwave And SHortwave Radiative Flux (FLASHFlux) Version4A.

NASA Astrophysics Data System (ADS)

Sawaengphokhai, P.; Stackhouse, P. W., Jr.; Kratz, D. P.; Gupta, S. K.

2017-12-01

The agricultural, renewable energy management, and science communities need global surface and top-of-atmosphere (TOA) radiative fluxes on a low latency basis. The Clouds and Earth's Radiant Energy System (CERES) FLASHFlux (Fast Longwave and SHortwave radiative Flux) data products address this need by enhancing the speed of CERES processing using simplified calibration and parameterized model of surface fluxes to provide a daily global radiative fluxes data set within one week of satellite observations. The CERES FLASHFlux provides two data products: 1) an overpass swath Level 2 Single Scanner Footprint (SSF) data products separately for both Aqua and Terra observations, and 2) a daily Level 3 Time Interpolated and Spatially Averaged (TISA) 1o x 1o gridded data that combines Aqua and Terra observations. The CERES FLASHFlux data product is being promoted to Version4A. Updates to FLASHFlux Version4A include a new cloud retrieval algorithm and an improved shortwave surface flux parameterization. We inter-compared FLASHFlux Version4A, FLASHFlux Version3C, CERES Edition 4 Syn1Deg and at the monthly scale CERES Edition4 EBAF (Energy Balanced and Filled) Top-of-Atmosphere and Edition 4 Surface EBAF fluxes to evaluate these improvements. We also analyze the impact of the new inputs and cloud algorithm to the surface shortwave and longwave radiative fluxes using ground sites measurement provided by CAVE (CERES/ARM Validation Experiment).

Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface. 2; Phase-Averages

NASA Technical Reports Server (NTRS)

Houser, Paul (Technical Monitor); Patton, Edward G.; Sullivan, Peter P.; Moeng, Chin-Hoh

2003-01-01

We examine the influence of surface heterogeneity on boundary layers using a large-eddy simulation coupled to a land-surface model. Heterogeneity, imposed in strips varying from 2-30 km (1 less than lambda/z(sub i) less than 18), is found to dramatically alter the structure of the free convective boundary layer by inducing significant organized circulations. A conditional sampling technique, based on the scale of the surface heterogeneity (phase averaging), is used to identify and quantify the organized surface fluxes and motions in the atmospheric boundary layer. The impact of the organized motions on turbulent transport depends critically on the scale of the heterogeneity lambda, the boundary layer height zi and the initial moisture state of the boundary layer. Dynamical and scalar fields respond differently as the scale of the heterogeneity varies. Surface heterogeneity of scale 4 less than lamba/z(sub i) less than 9 induces the strongest organized flow fields (up, wp) while heterogeneity with smaller or larger lambda/z(sub i) induces little organized motion. However, the organized components of the scalar fields (virtual potential temperature and mixing ratio) grow continuously in magnitude and horizontal scale, as lambda/z(sub i) increases. For some cases, the organized motions can contribute nearly 100% of the total vertical moisture flux. Patch-induced fluxes are shown to dramatically impact point measurements that assume the time-average vertical velocity to be zero. The magnitude and sign of this impact depends on the location of the measurement within the region of heterogeneity.

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.

Meltwater flux and runoff modeling in the abalation area of jakobshavn Isbrae, West Greenland

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

Mernild, Sebastian Haugard; Chylek, Petr; Liston, Glen

2009-01-01

The temporal variability in surface snow and glacier melt flux and runoff were investigated for the ablation area of lakobshavn Isbrae, West Greenland. High-resolution meteorological observations both on and outside the Greenland Ice Sheet (GrIS) were used as model input. Realistic descriptions of snow accumulation, snow and glacier-ice melt, and runoff are essential to understand trends in ice sheet surface properties and processes. SnowModel, a physically based, spatially distributed meteorological and snow-evolution modeling system was used to simulate the temporal variability of lakobshavn Isbrre accumulation and ablation processes for 2000/01-2006/07. Winter snow-depth observations and MODIS satellite-derived summer melt observations weremore » used for model validation of accumulation and ablation. Simulations agreed well with observed values. Simulated annual surface melt varied from as low as 3.83 x 10{sup 9} m{sup 3} (2001/02) to as high as 8.64 x 10{sup 9} m{sup 3} (2004/05). Modeled surface melt occurred at elevations reaching 1,870 m a.s.l. for 2004/05, while the equilibrium line altitude (ELA) fluctuated from 990 to 1,210 m a.s.l. during the simulation period. The SnowModel meltwater retention and refreezing routines considerably reduce the amount of meltwater available as ice sheet runoff; without these routines the lakobshavn surface runoff would be overestimated by an average of 80%. From September/October through May/June no runoff events were simulated. The modeled interannual runoff variability varied from 1.81 x 10{sup 9} m{sup 3} (2001/02) to 5.21 x 10{sup 9} m{sup 3} (2004/05), yielding a cumulative runoff at the Jakobshavn glacier terminus of {approx}2.25 m w.eq. to {approx}4.5 m w.eq., respectively. The average modeled lakobshavn runoff of {approx}3.4 km{sup 3} y{sup -1} was merged with previous estimates of Jakobshavn ice discharge to quantify the freshwater flux to Illulissat Icefiord. For both runoff and ice discharge the average trends are similar, indicating increasing (insignificant) influx of freshwater to the Illulissat Icefiord for the period 2000/01-2006/07. This study suggests that surface runoff forms a minor part of the overall Jakobshavn freshwater flux to the fiord: around 7% ({approx}3.4 km{sup 3} y{sup -1}) of the average annual freshwater flux of {approx}51.0 km{sup 3} y{sup -1} originates from the surface runoff.« less

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.

The OceanFlux Greenhouse Gases methodology for deriving a sea surface climatology of CO2 fugacity in support of air-sea gas flux studies

NASA Astrophysics Data System (ADS)

Goddijn-Murphy, L. M.; Woolf, D. K.; Land, P. E.; Shutler, J. D.; Donlon, C.

2015-07-01

Climatologies, or long-term averages, of essential climate variables are useful for evaluating models and providing a baseline for studying anomalies. The Surface Ocean CO2 Atlas (SOCAT) has made millions of global underway sea surface measurements of CO2 publicly available, all in a uniform format and presented as fugacity, fCO2. As fCO2 is highly sensitive to temperature, the measurements are only valid for the instantaneous sea surface temperature (SST) that is measured concurrently with the in-water CO2 measurement. To create a climatology of fCO2 data suitable for calculating air-sea CO2 fluxes, it is therefore desirable to calculate fCO2 valid for a more consistent and averaged SST. This paper presents the OceanFlux Greenhouse Gases methodology for creating such a climatology. We recomputed SOCAT's fCO2 values for their respective measurement month and year using monthly composite SST data on a 1° × 1° grid from satellite Earth observation and then extrapolated the resulting fCO2 values to reference year 2010. The data were then spatially interpolated onto a 1° × 1° grid of the global oceans to produce 12 monthly fCO2 distributions for 2010, including the prediction errors of fCO2 produced by the spatial interpolation technique. The partial pressure of CO2 (pCO2) is also provided for those who prefer to use pCO2. The CO2 concentration difference between ocean and atmosphere is the thermodynamic driving force of the air-sea CO2 flux, and hence the presented fCO2 distributions can be used in air-sea gas flux calculations together with climatologies of other climate variables.

Quantifying the drivers of ocean-atmosphere CO2 fluxes

NASA Astrophysics Data System (ADS)

Lauderdale, Jonathan M.; Dutkiewicz, Stephanie; Williams, Richard G.; Follows, Michael J.

2016-07-01

A mechanistic framework for quantitatively mapping the regional drivers of air-sea CO2 fluxes at a global scale is developed. The framework evaluates the interplay between (1) surface heat and freshwater fluxes that influence the potential saturated carbon concentration, which depends on changes in sea surface temperature, salinity and alkalinity, (2) a residual, disequilibrium flux influenced by upwelling and entrainment of remineralized carbon- and nutrient-rich waters from the ocean interior, as well as rapid subduction of surface waters, (3) carbon uptake and export by biological activity as both soft tissue and carbonate, and (4) the effect on surface carbon concentrations due to freshwater precipitation or evaporation. In a steady state simulation of a coarse-resolution ocean circulation and biogeochemistry model, the sum of the individually determined components is close to the known total flux of the simulation. The leading order balance, identified in different dynamical regimes, is between the CO2 fluxes driven by surface heat fluxes and a combination of biologically driven carbon uptake and disequilibrium-driven carbon outgassing. The framework is still able to reconstruct simulated fluxes when evaluated using monthly averaged data and takes a form that can be applied consistently in models of different complexity and observations of the ocean. In this way, the framework may reveal differences in the balance of drivers acting across an ensemble of climate model simulations or be applied to an analysis and interpretation of the observed, real-world air-sea flux of CO2.

Methanethiol Concentrations and Sea-Air Fluxes in the Subarctic NE Pacific Ocean

NASA Astrophysics Data System (ADS)

Kiene, R. P.; Williams, T. E.; Esson, K.; Tortell, P. D.; Dacey, J. W. H.

2017-12-01

Exchange of volatile organic sulfur from the ocean to the atmosphere impacts the global sulfur cycle and the climate system and is thought to occur mainly via the gas dimethylsulfide (DMS). DMS is produced during degradation of the abundant phytoplankton osmolyte dimethylsulfoniopropionate (DMSP) but bacteria can also convert dissolved DMSP into the sulfur gas methanethiol (MeSH). MeSH has been difficult to measure in seawater because of its high chemical and biological reactivity and, thus, information on MeSH concentrations, distribution and sea-air fluxes is limited. We measured MeSH in the northeast subarctic Pacific Ocean in July 2016, along transects with strong phytoplankton abundance gradients. Water samples obtained with Niskin bottles were analyzed for MeSH by purge-and-trap gas chromatography. Depth profiles showed that MeSH concentrations were high near the surface and declined with depth. Surface waters (5 m depth) had an average MeSH concentration of 0.75 nM with concentrations reaching up to 3nM. MeSH concentrations were correlated (r = 0.47) with microbial turnover of dissolved DMSP which ranged up to 236 nM per day. MeSH was also correlated with total DMSP (r = 0.93) and dissolved DMS (r = 0.63), supporting the conclusion that DMSP was a major precursor of MeSH. Surface water MeSH:DMS concentration ratios averaged 0.19 and ranged up to 0.50 indicating that MeSH was a significant fraction of the volatile sulfur pool in surface waters. Sea-air fluxes of MeSH averaged 15% of the combined DMS+MeSH flux, therefore MeSH contributed an important fraction of the sulfur emitted to the atmosphere from the subarctic NE Pacific Ocean.

Clear-Sky Surface Solar Radiation During South China Sea Monsoon Experiment

NASA Technical Reports Server (NTRS)

Lin, Po-Hsiung; Chou, Ming-Dah; Ji, Qiang; Tsay, Si-Chee; Einaudi, Franco (Technical Monitor)

2000-01-01

Downward solar fluxes measured at Dungsha coral island (20 deg. 42 min. N, 116 deg. 43 min. E) during the South China Sea Monsoon Experiment (May-June 1998) have been calibrated and compared with radiative transfer calculations for three clear-sky days. Model calculations use water vapor and temperature profiles from radiosound measurements and the aerosol optical thickness derived from sunphotometric radiance measurements at the surface. Results show that the difference between observed and model-calculated downward fluxes is less than 3% of the daily mean. Averaged over the three clear days, the difference reduces to 1%. The downward surface solar flux averaged over the three days is 314 W per square meters from observations and 317 W per square meters from model calculations, This result is consistent with a previous study using TOGA CAORE measurements, which found good agreements between observations and model calculations. This study provides an extra piece of useful information on the modeling of radiative transfer, which fills in the puzzle of the absorption of solar radiation in the atmosphere.

A spatially resolved retarding field energy analyzer design suitable for uniformity analysis across the surface of a semiconductor wafer

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

Sharma, S., E-mail: shailesh.sharma6@mail.dcu.ie; National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9; Gahan, D., E-mail: david.gahan@impedans.com

2014-04-15

A novel retarding field energy analyzer design capable of measuring the spatial uniformity of the ion energy and ion flux across the surface of a semiconductor wafer is presented. The design consists of 13 individual, compact-sized, analyzers, all of which are multiplexed and controlled by a single acquisition unit. The analyzers were tested to have less than 2% variability from unit to unit due to tight manufacturing tolerances. The main sensor assembly consists of a 300 mm disk to mimic a semiconductor wafer and the plasma sampling orifices of each sensor are flush with disk surface. This device is placedmore » directly on top of the rf biased electrode, at the wafer location, in an industrial capacitively coupled plasma reactor without the need for any modification to the electrode structure. The ion energy distribution, average ion energy, and average ion flux were measured at the 13 locations over the surface of the powered electrode to determine the degree of spatial nonuniformity. The ion energy and ion flux are shown to vary by approximately 20% and 5%, respectively, across the surface of the electrode for the range of conditions investigated in this study.« less

Structural equation modelling reveals factors regulating surface sediment organic carbon content and CO2 efflux in a subtropical mangrove.

PubMed

Ouyang, Xiaoguang; Lee, Shing Yip; Connolly, Rod M

2017-02-01

Mangroves are blue carbon ecosystems that sequester significant carbon but release CO 2 , and to a lesser extent CH 4, from the sediment through oxidation of organic carbon or from overlying water when flooded. Previous studies, e.g. Leopold et al. (2015), have investigated sediment organic carbon (SOC) content and CO 2 flux separately, but could not provide a holistic perspective for both components of blue carbon. Based on field data from a mangrove in southeast Queensland, Australia, we used a structural equation model to elucidate (1) the biotic and abiotic drivers of surface SOC (10cm) and sediment CO 2 flux; (2) the effect of SOC on sediment CO 2 flux; and (3) the covariation among the environmental drivers assessed. Sediment water content, the percentage of fine-grained sediment (<63μm), surface sediment chlorophyll and light condition collectively drive sediment CO 2 flux, explaining 41% of their variation. Sediment water content, the percentage of fine sediment, season, landform setting, mangrove species, sediment salinity and chlorophyll collectively drive surface SOC, explaining 93% of its variance. Sediment water content and the percentage of fine sediment have a negative impact on sediment CO 2 flux but a positive effect on surface SOC content, while sediment chlorophyll is a positive driver of both. Surface SOC was significantly higher in Avicennia marina (2994±186gm -2 , mean±SD) than in Rhizophora stylosa (2383±209gm -2 ). SOC was significantly higher in winter (2771±192gm -2 ) than in summer (2599±211gm -2 ). SOC significantly increased from creek-side (865±89gm -2 ) through mid (3298±137gm -2 ) to landward (3933±138gm -2 ) locations. Sediment salinity was a positive driver of SOC. Sediment CO 2 flux without the influence of biogenic structures (crab burrows, aerial roots) averaged 15.4mmolm -2 d -1 in A. marina stands under dark conditions, lower than the global average dark flux (61mmolm -2 d -1 ) for mangroves. Copyright © 2016 Elsevier B.V. All rights reserved.

Assessment of land surface temperature and heat fluxes over Delhi using remote sensing data.

PubMed

Chakraborty, Surya Deb; Kant, Yogesh; Mitra, Debashis

2015-01-15

Surface energy processes has an essential role in urban weather, climate and hydrosphere cycles, as well in urban heat redistribution. The research was undertaken to analyze the potential of Landsat and MODIS data in retrieving biophysical parameters in estimating land surface temperature & heat fluxes diurnally in summer and winter seasons of years 2000 and 2010 and understanding its effect on anthropogenic heat disturbance over Delhi and surrounding region. Results show that during years 2000-2010, settlement and industrial area increased from 5.66 to 11.74% and 4.92 to 11.87% respectively which in turn has direct effect on land surface temperature (LST) and heat fluxes including anthropogenic heat flux. Based on the energy balance model for land surface, a method to estimate the increase in anthropogenic heat flux (Has) has been proposed. The settlement and industrial areas has higher amounts of energy consumed and has high values of Has in all seasons. The comparison of satellite derived LST with that of field measured values show that Landsat estimated values are in close agreement within error of ±2 °C than MODIS with an error of ±3 °C. It was observed that, during 2000 and 2010, the average change in surface temperature using Landsat over settlement & industrial areas of both seasons is 1.4 °C & for MODIS data is 3.7 °C. The seasonal average change in anthropogenic heat flux (Has) estimated using Landsat & MODIS is up by around 38 W/m(2) and 62 W/m(2) respectively while higher change is observed over settlement and concrete structures. The study reveals that the dynamic range of Has values has increased in the 10 year period due to the strong anthropogenic influence over the area. The study showed that anthropogenic heat flux is an indicator of the strength of urban heat island effect, and can be used to quantify the magnitude of the urban heat island effect. Copyright © 2013 Elsevier Ltd. All rights reserved.

Interannual and Decadal Variability of Ocean Surface Latent Heat Flux as Seen from Passive Microwave Satellite Algorithms

NASA Technical Reports Server (NTRS)

Robertson, Franklin R.; Jackson, Darren L.; Wick, Gary A.; Roberts, Brent; Miller, Tim L.

2007-01-01

Ocean surface turbulent fluxes are critical links in the climate system since they mediate energy exchange between the two fluid systems (ocean and atmosphere) whose combined heat transport determines the basic character of Earth's climate. Deriving physically-based latent and sensible heat fluxes from satellite is dependent on inferences of near surface moisture and temperature from coarser layer retrievals or satellite radiances. Uncertainties in these "retrievals" propagate through bulk aerodynamic algorithms, interacting as well with error properties of surface wind speed, also provided by satellite. By systematically evaluating an array of passive microwave satellite algorithms, the SEAFLUX project is providing improved understanding of these errors and finding pathways for reducing or eliminating them. In this study we focus on evaluating the interannual variability of several passive microwave-based estimates of latent heat flux starting from monthly mean gridded data. The algorithms considered range from those based essentially on SSM/I (e.g. HOAPS) to newer approaches that consider additional moisture information from SSM/T-2 or AMSU-B and lower tropospheric temperature data from AMSU-A. On interannual scales, variability arising from ENSO events and time-lagged responses of ocean turbulent and radiative fluxes in other ocean basins (as well as the extratropical Pacific) is widely recognized, but still not well quantified. Locally, these flux anomalies are of order 10-20 W/sq m and present a relevant "target" with which to verify algorithm performance in a climate context. On decadal time scales there is some evidence from reanalyses and remotely-sensed fluxes alike that tropical ocean-averaged latent heat fluxes have increased 5-10 W/sq m since the early 1990s. However, significant uncertainty surrounds this estimate. Our work addresses the origin of these uncertainties and provides statistics on time series of tropical ocean averages, regional space / time correlation analysis, and separation of contributions by variations in wind and near surface humidity deficit. Comparison to variations in reanalysis data sets is also provided for reference.

Dimethyl Sulfide in the Surface Ocean and the Marine Atmosphere: A Global View

NASA Astrophysics Data System (ADS)

Andreae, Meinrat O.; Raemdonck, Hans

1983-08-01

Dimethyl sulfide (DMS) has been identified as the major volatile sulfur compound in 628 samples of surface seawater representing most of the major oceanic ecozones. In at least three respects, its vertical distribution, its local patchiness, and its distribution in oceanic ecozones, the concentration of DMS in the sea exhibits a pattern similar to that of primary production. The global weighted-average concentration of DMS in surface seawater is 102 nanograms of sulfur (DMS) per liter, corresponding to a global sea-to-air flux of 39 × 1012 grams of sulfur per year. When the biogenic sulfur contributions from the land surface are added, the biogenic sulfur gas flux is approximately equal to the anthropogenic flux of sulfur dioxide. The DMS concentration in air over the equatorial Pacific varies diurnally between 120 and 200 nanograms of sulfur (DMS) per cubic meter, in agreement with the predictions of photochemical models. The estimated source flux of DMS from the oceans to the marine atmosphere is in agreement with independently obtained estimates of the removal fluxes of DMS and its oxidation products from the atmosphere.

Effect of Running Parameters on Flow Boiling Instabilities in Microchannels.

PubMed

Zong, Lu-Xiang; Xu, Jin-Liang; Liu, Guo-Hua

2015-04-01

Flow boiling instability (FBI) in microchannels is undesirable because they can induce the mechanical vibrations and disturb the heat transfer characteristics. In this study, the synchronous optical visualization experimental system was set up. The pure acetone liquid was used as the working fluid, and the parallel triangle silicon microchannel heat sink was designed as the experimental section. With the heat flux ranging from 0-450 kW/m2 the microchannel demand average pressure drop-heater length (Δp(ave)L) curve for constant low mass flux, and the demand pressure drop-mass flux (Δp(ave)G) curve for constant length on main heater surface were obtained and studied. The effect of heat flux (q = 188.28, 256.00, and 299.87 kW/m2), length of main heater surface (L = 4.5, 6.25, and 8.00 mm), and mass flux (G = 188.97, 283.45, and 377.94 kg/m2s) on pressure drops (Ap) and temperatures at the central point of the main heater surface (Twc) were experimentally studied. The results showed that, heat flux, length of the main heater surface, and mass flux were identified as the important parameters to the boiling instability process. The boiling incipience (TBI) and critical heat flux (CHF) were early induced for the lower mass flux or the main heater surface with longer length. With heat flux increasing, the pressure drops were linearly and slightly decreased in the single liquid region but increased sharply in the two phase flow region, in which the flow boiling instabilities with apparent amplitude and long period were more easily triggered at high heat flux. Moreover, the system pressure was increased with the increase of the heat flux.

Estimating lake-atmosphere CO2 exchange

USGS Publications Warehouse

Anderson, D.E.; Striegl, Robert G.; Stannard, D.I.; Michmerhuizen, C.M.; McConnaughey, T.A.; LaBaugh, J.W.

1999-01-01

Lake-atmosphere CO2 flux was directly measured above a small, woodland lake using the eddy covariance technique and compared with fluxes deduced from changes in measured lake-water CO2 storage and with flux predictions from boundary-layer and surface-renewal models. Over a 3-yr period, lake-atmosphere exchanges of CO2 were measured over 5 weeks in spring, summer, and fall. Observed springtime CO2 efflux was large (2.3-2.7 ??mol m-2 s-1) immediately after lake-thaw. That efflux decreased exponentially with time to less than 0.2 ??mol m-2 s-1 within 2 weeks. Substantial interannual variability was found in the magnitudes of springtime efflux, surface water CO2 concentrations, lake CO2 storage, and meteorological conditions. Summertime measurements show a weak diurnal trend with a small average downward flux (-0.17 ??mol m-2 s-1) to the lake's surface, while late fall flux was trendless and smaller (-0.0021 ??mol m-2 s-1). Large springtime efflux afforded an opportunity to make direct measurement of lake-atmosphere fluxes well above the detection limits of eddy covariance instruments, facilitating the testing of different gas flux methodologies and air-water gas-transfer models. Although there was an overall agreement in fluxes determined by eddy covariance and those calculated from lake-water storage change in CO2, agreement was inconsistent between eddy covariance flux measurements and fluxes predicted by boundary-layer and surface-renewal models. Comparison of measured and modeled transfer velocities for CO2, along with measured and modeled cumulative CO2 flux, indicates that in most instances the surface-renewal model underpredicts actual flux. Greater underestimates were found with comparisons involving homogeneous boundary-layer models. No physical mechanism responsible for the inconsistencies was identified by analyzing coincidentally measured environmental variables.

Characterizing groundwater/surface-water interactions in the interior of Jianghan Plain, central China

NASA Astrophysics Data System (ADS)

Du, Yao; Ma, Teng; Deng, Yamin; Shen, Shuai; Lu, Zongjie

2018-06-01

Quantifying groundwater/surface-water interactions is essential for managing water resources and revealing contaminant fate. There has been little concern on the exchange between streams and aquifers through an extensive aquitard thus far. In this study, hydrogeologic calculation and tritium modeling were jointly applied to characterize such interactions through an extensive aquitard in the interior of Jianghan Plain, an alluvial plain of Yangtze River, China. One groundwater simulation suggested that the lateral distance of influence from the river was about 1,000 m; vertical flow in the aquitard followed by lateral flow in the aquifer contributed significantly more ( 90%) to the aquifer head change near the river than lateral bank storage in the aquitard followed by infiltration. The hydrogeologic calculation produced vertical fluxes of the order 0.01 m/day both near and farther from the river, suggesting that similar shorter-lived (half-monthly) vertical fluxes occur between the river and aquitard near the river, and between the surface end members and aquitard farther from the river. Tritium simulation based on the OTIS model produced an average groundwater residence time of about 15 years near the river and a resulting vertical flux of the order 0.001 m/day. Another tritium simulation based on a dispersion model produced a vertical flux of the order 0.0001 m/day away from the river, coupled with an average residence time of around 90 years. These results suggest an order of magnitude difference for the longer-lived (decadal) vertical fluxes between surface waters and the aquifer near and away from the river.

Characterizing groundwater/surface-water interactions in the interior of Jianghan Plain, central China

NASA Astrophysics Data System (ADS)

Du, Yao; Ma, Teng; Deng, Yamin; Shen, Shuai; Lu, Zongjie

2018-01-01

Quantifying groundwater/surface-water interactions is essential for managing water resources and revealing contaminant fate. There has been little concern on the exchange between streams and aquifers through an extensive aquitard thus far. In this study, hydrogeologic calculation and tritium modeling were jointly applied to characterize such interactions through an extensive aquitard in the interior of Jianghan Plain, an alluvial plain of Yangtze River, China. One groundwater simulation suggested that the lateral distance of influence from the river was about 1,000 m; vertical flow in the aquitard followed by lateral flow in the aquifer contributed significantly more ( 90%) to the aquifer head change near the river than lateral bank storage in the aquitard followed by infiltration. The hydrogeologic calculation produced vertical fluxes of the order 0.01 m/day both near and farther from the river, suggesting that similar shorter-lived (half-monthly) vertical fluxes occur between the river and aquitard near the river, and between the surface end members and aquitard farther from the river. Tritium simulation based on the OTIS model produced an average groundwater residence time of about 15 years near the river and a resulting vertical flux of the order 0.001 m/day. Another tritium simulation based on a dispersion model produced a vertical flux of the order 0.0001 m/day away from the river, coupled with an average residence time of around 90 years. These results suggest an order of magnitude difference for the longer-lived (decadal) vertical fluxes between surface waters and the aquifer near and away from the river.

Mapping Surface Heat Fluxes by Assimilating SMAP Soil Moisture and GOES Land Surface Temperature Data

NASA Astrophysics Data System (ADS)

Lu, Yang; Steele-Dunne, Susan C.; Farhadi, Leila; van de Giesen, Nick

2017-12-01

Surface heat fluxes play a crucial role in the surface energy and water balance. In situ measurements are costly and difficult, and large-scale flux mapping is hindered by surface heterogeneity. Previous studies have demonstrated that surface heat fluxes can be estimated by assimilating land surface temperature (LST) and soil moisture to determine two key parameters: a neutral bulk heat transfer coefficient (CHN) and an evaporative fraction (EF). Here a methodology is proposed to estimate surface heat fluxes by assimilating Soil Moisture Active Passive (SMAP) soil moisture data and Geostationary Operational Environmental Satellite (GOES) LST data into a dual-source (DS) model using a hybrid particle assimilation strategy. SMAP soil moisture data are assimilated using a particle filter (PF), and GOES LST data are assimilated using an adaptive particle batch smoother (APBS) to account for the large gap in the spatial and temporal resolution. The methodology is implemented in an area in the U.S. Southern Great Plains. Assessment against in situ observations suggests that soil moisture and LST estimates are in better agreement with observations after assimilation. The RMSD for 30 min (daytime) flux estimates is reduced by 6.3% (8.7%) and 31.6% (37%) for H and LE on average. Comparison against a LST-only and a soil moisture-only assimilation case suggests that despite the coarse resolution, assimilating SMAP soil moisture data is not only beneficial but also crucial for successful and robust flux estimation, particularly when the uncertainties in the model estimates are large.

Investigating scintillometer source areas

NASA Astrophysics Data System (ADS)

Perelet, A. O.; Ward, H. C.; Pardyjak, E.

2017-12-01

Scintillometry is an indirect ground-based method for measuring line-averaged surface heat and moisture fluxes on length scales of 0.5 - 10 km. These length scales are relevant to urban and other complex areas where setting up traditional instrumentation like eddy covariance is logistically difficult. In order to take full advantage of scintillometry, a better understanding of the flux source area is needed. The source area for a scintillometer is typically calculated as a convolution of point sources along the path. A weighting function is then applied along the path to compensate for a total signal contribution that is biased towards the center of the beam path, and decreasing near the beam ends. While this method of calculating the source area provides an estimate of the contribution of the total flux along the beam, there are still questions regarding the physical meaning of the weighted source area. These questions are addressed using data from an idealized experiment near the Salt Lake City International Airport in northern Utah, U.S.A. The site is a flat agricultural area consisting of two different land uses. This simple heterogeneity in the land use facilitates hypothesis testing related to source areas. Measurements were made with a two wavelength scintillometer system spanning 740 m along with three standard open-path infrared gas analyzer-based eddy-covariance stations along the beam path. This configuration allows for direct observations of fluxes along the beam and comparisons to the scintillometer average. The scintillometer system employed measures the refractive index structure parameter of air for two wavelengths of electromagnetic radiation, 880 μm and 1.86 cm to simultaneously estimate path-averaged heat and moisture fluxes, respectively. Meteorological structure parameters (CT2, Cq2, and CTq) as well as surface fluxes are compared for various amounts of source area overlap between eddy covariance and scintillometry. Additionally, surface properties from LANDSAT 7 & 8 are used to help understand source area composition for different times throughout the experiment.

Seasonal and Vegetational Variation in Albedo Measured During CERES Ground-Validation Pilot Study

NASA Technical Reports Server (NTRS)

Schuster, G. L.; Whitlock, C. H.; Plant, J. V.; Wheeler, R. J.; Moats, C. D.; Larman, K. T.; Ayers, J. K.; Feldl, E. K.

1997-01-01

The Clouds and the Earth's Radiant Energy System (CERES) satellite is scheduled for launch in the Fall of 1997 aboard the Tropical Rainfall Measuring Mission (TRMM). A surface measurement pilot study has been initiated in a 37-km region near Richmond, VA, for comparison with the CERES surface flux retrievals. Two-minute averaged upwelling and downwelling surface fluxes over a mostly deciduous forest have been recorded daily for the past two years, and show a broadband, shortwave daily albedo increase during the summer months. Evidence is presented that indicates vegetational changes in the forest as the overriding mechanism for this change. Upwelling flux measured over the entire region by helicopter-mounted instrumentation has been processed for four solar seasons. Future plans include the installation of four more albedo surface sites over various types of vegetation throughout the region.

Gaseous Elemental Mercury (GEM) Emissions from Snow Surfaces in Northern New York

PubMed Central

Maxwell, J. Alexander; Holsen, Thomas M.; Mondal, Sumona

2013-01-01

Snow surface-to-air exchange of gaseous elemental mercury (GEM) was measured using a modified Teflon fluorinated ethylene propylene (FEP) dynamic flux chamber (DFC) in a remote, open site in Potsdam, New York. Sampling was conducted during the winter months of 2011. The inlet and outlet of the DFC were coupled with a Tekran Model 2537A mercury (Hg) vapor analyzer using a Tekran Model 1110 two port synchronized sampler. The surface GEM flux ranged from −4.47 ng m−2 hr−1 to 9.89 ng m−2 hr−1. For most sample periods, daytime GEM flux was strongly correlated with solar radiation. The average nighttime GEM flux was slightly negative and was not well correlated with any of the measured meteorological variables. Preliminary, empirical models were developed to estimate GEM emissions from snow surfaces in northern New York. These models suggest that most, if not all, of the Hg deposited with and to snow is reemitted to the atmosphere. PMID:23874951

Gaseous elemental mercury (GEM) emissions from snow surfaces in northern New York.

PubMed

Maxwell, J Alexander; Holsen, Thomas M; Mondal, Sumona

2013-01-01

Snow surface-to-air exchange of gaseous elemental mercury (GEM) was measured using a modified Teflon fluorinated ethylene propylene (FEP) dynamic flux chamber (DFC) in a remote, open site in Potsdam, New York. Sampling was conducted during the winter months of 2011. The inlet and outlet of the DFC were coupled with a Tekran Model 2537A mercury (Hg) vapor analyzer using a Tekran Model 1110 two port synchronized sampler. The surface GEM flux ranged from -4.47 ng m(-2) hr(-1) to 9.89 ng m(-2) hr(-1). For most sample periods, daytime GEM flux was strongly correlated with solar radiation. The average nighttime GEM flux was slightly negative and was not well correlated with any of the measured meteorological variables. Preliminary, empirical models were developed to estimate GEM emissions from snow surfaces in northern New York. These models suggest that most, if not all, of the Hg deposited with and to snow is reemitted to the atmosphere.

Dry deposition of PM2.5 sulfate above a hilly forest using relaxed eddy accumulation

NASA Astrophysics Data System (ADS)

Matsuda, Kazuhide; Watanabe, Ichiro; Mizukami, Kou; Ban, Satomi; Takahashi, Akira

2015-04-01

Sulfur compounds continue to be an important component of atmospheric deposition in East Asia. In order to better understand the dry deposition of PM2.5 sulfate, which is one of the most significant transboundary air pollutants in this region, we measured the dry deposition flux of PM2.5 sulfate above a hilly forest of the Field Museum Tamakyuryo (FM Tama) site in suburban Tokyo. We used the relaxed eddy accumulation (REA) method and took measurements during the summer, from 26 July to 2 August 2013, and the autumn, from 18 to 22 November 2013. We primarily focused on the evaluation of dry deposition above a forest on complex terrain. The total flux and 80% of the runs showed downward flux. The deposition velocities measured by the REA method during times when the wind direction was from a relatively uniform sloping surface over the forest were more reasonable than those measured when the wind direction was from a more complex surface. Using a resistance model that includes the effect of growth of hygroscopic aerosols, we inferred the deposition velocities during two experimental periods. When the fluxes were averaged for a long time (i.e., about 2 weeks) the inferred fluxes and deposition velocities were in reasonable agreement with the measurements. Although averages over long periods showed good agreement, the measured deposition velocities were distributed in a wider range than those inferred by the model. An increased range of deposition velocities was associated with flux footprints from complex terrain. It is possible that the agreements between measured and inferred fluxes or deposition velocities at the site are because the depositions of sulfate are largely controlled by surface factors rather than aerodynamic resistance.

Evaluating Surface Flux Results from CERES-FLASHFlux

NASA Astrophysics Data System (ADS)

Wilber, A. C.; Stackhouse, P. W., Jr.; Kratz, D. P.; Gupta, S. K.; Sawaengphokhai, P.

2016-12-01

The Clouds and Earth's Radiant Energy System (CERES) mission provides TOA (Top-of-Atmosphere) and surface radiative flux products for each CERES footprint (Single Scanner Footprint) and also time integrated and spatially averaged (TISA) to provide 1ox1o fluxes at various temporal averages. The CERES TISA products are available to the public within 3-6 months of observation. The CERES Fast Longwave and SHortwave radiative Flux (FLASHFlux) data products were developed to provide a rapid release version of the CERES data products. FLASHFlux data products are made available to the research and applications communities within one week of the satellite observations. Over the last several years, the CERES team has contributed to a section on the variability of radiation budget at the Top-of-Atmosphere in the annual "State of the Climate Report" published in BAMS using CERES TISA and FLASHFlux data products. Recently, the FLASHFlux data were used to investigate the radiative impacts of the intense 2015-2016 El Nino event. In addition FLASHFlux date are routinely used by applied science in energy related and agricultural sectors. The current version of FLASHFlux is being upgraded to FLASHFlux Version4A to improve consistency with the climate quality Edition 4 CERES data products. This presentation will describe the planned changes including the change to the latest meteorological product from Global Modeling and Assimilation Office (GMAO), GEOS FP-IT (5.12.4). GEOS 5.12.4 is an assimilation that is consistent with MERRA-2. We present comparisons of global and regional changes in the TOA and surface radiative fluxes as a result of the upgrade for both longwave (LW) and shortwave (SW) surface fluxes. We also compare the data products against ground measurements using data from the Baseline Surface Radiation Network (BSRN) - including NOAA SURFRAD, Atmospheric Radiation Measurement (ARM) and Ocean buoy measurements from Woods Hole Oceanographic Institute (WHOI).

Our contaminated atmosphere: The danger of climate change, phases 1 and 2. [effect of atmospheric particulate matter on surface temperature and earth's radiation budget

NASA Technical Reports Server (NTRS)

Cimorelli, A. J.; House, F. B.

1974-01-01

The effects of increased concentrations of atmospheric particulate matter on average surface temperature and on the components of the earth's radiation budget are studied. An atmospheric model which couples particulate loading to surface temperature and to changes in the earth's radiation budget was used. A determination of the feasibility of using satellites to monitor the effect of increased atmospheric particulate concentrations is performed. It was found that: (1) a change in man-made particulate loading of a factor of 4 is sufficient to initiate an ice age; (2) variations in the global and hemispheric weighted averages of surface temperature, reflected radiant fluz and emitted radiant flux are nonlinear functions of particulate loading; and (3) a black satellite sphere meets the requirement of night time measurement sensitivity, but not the required day time sensitivity. A nonblack, spherical radiometer whose external optical properties are sensitive to either the reflected radiant fluz or the emitted radiant flux meets the observational sensitivity requirements.

The Effects of Fine-scale Soil Moisture and Canopy Heterogeneities on Energy and Soil Water Fluxes in a Temperate Mixed Deciduous Forest

NASA Astrophysics Data System (ADS)

He, L.; Ivanov, V. Y.; Bohrer, G.; Maurer, K.; Vogel, C. S.; Moghaddam, M.

2011-12-01

Vegetation is heterogeneous at different scales, influencing spatially variable energy and water exchanges between land-surface and atmosphere. Current land surface parameterizations of large-scale models consider spatial variability at a scale of a few kilometers and treat vegetation cover as aggregated patches with uniform properties. However, the coupling mechanisms between fine-scale soil moisture, vegetation, and energy fluxes such as evapotranspiration are strongly nonlinear; the aggregation of surface variations may produce biased energy fluxes. This study aims to improve the understanding of the scale impact in atmosphere-biosphere-hydrosphere interactions, which affects predictive capabilities of land surface models. The study uses a high-resolution, physically-based ecohydrological model tRIBS + VEGGIE as a data integration tool to upscale the heterogeneity of canopy distribution resolved at a few meters to the watershed scale. The study was carried out for a spatially heterogeneous, temperate mixed forest environment of Northern Michigan located near the University of Michigan Biological Station (UMBS). Energy and soil water dynamics were simulated at the tree-canopy resolution in the horizontal plane for a small domain (~2 sq. km) located within a footprint of the AmeriFlux tower. A variety of observational data were used to constrain and confirm the model, including a 3-m profile continuous soil moisture dataset and energy flux data (measured at the AmeriFlux tower footprint). A scenario with a spatially uniform canopy, corresponding to the commonly used 'big-leaf' scheme in land surface parameterizations was used to infer the effects of coarse-scale averaging. To gain insights on how heterogeneous canopy and soil moisture interact and contribute to the domain-averaged transpiration, several scenarios of tree-scale leaf area and soil moisture spatial variability were designed. Specifically, for the same mean states, the scenarios of variability of canopy biomass account for the spatial distribution of photosynthesis (and thus the stomatal resistance), the aerodynamic and leaf boundary layer resistances as well as the differential radiation forcing due to tall tree exposure and lateral shading of short trees. The numerical experiments show that by transpiring spatially varying amounts of water, heterogeneous canopies adjust the spatial soil water state to the scaled inverse of the canopy biomass regardless of the initial moisture state. Such a spatial distribution can be further wiped out because of the differential water stress. The aggregation of canopy-scale atmosphere-biosphere-hydrosphere interactions demonstrates non-linear relationship between soil moisture and evapotranspiration, influencing domain-averaged energy fluxes.

A 28-ka history of sea surface temperature, primary productivity and planktonic community variability in the western Arabian Sea

NASA Astrophysics Data System (ADS)

Pourmand, Ali; Marcantonio, Franco; Bianchi, Thomas S.; Canuel, Elizabeth A.; Waterson, Elizabeth J.

2007-12-01

Uranium series radionuclides and organic biomarkers, which represent major groups of planktonic organisms, were measured in western Arabian Sea sediments that span the past 28 ka. Variability in the past strength of the southwest and northeast monsoons and its influence on primary productivity, sea surface temperature (SST), and planktonic community structure were investigated. The average alkenone-derived SST for the last glacial period was ˜3°C lower than that measured for the Holocene. Prior to the deglacial, the lowest SSTs coincide with the highest measured fluxes of organic biomarkers, which represent primarily a planktonic suite of diatoms, coccolithophorids, dinoflagellates, and zooplankton. We propose that intensification of winter northeast monsoon winds during the last glacial period resulted in deep convective mixing, cold SSTs and enhanced primary productivity. In contrast, postdeglacial (<17 ka) SSTs are warmer during times in which biomarker fluxes are high. Associated with this transition is a planktonic community structure change, in which the ratio of the average cumulative flux of diatom biomarkers to the cumulative flux of coccolithophorid biomarkers is twice as high during the deglacial and Holocene than the average ratio during the last glacial period. We suggest that this temporal transition represents a shift from a winter northeast monsoon-dominated (pre-17 ka) to a summer southwest monsoon-dominated (post-17 ka) wind system.

Experimental measurements and analytical analysis related to gas turbine heat transfer. Part 1: Time-averaged heat-flux and surface-pressure measurements on the vanes and blades of the SSME fuel-side turbine and comparison with prediction. Part 2: Phase-resolved surface-pressure and heat-flux measurements on the first blade of the SSME fuel-side turbine

NASA Technical Reports Server (NTRS)

1994-01-01

Time averaged Stanton number and surface-pressure distributions are reported for the first-stage vane row, the first stage blade row, and the second stage vane row of the Rocketdyne Space Shuttle Main Engine two-stage fuel-side turbine. Unsteady pressure envelope measurements for the first blade are also reported. These measurements were made at 10 percent, 50 percent, and 90 percent span on both the pressure and suction surfaces of the first stage components. Additional Stanton number measurements were made on the first stage blade platform blade tip, and shroud, and at 50 percent span on the second vane. A shock tube was used as a short duration source of heated and pressurized air to which the turbine was subjected. Platinum thin-film heat flux gages were used to obtain the heat flux measurements, while miniature silicon-diaphragm flush-mounted pressure transducers were used to obtain the pressure measurements. The first stage vane Stanton number distributions are compared with predictions obtained using a version of STAN5 and a quasi-3D Navier-Stokes solution. This same quasi-3D N-S code was also used to obtain predictions for the first blade and the second vane.

Mapping Surface Cover Parameters Using Aggregation Rules and Remotely Sensed Cover Classes. Version 1.9

NASA Technical Reports Server (NTRS)

Arain, Altaf M.; Shuttleworth, W. James; Yang, Z-Liang; Michaud, Jene; Dolman, Johannes

1997-01-01

A coupled model, which combines the Biosphere-Atmosphere Transfer Scheme (BATS) with an advanced atmospheric boundary-layer model, was used to validate hypothetical aggregation rules for BATS-specific surface cover parameters. The model was initialized and tested with observations from the Anglo-Brazilian Amazonian Climate Observational Study and used to simulate surface fluxes for rain forest and pasture mixes at a site near Manaus in Brazil. The aggregation rules are shown to estimate parameters which give area-average surface fluxes similar to those calculated with explicit representation of forest and pasture patches for a range of meteorological and surface conditions relevant to this site, but the agreement deteriorates somewhat when there are large patch-to-patch differences in soil moisture. The aggregation rules, validated as above, were then applied to remotely sensed 1 km land cover data set to obtain grid-average values of BATS vegetation parameters for 2.8 deg x 2.8 deg and 1 deg x 1 deg grids within the conterminous United States. There are significant differences in key vegetation parameters (aerodynamic roughness length, albedo, leaf area index, and stomatal resistance) when aggregate parameters are compared to parameters for the single, dominant cover within the grid. However, the surface energy fluxes calculated by stand-alone BATS with the 2-year forcing, data from the International Satellite Land Surface Climatology Project (ISLSCP) CDROM were reasonably similar using aggregate-vegetation parameters and dominant-cover parameters, but there were some significant differences, particularly in the western USA.

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.

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.

Albedo as a modulator of climate response to tropical deforestation

NASA Technical Reports Server (NTRS)

Dirmeyer, Paul A.; Shukla, J.

1994-01-01

An atmospheric general circulation model with land surface properties represented by the simplified Simple Biosphere model is used to investigate the effects on local climate due to tropical deforestation for the Amazon basin. One control and three anomaly integrations of 4 years' duration are performed. In the anomaly integrations, rain forest in South America is replaced by degraded grassland. The anomaly integrations differ only in the optical properties of the grassland vegetation, with net surface albedos ranging from the same as to 0.09 lighter than that of rain forest. It is found that the change in climate, particularly rainfall, is strongly dependent on the change in surface albedo that accompanies deforestation. Replacement of forest by grass causes a reduction in transpiration and reduces frictional convergence by decreasing surface roughness. However, precipitation averaged over the deforested area is not necessarily reduced. Average precipitation decreases when the increase in albedo is greater than 0.03. If surface albedo is not increased appreciably as a result of deforestation, moisture flux convergence driven by the increase in surface temperature can offset the other effects, and average precipitation increases. As albedo is increased, surface temperature does not change, but surface latent and sensible heat flux decreases due to reduced radiational energy absorbed at the surface, resulting in a reduction in convection and precipitation. A change in the distribution of precipitation due to deforestation that appears to be independent of the albedo is observed.

Albedo as a modulator of climate response to tropical deforestation

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

Dirmeyer, P.A.; Shukla, J.

1994-10-01

An atmospheric general circulation model with land surface properties represented by the simplified Simple Biosphere model is used to investigate the effects on local climate due to tropical deforestation for the Amazon basin. One control and three anomaly integrations of 4 years` duration are performed. In the anomaly integrations, rain forest in South America is replaced by degraded grassland. The anomaly integrations differ only in the optical properties of the grassland vegetation, with net surface albedos ranging from the same as to 0.09 lighter than that of rain forest. It is found that the change in climate, particularly rainfall, ismore » strongly dependent on the change in surface albedo that accompanies deforestation. Replacement of forest by grass causes a reduction in transpiration and reduces frictional convergence by decreasing surface roughness. However, precipitation averaged over the deforested area is not necessarily reduced. Average precipitation decreases when the increase in albedo is greater than 0.03. If surface albedo is not increased appreciably as a result of deforestation, moisture flux convergence driven by the increase in surface temperature can offset the other effects, and average precipitation increases. As albedo is increased, surface temperature does not change, but surface latent and sensible heat flux decreases due to reduced radiational energy absorbed at the surface, resulting in a reduction in convection and precipitation. A change in the distribution of precipitation due to deforestation that appears to be independent of the albedo is observed.« less

Evapotranspiration and runoff from large land areas: Land surface hydrology for atmospheric general circulation models

NASA Technical Reports Server (NTRS)

Famiglietti, J. S.; Wood, Eric F.

1993-01-01

A land surface hydrology parameterization for use in atmospheric GCM's is presented. The parameterization incorporates subgrid scale variability in topography, soils, soil moisture and precipitation. The framework of the model is the statistical distribution of a topography-soils index, which controls the local water balance fluxes, and is therefore taken to represent the large land area. Spatially variable water balance fluxes are integrated with respect to the topography-soils index to yield our large topography-soils distribution, and interval responses are weighted by the probability of occurrence of the interval. Grid square averaged land surface fluxes result. The model functions independently as a macroscale water balance model. Runoff ratio and evapotranspiration efficiency parameterizations are derived and are shown to depend on the spatial variability of the above mentioned properties and processes, as well as the dynamics of land surface-atmosphere interactions.

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

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. It is also demonstrated that the parameterization may be applied to irradiances at the top of the atmosphere that have been temporally averaged. 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.

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.

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.

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.

Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica

NASA Technical Reports Server (NTRS)

Obryk, M. K.; Doran, P. T.; Hicks, J. A.; McKay, C. P.; Priscu, J. C.

2016-01-01

A one-dimensional ice cover model was developed to predict and constrain drivers of long term ice thickness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface radiative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 years (between 1996 and 2012) of ice thickness changes for west lobe of Lake Bonney (average ice thickness = 3.53 m; RMSE = 0.09 m, n = 118) and Lake Fryxell (average ice thickness = 4.22 m; RMSE = 0.21 m, n = 128). Long-term ice thickness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or facilitate ice thickness change depending on the predominant climatic trend (temperature cooling or warming). As such, shallow (< 20 m deep water columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation.

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).

Soil surface CO2 flux in a boreal black spruce fire chronosequence

NASA Astrophysics Data System (ADS)

Wang, Chuankuan; Bond-Lamberty, Ben; Gower, Stith T.

2003-02-01

Understanding the effects of wildfire on the carbon (C) cycle of boreal forests is essential to quantifying the role of boreal forests in the global carbon cycle. Soil surface CO2 flux (Rs), the second largest C flux in boreal forests, is directly and indirectly affected by fire and is hypothesized to change during forest succession following fire. The overall objective of this study was to measure and model Rs for a black spruce (Picea mariana [Mill.] BSP) postfire chronosequence in northern Manitoba, Canada. The experiment design was a nested factorial that included two soil drainage classes (well and poorly drained) × seven postfire aged stands. Specific objectives were (1) to quantify the relationship between Rs and soil temperature for different aged boreal black spruce forests in well-drained and poorly drained soil conditions, (2) to examine Rs dynamics along postfire successional stands, and (3) to estimate annual soil surface CO2 flux for these ecosystems. Soil surface CO2 flux was significantly affected by soil drainage class (p = 0.014) and stand age (p = 0.006). Soil surface CO2 flux was positively correlated to soil temperature (R2 = 0.78, p < 0.001), but different models were required for each drainage class × aged stand combination. Soil surface CO2 flux was significantly greater at the well-drained than the poorly drained stands (p = 0.007) during growing season. Annual soil surface CO2 flux for the 1998, 1995, 1989, 1981, 1964, 1930, and 1870 burned stands averaged 226, 412, 357, 413, 350, 274, and 244 g C m-2 yr-1 in the well-drained stands and 146, 380, 300, 303, 256, 233, and 264 g C m-2 yr-1 in the poorly drained stands. Soil surface CO2 flux during the winter (from 1 November to 30 April) comprised from 5 to 19% of the total annual Rs. We speculate that the smaller soil surface CO2 flux in the recently burned than the older stands is mainly caused by decreased root respiration.

Soil surface CO2 flux in a boreal black spruce fire chronosequence

NASA Astrophysics Data System (ADS)

Wang, Chuankuan; Bond-Lamberty, Ben; Gower, Stith T.

2002-02-01

Understanding the effects of wildfire on the carbon (C) cycle of boreal forests is essential to quantifying the role of boreal forests in the global carbon cycle. Soil surface CO2 flux (Rs), the second largest C flux in boreal forests, is directly and indirectly affected by fire and is hypothesized to change during forest succession following fire. The overall objective of this study was to measure and model Rs for a black spruce (Picea mariana [Mill.] BSP) postfire chronosequence in northern Manitoba, Canada. The experiment design was a nested factorial that included two soil drainage classes (well and poorly drained) × seven postfire aged stands. Specific objectives were (1) to quantify the relationship between Rs and soil temperature for different aged boreal black spruce forests in well-drained and poorly drained soil conditions, (2) to examine Rs dynamics along postfire successional stands, and (3) to estimate annual soil surface CO2 flux for these ecosystems. Soil surface CO2 flux was significantly affected by soil drainage class (p = 0.014) and stand age (p = 0.006). Soil surface CO2 flux was positively correlated to soil temperature (R2 = 0.78, p < 0.001), but different models were required for each drainage class × aged stand combination. Soil surface CO2 flux was significantly greater at the well-drained than the poorly drained stands (p = 0.007) during growing season. Annual soil surface CO2 flux for the 1998, 1995, 1989, 1981, 1964, 1930, and 1870 burned stands averaged 226, 412, 357, 413, 350, 274, and 244 g C m-2 yr-1 in the well-drained stands and 146, 380, 300, 303, 256, 233, and 264 g C m-2 yr-1 in the poorly drained stands. Soil surface CO2 flux during the winter (from 1 November to 30 April) comprised from 5 to 19% of the total annual Rs. We speculate that the smaller soil surface CO2 flux in the recently burned than the older stands is mainly caused by decreased root respiration.

Influence of Arctic cloud thermodynamic phase on surface shortwave flux

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

Lubin, D.; Vogelmann, A.

2010-03-15

As part of the Indirect and Semi-Direct Aerosol Campaign (ISDAC) an Analytical Spectral Devices (ASD, Inc.) spectroradiometer was deployed at the Barrow NSA site during April and May of 2008, and in April-October of 2009. This instrument recorded one-minute averages of surface downwelling spectral flux in the wavelength interval 350-2200 nm, thus sampling the two major near infrared windows (1.6 and 2.2 microns) in which the flux is influenced by cloud microphysical properties including thermodynamic phase and effective particle size. Aircraft in situ measurements of cloud properties show mostly mixed-phase clouds over Barrow during the campaign, but with wide variabilitymore » in relative liquid versus ice water content. At fixed total optical depth, this variability in phase composition can yield of order 5-10 Watts per square meter in surface flux variability, with greater cloud attenuation of the surface flux usually occurring under higher ice water content. Thus our data show that changes in cloud phase properties, even within the 'mixed-phase' category, can affect the surface energy balance at the same order of magnitude as greenhouse gas increases. Analysis of this spectral radiometric data provides suggestions for testing new mixed-phase parameterizations in climate models.« less

Forcing and Responses of the Surface Energy Budget at Summit, Greenland

NASA Astrophysics Data System (ADS)

Miller, Nathaniel B.

Energy exchange at the Greenland Ice Sheet surface governs surface temperature variability, a factor critical for representing increasing surface melt extent, which portends a rise in global sea level. A comprehensive set of cloud, tropospheric, near-surface and sub-surface measurements at Summit Station is utilized to determine the driving forces and subsequent responses of the surface energy budget (SEB). This budget includes radiative, turbulent, and ground heat fluxes, and ultimately controls the evolution of surface temperature. At Summit Station, clouds radiatively warm the surface in all months with an annual average cloud radiative forcing value of 33 W m -2, largely driven by the occurrence of liquid-bearing clouds. The magnitude of the surface temperature response is dependent on how turbulent and ground heat fluxes modulate changes to radiative forcing. Relationships between forcing terms and responding surface fluxes show that changes in the upwelling longwave radiation compensate for 65-85% (50- 60%) of the total change in radiative forcing in the winter (summer). The ground heat flux is the second largest response term (16% annually), especially during winter. Throughout the annual cycle, the sensible heat flux response is comparatively constant (9%) and latent heat flux response is only 1.5%, becoming more of a factor in modulating surface temperature responses during the summer. Combining annual cycles of these responses with cloud radiative forcing results, clouds warm the surface by an estimated 7.8°C annually. A reanalysis product (ERA-I), operational model (CFSv2), and climate model (CESM) are evaluated utilizing the comprehensive set of SEB observations and process-based relationships. Annually, surface temperatures in each model are warmer than observed with overall poor representation of the coldest surface temperatures. Process-based relationships between different SEB flux terms offer insight into how well a modeling framework represents physical processes and the ability to distinguish errors in forcing versus those in physical representation. Such relationships convey that all three models underestimate the response of surface temperatures to changes in radiative forcing. These results provide a method to expose model deficiencies and indicate the importance of representing surface, sub-surface and boundary-layer processes when portraying cloud impacts on surface temperature variability.

Analysis of Water Vapour Flux Between Alpine Wetlands Underlying the Surface and Atmosphere in the Source Region of the Yellow River

NASA Astrophysics Data System (ADS)

Xie, Y.; Wen, J.; Liu, R.; Wang, X.; JIA, D.

2017-12-01

Wetland underlying surface is sensitive to climate change. Analysis of the degree of coupling between wetlands and the atmosphere and a quantitative assessment of how environmental factors influence latent heat flux have considerable scientific significance. Previous studies, which focused on the forest, grassland and farmland ecosystems, lack research on the alpine wetlands. In addition, research on the environmental control mechanism of latent heat flux is still qualitative and lacks quantitative evaluations and calculations. Using data from the observational tests of the Maduo Observatory of Climate and Environment of the Northwest Institute of Eco-Environment and Resource, CAS, from June 1 to August 31, 2014, this study analysed the time-varying characteristics and causes of the degree of coupling between alpine wetlands underlying surface and the atmosphere and quantitatively calculated the influences of different environmental factors (solar radiation and vapour pressure deficit) on latent heat flux. The results were as follows: Due to the diurnal variations of solar radiation and wind speed, the diurnal variations of the Ω factor present a trend in which the Ω factor are small in the morning and large in the evening. Due to the vegetation growing cycle, the seasonal variations of the Ω factor present a reverse "U" trend . These trends are similar to the diurnal and seasonal variations of the absolute control exercised by solar radiation over the latent heat flux. This conforms to omega theory. The values for average absolute atmospheric factor (surface factor or total ) control exercised by solar radiation and water vapour pressure are 0.20 (0.02 or 0.22 ) and 0.005 (-0.07 or -0.06) W·m-2·Pa-1, respectively.. Generally speaking, solar radiation and water vapour pressure deficit exert opposite forces on the latent heat flux. The average Ω factor is high during the vegetation growing season, with a value of 0.38, and the degree of coupling between the alpine wetland surface and the atmosphere system is low. The actual measurements agree with omega theory. The latent heat flux is mainly influenced by solar radiation. From the above, our study has provided reference information for exploring the influences of environmental factors on the latent heat flux over the alpine wetlands of the Yellow River source region.

Fluxes by eddy correlation over heterogeneous landscape: How shall we apply the Reynolds average?

NASA Astrophysics Data System (ADS)

Dobosy, R.

2007-12-01

Top-down estimates of carbon exchange across the earth's surface are implicitly an integral scheme, deriving bulk exchanges over large areas. Bottom-up estimates explicitly integrate the individual components of exchange to derive a bulk value. If these approaches are to be properly compared, their estimates should represent the same quantity. Over heterogeneous landscape, eddy-covariance flux computations from towers or aircraft intended for comparison with top-down approach face a question of the proper definition of the mean or base state, the departures from which yield the fluxes by Reynolds averaging. 1)≠Use a global base state derived over a representative sample of the surface, insensitive to land use. The departure quantities then fail to sum to zero over any subsample representing an individual surface type, violating Reynolds criteria. Yet fluxes derived from such subsamples can be directly composed into a bulk flux, globally satisfying Reynolds criteria. 2)≠Use a different base state for each surface type. satisfying Reynolds criteria individually. Then some of the flux may get missed if a surface's characteristics significantly bias its base state. Base state≠(2) is natural for tower samples. Base state≠(1) is natural for airborne samples over heterogeneous landscape, especially in patches smaller than an appropriate averaging length. It appears (1) incorporates a more realistic sample of the flux, though desirably there would be no practical difference between the two schemes. The schemes are related by the expression w¯*a*)C - w¯'a¯')C = w¯'ã¯)C+ wtilde ¯a¯')C+ wtilde ¯ã¯)C Here w is vertical motion, and a is some scalar, such as CO2. The star denotes departure from the global base state≠(1), and the prime from the base state≠(2), defined only over surface class≠C. The overbar with round bracket denotes average over samples drawn from class≠C, determined by footprint model. Thus a¯')C = 0 but a¯*)C ≠ 0 in general. The tilde denotes the departure of base-state≠(2) from base-state≠(1). It represents surface≠C's characteristic bias. The equation is defined only over class≠C. A similar equation applies to each surface class. The first and second righthand terms express interaction of the departure quantities with surface≠C's characteristic bias. These terms are zero if the base states are simple means. The third term becomes important if class C has a significant bias both in vertical motion and in its characteristic values of a. A practical example from 2005 June 18 at 1015 LST in Illinois is illustrative. Turbulence measurements were made by aircraft at 20≠m above ground along a 50≠km track approximately evenly divided between corn and soybean. Corn (type≠C) was growing quickly, increasing the mixing ratio of moisture (r) and reducing that of CO2 (a), relative to soybean. Soybean characteristically heated the air and favored updrafts. These biases were evident in r¯*)C, a¯*)C, θ¯*)C, and w¯*)C relative to their corresponding averages over soybean. In particular the bias in CO2 mixing ratio, negative over corn and positive over soybean, was about 20% of the standard deviation of a*. Nevertheless, neither surface type strongly favored vertical motion, giving the encouraging result that the two approaches do not differ by more than an insignificant few per cent. The theoretical analysis indicates care, however, where extensive areas of both bare soil and vegetated land may enhance the bias in vertical motion between different components of the landscape.

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

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.

Aeolian transport in the field: A comparison of the effects of different surface treatments

NASA Astrophysics Data System (ADS)

Dong, Zhibao; Lv, Ping; Zhang, Zhengcai; Qian, Guangqiang; Luo, Wanyin

2012-05-01

Aeolian transport represents the result of wind-surface interactions, and therefore depends strongly on variations in the characteristics of the sediment surface. We conducted field observations of aeolian transport of typical dune sand in three 80 m × 80 m plots with different surface treatments: gravel-covered sand, enclosed shifting sand, and open (unprotected) shifting sand. The study was performed at the Shapotou Aeolian Experiment Site in the southeastern part of China's Tengger Desert to compare the effects of these different surface treatments on aeolian transport. To do so, we analyzed the flux density profiles and transport rates above each surface. The flux density profiles for all three treatments followed the exponential decay law that was proposed by most previous researchers to describe the saltation flux density profiles. Coefficients of the exponential decay function were defined as a function of the surface and the wind velocity. The enclosed and open plots with shifting sand had similar flux density profiles, but the flux density above gravel-covered plots showed that transport decayed more slowly with increasing height, producing flux density profiles with a higher average saltation height. The transport rate above the three treatment plots tended to increase proportionally with the cube of the mean wind velocity and with the maximum wind velocity during the observation period, but was more strongly correlated with the square of drift potential. Transport rates above the plot with open shifting sand were greater than those above the plots with enclosed shifting sand and the gravel-covered plot.

Stick-Jump (SJ) Evaporation of Strongly Pinned Nanoliter Volume Sessile Water Droplets on Quick Drying, Micropatterned Surfaces.

PubMed

Debuisson, Damien; Merlen, Alain; Senez, Vincent; Arscott, Steve

2016-03-22

We present an experimental study of stick-jump (SJ) evaporation of strongly pinned nanoliter volume sessile water droplets drying on micropatterned surfaces. The evaporation is studied on surfaces composed of photolithographically micropatterned negative photoresist (SU-8). The micropatterning of the SU-8 enables circular, smooth, trough-like features to be formed which causes a very strong pinning of the three phase (liquid-vapor-solid) contact line of an evaporating droplet. This is ideal for studying SJ evaporation as it contains sequential constant contact radius (CCR) evaporation phases during droplet evaporation. The evaporation was studied in nonconfined conditions, and forced convection was not used. Micropatterned concentric circles were defined having an initial radius of 1000 μm decreasing by a spacing ranging from 500 to 50 μm. The droplet evaporates, successively pinning and depinning from circle to circle. For each pinning radius, the droplet contact angle and volume are observed to decrease quasi-linearly with time. The experimental average evaporation rates were found to decrease with decreasing pining radii. In contrast, the experimental average evaporation flux is found to increase with decreasing droplet radii. The data also demonstrate the influence of the initial contact angle on evaporation rate and flux. The data indicate that the total evaporation time of a droplet depends on the specific micropattern spacing and that the total evaporation time on micropatterned surfaces is always less than on flat, homogeneous surfaces. Although the surface patterning is observed to have little effect on the average droplet flux-indicating that the underlying evaporation physics is not significantly changed by the patterning-the total evaporation time is considerably modified by patterning, up to a factor or almost 2 compared to evaporation on a flat, homogeneous surface. The closely spaced concentric circle pinning maintains a large droplet radius and small contact angle from jump to jump; the result is a large evaporation rate leading to faster evaporation.

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.

Response of Moist Convection to Multi-scale Surface Flux Heterogeneity

NASA Astrophysics Data System (ADS)

Kang, S. L.; Ryu, J. H.

2015-12-01

We investigate response of moist convection to multi-scale feature of the spatial variation of surface sensible heat fluxes (SHF) in the afternoon evolution of the convective boundary layer (CBL), utilizing a mesoscale-domain large eddy simulation (LES) model. The multi-scale surface heterogeneity feature is analytically created as a function of the spectral slope in the wavelength range from a few tens of km to a few hundreds of m in the spectrum of surface SHF on a log-log scale. The response of moist convection to the κ-3 - slope (where κ is wavenumber) surface SHF field is compared with that to the κ-2 - slope surface, which has a relatively weak mesoscale feature, and the homogeneous κ0 - slope surface. Given the surface energy balance with a spatially uniform available energy, the prescribed SHF has a 180° phase lag with the latent heat flux (LHF) in a horizontal domain of (several tens of km)2. Thus, warmer (cooler) surface is relatively dry (moist). For all the cases, the same observation-based sounding is prescribed for the initial condition. For all the κ-3 - slope surface heterogeneity cases, early non-precipitating shallow clouds further develop into precipitating deep thunderstorms. But for all the κ-2 - slope cases, only shallow clouds develop. We compare the vertical profiles of domain-averaged fluxes and variances, and the contribution of the mesoscale and turbulence contributions to the fluxes and variances, between the κ-3 versus κ-2 slope cases. Also the cross-scale processes are investigated.

Atmospheric organochlorine pollutants and air-sea exchange of hexachlorocyclohexane in the Bering and Chukchi Seas

USGS Publications Warehouse

Hinckley, D.A.; Bidleman, T.F.; Rice, C.P.

1991-01-01

Organochlorine pesticides have been found in Arctic fish, marine mammals, birds, and plankton for some time. The lack of local sources and remoteness of the region imply long-range transport and deposition of contaminants into the Arctic from sources to the south. While on the third Soviet-American Joint Ecological Expedition to the Bering and Chukchi Seas (August 1988), high-volume air samples were taken and analyzed for organochlorine pesticides. Hexachlorocyclohexane (HCH), hexachlorobenzene, polychlorinated camphenes, and chlordane (listed in order of abundance, highest to lowest) were quantified. The air-sea gas exchange of HCH was estimated at 18 stations during the cruise. Average alpha-HCH concentrations in concurrent atmosphere and surface water samples were 250 pg m-3 and 2.4 ng L-1, respectively, and average gamma-HCH concentrations were 68 pg m-3 in the atmosphere and 0.6 ng L-1 in surface water. Calculations based on experimentally derived Henry's law constants showed that the surface water was undersaturated with respect to the atmosphere at most stations (alpha-HCH, average 79% saturation; gamma-HCH, average 28% saturation). The flux for alpha-HCH ranged from -47 ng m-2 day-1 (sea to air) to 122 ng m-2 d-1 (air to sea) and averaged 25 ng m-2 d-1 air to sea. All fluxes of gamma-HCH were from air to sea, ranged from 17 to 54 ng m-2 d-1, and averaged 31 ng m-2 d-1.

Evaluation of surface renewal and flux-variance methods above agricultural and forest surfaces

NASA Astrophysics Data System (ADS)

Fischer, M.; Katul, G. G.; Noormets, A.; Poznikova, G.; Domec, J. C.; Trnka, M.; King, J. S.

2016-12-01

Measurements of turbulent surface energy fluxes are of high interest in agriculture and forest research. During last decades, eddy covariance (EC), has been adopted as the most commonly used micrometeorological method for measuring fluxes of greenhouse gases, energy and other scalars at the surface-atmosphere interface. Despite its robustness and accuracy, the costs of EC hinder its deployment at some research experiments and in practice like e.g. for irrigation scheduling. Therefore, testing and development of other cost-effective methods is of high interest. In our study, we tested performance of surface renewal (SR) and flux variance method (FV) for estimates of sensible heat flux density. Surface renewal method is based on the concept of non-random transport of scalars via so-called coherent structures which if accurately identified can be used for the computing of associated flux. Flux variance method predicts the flux from the scalar variance following the surface-layer similarity theory. We tested SR and FV against EC in three types of ecosystem with very distinct aerodynamic properties. First site was represented by agricultural wheat field in the Czech Republic. The second site was a 20-m tall mixed deciduous wetland forest on the coast of North Carolina, USA. The third site was represented by pine-switchgrass intercropping agro-forestry system located in coastal plain of North Carolina, USA. Apart from solving the coherent structures in a SR framework from the structure functions (representing the most common approach), we applied ramp wavelet detection scheme to test the hypothesis that the duration and amplitudes of the coherent structures are normally distributed within the particular 30-minutes time intervals and so just the estimates of their averages is sufficient for the accurate flux determination. Further, we tested whether the orthonormal wavelet thresholding can be used for isolating of the coherent structure scales which are associated with flux transport. Finally, we tested whether low-pass filtering in the Fourier domain based on integral length scale can improve estimates of both SR and FV as it supposedly removes the low frequency portion of the signal not related with the investigated fluxes.

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.

Improved simulation of regional CO2 surface concentrations using GEOS-Chem and fluxes from VEGAS

NASA Astrophysics Data System (ADS)

Chen, Z. H.; Zhu, J.; Zeng, N.

2013-08-01

CO2 measurements have been combined with simulated CO2 distributions from a transport model in order to produce the optimal estimates of CO2 surface fluxes in inverse modeling. However, one persistent problem in using model-observation comparisons for this goal relates to the issue of compatibility. Observations at a single station reflect all underlying processes of various scales. These processes usually cannot be fully resolved by model simulations at the grid points nearest the station due to lack of spatial or temporal resolution or missing processes in the model. In this study the stations in one region were grouped based on the amplitude and phase of the seasonal cycle at each station. The regionally averaged CO2 at all stations in one region represents the regional CO2 concentration of this region. The regional CO2 concentrations from model simulations and observations were used to evaluate the regional model results. The difference of the regional CO2 concentration between observation and modeled results reflects the uncertainty of the large-scale flux in the region where the grouped stations are. We compared the regional CO2 concentrations between model results with biospheric fluxes from the Carnegie-Ames-Stanford Approach (CASA) and VEgetation-Global-Atmosphere-Soil (VEGAS) models, and used observations from GLOBALVIEW-CO2 to evaluate the regional model results. The results show the largest difference of the regionally averaged values between simulations with fluxes from VEGAS and observations is less than 5 ppm for North American boreal, North American temperate, Eurasian boreal, Eurasian temperate and Europe, which is smaller than the largest difference between CASA simulations and observations (more than 5 ppm). There is still a large difference between two model results and observations for the regional CO2 concentration in the North Atlantic, Indian Ocean, and South Pacific tropics. The regionally averaged CO2 concentrations will be helpful for comparing CO2 concentrations from modeled results and observations and evaluating regional surface fluxes from different methods.

Scaling Properties of Turbulent Mixing for Scalars Measured at Arctic Terrestrial Sites

NASA Astrophysics Data System (ADS)

Grachev, A. A.; Uttal, T.; Persson, O. P. G.; Crepinsek, S.; Fairall, C. W.; Albee, R.; Makshtas, A.; Kustov, V. Y.; Repina, I.; Artamonov, A. Y.

2014-12-01

Measurements of atmospheric turbulence made at two different sites located near the coast of the Arctic Ocean at Eureka (Canadian territory of Nunavut) and Tiksi (East Siberia) are used to study turbulent fluxes, scaling laws for turbulent mixing, dissipation rates, and structure parameters of various scalars (temperature, water vapour, and carbon dioxide). Turbulent fluxes along with other turbulent statistics and mean meteorological data were measured continuously throughout the year and reported hourly at various levels on 10-m (Eureka) and 20-m (Tiksi) flux towers. According to our data, strong upward sensible and latent heat fluxes are observed throughout the summer months indicating unstable stratification on average. During the Polar winter and cold seasons when the air temperature falls below freezing, the near-surface environment is generally stably stratified (downward sensible but upward latent heat fluxes). It is found that observed temporal variability of the carbon dioxide vertical flux for both sites was generally in phase with Monin-Obukhov stability parameter, z/L (L is the Obukhov length scale). On average the turbulent flux of carbon dioxide was mostly negative (uptake by the surface) for z/L < 0 and vice versa. Our study also analyses the similarity between the turbulent mixing of sensible heat, water vapour, and carbon dioxide with a specific focus on the difference between the similarity functions for the dissipation rates. 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.

Long-term elemental dry deposition fluxes measured around Lake Michigan with an automated dry deposition sampler

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

Shahin, U. Yi, S.M.; Paode, R.D.; Holsen, T.M.

2000-05-15

Long-term measurements of mass and elemental dry deposition (MG, Al, V, Cr, Mn, Ni, Co, Cu, Zn, As, Sr, Mo, Cd, Sb, Ba, and Pb) were made with an automated dry deposition sampler (Eagle II) containing knife-edge surrogate surfaces during the Lake Michigan Mass Balance/Mass Budget Study. Measurements were made over a roughly 700-day period in Chicago, IL; in South Haven and Sleeping Bear Dunes, MI; and over Lake Michigan on the 68th Street drinking water intake cribs from December 1993 to October 1995. Average mass fluxes in Chicago, South Haven, Sleeping Bear Dunes, and the 68th Street crib weremore » 65, 10, 3.6, and 12 mg m{sup {minus}2} day{sup {minus}1}, respectively. Primarily crustal elemental fluxes were significantly smaller than the mass fluxes but higher than primarily anthropogenic elemental fluxes. For example, the average elemental flux of Al in Chicago, South Haven, Sleeping Bear Dunes, and the 68th Street crib were 1.0, 0.34, 0.074, and 0.34 mg m{sup {minus}2}day{sup {minus}1}, respectively. The average Pb fluxes in Chicago, South Haven, Sleeping Bear Dunes, and the 68th Street crib were 0.038, 0.023, 0.035, and 0.032 mg m{sup {minus}2}day{sup {minus}1}, respectively. The measured fluxes at the various sites were used to calculate the dry deposition loadings to the lake. These estimated fluxes were highest for Mg and lowest for Cd.« less

Spatio-temporal variability of lake CH4 fluxes and its influence on annual estimates

NASA Astrophysics Data System (ADS)

Natchimuthu, S.; Sundgren, I.; Gålfalk, M.; Klemedtsson, L.; Crill, P. M.; Danielsson, Å.; Bastviken, D.

2014-12-01

Lakes are major sources of methane (CH4) to the atmosphere and it has been shown that lakes contribute significantly to the global CH4 budget. However, the data behind these global estimates are snapshots in time and space only and they typically lack information on spatial and temporal variability of fluxes which can potentially lead to biased estimates. Recent studies have shown that diffusive flux, gas exchange velocity (k), ebullition and concentration of CH4 in the surface water can vary significantly in space within lakes. CH4 fluxes can also change at a broad range of temporal scales in response to seasons, temperature, lake mixing events, short term weather events like pressure variations, shifting winds and diel cycles. We sampled CH4 fluxes and surface water concentrations from three lakes of differing characteristics in southwest Sweden over two annual cycles, approximately every 14 days from April to October 2012 and from April to November 2013. CH4 fluxes were measured using floating chambers distributed in the lakes based on depth categories and dissolved CH4 concentrations were determined by a headspace equilibration method. We observed significant differences in CH4 concentration, diffusion, ebullition and total fluxes between and within the lakes. The fluxes increased exponentially with temperature in all three lakes and water temperature, for example, explained 53-78% of variations in total fluxes in the lakes. Based on our data which relied on improved spatial and temporal information, we demonstrate that measurements which do not take into account of the spatial variability in the lakes could substantially bias the whole lake estimates. For instance, in one of the lakes, measurements from the central parts of the lake represented only 58% of our estimates from all chambers on an average. In addition, we consider how intensive sampling in one season of the year may affect the annual estimates due to the complex interaction of temperature, air pressure and lake mixing events on CH4 fluxes. For example, samples collected when the average air temperatures during chamber deployments were above 15 °C overestimated the total fluxes by 17-157% in all lakes when compared to averages from all measurement times.

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.

Distribution and Emission of Methane in Nakdong Estuary

NASA Astrophysics Data System (ADS)

Ryu, J.; An, S.

2014-12-01

Despite a small area, coastal areas contribute most to the oceanic methane flux. A wide range of methane fluxes have been reported in the coastal areas, but limited data were presented for Korean coastal areas. The air and surface water was sampled in Nakdong Estuary where the barrage had been constructed, and methane concentrations were measured using Gas Chromatography. To see the influence of the barrage, surface water was sampled outside and inside the barrage respectively. In the expectation that methane distribution would be different depending on the tides, surface water outside the barrage was collected at high and low tide respectively. Headspace technique and Membrane Inlet Mass Spectrometry were also used. The average atmospheric concentration (1.82ppm) was lower than the global average concentration expected from the IPCC scenario. The concentrations of water inside the barrage (average 173nM) were similar to those measured in other rivers but in the lower side. The average concentrations outside the barrage (52nM at high tide, 85nM at low tide) were lower than those measured in other coastal areas, but of the same order of magnitude as the European tidal estuaries. Methane concentrations in Nakdong estuary were higher than the methane concentration equilibrated with the atmosphere. The spatial variability of methane concentration in Nakdong estuary seems to be the result of the fresh (high methane) and sea (low methane) water mixing. Meanwhile large tidal flat area in Nakdong estuary should play a major role in methane dynamics and methane flux measurements during sediment incubation were conducted to evaluate the immersion/emersion cycle and photosynthesis by MPB (micro phyto benthos) effect.

Surface Water pCO2 Variations and Sea-Air CO2 Fluxes During Summer in the Eastern Canadian Arctic

NASA Astrophysics Data System (ADS)

Burgers, T. M.; Miller, L. A.; Thomas, H.; Else, B. G. T.; Gosselin, M.; Papakyriakou, T.

2017-12-01

Based on a 2 year data set, the eastern Canadian Arctic Archipelago and Baffin Bay appear to be a modest summertime sink of atmospheric CO2. We measured surface water CO2 partial pressure (pCO2), salinity, and temperature throughout northern Baffin Bay, Nares Strait, and Lancaster Sound from the CCGS Amundsen during its 2013 and 2014 summer cruises. Surface water pCO2 displayed considerable variability (144-364 μatm) but never exceeded atmospheric concentrations, and average calculated CO2 fluxes in 2013 and 2014 were -12 and -3 mmol C m-2 d-1 (into the ocean), respectively. Ancillary measurements of chlorophyll a reveal low summertime productivity in surface waters. Based on total alkalinity and stable oxygen isotopes (δ18O) data, a strong riverine signal in northern Nares Strait coincided with relatively high surface pCO2, whereas areas of sea-ice melt occur with low surface pCO2. Further assessments, extending the seasonal observation period, are needed to properly constrain both seasonal and annual CO2 fluxes in this region.

Analysis of Surface Fluxes at Eureka Climate Observatory in Arctic

NASA Astrophysics Data System (ADS)

Grachev, Andrey; Albee, Robert; Fairall, Christopher; Hare, Jeffrey; Persson, Ola; Uttal, Taneil

2010-05-01

The Arctic region is experiencing unprecedented changes associated with increasing average temperatures (faster than the pace of the globally-averaged increase) and significant decreases in both the areal extent and thickness of the Arctic pack ice. These changes are early warning signs of shifts in the global climate system that justifies increased scientific focus on this region. The increase in atmospheric carbon dioxide has raised concerns worldwide about future climate change. Recent studies suggest that huge stores of carbon dioxide (and other climate relevant compounds) locked up in Arctic soils could be unexpectedly released due to global warming. Observational evidence suggests that atmospheric energy fluxes are a major contributor to the decrease of the Arctic pack ice, seasonal land snow cover and the warming of the surrounding land areas and permafrost layers. To better understand the atmosphere-surface exchange mechanisms, improve models, and to diagnose climate variability in the Arctic, accurate measurements are required of all components of the net surface energy budget and the carbon dioxide cycle over representative areas and over multiple years. In this study we analyze variability of turbulent fluxes including water vapor and carbon dioxide transfer based on long-term measurements made at Eureka observatory (80.0 N, 85.9 W) located near the coast of the Arctic Ocean (Canadian territory of Nunavut). Turbulent fluxes and mean meteorological data are continuously measured and reported hourly at various levels on a 10-m flux tower. Sonic anemometers are located at 3 and 8 m heights while high-speed Licor 7500 infrared gas analyzer (water moisture and carbon dioxide measurements) at 7.5 m height. According to our data, that the sensible heat flux, carbon dioxide and water vapor fluxes exhibited clear diurnal cycles in Arctic summer. This behavior is similar to the diurnal variation of the fluxes in mid-latitudes during the plants growing season, with carbon dioxide uptake from the atmosphere during the day due to photosynthesis, and carbon dioxide loss to the atmosphere due to vegetation respiration during the night. However, at Eureka vegetation was a source of carbon dioxide during sunlit periods. Thus the sign of carbon dioxide flux was controlled by air temperature even during Arctic summer.

Effects of historical and modern mining on mercury deposition in southeastern Peru.

PubMed

Beal, Samuel A; Jackson, Brian P; Kelly, Meredith A; Stroup, Justin S; Landis, Joshua D

2013-11-19

Both modern anthropogenic emissions of mercury (Hg), primarily from artisanal and small-scale gold mining (ASGM), and preindustrial anthropogenic emissions from mining are thought to have a large impact on present-day atmospheric Hg deposition. We study the spatial distribution of Hg and its depositional history over the past ∼400 years in sediment cores from lakes located regionally proximal (∼90-150 km) to the largest ASGM in Peru and distal (>400 km) to major preindustrial mining centers. Total Hg concentrations in surface sediments from fourteen lakes are typical of remote regions (10-115 ng g(-1)). Hg fluxes in cores from four lakes demonstrate preindustrial Hg deposition in southeastern Peru was spatially variable and at least an order of magnitude lower than previously reported fluxes in lakes located closer to mining centers. Average modern (A.D. 2000-2011) Hg fluxes in these cores are 3.4-6.9 μg m(-2) a(-1), compared to average preindustrial (A.D. 1800-1850) fluxes of 0.8-2.5 μg m(-2) a(-1). Modern Hg fluxes determined from the four lakes are on average 3.3 (±1.5) times greater than their preindustrial fluxes, similar to those determined in other remote lakes around the world. This agreement suggests that Hg emissions from ASGM are likely not significantly deposited in nearby down-wind regions.

Effects of historical and modern mining on mercury deposition in southeastern Peru

PubMed Central

Beal, Samuel A.; Jackson, Brian P.; Kelly, Meredith A.; Stroup, Justin S.; Landis, Joshua D.

2013-01-01

Both modern anthropogenic emissions of mercury (Hg), primarily from artisanal and small-scale gold mining (ASGM), and preindustrial anthropogenic emissions from mining are thought to have a large impact on present-day atmospheric Hg deposition. We study the spatial distribution of Hg and its depositional history over the past ~400 years in sediment cores from lakes located regionally proximal (~90–150 km) to the largest ASGM in Peru and distal (>400 km) to major preindustrial mining centers. Total Hg concentrations in surface sediments from fourteen lakes are typical of remote regions (10–115 ng g−1). Hg fluxes in cores from four lakes demonstrate preindustrial Hg deposition in southeastern Peru was spatially variable and at least an order of magnitude lower than previously reported fluxes in lakes located closer to mining centers. Average modern (A.D. 2000–2011) Hg fluxes in these cores are 3.4–6.9 μg m−2 a−1, compared to average preindustrial (A.D. 1800–1850) fluxes of 0.8–2.5 μg m−2 a−1. Modern Hg fluxes determined from the four lakes are on average 3.3 (±1.5) times greater than their preindustrial fluxes, similar to those determined in other remote lakes around the world. This agreement suggests that Hg emissions from ASGM are likely not significantly deposited in nearby downwind regions. PMID:24124645

The Characterization of Atmospheric Boundary Layer Depth and Turbulence in a Mixed Rural and Urban Convective Environment

NASA Astrophysics Data System (ADS)

Hicks, Micheal M.

A comprehensive analysis of surface-atmosphere flux exchanges over a mixed rural and urban convective environment is conducted at Howard University Beltsville, MD Research Campus. This heterogeneous site consists of rural, suburban and industrial surface covers to its south, east and west, within a 2 km radius of a flux sensor. The eddy covariance method is utilized to estimate surface-atmosphere flux exchanges of momentum, heat and moisture. The attributes of these surface flux exchanges are contrasted to those of classical homogeneous sites and assessed for accuracy, to evaluate the following: (I) their similarity to conventional convective boundary layer (CBL) processes and (II) their representativeness of the surrounding environment's turbulent properties. Both evaluations are performed as a function of upwind surface conditions. In particular, the flux estimates' obedience to spectrum power laws and similarity theory relationships is used for performing the first evaluation, and their ability to close the surface energy balance and accurately model CBL heights is used for the latter. An algorithm that estimates atmospheric boundary layer heights from observed lidar extinction backscatter was developed, tested and applied in this study. The derived lidar based CBL heights compared well with those derived from balloon borne soundings, with an overall Pearson correlation coefficient and standard deviation of 0.85 and 223 m, respectively. This algorithm assisted in the evaluation of the response of CBL processes to surface heterogeneity, by deriving high temporal CBL heights and using them as independent references of the surrounding area averaged sensible heat fluxes. This study found that the heterogeneous site under evaluation was rougher than classical homogeneous sites, with slower dissipation rates of turbulent kinetic energy. Flux measurements downwind of the industrial complexes exhibited enhanced efficiency in surface-atmosphere momentum, heat, and moisture transport relative to their similarity theory predictions. In addition, these enhanced heat flux estimates ingested into the CBL slab model overestimated observed CBL heights. More spatial flux observations are needed to better understand the role that the industrial complexes are playing in enhancing the efficiency of turbulent processes, which may have important implications on the role humans are assuming in regional climate change.

Estimating regional methane surface fluxes: the relative importance of surface and GOSAT mole fraction measurements

NASA Astrophysics Data System (ADS)

Fraser, A.; Palmer, P. I.; Feng, L.; Boesch, H.; Cogan, A.; Parker, R.; Dlugokencky, E. J.; Fraser, P. J.; Krummel, P. B.; Langenfelds, R. L.; O'Doherty, S.; Prinn, R. G.; Steele, L. P.; van der Schoot, M.; Weiss, R. F.

2013-06-01

We use an ensemble Kalman filter (EnKF), together with the GEOS-Chem chemistry transport model, to estimate regional monthly methane (CH4) fluxes for the period June 2009-December 2010 using proxy dry-air column-averaged mole fractions of methane (XCH4) from GOSAT (Greenhouse gases Observing SATellite) and/or NOAA ESRL (Earth System Research Laboratory) and CSIRO GASLAB (Global Atmospheric Sampling Laboratory) CH4 surface mole fraction measurements. Global posterior estimates using GOSAT and/or surface measurements are between 510-516 Tg yr-1, which is less than, though within the uncertainty of, the prior global flux of 529 ± 25 Tg yr-1. We find larger differences between regional prior and posterior fluxes, with the largest changes in monthly emissions (75 Tg yr-1) occurring in Temperate Eurasia. In non-boreal regions the error reductions for inversions using the GOSAT data are at least three times larger (up to 45%) than if only surface data are assimilated, a reflection of the greater spatial coverage of GOSAT, with the two exceptions of latitudes >60° associated with a data filter and over Europe where the surface network adequately describes fluxes on our model spatial and temporal grid. We use CarbonTracker and GEOS-Chem XCO2 model output to investigate model error on quantifying proxy GOSAT XCH4 (involving model XCO2) and inferring methane flux estimates from surface mole fraction data and show similar resulting fluxes, with differences reflecting initial differences in the proxy value. Using a series of observing system simulation experiments (OSSEs) we characterize the posterior flux error introduced by non-uniform atmospheric sampling by GOSAT. We show that clear-sky measurements can theoretically reproduce fluxes within 10% of true values, with the exception of tropical regions where, due to a large seasonal cycle in the number of measurements because of clouds and aerosols, fluxes are within 15% of true fluxes. We evaluate our posterior methane fluxes by incorporating them into GEOS-Chem and sampling the model at the location and time of surface CH4 measurements from the AGAGE (Advanced Global Atmospheric Gases Experiment) network and column XCH4 measurements from TCCON (Total Carbon Column Observing Network). The posterior fluxes modestly improve the model agreement with AGAGE and TCCON data relative to prior fluxes, with the correlation coefficients (r2) increasing by a mean of 0.04 (range: -0.17 to 0.23) and the biases decreasing by a mean of 0.4 ppb (range: -8.9 to 8.4 ppb).

Estimating regional methane surface fluxes: the relative importance of surface and GOSAT mole fraction measurements

NASA Astrophysics Data System (ADS)

Fraser, A.; Palmer, P. I.; Feng, L.; Boesch, H.; Cogan, A.; Parker, R.; Dlugokencky, E. J.; Fraser, P. J.; Krummel, P. B.; Langenfelds, R. L.; O'Doherty, S.; Prinn, R. G.; Steele, L. P.; van der Schoot, M.; Weiss, R. F.

2012-12-01

We use an ensemble Kalman filter (EnKF), together with the GEOS-Chem chemistry transport model, to estimate regional monthly methane (CH4) fluxes for the period June 2009-December 2010 using proxy dry-air column-averaged mole fractions of methane (XCH4) from GOSAT (Greenhouse gases Observing SATellite) and/or NOAA ESRL (Earth System Research Laboratory) and CSIRO GASLAB (Global Atmospheric Sampling Laboratory) CH4 surface mole fraction measurements. Global posterior estimates using GOSAT and/or surface measurements are between 510-516 Tg yr-1, which is less than, though within the uncertainty of, the prior global flux of 529 ± 25 Tg yr-1. We find larger differences between regional prior and posterior fluxes, with the largest changes (75 Tg yr-1) occurring in Temperate Eurasia. In non-boreal regions the error reductions for inversions using the GOSAT data are at least three times larger (up to 45%) than if only surface data are assimilated, a reflection of the greater spatial coverage of GOSAT, with the two exceptions of latitudes > 60° associated with a data filter and over Europe where the surface network adequately describes fluxes on our model spatial and temporal grid. We use CarbonTracker and GEOS-Chem XCO2 model output to investigate model error on quantifying proxy GOSAT XCH4 (involving model XCO2) and inferring methane flux estimates from surface mole fraction data and show similar resulting fluxes, with differences reflecting initial differences in the proxy value. Using a series of observing system simulation experiments (OSSEs) we characterize the posterior flux error introduced by non-uniform atmospheric sampling by GOSAT. We show that clear-sky measurements can theoretically reproduce fluxes within 5% of true values, with the exception of South Africa and Tropical South America where, due to a large seasonal cycle in the number of measurements because of clouds and aerosols, fluxes are within 17% and 19% of true fluxes, respectively. We evaluate our posterior methane fluxes by incorporating them into GEOS-Chem and sampling the model at the location and time of independent surface CH4 measurements from the AGAGE (Advanced Global Atmospheric Gases Experiment) network and column XCH4 measurements from TCCON (Total Carbon Column Observing Network). The posterior fluxes modestly improve the model agreement with AGAGE and TCCON data relative to prior fluxes, with the correlation coefficients (r2) increasing by a mean of 0.04 (range: -0.17, 0.23) and the biases decreasing by a mean of 0.4 ppb (range: -8.9, 8.4 ppb).

STELLTRANS: A Transport Analysis Suite for Stellarators

NASA Astrophysics Data System (ADS)

Mittelstaedt, Joseph; Lazerson, Samuel; Pablant, Novimir; Weir, Gavin; W7-X Team

2016-10-01

The stellarator transport code STELLTRANS allows us to better analyze the power balance in W7-X. Although profiles of temperature and density are measured experimentally, geometrical factors are needed in conjunction with these measurements to properly analyze heat flux densities in stellarators. The STELLTRANS code interfaces with VMEC to find an equilibrium flux surface configuration and with TRAVIS to determine the RF heating and current drive in the plasma. Stationary transport equations are then considered which are solved using a boundary value differential equation solver. The equations and quantities considered are averaged over flux surfaces to reduce the system to an essentially one dimensional problem. We have applied this code to data from W-7X and were able to calculate the heat flux coefficients. We will also present extensions of the code to a predictive capacity which would utilize DKES to find neoclassical transport coefficients to update the temperature and density profiles.

Ensemble formulation of surface fluxes and improvement in evapotranspiration and cloud parameterizations in a GCM. [General Circulation Model

NASA Technical Reports Server (NTRS)

Sud, Y. C.; Smith, W. E.

1984-01-01

The influence of some modifications to the parameters of the current general circulation model (GCM) is investigated. The aim of the modifications was to eliminate strong occasional bursts of oscillations in planetary boundary layer (PBL) fluxes. Smoothly varying bulk aerodynamic friction and heat transport coefficients were found by ensemble averaging of the PBL fluxes in the current GCM. A comparison was performed of the simulations of the modified model and the unmodified model. The comparison showed that the surface fluxes and cloudiness in the modified model simulations were much more accurate. The planetary albedo in the model was also realistic. Weaknesses persisted in the models positioning of the Inter-tropical convergence zone (ICTZ) and in the temperature estimates for polar regions. A second simulation of the model following reparametrization of the cloud data showed improved results and these are described in detail.

The Temperature and Structure Dependence of Surface Tension of CaO-SiO2-Na2O-CaF2 Mold Fluxes

NASA Astrophysics Data System (ADS)

Gao, Qiang; Min, Yi; Jiang, Maofa

2018-06-01

The surface tension of mold flux is one of the most important properties and varies with the temperature from the top to the bottom of the mold, which influences the adhesion and lubrication between the liquid mold flux and the solidified shell, further influencing the quality of the continuous billet. In the present paper, the effect of temperature on the surface tension of CaO-SiO2-Na2O-CaF2 mold-flux melts with different CaO/SiO2 mass ratios was investigated using the maximum-pull method. Furthermore, the microstructure of mold fluxes was analyzed using FT-IR and Raman spectra to discuss the change mechanism of surface tension. The results indicated that the temperature dependence of surface tension was different with different CaO/SiO2 mass ratios, and agreed with the modification of melt structure. When the CaO/SiO2 mass ratio was 0.67 and 0.85, the change of surface tension with temperature was relatively stable, and the influence of temperature on the structure was small. When the CaO/SiO2 mass ratio was 1.03 and 1.16, with an increase of temperature, the surface tension decreased linearly and the changing amplitude was large; the degree of polymerization of melts and average radii of silicon-oxygen anions also decreased, which intensified the molecular thermal motion and weakened the intermolecular interaction, resulting in a decrease of surface tension of melts.

The Temperature and Structure Dependence of Surface Tension of CaO-SiO2-Na2O-CaF2 Mold Fluxes

NASA Astrophysics Data System (ADS)

Gao, Qiang; Min, Yi; Jiang, Maofa

2018-02-01

The surface tension of mold flux is one of the most important properties and varies with the temperature from the top to the bottom of the mold, which influences the adhesion and lubrication between the liquid mold flux and the solidified shell, further influencing the quality of the continuous billet. In the present paper, the effect of temperature on the surface tension of CaO-SiO2-Na2O-CaF2 mold-flux melts with different CaO/SiO2 mass ratios was investigated using the maximum-pull method. Furthermore, the microstructure of mold fluxes was analyzed using FT-IR and Raman spectra to discuss the change mechanism of surface tension. The results indicated that the temperature dependence of surface tension was different with different CaO/SiO2 mass ratios, and agreed with the modification of melt structure. When the CaO/SiO2 mass ratio was 0.67 and 0.85, the change of surface tension with temperature was relatively stable, and the influence of temperature on the structure was small. When the CaO/SiO2 mass ratio was 1.03 and 1.16, with an increase of temperature, the surface tension decreased linearly and the changing amplitude was large; the degree of polymerization of melts and average radii of silicon-oxygen anions also decreased, which intensified the molecular thermal motion and weakened the intermolecular interaction, resulting in a decrease of surface tension of melts.

The influence of idealized surface heterogeneity on virtual turbulent flux measurements

NASA Astrophysics Data System (ADS)

De Roo, Frederik; Mauder, Matthias

2018-04-01

The imbalance of the surface energy budget in eddy-covariance measurements is still an unsolved problem. A possible cause is the presence of land surface heterogeneity, which affects the boundary-layer turbulence. To investigate the impact of surface variables on the partitioning of the energy budget of flux measurements in the surface layer under convective conditions, we set up a systematic parameter study by means of large-eddy simulation. For the study we use a virtual control volume approach, which allows the determination of advection by the mean flow, flux-divergence and storage terms of the energy budget at the virtual measurement site, in addition to the standard turbulent flux. We focus on the heterogeneity of the surface fluxes and keep the topography flat. The surface fluxes vary locally in intensity and these patches have different length scales. Intensity and length scales can vary for the two horizontal dimensions but follow an idealized chessboard pattern. Our main focus lies on surface heterogeneity of the kilometer scale, and one order of magnitude smaller. For these two length scales, we investigate the average response of the fluxes at a number of virtual towers, when varying the heterogeneity length within the length scale and when varying the contrast between the different patches. For each simulation, virtual measurement towers were positioned at functionally different positions (e.g., downdraft region, updraft region, at border between domains, etc.). As the storage term is always small, the non-closure is given by the sum of the advection by the mean flow and the flux-divergence. Remarkably, the missing flux can be described by either the advection by the mean flow or the flux-divergence separately, because the latter two have a high correlation with each other. For kilometer scale heterogeneity, we notice a clear dependence of the updrafts and downdrafts on the surface heterogeneity and likewise we also see a dependence of the energy partitioning on the tower location. For the hectometer scale, we do not notice such a clear dependence. Finally, we seek correlators for the energy balance ratio in the simulations. The correlation with the friction velocity is less pronounced than previously found, but this is likely due to our concentration on effectively strongly to freely convective conditions.

Comparative study of elemental mercury flux measurement techniques over a Fennoscandian boreal peatland

NASA Astrophysics Data System (ADS)

Osterwalder, S.; Sommar, J.; Åkerblom, S.; Jocher, G.; Fritsche, J.; Nilsson, M. B.; Bishop, K.; Alewell, C.

2018-01-01

Quantitative estimates of the land-atmosphere exchange of gaseous elemental mercury (GEM) are biased by the measurement technique employed, because no standard method or scale in space and time are agreed upon. Here we present concurrent GEM exchange measurements over a boreal peatland using a novel relaxed eddy accumulation (REA) system, a rectangular Teflon® dynamic flux chamber (DFC) and a DFC designed according to aerodynamic considerations (Aero-DFC). During four consecutive days the DFCs were placed alternately on two measurement plots in every cardinal direction around the REA sampling mast. Spatial heterogeneity in peat surface characteristics (0-34 cm) was identified by measuring total mercury in eight peat cores (57 ± 8 ng g-1, average ± SE), vascular plant coverage (32-52%), water table level (4.5-14.1 cm) and dissolved gaseous elemental mercury concentrations (28-51 pg L-1) in the peat water. The GEM fluxes measured by the DFCs showed a distinct diel pattern, but no spatial difference in the average fluxes was detected (ANOVA, α = 0.05). Even though the correlation between the Teflon® DFC and Aero-DFC was significant (r = 0.76, p < 0.05) the cumulative flux of the Aero-DFC was a factor of three larger. The average flux of the Aero-DFC (1.9 ng m-2 h-1) and REA (2 ng m-2 h-1) were in good agreement. The results indicate that the novel REA design is in agreement for cumulative flux estimates with the Aero-DFC, which incorporates the effect of atmospheric turbulence. The comparison was performed over a fetch with spatially rather homogenous GEM flux dynamics under fairly consistent weather conditions, minimizing the effect of weather influence on the data from the three measurement systems. However, in complex biomes with heterogeneous surface characteristics where there can be large spatial variability in GEM gas exchange, the small footprint of chambers (<0.2 m2) makes for large coefficients of variation. Thus many chamber measurement replications are needed to establish a credible biome GEM flux estimate, even for a single point in time. Dynamic flux chambers will, however, be able to resolve systematic differences between small scale features, such as experimentally manipulated plots or small scale spatial heterogeneity.

Aircraft- and tower-based fluxes of carbon dioxide, latent, and sensible heat

NASA Technical Reports Server (NTRS)

Desjardins, R. L.; Hart, R. L.; Macpherson, J. I.; Schuepp, P. H.; Verma, S. B.

1992-01-01

Fluxes of carbon dioxide, water vapor, and sensible heat obtained over a grassland ecosystem, during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE), using an aircraft- and two tower-based systems are compared for several days in 1987 and in 1989. The tower-based cospectral estimates of CO2, sensible heat, water vapor, and momentum, expressed as a function of wavenumber K times sampling height z, are relatively similar to the aircraft-based estimates for K x z greater than 0.1. A measurable contribution to the fluxes is observed by tower-based systems at K x z less than 0.01 but not by the aircraft-based system operating at an altitude of approximately 100 m over a 15 x 15 km area. Using all available simultaneous aircraft and tower data, flux estimates by both systems were shown to be highly correlated. As expected from the spatial variations of the greenness index, surface extrapolation of airborne flux estimates tended to lie between those of the two tower sites. The average fluxes obtained, on July 11, 1987, and August 4, 1989, by flying a grid pattern over the FIFE site agreed with the two tower data sets for CO2, but sensible and latent heat were smaller than those obtained by the tower-based systems. However, in general, except for a small underestimation due to the long wavelength contributions and due to flux divergence with height, the differences between the aircraft- and tower-based surface estimates of fluxes appear to be mainly attributable to differences in footprint, that is, differences in the area contributing to the surface flux estimates.

Characterization of Single Phase and Two Phase Heat and Momentum Transport in a Spiraling Radial Inow Microchannel Heat Sink

NASA Astrophysics Data System (ADS)

Ruiz, Maritza

Thermal management of systems under high heat fluxes on the order of hundreds of W/cm2 is important for the safety, performance and lifetime of devices, with innovative cooling technologies leading to improved performance of electronics or concentrating solar photovoltaics. A novel, spiraling radial inflow microchannel heat sink for high flux cooling applications, using a single phase or vaporizing coolant, has demonstrated enhanced heat transfer capabilities. The design of the heat sink provides an inward swirl flow between parallel, coaxial disks that form a microchannel of 1 cm radius and 300 micron channel height with a single inlet and a single outlet. The channel is heated on one side through a conducting copper surface, and is essentially adiabatic on the opposite side to simulate a heat sink scenario for electronics or concentrated photovoltaics cooling. Experimental results on the heat transfer and pressure drop characteristics in the heat sink, using single phase water as a working fluid, revealed heat transfer enhancements due to flow acceleration and induced secondary flows when compared to unidirectional laminar fully developed flow between parallel plates. Additionally, thermal gradients on the surface are small relative to the bulk fluid temperature gain, a beneficial feature for high heat flux cooling applications. Heat flux levels of 113 W/cm2 at a surface temperature of 77 deg C were reached with a ratio of pumping power to heat rate of 0.03%. Analytical models on single phase flow are used to explore the parametric trends of the flow rate and passage geometry on the streamlines and pressure drop through the device. Flow boiling heat transfer and pressure drop characteristics were obtained for this heat sink using water at near atmospheric pressure as the working fluid for inlet subcooling levels ranging from 20 to 80 deg C and mean mass flux levels ranging from 184-716 kg/m. 2s. Flow enhancements similar to singlephase flow were expected, as well as enhancements due to increased buoyant forces on vapor bubbles resulting from centripetal acceleration in the flow which will tend to draw the vapor towards the outlet. This can also aid in the reduction of vapor obstruction of the flow. The flow was identified as transitioning through three regimes as the heat rate was increased: partial subcooled flow boiling, oscillating boiling and fully developed flow boiling. During partial subcooled flow boiling, both forced convective and nucleate boiling effects are important. During oscillating boiling, the system fluctuated between partial subcooled flow boiling and fully developed nucleate boiling. Temperature and pressure oscillations were significant in this regime and are likely due to bubble constriction of flow in the microchannel. This regime of boiling is generally undesirable due to the large oscillations in temperatures and pressure and design constraints should be established to avoid large oscillations from occurring. During fully developed flow boiling, water vapor rapidly leaves the surface and the flow does not sustain large oscillations. Reducing inlet subcooling levels was found to reduce the magnitude of oscillations in the oscillating boiling regime. Additionally, reduced inlet subcooling levels reduced the average surface temperature at the highest heat flux levels tested when heat transfer was dominated by nucleate boiling, yet increased the average surface temperatures at low heat flux levels when heat transfer was dominated by forced convection. Experiments demonstrated heat fluxes up to 301 W/cm. 2at an average surface temperature of 134 deg C under partial subcooled flow boiling conditions. At this peak heat flux, the system required a pumping power to heat rate ratio of 0.01%. This heat flux is 2.4 times the typical values for critical heat flux in pool boiling under similar conditions.

Turbulent variance characteristics of temperature and humidity over a non-uniform land surface for an agricultural ecosystem in China

NASA Astrophysics Data System (ADS)

Gao, Z. Q.; Bian, L. G.; Chen, Z. G.; Sparrow, M.; Zhang, J. H.

2006-05-01

This paper describes the application of the variance method for flux estimation over a mixed agricultural region in China. Eddy covariance and flux variance measurements were conducted in a near-surface layer over a non-uniform land surface in the central plain of China from 7 June to 20 July 2002. During this period, the mean canopy height was about 0.50 m. The study site consisted of grass (10% of area), beans (15%), corn (15%) and rice (60%). Under unstable conditions, the standard deviations of temperature and water vapor density (normalized by appropriate scaling parameters), observed by a single instrument, followed the Monin-Obukhov similarity theory. The similarity constants for heat (C-T) and water vapor (C-q) were 1.09 and 1.49, respectively. In comparison with direct measurements using eddy covariance techniques, the flux variance method, on average, underestimated sensible heat flux by 21% and latent heat flux by 24%, which may be attributed to the fact that the observed slight deviations (20% or 30% at most) of the similarity "constants" may be within the expected range of variation of a single instrument from the generally-valid relations.

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.

Dissolved inorganic nitrogen pools and surface flux under different brackish marsh vegetation types, common reed (Phragmites australis) and salt hay (Spartina patens)

USGS Publications Warehouse

Windham-Myers, L.

2005-01-01

The current expansion of Phragmites australis into the high marsh shortgrass (Spartina patens, Distichlis spicata) communities of eastern U.S. salt marshes provided an opportunity to identify the influence of vegetation types on pools and fluxes of dissolved inorganic nitrogen (DIN). Two brackish tidal marshes of the National Estuarine Research Reserve system were examined, Piermont Marsh of the Hudson River NERR in New York and Hog Island in the Jacques Coustaeu NERR of New Jersey. Pools of DIN in porewater and rates of DIN surface flux were compared in replicated pairs of recently-expanded P. australis and neighboring S. patens-dominated patches on the high marsh surface. Both marshes generally imported nitrate (NO3-) and exported ammonium (NH4+), such that overall DIN was exported. No differences in surface exchange of NO3- or NH4+ were observed between vegetation types. Depth-averaged porewater NH4+ concentrations over the entire growing season were 56% lower under P. australis than under S. patens (average 1.4 vs. 3.2 mg NH4+ L-1) with the most profound differences in November. Porewater profiles showed an accumulation of NH4+ at depth in S. patens and constant low concentrations in P. australis from the soil surface to 50 cm depth, with no significant differences in porewater salinity. Despite these profound differences in porewater, NH 4+ diffusion from soils of P. australis and S. patens were not measurably different, were similar to other published rates, and were well below estimated rates based on passive diffusion alone. Rapid adsorption and uptake by litter and microbes in surface soils of both communities may buffer NH4+ loss to flooding tides in both communities, thereby reducing the impact of P. australis invasion on NH4+ flux to flooding waters. ?? Springer 2005.

Quantifying the Observability of CO2 Flux Uncertainty in Atmospheric CO2 Records Using Products from Nasa's Carbon Monitoring Flux Pilot Project

NASA Technical Reports Server (NTRS)

Ott, Lesley; Pawson, Steven; Collatz, Jim; Watson, Gregg; Menemenlis, Dimitris; Brix, Holger; Rousseaux, Cecile; Bowman, Kevin; Bowman, Kevin; Liu, Junjie;

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.

The Effect of Soil Hydraulic Properties vs. Soil Texture in Land Surface Models

NASA Technical Reports Server (NTRS)

Gutmann, E. D.; Small, E. E.

2005-01-01

This study focuses on the effect of Soil Hydraulic Property (SHP) selection on modeled surface fluxes following a rain storm in a semi-arid environment. SHPs are often defined based on a Soil Texture Class (STC). To examine the effectiveness of this approach, the Noah land surface model was run with each of 1306 soils in a large SHP database. Within most STCs, the outputs have a range of 350 W/m2 for latent and sensible heat fluxes, and 8K for surface temperature. The average difference between STC median values is only 100 W/m2 for latent and sensible heat. It is concluded that STC explains 5-15% of the variance in model outputs and should not be used to determine SHPs.

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.

The Plumbing of Land Surface Models: Is Poor Performance a Result of Methodology or Data Quality?

NASA Technical Reports Server (NTRS)

Haughton, Ned; Abramowitz, Gab; Pitman, Andy J.; Or, Dani; Best, Martin J.; Johnson, Helen R.; Balsamo, Gianpaolo; Boone, Aaron; Cuntz, Matthais; Decharme, Bertrand;

Scintillometer measurements above the urban area of London

NASA Astrophysics Data System (ADS)

Pauscher, Lukas; Salmond, Jennifer; Grimmond, C. S. B.; Foken, Thomas

2010-05-01

The spatial heterogeneity of urban surfaces presents a particular challenge to the measurement of turbulent fluxes. This is particularly true close to the urban surface (in the roughness sub-layer (RSL)) where the mosaic of roof top and street canyon surfaces present a complex three dimensional source area. Scintillometery, which offers the ability to make path-averaged measurements of turbulent fluxes of heat and momentum, provides an alternative approach to obtaining more spatially representative data sets in the RSL. In this study three Scintec small aperture scintillometers (SLS 20) were used to measure the sensible heat flux (QH) at a densely built up site at Strand Campus, King's College London, UK. Two different surfaces (courtyard and rooftop) characteristic of the urban environment were investigated simultaneously. One of the SLS was aligned just atop a courtyard (z/zH= 0.9), while the other two were set up in two different heights (z/zH= 1 and z/zH= 1.25) above a rooftop line. Where zH is the mean building height and z is the measurement height above ground level. Special consideration was given to the estimation of the displacement height and the influence of the Monin-Obukov function used for the analysis. To estimate the contribution of the different surface types to the observed fluxes a footprint analysis was carried out for the two rooftop SLS and the eddy covariance system. Fluxes from the two SLS above the rooftop generally agreed well with each other and exhibited a pronounced diurnal cycle. They also showed similar patterns and magnitudes as those measured by an eddy covariance system located close by. In contrast, diurnal flux patterns derived from the measurements atop the courtyard showed marked differences, especially during day time when fluxes often remained smaller.

Dissolved methane concentrations in the water column and surface sediments of Hanna Shoal and Barrow Canyon, Northern Chukchi Sea

NASA Astrophysics Data System (ADS)

Lapham, Laura; Marshall, Kathleen; Magen, Cédric; Lyubchich, Viacheslav; Cooper, Lee W.; Grebmeier, Jacqueline M.

2017-10-01

Current estimates of methane (CH4) flux suggest that Arctic shelves may be a significant source of atmospheric CH4, a potent greenhouse gas. However, little information is known about the CH4 flux from most Arctic shelves, other than the East Siberian Arctic Shelf. We report here dissolved CH4 concentrations in the water column and within surface sediments of the Northern Chukchi Sea. We hypothesized that this area contains high concentrations of CH4 because it receives nutrient rich waters through the Bering Strait, promoting primary production that enhances an organic-rich material flux to the seafloor and eventual microbial methanogenesis in the sediments. In August 2012, as part of the Chukchi Sea Offshore Monitoring in Drilling Area (COMIDA) project, fourteen stations were sampled on Hanna Shoal, a shallow feature on the shelf, and ten stations across the undersea Barrow Canyon. On Hanna Shoal, water column CH4 concentrations ranged from 14 to 74 nM, and surface concentrations were up to 15 times supersaturated in CH4 compared to equilibrium with the average atmospheric concentrations (3 nM). CH4 concentrations at the sediment-water interface were around 1,500 nM, and typically increased with depth in the sediment. At the head of Barrow Canyon, water column CH4 concentrations ranged from 5 to 46 nM, with the highest concentrations in the deepest waters that were sampled (118 m). Overall, the calculated fluxes to the atmosphere ranged from 1 to 80 μmol CH4 m-2 d-1 for Hanna Shoal and 4 to 17 μmol CH4 m-2 d-1 across the Barrow Canyon stations. Although there was a large range in these fluxes, the average atmospheric flux (20 μmol CH4 m-2 d-1) across Hanna Shoal was 12 times lower than the flux reported from the East Siberian Arctic Shelf in summer. We conclude that while there is a positive flux of CH4 to the atmosphere, this part of the Chukchi Sea is not a significant source of atmospheric CH4 compared to the East Siberian Sea shelf.

THE FIRST LUNAR MAP OF THE AVERAGE SOIL ATOMIC MASS

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

O. GASNAULT; W. FELDMAN; ET AL

2001-01-01

Measurements of indexes of lunar surface composition were successfully made during Lunar Prospector (LP) mission, using the Neutron Spectrometers (NS) [1]. This capability is demonstrated for fast neutrons in Plates 1 of Maurice et al. [2] (similar to Figure 2 here). Inspection shows a clear distinction between mare basalt (bright) and highland terranes [2]. Fast neutron simulations demonstrate the sensitivity of the fast neutron leakage flux to the presence of iron and titanium in the soil [3]. The dependence of the flux to a third element (calcium or aluminum) was also suspected [4]. We expand our previous work in thismore » study by estimating fast neutron leakage fluxes for a more comprehensive set of assumed lunar compositions. We find a strong relationship between the fast neutron fluxes and the average soil atomic mass: . This relation can be inverted to provide a map of from the measured map of fast neutrons from the Moon.« less

Distributed Sensible Heat Flux Measurements for Wireless Sensor Networks

NASA Astrophysics Data System (ADS)

Huwald, H.; Brauchli, T.; Lehning, M.; Higgins, C. W.

2015-12-01

The sensible heat flux component of the surface energy balance is typically computed using eddy covariance or two point profile measurements while alternative approaches such as the flux variance method based on convective scaling has been much less explored and applied. Flux variance (FV) certainly has a few limitations and constraints but may be an interesting and competitive method in low-cost and power limited wireless sensor networks (WSN) with the advantage of providing spatio-temporal sensible heat flux over the domain of the network. In a first step, parameters such as sampling frequency, sensor response time, and averaging interval are investigated. Then we explore the applicability and the potential of the FV method for use in WSN in a field experiment. Low-cost sensor systems are tested and compared against reference instruments (3D sonic anemometers) to evaluate the performance and limitations of the sensors as well as the method with respect to the standard calculations. Comparison experiments were carried out at several sites to gauge the flux measurements over different surface types (gravel, grass, water) from the low-cost systems. This study should also serve as an example of spatially distributed sensible heat flux measurements.

Estimation of nocturnal CO2 and N2O soil emissions from changes in surface boundary layer mass storage

NASA Astrophysics Data System (ADS)

Grant, Richard H.; Omonode, Rex A.

2018-04-01

Annual budgets of greenhouse and other trace gases require knowledge of the emissions throughout the year. Unfortunately, emissions into the surface boundary layer during stable, calm nocturnal periods are not measurable using most micrometeorological methods due to non-stationarity and uncoupled flow. However, during nocturnal periods with very light winds, carbon dioxide (CO2) and nitrous oxide (N2O) frequently accumulate near the surface and this mass accumulation can be used to determine emissions. Gas concentrations were measured at four heights (one within and three above canopy) and turbulence was measured at three heights above a mature 2.5 m maize canopy from 23 July to 10 September 2015. Nocturnal CO2 and N2O fluxes from the canopy were determined using the accumulation of mass within a 6.3 m control volume and out the top of the control volume within the nocturnal surface boundary layer. Diffusive fluxes were estimated by flux gradient method. The total accumulative and diffusive fluxes during near-calm nights (friction velocities < 0.05 ms-1) averaged 1.16 µmol m-2 s-1 CO2 and 0.53 nmol m-2 s-1 N2O. Fluxes were also measured using chambers. Daily mean CO2 fluxes determined by the accumulation method were 90 to 130 % of those determined using soil chambers. Daily mean N2O fluxes determined by the accumulation method were 60 to 80 % of that determined using soil chambers. The better signal-to-noise ratios of the chamber method for CO2 over N2O, non-stationary flow, assumed Schmidt numbers, and anemometer tilt were likely contributing reasons for the differences in chambers versus accumulated nocturnal mass flux estimates. Near-surface N2O accumulative flux measurements in more homogeneous regions and with greater depth are needed to confirm the conclusion that mass accumulation can be effectively used to estimate soil emissions during nearly calm nights.

Arctic ocean radiative fluxes and cloud forcing estimated from the ISCCP C2 cloud dataset, 1983-1990

NASA Technical Reports Server (NTRS)

Schweiger, Axel J.; Key, Jeffrey R.

1994-01-01

Radiative fluxes and cloud forcings for the ocean areas of the Arctic are computed from the monthly cloud product of the International Satellite Cloud Climatology Project (ISCCP) for 1983-90. Spatially averaged short-wave fluxes are compared well with climatological values, while downwelling longwave fluxes are significantly lower. This is probably due to the fact that the ISCCP cloud amounts are underestimates. Top-of-the-atmosphere radiative fluxes are in excellent agreement with measurements from the Earth Radiation Budget Experiment (ERBE). Computed cloud forcings indicate that clouds have a warming effect at the surface and at the top of the atmosphere during winter and a cooling effect during summer. The net radiative effect of clouds is larger at the surface during winter but greater at the top of the atmosphere during summer. Overall the net radiative effect of clouds at the top of the atmosphere is one of cooling. This is in contrast to a previous result from ERBE data showing arctic cloud forcings have a net warming effect. Sensitivities to errors in input parameters are generally greater during winter with cloud amount being the most important paarameter. During summer the surface radiation balance is most sensitive to errors in the measurements of surface reflectance. The results are encouraging, but the estimated error of 20 W/sq m in surface net radiative fluxes is too large, given that estimates of the net radiative warming effect due to a doubling of CO2 are on the order of 4 W/sq m. Because it is difficult to determine the accuracy of results with existing in situ observations, it is recommended that the development of improved algorithms for the retrieval of surface radiative properties be accompanied by the simultaneous assembly of validation datasets.

[Distribution, flux and biological consumption of carbon monoxide in the East China Sea and the South Yellow Sea in summer].

PubMed

Wang, Jing; Lu, Xiao-Lan; Yang, Gui-Peng; Xu, Guan-Qiu

2014-11-01

Carbon monoxide (CO) concentration distribution, sea-to-air flux and microbial consumption rate constant, along with atmospheric CO mixing ratio, were measured in the East China Sea and the South Yellow Sea in summer. Atmospheric CO mixing ratios varied from 68 x 10(-9) -448 x 10(-9), with an average of 117 x 10(-9) (SD = 68 x 10(-9), n = 36). Overall, the concentrations of atmospheric CO displayed a decreasing trend from the coastal stations to the offshore stations. The surface water CO concentrations in the investigated area ranged from 0.23-7.10 nmol x L(-1), with an average of 2.49 nmol x L(-1) (SD = 2.11, n = 36). The surface water CO concentrations were significantly affected by sunlight. Vertical profiles showed that CO concentrations rapidly declined with depth, with the maximum values appearing in the surface water. CO concentrations exhibited obvious diurnal variations in the study area, with the maximum values being 6-40 folds higher than the minimum values. Minimal concentrations of CO all occurred before dawn. However, the maximal concentrations of CO occurred at noon. Marked diurnal variation in the concentrations of CO in the water column indicated that CO was produced primarily by photochemistry. The surface CO concentrations were oversaturated relative to the atmospheric concentrations and the saturation factors ranged from 1.99-99.18, with an average of 29.36 (SD = 24.42, n = 29). The East China Sea and the South Yellow Sea was a net source of atmospheric CO. The sea-to-air fluxes of CO in the East China Sea and the South Yellow Sea ranged 0.37-44.84 μmol x (m2 x d)(-1), with an average of 12.73 μmol x (m2 x d)(-1) (SD = 11.40, n = 29). In the incubation experiments, CO concentrations decreased exponentially with incubation time and the processes conformed to the first order reaction characteristics. The microbial CO consumption rate constants (K(co)) in the surface water ranged from 0.12 to 1.45 h(-1), with an average of 0.47 h(-1) (SD = 0.55, n = 5). A negative correlation between K(co) and salinity was observed in the present study.

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.

Simple map in action-angle coordinates

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

Kerwin, Olivia; Punjabi, Alkesh; Ali, Halima

A simple map [A. Punjabi, A. Verma, and A. Boozer, Phys. Rev. Lett. 69, 3322 (1992)] is the simplest map that has the topology of divertor tokamaks [A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys. Lett. A 364, 140 (2007)]. Here, action-angle coordinates, the safety factor, and the equilibrium generating function for the simple map are calculated analytically. The simple map in action-angle coordinates is derived from canonical transformations. This map cannot be integrated across the separatrix surface because of the singularity in the safety factor there. The stochastic broadening of the ideal separatrix surface in action-angle representationmore » is calculated by adding a perturbation to the simple map equilibrium generating function. This perturbation represents the spatial noise and field errors typical of the DIII-D [J. L. Luxon and L. E. Davis, Fusion Technol. 8, 441 (1985)] tokamak. The stationary Fourier modes of the perturbation have poloidal and toroidal mode numbers (m,n,)=((3,1),(4,1),(6,2),(7,2),(8,2),(9,3),(10,3),(11,3)) with amplitude {delta}=0.8x10{sup -5}. Near the X-point, about 0.12% of toroidal magnetic flux inside the separatrix, and about 0.06% of the poloidal flux inside the separatrix is lost. When the distance from the O-point to the X-point is 1 m, the width of stochastic layer near the X-point is about 1.4 cm. The average value of the action on the last good surface is 0.19072 compared to the action value of 3/5{pi} on the separatrix. The average width of stochastic layer in action coordinate is 2.7x10{sup -4}, while the average area of the stochastic layer in action-angle phase space is 1.69017x10{sup -3}. On average, about 0.14% of action or toroidal flux inside the ideal separatrix is lost due to broadening. Roughly five times more toroidal flux is lost in the simple map than in DIII-D for the same perturbation [A. Punjabi, H. Ali, A. Boozer, and T. Evans, Bull. Amer. Phys. Soc. 52, 124 (2007)].« less

Simple map in action-angle coordinates

NASA Astrophysics Data System (ADS)

Kerwin, Olivia; Punjabi, Alkesh; Ali, Halima

2008-07-01

A simple map [A. Punjabi, A. Verma, and A. Boozer, Phys. Rev. Lett. 69, 3322 (1992)] is the simplest map that has the topology of divertor tokamaks [A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys. Lett. A 364, 140 (2007)]. Here, action-angle coordinates, the safety factor, and the equilibrium generating function for the simple map are calculated analytically. The simple map in action-angle coordinates is derived from canonical transformations. This map cannot be integrated across the separatrix surface because of the singularity in the safety factor there. The stochastic broadening of the ideal separatrix surface in action-angle representation is calculated by adding a perturbation to the simple map equilibrium generating function. This perturbation represents the spatial noise and field errors typical of the DIII-D [J. L. Luxon and L. E. Davis, Fusion Technol. 8, 441 (1985)] tokamak. The stationary Fourier modes of the perturbation have poloidal and toroidal mode numbers (m,n,)={(3,1),(4,1),(6,2),(7,2),(8,2),(9,3),(10,3),(11,3)} with amplitude δ =0.8×10-5. Near the X-point, about 0.12% of toroidal magnetic flux inside the separatrix, and about 0.06% of the poloidal flux inside the separatrix is lost. When the distance from the O-point to the X-point is 1m, the width of stochastic layer near the X-point is about 1.4cm. The average value of the action on the last good surface is 0.19072 compared to the action value of 3/5π on the separatrix. The average width of stochastic layer in action coordinate is 2.7×10-4, while the average area of the stochastic layer in action-angle phase space is 1.69017×10-3. On average, about 0.14% of action or toroidal flux inside the ideal separatrix is lost due to broadening. Roughly five times more toroidal flux is lost in the simple map than in DIII-D for the same perturbation [A. Punjabi, H. Ali, A. Boozer, and T. Evans, Bull. Amer. Phys. Soc. 52, 124 (2007)].

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.

Visualization and Quality Control Web Tools for CERES Products

NASA Astrophysics Data System (ADS)

Mitrescu, C.; Doelling, D. R.; Rutan, D. A.

2016-12-01

The CERES project continues to provide the scientific community a wide variety of satellite-derived data products such as observed TOA broadband shortwave and longwave observed fluxes, computed TOA and Surface fluxes, as well as cloud, aerosol, and other atmospheric parameters. They encompass a wide range of temporal and spatial resolutions, suited to specific applications. Now in its 16-year, CERES products are mostly used by climate modeling communities that focus on global mean energetics, meridianal heat transport, and climate trend studies. In order to serve all our users, we developed a web-based Ordering and Visualization Tool (OVT). Using Opens Source Software such as Eclipse, java, javascript, OpenLayer, Flot, Google Maps, python, and others, the OVT Team developed a series of specialized functions to be used in the process of CERES Data Quality Control (QC). We mention 1- and 2-D histogram, anomaly, deseasonalization, temporal and spatial averaging, side-by-side parameter comparison, and others that made the process of QC far easier and faster, but more importantly far more portable. We are now in the process of integrating ground site observed surface fluxes to further facilitate the CERES project to QC the CERES computed surface fluxes. These features will give users the opportunity to perform their own comparisons of the CERES computed surface fluxes and observed ground site fluxes. An overview of the CERES OVT basic functions using Open Source Software, as well as future steps in expanding its capabilities will be presented at the meeting.

Comparative analysis of different underlying surfaces using a high-resolution assimilation dataset in semi-arid areas in China

NASA Astrophysics Data System (ADS)

Ruan, Jinshuai; Wen, Xiaohang; Fan, Guangzhou; Li, Deqin; Hua, Wei; Wang, Bingyun; Zhang, Yi; Zhang, Mingjun; Wang, Chao; Wang, Lei

2017-11-01

To study the land surface and atmospheric meteorological characteristics of non-uniform underlying surfaces in the semi-arid area of Northeast China, we use a "High-Resolution Assimilation Dataset of the water-energy cycle in China (HRADC)". The grid points of three different underlying surfaces were selected, and their meteorological elements were averaged for each type (i.e., mixed forest, grassland, and cropland). For 2009, we compared and analyzed the different components of leaf area index (LAI), soil temperature and moisture, surface albedo, precipitation, and surface energy for various underlying surfaces in Northeast China. The results indicated that the LAI of mixed forest and cropland during the summer is greater than 5 m2 m-2 and below 2.5 m2 m-2 for grassland; in the winter and spring seasons, the Green Vegetation Fraction (GVF) is below 30%. The soil temperature and moisture both vary greatly. Throughout the year, the mixed forest is dominated by latent heat evaporation; in grasslands and croplands, the sensible heat flux and the latent heat flux are approximately equal, and the GVF contributed more to latent heat flux than sensible heat flux in the summer. This study compares meteorological characteristics between three different underlying surfaces of the semi-arid area of Northeast China and makes up for the insufficiency of purely using observations for the study. This research is important for understanding the water-energy cycle and transport in the semi-arid area.

Forest Surface Energy Balance and Evapotranspiration Estimated From Four Eddy Covariance Towers

NASA Astrophysics Data System (ADS)

Rabbani, G. A.; Adam, J. C.; Elliot, W. J.; Liu, H.

2016-12-01

Evapotranspiration (ET), which refers to the combined effect of surface water evaporation and plant transpiration, is one of the vital elements of the global water balance. It is also an important process for plants, providing water, nutrient, and cooling needs, and helping to regulate carbon dioxide entry through open/closure of the plant's stomata. Quantifying ET in forested environments is an ongoing research area. Complex physiological responses with climatic variation, combined with difficulty in making wide-spread measurements, makes ET one of the least understood components of a forest water balance. The objective of this study is to estimate ET and energy balance closure by using flux net data from eddy covariance towers. ET is estimated for different forest types with multiple age classes during the years of 2011, 2012 and 2013. We studied two coniferous forests (F1, F2), one deciduous forest (F3) and one mixed forest (F4) in Washington, Wyoming, Wisconsin and New Jersey, respectively. Label 2 (Data checked and formatted by Carbon Dioxide Information Analysis Center) gap filled flux data were collected from the AmeriFlux database (ameriflux.ornl.gov). Discrepancies between turbulent fluxes and available energy are investigated. Among the studied forests, the highest and lowest average monthly ET are exhibited by the mixed forest (F4) and coniferous forest (F1) in 2012 which are 2,692 and 633 mm/month, respectively. Difference in average monthly ET can be an implication of substantial age difference between these two types of forest. The regression analysis showed significant correlation between turbulent fluxes and available energy (R2=0.91) for mixed forest where the discrepancy varied from 5-11%. Conversely, for coniferous and deciduous forests, the discrepancy varied from 46-49% and 28%, respectively, with almost similar correlation between the fluxes (0.86 and 0.84, respectively). This study will facilitate an improved understanding of how forest type and age pose differences in ET and surface energy components.

Eddy-Covariance Observations and Large-Eddy-Simulations of Near-Shore Fluxes from Water Bodies

NASA Astrophysics Data System (ADS)

Bohrer, G.; Rey Sanchez, C.; Kenny, W.; Morin, T. H.

2017-12-01

Eddy covariance (EC) measurement techniques are increasingly used in the study of lakes and coastal ecosystems. The sharp water-shore transitions in energy forcing and surface roughness are challenging the validity of the EC approach at these sites. We discuss the results of two seasonal campaigns to measure CO2 and water-vapor fluxes in coastal environments - a small lake in Michigan, and the water over a coral reef in the Red, Sea, Israel. We show that in both environments, horizontal advection of CO2 and water vapor is responsible to a non-negligible component of the total flux to/from the water. We used a two-tower approach to measure fluxes from the water and from the shore and calculate the advection and flux divergence between the two. An empirical footprint model was used to filter the observations and keep only the times when interference from the shore-line transition is minimal. Observations of both vertical turbulent fluxes and advection were gapfilled with a neural-network model, based on their observed relationships with environmental forcing. Gap-filled observations were used to determine the seasonal net fluxes for the tow ecosystems. We used Large-Eddy Simulations (LES) to conduct a case study of airflow patterns associated with a small inland lake surrounded by forest (i.e. radius of lake only ten times the height of the forest). We combined LES outputs with scalar dispersion simulations to model potential biases in EC flux measurements due to the heterogeneity of surface fluxes and vertical advection. Our simulations show that the lake-to-forest transition can induce a non-zero vertical wind component, which will strongly affect the interpretation of wind and flux measurements. Furthermore, significant horizontal gradients of CO2 are generated by the forest carbon sink and lake carbon source, which are further transported by local roughness-induced circulation. We simulated six hypothetical flux tower locations along a downwind gradient at various heights and calculated the effects of both average vertical advection and average turbulent flux divergence of CO2 at each.

The influence of neap-spring tidal variation and wave energy on sediment flux in salt marsh tidal creeks

USGS Publications Warehouse

Lacy, Jessica; Ferner, Matthew C.; Callaway, John C.

2018-01-01

Sediment flux in marsh tidal creeks is commonly used to gage sediment supply to marshes. We conducted a field investigation of temporal variability in sediment flux in tidal creeks in the accreting tidal marsh at China Camp State Park adjacent to northern San Francisco Bay. Suspended-sediment concentration (SSC), velocity, and depth were measured near the mouths of two tidal creeks during three six-to-ten-week deployments: two in winter and one in summer. Currents, wave properties and SSC were measured in the adjacent shallows. All deployments spanned the largest spring tides of the season. Results show that tidally-averaged suspended-sediment flux (SSF) in the tidal creeks decreased with increasing tidal energy, and SSF was negative (bayward) for tidal cycles with maximum water surface elevation above the marsh plain. Export during the largest spring tides dominated the cumulative SSF measured during the deployments. During ebb tides following the highest tides, velocities exceeded 1 m/s in the narrow tidal creeks, resulting in negative tidally-averaged water flux, and mobilizing sediment from the creek banks or bed. Storm surge also produced negative SSF. Tidally-averaged SSF was positive in wavey conditions with moderate tides. Spring-tide sediment export was about 50% less at a station 130 m further up the tidal creek than at the creek mouth. The negative tidally-averaged water flux near the creek mouth during spring tides indicates that in the lower marsh, some of the water flooding directly across the bay--marsh interface drains through the tidal creeks, and suggests that this interface may be a pathway for sediment supply to the lower marsh as well.

CERES Monthly Gridded Single Satellite Fluxes and Clouds (FSW) in HDF (CER_FSW_TRMM-PFM-VIRS_Beta1)

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A. (Principal Investigator); Barkstrom, Bruce R. (Principal Investigator)

The Monthly Gridded Radiative Fluxes and Clouds (FSW) product contains a month of space and time averaged Clouds and the Earth's Radiant Energy System (CERES) data for a single scanner instrument. The FSW is also produced for combinations of scanner instruments. All instantaneous fluxes from the CERES CRS product for a month are sorted by 1-degree spatial regions and by the Universal Time (UT) hour of observation. The mean of the instantaneous fluxes for a given region-hour bin is determined and recorded on the FSW along with other flux statistics and scene information. The mean adjusted fluxes at the four atmospheric levels defined by CRS are also included for both clear-sky and total-sky scenes. In addition, four cloud height categories are defined by dividing the atmosphere into four intervals with boundaries at the surface, 700-, 500-, 300-hPa, and the Top-of-the-Atmosphere (TOA). The cloud layers from CRS are put into one of the cloud height categories and averaged over the region. The cloud properties are also column averaged and included on the FSW. [Location=GLOBAL] [Temporal_Coverage: Start_Date=1998-01-01; Stop_Date=2000-03-31] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180] [Data_Resolution: Latitude_Resolution=1 degree; Longitude_Resolution=1 degree; Horizontal_Resolution_Range=100 km - < 250 km or approximately 1 degree - < 2.5 degrees; Temporal_Resolution=1 month; Temporal_Resolution_Range=Monthly - < Annual].

CERES Monthly Gridded Single Satellite Fluxes and Clouds (FSW) in HDF (CER_FSW_Terra-FM1-MODIS_Edition2C)

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A. (Principal Investigator); Barkstrom, Bruce R. (Principal Investigator)

The Monthly Gridded Radiative Fluxes and Clouds (FSW) product contains a month of space and time averaged Clouds and the Earth's Radiant Energy System (CERES) data for a single scanner instrument. The FSW is also produced for combinations of scanner instruments. All instantaneous fluxes from the CERES CRS product for a month are sorted by 1-degree spatial regions and by the Universal Time (UT) hour of observation. The mean of the instantaneous fluxes for a given region-hour bin is determined and recorded on the FSW along with other flux statistics and scene information. The mean adjusted fluxes at the four atmospheric levels defined by CRS are also included for both clear-sky and total-sky scenes. In addition, four cloud height categories are defined by dividing the atmosphere into four intervals with boundaries at the surface, 700-, 500-, 300-hPa, and the Top-of-the-Atmosphere (TOA). The cloud layers from CRS are put into one of the cloud height categories and averaged over the region. The cloud properties are also column averaged and included on the FSW. [Location=GLOBAL] [Temporal_Coverage: Start_Date=1998-01-01; Stop_Date=2005-12-31] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180] [Data_Resolution: Latitude_Resolution=1 degree; Longitude_Resolution=1 degree; Horizontal_Resolution_Range=100 km - < 250 km or approximately 1 degree - < 2.5 degrees; Temporal_Resolution=1 month; Temporal_Resolution_Range=Monthly - < Annual].

CERES) Monthly Gridded Single Satellite Fluxes and Clouds (FSW) in HDF (CER_FSW_Terra-FM2-MODIS_Edition2C)

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A. (Principal Investigator); Barkstrom, Bruce R. (Principal Investigator)

The Monthly Gridded Radiative Fluxes and Clouds (FSW) product contains a month of space and time averaged Clouds and the Earth's Radiant Energy System (CERES) data for a single scanner instrument. The FSW is also produced for combinations of scanner instruments. All instantaneous fluxes from the CERES CRS product for a month are sorted by 1-degree spatial regions and by the Universal Time (UT) hour of observation. The mean of the instantaneous fluxes for a given region-hour bin is determined and recorded on the FSW along with other flux statistics and scene information. The mean adjusted fluxes at the four atmospheric levels defined by CRS are also included for both clear-sky and total-sky scenes. In addition, four cloud height categories are defined by dividing the atmosphere into four intervals with boundaries at the surface, 700-, 500-, 300-hPa, and the Top-of-the-Atmosphere (TOA). The cloud layers from CRS are put into one of the cloud height categories and averaged over the region. The cloud properties are also column averaged and included on the FSW. [Location=GLOBAL] [Temporal_Coverage: Start_Date=1998-01-01; Stop_Date=2001-10-31] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180] [Data_Resolution: Latitude_Resolution=1 degree; Longitude_Resolution=1 degree; Horizontal_Resolution_Range=100 km - < 250 km or approximately 1 degree - < 2.5 degrees; Temporal_Resolution=1 month; Temporal_Resolution_Range=Monthly - < Annual].

Tailoring the charged particle fluxes across the target surface of Magnum-PSI

NASA Astrophysics Data System (ADS)

Costin, C.; Anita, V.; Popa, G.; Scholten, J.; De Temmerman, G.

2016-04-01

Linear plasma generators are plasma devices designed to study fusion-relevant plasma-surface interactions. The first requirement for such devices is to operate with adjustable and well characterized plasma parameters. In the linear plasma device Magnum-PSI, the distribution of the charged particle flux across the target surface can be tailored by the target bias. The process is based on the radial inhomogeneity of the plasma column and it is evidenced by electrical measurements via a 2D multi-probe system installed as target. Typical results are reported for a hydrogen discharge operated at 125 A and confined by a magnetic field strength of 0.95 T in the middle of the coils. The probes were biased in the range of  -80 to  -25 V, while the floating potential of the target was about  -35 V. The results were obtained in steady-state regime of Magnum-PSI, being time-averaged over any type of fluctuations. Depending on the relative value of the target bias voltage with respect to the local floating potential in the plasma column, the entire target surface can be exposed to ion or electron dominated flux, respectively, or it can be divided into two adjacent zones: one exposed to electron flux and the other to ion flux. As a consequence of this effect, a floating conductive surface that interacts with an inhomogeneous plasma is exposed to non-zero local currents despite its overall null current and it is subjected to internal current flows.

Effects of thermal vapor diffusion on seasonal dynamics of water in the unsaturated zone

USGS Publications Warehouse

Milly, Paul C.D.

1996-01-01

The response of water in the unsaturated zone to seasonal changes of temperature (T) is determined analytically using the theory of nonisothermal water transport in porous media, and the solutions are tested against field observations of moisture potential and bomb fallout isotopic (36Cl and 3H) concentrations. Seasonally varying land surface temperatures and the resulting subsurface temperature gradients induce thermal vapor diffusion. The annual mean vertical temperature gradient is close to zero; however, the annual mean thermal vapor flux is downward, because the temperature‐dependent vapor diffusion coefficient is larger, on average, during downward diffusion (occurring at high T) than during upward diffusion (low T). The annual mean thermal vapor flux is shown to decay exponentially with depth; the depth (about 1 m) at which it decays to e−1of its surface value is one half of the corresponding decay depth for the amplitude of seasonal temperature changes. This depth‐dependent annual mean flux is effectively a source of water, which must be balanced by a flux divergence associated with other transport processes. In a relatively humid environment the liquid fluxes greatly exceed the thermal vapor fluxes, so such a balance is readily achieved without measurable effect on the dynamics of water in the unsaturated zone. However, if the mean vertical water flux through the unsaturated zone is very small (<1 mm y−1), as it may be at many locations in a desert landscape, the thermal vapor flux must be balanced mostly by a matric‐potential‐induced upward flux of water. This return flux may include both vapor and liquid components. Below any near‐surface zone of weather‐related fluctuations of matric potential, maintenance of this upward flux requires an increase with depth in the annual mean matric potential; this theoretical prediction is supported by long‐term field measurements in the Chihuahuan Desert. The analysis also makes predictions, confirmed by the field observations, regarding the seasonal variations of matric potential at a given depth. The conceptual model of unsaturated zone water transport developed here implies the possibility of near‐surface trapping of any aqueous constituent introduced at the surface.

Impact of Te and ne on edge current density profiles in ELM mitigated regimes on ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Dunne, M. G.; Rathgeber, S.; Burckhart, A.; Fischer, R.; Giannone, L.; McCarthy, P. J.; Schneider, P. A.; Wolfrum, E.; the ASDEX Upgrade Team

2015-01-01

ELM resolved edge current density profiles are reconstructed using the CLISTE equilibrium code. As input, highly spatially and temporally resolved edge electron temperature and density profiles are used in addition to data from the extensive set of external poloidal field measurements available at ASDEX Upgrade, flux loop difference measurements, and current measurements in the scrape-off layer. Both the local and flux surface averaged current density profiles are analysed for several ELM mitigation regimes. The focus throughout is on the impact of altered temperature and density profiles on the current density. In particular, many ELM mitigation regimes rely on operation at high density. Two reference plasmas with type-I ELMs are analysed, one with a deuterium gas puff and one without, in order to provide a reference for the behaviour in type-II ELMy regimes and high density ELM mitigation with external magnetic perturbations at ASDEX Upgrade. For type-II ELMs it is found that while a similar pedestal top pressure is sustained at the higher density, the temperature gradient decreases in the pedestal. This results in lower local and flux surface averaged current densities in these phases, which reduces the drive for the peeling mode. No significant differences between the current density measured in the type-I phase and ELM mitigated phase is seen when external perturbations are applied, though the pedestal top density was increased. Finally, ELMs during the nitrogen seeded phase of a high performance discharge are analysed and compared to ELMs in the reference phase. An increased pedestal pressure gradient, which is the source of confinement improvement in impurity seeded discharges, causes a local current density increase. However, the increased Zeff in the pedestal acts to reduce the flux surface averaged current density. This dichotomy, which is not observed in other mitigation regimes, could act to stabilize both the ballooning mode and the peeling mode at the same time.

Long-term variation of mesopelagic biogenic flux in the central South China Sea: Impact of monsoonal seasonality and mesoscale eddy

NASA Astrophysics Data System (ADS)

Li, Hongliang; Wiesner, Martin G.; Chen, Jianfang; Ling, Zheng; Zhang, Jingjing; Ran, Lihua

2017-08-01

The East Asian Monsoon and mesoscale eddies are known to regulate primary production in South China Sea (SCS), the largest tropical marginal sea; however, their contributions to the deep biogenic flux are yet to be quantified. Based on 7-year time series sediment trap observations at the depth of 1200 m in the central SCS, we used the monthly average sinking biogenic fluxes to evaluate the impact of the monsoon and mesoscale cyclonic eddies on biogenic fluxes in combination with remote sensing physical parameters. The monthly average particulate organic carbon (POC) and opal fluxes, ranging from 3.0 to 5.2 and 14.8-34.9 mg m-2 d-1, respectively, were higher during the northeastern monsoon period. This corresponded to the deeper mixed layer depth and higher net primary production in this area, due to nutrient replenishment from the subsurface induced by monsoon transition and surface cooling. In contrast, lower POC and opal fluxes occurred during well-stratified inter-monsoon periods. In addition, CaCO3 flux (23.6-37.0 mg m-2 d-1) exhibited less seasonality and was assumed to originate from foraminifera. In terms of the long-term record, the combined effect of cyclonic eddies and mixing in the upper ocean could effectively regulate the temporal variation in the biogenic flux. In particular, the opal and POC fluxes in cyclonic eddies were 116% and 41% higher on average, respectively, than those during the non-cyclonic eddy period. Since the cyclonic eddies mainly occurred during the northeastern monsoon period, their contributions to biogenic flux via diatom blooms might overlap the regular winter flux peak, which could make the biological carbon pump more efficient at CO2 sequestration during this period thus amplifying the impact of seasonal transition.

Data-based estimates of the ocean carbon sink variability - results of the Surface Ocean pCO2 Mapping intercomparison (SOCOM)

NASA Astrophysics Data System (ADS)

Rödenbeck, Christian; Bakker, Dorothee; Gruber, Nicolas; Iida, Yosuke; Jacobson, Andy; Jones, Steve; Landschützer, Peter; Metzl, Nicolas; Nakaoka, Shin-ichiro; Olsen, Are; Park, Geun-Ha; Peylin, Philippe; Rodgers, Keith; Sasse, Tristan; Schuster, Ute; Shutler, James; Valsala, Vinu; Wanninkhof, Rik; Zeng, Jiye

2016-04-01

Using measurements of the surface-ocean COtwo partial pressure (pCOtwo) from the SOCAT and LDEO data bases and 14 different pCOtwo mapping methods recently collated by the Surface Ocean pCOtwo Mapping intercomparison (SOCOM) initiative, variations in regional and global sea-air COtwo fluxes are investigated. Though the available mapping methods use widely different approaches, we find relatively consistent estimates of regional pCOtwo seasonality, in line with previous estimates. In terms of interannual variability (IAV), all mapping methods estimate the largest variations to occur in the Eastern equatorial Pacific. Despite considerable spread in the detailed variations, mapping methods that fit the data more closely also tend to agree more closely with each other in regional averages. Encouragingly, this includes mapping methods belonging to complementary types - taking variability either directly from the pCOtwo data or indirectly from driver data via regression. From a weighted ensemble average, we find an IAV amplitude of the global sea-air COtwo flux of IAVampl (standard deviation over AnalysisPeriod), which is larger than simulated by biogeochemical process models. On a decadal perspective, the global ocean COtwo uptake is estimated to have gradually increased since about 2000, with little decadal change prior to that. The weighted mean net global ocean COtwo sink estimated by the SOCOM ensemble is -1.75 UPgCyr (AnalysisPeriod), consistent within uncertainties with estimates from ocean-interior carbon data or atmospheric oxygen trends. Using data-based sea-air COtwo fluxes in atmospheric COtwo inversions also helps to better constrain land-atmosphere COtwo fluxes.

The role of land surface fluxes in Saudi-KAU AGCM: Temperature climatology over the Arabian Peninsula for the period 1981-2010

NASA Astrophysics Data System (ADS)

Ashfaqur Rahman, M.; Almazroui, Mansour; Nazrul Islam, M.; O'Brien, Enda; Yousef, Ahmed Elsayed

2018-02-01

A new version of the Community Land Model (CLM) was introduced to the Saudi King Abdulaziz University Atmospheric Global Climate Model (Saudi-KAU AGCM) for better land surface component representation, and so to enhance climate simulation. CLM replaced the original land surface model (LSM) in Saudi-KAU AGCM, with the aim of simulating more accurate land surface fluxes globally, but especially over the Arabian Peninsula. To evaluate the performance of Saudi-KAU AGCM, simulations were completed with CLM and LSM for the period 1981-2010. In comparison with LSM, CLM generates surface air temperature values that are closer to National Centre for Environmental Prediction (NCEP) observations. The global annual averages of land surface air temperature are 9.51, 9.52, and 9.57 °C for NCEP, CLM, and LSM respectively, although the same atmospheric radiative and surface forcing from Saudi-KAU AGCM are provided to both LSM and CLM at every time step. The better temperature simulations when using CLM can be attributed to the more comprehensive plant functional type and hierarchical tile approach to the land cover type in CLM, along with better parameterization of upward land surface fluxes compared to LSM. At global scale, CLM exhibits smaller annual and seasonal mean biases of temperature with respect to NCEP data. Moreover, at regional scale, CLM demonstrates reasonable seasonal and annual mean temperature over the Arabian Peninsula as compared to the Climatic Research Unit (CRU) data. Finally, CLM generated better matches to single point-wise observations of surface air temperature and surface fluxes for some case studies.

The impact of the fast ion fluxes and thermal plasma loads on the design of the ITER fast ion loss detector

NASA Astrophysics Data System (ADS)

Kocan, M.; Garcia-Munoz, M.; Ayllon-Guerola, J.; Bertalot, L.; Bonnet, Y.; Casal, N.; Galdon, J.; Garcia-Lopez, J.; Giacomin, T.; Gonzalez-Martin, J.; Gunn, J. P.; Rodriguez-Ramos, M.; Reichle, R.; Rivero-Rodriguez, J. F.; Sanchis-Sanchez, L.; Vayakis, G.; Veshchev, E.; Vorpahl, C.; Walsh, M.; Walton, R.

2017-12-01

Thermal plasma loads to the ITER Fast Ion Loss Detector are studied for QDT = 10 burning plasma equilibrium using the 3D field line tracing. The simulations are performed for a FILD insertion 9-13 cm past the port plasma facing surface, optimized for fast ion measurements, and include the worst-case perturbation of the plasma boundary and the error in the magnetic reconstruction. The FILD head is exposed to superimposed time-averaged ELM heat load, static inter-ELM heat flux and plasma radiation. The study includes the estimate of the instantaneous temperature rise due to individual 0.6 MJ controlled ELMs. The maximum time-averaged surface heat load is lesssim 12 MW/m2 and will lead to increase of the FILD surface temperature well below the melting temperature of the materials considered here, for the FILD insertion time of 0.2 s. The worst-case instantaneous temperature rise during controlled 0.6 MJ ELMs is also significantly smaller than the melting temperature of e.g. Tungsten or Molybdenum, foreseen for the FILD housing.

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.

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.

Detailed characterisation of the incident neutron beam on the TOSCA spectrometer

NASA Astrophysics Data System (ADS)

Pinna, Roberto S.; Rudić, Svemir; Capstick, Matthew J.; McPhail, David J.; Pooley, Daniel E.; Howells, Gareth D.; Gorini, Giuseppe; Fernandez-Alonso, Felix

2017-10-01

We report a detailed characterisation of the incident neutron beam on the TOSCA spectrometer. A bespoke time-of-flight neutron monitor has been designed, constructed and used to perform extensive spatially resolved measurements of the absolute neutron flux and its underlying time structure at the instrument sample position. The obtained data give a quantitative understanding of the current instrument beyond neutronic simulations and provide a baseline in order to assess the performance of the upgraded instrument. At an average proton current-on-target of 153 μA (ISIS Target Station 1; at the time of measurements) we have found that the wavelength-integrated neutron flux (from 0.28 Å to 4.65 Å) at the position of the TOSCA instrument sample (spatially averaged across the 3 × 3cm2 surface centred around (0,0) position) is approximately 1 . 2 × 106 neutrons cm-2s-1, while the whole beam has a homogeneous distribution across the 3 . 0 × 3 . 5cm2 sample surface. The spectra reproduced the well-known shape of the neutrons moderated by the room temperature water moderator and exhibit a neutron flux of 7 . 3 × 105 neutrons cm-2s-1Å-1 at 1 Å.

Regional warming of hot extremes accelerated by surface energy fluxes consistent with drying soils

NASA Astrophysics Data System (ADS)

Donat, M.; Pitman, A.; Seneviratne, S. I.

2017-12-01

Strong regional differences exist in how hot temperature extremes increase under global warming. Using an ensemble of coupled climate models, we examine the regional warming rates of hot extremes relative to annual average warming rates in the same regions. We identify hotspots of accelerated warming of model-simulated hot extremes in Europe, North America, South America and Southeast China. These hotspots indicate where the warm tail of a distribution of temperatures increases faster than the average and are robust across most CMIP5 models. Exploring the conditions on the specific day the hot extreme occurs demonstrates the hotspots are explained by changes in the surface energy fluxes consistent with drying soils. Furthermore, in these hotspot regions we find a relationship between the temperature - heat flux correlation under current climate conditions and the magnitude of future projected changes in hot extremes, pointing to a potential emergent constraint for simulations of future hot extremes. However, the model-simulated accelerated warming of hot extremes appears inconsistent with observations of the past 60 years, except over Europe. The simulated acceleration of hot extremes may therefore be unreliable, a result that necessitates a re-evaluation of how climate models resolve the relevant terrestrial processes.

Natural convection with evaporation in a vertical cylindrical cavity under the effect of temperature-dependent surface tension

NASA Astrophysics Data System (ADS)

Kozhevnikov, Danil A.; Sheremet, Mikhail A.

2018-01-01

The effect of surface tension on laminar natural convection in a vertical cylindrical cavity filled with a weak evaporating liquid has been analyzed numerically. The cylindrical enclosure is insulated at the bottom, heated by a constant heat flux from the side, and cooled by a non-uniform evaporative heat flux from the top free surface having temperature-dependent surface tension. Governing equations with corresponding boundary conditions formulated in dimensionless stream function, vorticity, and temperature have been solved by finite difference method of the second-order accuracy. The influence of Rayleigh number, Marangoni number, and aspect ratio on the liquid flow and heat transfer has been studied. Obtained results have revealed that the heat transfer rate at free surface decreases with Marangoni number and increases with Rayleigh number, while the average temperature inside the cavity has an opposite behavior; namely, it growths with Marangoni number and reduces with Rayleigh number.

AmeriFlux CA-Qcu Quebec - Eastern Boreal, Black Spruce/Jack Pine Cutover

DOE Data Explorer

Margolis, Hank A. [Université Laval

2016-01-01

This is the AmeriFlux version of the carbon flux data for the site CA-Qcu Quebec - Eastern Boreal, Black Spruce/Jack Pine Cutover. Site Description - The ground is gently rolling with a weak slope (<5%). In mesic areas (designated as well to moderately well drained areas, according to the Canadian System of Soil Classification (Agriculture Canada Expert Committee on Soil Survey, 1983)), the soil is a ferro-humic to humic podzol covered by an organic layer having an average depth of 26 cm (Fig. 1). In humid areas, the soil is organic (imperfectly to poorly drained) with an average organic layer of 125 cm. Mesic areas accounted for approximately 75% of the total surface area of the footprint and humid areas accounted for 25%. Full-time continuous measurements eneded in 2011. Intermittent measurements are on-going as resources permit.

Averaging Bias Correction for Future IPDA Lidar Mission MERLIN

NASA Astrophysics Data System (ADS)

Tellier, Yoann; Pierangelo, Clémence; Wirth, Martin; Gibert, Fabien

2018-04-01

The CNES/DLR MERLIN satellite mission aims at measuring methane dry-air mixing ratio column (XCH4) and thus improving surface flux estimates. In order to get a 1% precision on XCH4 measurements, MERLIN signal processing assumes an averaging of data over 50 km. The induced biases due to the non-linear IPDA lidar equation are not compliant with accuracy requirements. This paper analyzes averaging biases issues and suggests correction algorithms tested on realistic simulated scenes.

Evaluation of a new model of aeolian transport in the presence of vegetation

USGS Publications Warehouse

Li, Junran; Okin, Gregory S.; Herrick, Jeffrey E.; Belnap, Jayne; Miller, Mark E.; Vest, Kimberly; Draut, Amy E.

2013-01-01

Aeolian transport is an important characteristic of many arid and semiarid regions worldwide that affects dust emission and ecosystem processes. The purpose of this paper is to evaluate a recent model of aeolian transport in the presence of vegetation. This approach differs from previous models by accounting for how vegetation affects the distribution of shear velocity on the surface rather than merely calculating the average effect of vegetation on surface shear velocity or simply using empirical relationships. Vegetation, soil, and meteorological data at 65 field sites with measurements of horizontal aeolian flux were collected from the Western United States. Measured fluxes were tested against modeled values to evaluate model performance, to obtain a set of optimum model parameters, and to estimate the uncertainty in these parameters. The same field data were used to model horizontal aeolian flux using three other schemes. Our results show that the model can predict horizontal aeolian flux with an approximate relative error of 2.1 and that further empirical corrections can reduce the approximate relative error to 1.0. The level of error is within what would be expected given uncertainties in threshold shear velocity and wind speed at our sites. The model outperforms the alternative schemes both in terms of approximate relative error and the number of sites at which threshold shear velocity was exceeded. These results lend support to an understanding of the physics of aeolian transport in which (1) vegetation's impact on transport is dependent upon the distribution of vegetation rather than merely its average lateral cover and (2) vegetation impacts surface shear stress locally by depressing it in the immediate lee of plants rather than by changing the bulk surface's threshold shear velocity. Our results also suggest that threshold shear velocity is exceeded more than might be estimated by single measurements of threshold shear stress and roughness length commonly associated with vegetated surfaces, highlighting the variation of threshold shear velocity with space and time in real landscapes.

Stepping towards new parameterizations for non-canonical atmospheric surface-layer conditions

NASA Astrophysics Data System (ADS)

Calaf, M.; Margairaz, F.; Pardyjak, E.

2017-12-01

Representing land-atmosphere exchange processes as a lower boundary condition remains a challenge. This is partially a result of the fact that land-surface heterogeneity exists at all spatial scales and its variability does not "average" out with decreasing scales. Such variability need not rapidly blend away from the boundary thereby impacting the near-surface region of the atmosphere. Traditionally, momentum and energy fluxes linking the land surface to the flow in NWP models have been parameterized using atmospheric surface layer (ASL) similarity theory. There is ample evidence that such representation is acceptable for stationary and planar-homogeneous flows in the absence of subsidence. However, heterogeneity remains a ubiquitous feature eliciting appreciable deviations when using ASL similarity theory, especially in scalars such moisture and air temperature whose blending is less efficient when compared to momentum. The focus of this project is to quantify the effect of surface thermal heterogeneity with scales Ο(1/10) the height of the atmospheric boundary layer and characterized by uniform roughness. Such near-canonical cases describe inhomogeneous scalar transport in an otherwise planar homogeneous flow when thermal stratification is weak or absent. In this work we present a large-eddy simulation study that characterizes the effect of surface thermal heterogeneities on the atmospheric flow using the concept of dispersive fluxes. Results illustrate a regime in which the flow is mostly driven by the surface thermal heterogeneities, in which the contribution of the dispersive fluxes can account for up to 40% of the total sensible heat flux. Results also illustrate an alternative regime in which the effect of the surface thermal heterogeneities is quickly blended, and the dispersive fluxes provide instead a quantification of the flow spatial heterogeneities produced by coherent turbulent structures result of the surface shear stress. A threshold flow-dynamics parameter is introduced to differentiate dispersive fluxes driven by surface thermal heterogeneities from those induced by surface shear. We believe that results from this research are a first step in developing new parameterizations appropriate for non-canonical ASL conditions.

Heat transfer and pressure measurements for the SSME fuel turbine

NASA Technical Reports Server (NTRS)

Dunn, Michael G.; Kim, Jungho

1991-01-01

A measurement program is underway using the Rocketdyne two-stage Space Shuttle Main Engine (SSME) fuel turbine. The measurements use a very large shock tunnel to produce a short-duration source of heated and pressurized gas which is subsequently passed through the turbine. Within this environment, the turbine is operated at the design values of flow function, stage pressure ratio, stage temperature ratio, and corrected speed. The first stage vane row and the first stage blade row are instrumented in both the spanwise and chordwise directions with pressure transducers and heat flux gages. The specific measurements to be taken include time averaged surface pressure and heat flux distributions on the vane and blade, flow passage static pressure, flow passage total pressure and total temperature distributions, and phase resolved surface pressure and heat flux on the blade.

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

Comparison of Adjective vs. Benthic Sources of Nutrients to a Former Salt Pond under Restoration

NASA Astrophysics Data System (ADS)

Topping, B.; Kuwabara, J. S.; Garrett, K.; Takekawa, J.; Piotter, S.; Parchaso, F.

2013-12-01

With the implementation of the South Bay Restoration Program in 2008, water quality in the Alviso Salt Ponds, California, has been monitored to document the effects of changing hydrologic connections among the ponds and the adjacent pond, slough and estuary. In 2010 and 2012, pore-water profilers (U.S. Patent 8,051,727 B1) were deployed in Pond A3W, a former salt pond just north of Moffett Federal Airfield that mixes hydrologically through culverts and weirs with Guadalupe Slough and neighboring ponds, to assess the magnitude of diffusive benthic flux, generated primarily by remobilization of surface-reactive solutes in bed sediment accumulated over annual to decadal time scales. The study, focusing on macronutrient sources that may stimulate harmful algal blooms, revealed that orthophosphate, ammonia, and silica benthic flux were consistently positive (out of the sediment) in both 2010 and 2012, while nitrate and nitrite fluxes were negligible. Because tidal height can affect the size and direction of flow, a diurnal study of nutrient advective flux into and out of the pond was measured during neap and spring tides. These advective fluxes (kg/yr) were compared to benthic flux estimates for the pond extrapolated over the 2.27 (km2) pond surface. Benthic flux of inorganic nitrogen species, averaged over all sites and dates, was about 80,000 + 48,000 kilograms per year (kg/yr), well above the adjective flux range of -50 to 1,500 kg/yr. By contrast, the average benthic flux of orthophosphate was about 12,000 + 4,400 kg/yr, well below the advective flux range of 21,500 to 30,000 kg/yr. Benthic flux estimates determined by porewater gradients do not include enhancement processes such as bioturbation, bioirrigation, wind resuspension, and potential groundwater inflows. However, they provide a conservative measure and can be an effective management screening tool. These results indicate that benthic transport may be an important source of biologically reactive solutes for both nutrients and toxicants, an important consideration during restoration since there are trophic transfer implications.

Comparison between the land surface response of the ECMWF model and the FIFE-1987 data

NASA Technical Reports Server (NTRS)

Betts, Alan K.; Ball, John H.; Beljaars, Anton C. M.

1993-01-01

An averaged time series for the surface data for the 15 x 15 km FIFE site was prepared for the summer of 1987. Comparisons with 48-hr forecasts from the ECMWF model for extended periods in July, August, and October 1987 identified model errors in the incoming SW radiation in clear skies, the ground heat flux, the formulation of surface evaporation, the soil-moisture model, and the entrainment at boundary-layer top. The model clear-sky SW flux is too high at the surface by 5-10 percent. The ground heat flux is too large by a factor of 2 to 3 because of the large thermal capacity of the first soil layer (which is 7 cm thick), and a time truncation error. The surface evaporation was near zero in October 1987, rather than of order 70 W/sq m at noon. The surface evaporation falls too rapidly after rainfall, with a time-scale of a few days rather than the 7-10 d (or more) of the observations. On time-scales of more than a few days the specified 'climate layer' soil moisture, rather than the storage of precipitation, has a large control on the evapotranspiration. The boundary-layer-top entrainment is too low. This results in a moist bias in the boundary-layer mixing ratio of order 2 g/Kg in forecasts from an experimental analysis with nearly realistic surface fluxes; this because there is insufficient downward mixing of dry air.

The Effect of Cumulus Cloud Field Anisotropy on Domain-Averaged Solar Fluxes and Atmospheric Heating Rates

NASA Technical Reports Server (NTRS)

Hinkelman, Laura M.; Evans, K. Franklin; Clothiaux, Eugene E.; Ackerman, Thomas P.; Stackhouse, Paul W., Jr.

2006-01-01

Cumulus clouds can become tilted or elongated in the presence of wind shear. Nevertheless, most studies of the interaction of cumulus clouds and radiation have assumed these clouds to be isotropic. This paper describes an investigation of the effect of fair-weather cumulus cloud field anisotropy on domain-averaged solar fluxes and atmospheric heating rate profiles. A stochastic field generation algorithm was used to produce twenty three-dimensional liquid water content fields based on the statistical properties of cloud scenes from a large eddy simulation. Progressively greater degrees of x-z plane tilting and horizontal stretching were imposed on each of these scenes, so that an ensemble of scenes was produced for each level of distortion. The resulting scenes were used as input to a three-dimensional Monte Carlo radiative transfer model. Domain-average transmission, reflection, and absorption of broadband solar radiation were computed for each scene along with the average heating rate profile. Both tilt and horizontal stretching were found to significantly affect calculated fluxes, with the amount and sign of flux differences depending strongly on sun position relative to cloud distortion geometry. The mechanisms by which anisotropy interacts with solar fluxes were investigated by comparisons to independent pixel approximation and tilted independent pixel approximation computations for the same scenes. Cumulus anisotropy was found to most strongly impact solar radiative transfer by changing the effective cloud fraction, i.e., the cloud fraction when the field is projected on a surface perpendicular to the direction of the incident solar beam.

Computational efficiency for the surface renewal method

NASA Astrophysics Data System (ADS)

Kelley, Jason; Higgins, Chad

2018-04-01

Measuring surface fluxes using the surface renewal (SR) method requires programmatic algorithms for tabulation, algebraic calculation, and data quality control. A number of different methods have been published describing automated calibration of SR parameters. Because the SR method utilizes high-frequency (10 Hz+) measurements, some steps in the flux calculation are computationally expensive, especially when automating SR to perform many iterations of these calculations. Several new algorithms were written that perform the required calculations more efficiently and rapidly, and that tested for sensitivity to length of flux averaging period, ability to measure over a large range of lag timescales, and overall computational efficiency. These algorithms utilize signal processing techniques and algebraic simplifications that demonstrate simple modifications that dramatically improve computational efficiency. The results here complement efforts by other authors to standardize a robust and accurate computational SR method. Increased speed of computation time grants flexibility to implementing the SR method, opening new avenues for SR to be used in research, for applied monitoring, and in novel field deployments.

Plasma-formed hyperthermal atomic beams for use in thin film fabrication

NASA Astrophysics Data System (ADS)

Gilson, E. P.; Cohen, S. A.; Berlinger, B.; Chan, W.

2013-10-01

Enhancing the surface mobility of adsorbents during thin-film growth processes is important for creating certain high-quality thin films. Under the auspices of a DARPA program to develop methods for supplying momentum to adsorbates during thin-film formation without using bulk heating, a hyperthermal atomic beam (HAB) was generated and directed at silicon surfaces with patterned coatings of pentacene, gold, and other surrogates for adsorbents relevant to various thin-film coatings. The HAB was created when the plasma from a helicon plasma source struck a tungsten neutralizer plate and was reflected as neutrals. Time averaged HAB fluxes 100 times greater than in previous PPPL HAB sources have been generated. The effect of the HAB on the patterned coatings was measured using atomic force microscopy (AFM). Results are presented on the flux and energy of the HAB for various system pressures, magnetic fields, and neutralizer biases. AFM measurements of the surface topology demonstrate that the HAB energy, species, and integrated flux are all important factors in altering surface mobility. This research is supported by the U.S. Defense Advanced Research Projects Agency.

Water, Energy, and Carbon with Artificial Neural Networks (WECANN): A statistically-based estimate of global surface turbulent fluxes and gross primary productivity using solar-induced fluorescence.

PubMed

Alemohammad, Seyed Hamed; Fang, Bin; Konings, Alexandra G; Aires, Filipe; Green, Julia K; Kolassa, Jana; Miralles, Diego; Prigent, Catherine; Gentine, Pierre

2017-01-01

A new global estimate of surface turbulent fluxes, latent heat flux (LE) and sensible heat flux (H), and gross primary production (GPP) is developed using a machine learning approach informed by novel remotely sensed Solar-Induced Fluorescence (SIF) and other radiative and meteorological variables. This is the first study to jointly retrieve LE, H and GPP using SIF observations. The approach uses an artificial neural network (ANN) with a target dataset generated from three independent data sources, weighted based on triple collocation (TC) algorithm. The new retrieval, named Water, Energy, and Carbon with Artificial Neural Networks (WECANN), provides estimates of LE, H and GPP from 2007 to 2015 at 1° × 1° spatial resolution and on monthly time resolution. The quality of ANN training is assessed using the target data, and the WECANN retrievals are evaluated using eddy covariance tower estimates from FLUXNET network across various climates and conditions. When compared to eddy covariance estimates, WECANN typically outperforms other products, particularly for sensible and latent heat fluxes. Analysing WECANN retrievals across three extreme drought and heatwave events demonstrates the capability of the retrievals in capturing the extent of these events. Uncertainty estimates of the retrievals are analysed and the inter-annual variability in average global and regional fluxes show the impact of distinct climatic events - such as the 2015 El Niño - on surface turbulent fluxes and GPP.

Design, Construction, and Qualification of a Microscale Heater Array for Use in Boiling Heat Transfer

NASA Technical Reports Server (NTRS)

Rule, T. D.; Kim, J.; Kalkur, T. S.

1998-01-01

Boiling heat transfer is an efficient means of heat transfer because a large amount of heat can be removed from a surface using a relatively small temperature difference between the surface and the bulk liquid. However, the mechanisms that govern boiling heat transfer are not well understood. Measurements of wall temperature and heat flux near the wall would add to the database of knowledge which is necessary to understand the mechanisms of nucleate boiling. A heater array has been developed which contains 96 heater elements within a 2.5 mm square area. The temperature of each heater element is held constant by an electronic control system similar to a hot-wire anemometer. The voltage that is being applied to each heater element can be measured and digitized using a high-speed A/D converter, and this digital information can be compiled into a series of heat-flux maps. Information for up to 10,000 heat flux maps can be obtained each second. The heater control system, the A/D system and the heater array construction are described in detail. Results are presented which show that this is an effective method of measuring the local heat flux during nucleate and transition boiling. Heat flux maps are obtained for pool boiling in FC-72 on a horizontal surface. Local heat flux variations are shown to be three to six times larger than variations in the spatially averaged heat flux.

Water, Energy, and Carbon with Artificial Neural Networks (WECANN): a statistically based estimate of global surface turbulent fluxes and gross primary productivity using solar-induced fluorescence

NASA Astrophysics Data System (ADS)

Hamed Alemohammad, Seyed; Fang, Bin; Konings, Alexandra G.; Aires, Filipe; Green, Julia K.; Kolassa, Jana; Miralles, Diego; Prigent, Catherine; Gentine, Pierre

2017-09-01

A new global estimate of surface turbulent fluxes, latent heat flux (LE) and sensible heat flux (H), and gross primary production (GPP) is developed using a machine learning approach informed by novel remotely sensed solar-induced fluorescence (SIF) and other radiative and meteorological variables. This is the first study to jointly retrieve LE, H, and GPP using SIF observations. The approach uses an artificial neural network (ANN) with a target dataset generated from three independent data sources, weighted based on a triple collocation (TC) algorithm. The new retrieval, named Water, Energy, and Carbon with Artificial Neural Networks (WECANN), provides estimates of LE, H, and GPP from 2007 to 2015 at 1° × 1° spatial resolution and at monthly time resolution. The quality of ANN training is assessed using the target data, and the WECANN retrievals are evaluated using eddy covariance tower estimates from the FLUXNET network across various climates and conditions. When compared to eddy covariance estimates, WECANN typically outperforms other products, particularly for sensible and latent heat fluxes. Analyzing WECANN retrievals across three extreme drought and heat wave events demonstrates the capability of the retrievals to capture the extent of these events. Uncertainty estimates of the retrievals are analyzed and the interannual variability in average global and regional fluxes shows the impact of distinct climatic events - such as the 2015 El Niño - on surface turbulent fluxes and GPP.

Soil surface Hg emission flux in coalfield in Wuda, Inner Mongolia, China.

PubMed

Li, Chunhui; Liang, Handong; Liang, Ming; Chen, Yang; Zhou, Yi

2018-06-01

Hg emission flux from various land covers, such as forests, wetlands, and urban areas, have been investigated. China has the largest area of coalfield in the world, but data of Hg flux of coalfields, especially, those with coal fires, are seriously limited. In this study, Hg fluxes of a coalfield were measured using the dynamic flux chamber (DFC) method, coupled with a Lumex multifunctional Hg analyzer RA-915+ (Lumex Ltd., Russia). The results show that the Hg flux in Wuda coalfield ranged from 4 to 318 ng m -2  h -1 , and the average value for different areas varied, e.g., coal-fire area 99 and 177 ng m -2  h -1 ; no coal-fire area 19 and 32 ng m -2  h -1 ; and backfilling area 53 ng m -2  h -1 . Hg continued to be emitted from an underground coal seam, even if there were no phenomena, such as vents, cracks, and smog, of coal fire on the soil surface. This phenomenon occurred in all area types, i.e., coal-fire area, no coal-fire area, and backfilling area, which is universal in Wuda coalfield. Considering that many coalfields in northern China are similar to Wuda coalfield, they may be large sources of atmospheric Hg. The correlations of Hg emission flux with influence factors, such as sunlight intensity, soil surface temperature, and atmospheric Hg content, were also investigated for Wuda coalfield. Graphical abstract ᅟ.

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.

Relating Radiative Fluxes on Arctic Sea Ice Area Using Arctic Observation and Reanalysis Integrated System (ArORIS)

NASA Astrophysics Data System (ADS)

Sledd, A.; L'Ecuyer, T. S.

2017-12-01

With Arctic sea ice declining rapidly and Arctic temperatures rising faster than the rest of the globe, a better understanding of the Arctic climate, and ice cover-radiation feedbacks in particular, is needed. Here we present the Arctic Observation and Reanalysis Integrated System (ArORIS), a dataset of integrated products to facilitate studying the Arctic using satellite, reanalysis, and in-situ datasets. The data include cloud properties, radiative fluxes, aerosols, meteorology, precipitation, and surface properties, to name just a few. Each dataset has uniform grid-spacing, time-averaging and naming conventions for ease of use between products. One intended use of ArORIS is to assess Arctic radiation and moisture budgets. Following that goal, we use observations from ArORIS - CERES-EBAF radiative fluxes and NSIDC sea ice fraction and area to quantify relationships between the Arctic energy balance and surface properties. We find a discernable difference between energy budgets for years with high and low September sea ice areas. Surface fluxes are especially responsive to the September sea ice minimum in months both leading up to September and the months following. In particular, longwave fluxes at the surface show increased sensitivity in the months preceding September. Using a single-layer model of solar radiation we also investigate the individual responses of surface and planetary albedos to changes in sea ice area. By partitioning the planetary albedo into surface and atmospheric contributions, we find that the atmospheric contribution to planetary albedo is less sensitive to changes in sea ice area than the surface contribution. Further comparisons between observations and reanalyses can be made using the available datasets in ArORIS.

The Galapagos Spreading Centre at 86o W: a detailed geothermal field study.

USGS Publications Warehouse

Green, K.E.; Von Herzen, R. P.; Williams, D.L.

1981-01-01

We report here measurements of the heat flow field of the Galapagos Spreading Center on crust of age less than 1.0 m.y. The 443 measurements in an area of about 570 km2 reveal the general planform of the geothermal flux and permit the first truly areal estimate of the near-axis conductive heat flux. The intrusion process and associated hydrothermal circulation dominate the surface heat flow pattern, with circulation apparently continuing beyong the limits of our survey. The areal average of the conductive heat flux is 7.1+-0.8 HFU (295+-33 m W/m2), about one-third the heat flux predicted by plate models. The remaining heat is apparently removed by venting of hydrothermal waters at the spreading axis and through basalt outcrops and hydrothermal mounds off axis. The pattern of surface heat flux is lineated parallel to the axis and the strongly lineated topography. Sharp lateral gradients in the heat flow, greater than 10 HFU/km near escarpments and commonly expressed as high heat flow at the tops of the scarps and lower heat flow in the valleys, may indicate a local concentration of the circulation by surface fault systems and/or variable sediment thickness. -Authors

Global correlation between surface heat fluxes and insolation in the 11-year solar cycle: The latitudinal effect

NASA Astrophysics Data System (ADS)

Volobuev, D. M.; Makarenko, N. G.

2014-12-01

Because of the small amplitude of insolation variations (1365.2-1366.6 W m-2 or 0.1%) from the 11-year solar cycle minimum to the cycle maximum and the structural complexity of the climatic dynamics, it is difficult to directly observe a solar signal in the surface temperature. The main difficulty is reduced to two factors: (1) a delay in the temperature response to external action due to thermal inertia, and (2) powerful internal fluctuations of the climatic dynamics suppressing the solar-driven component. In this work we take into account the first factor, solving the inverse problem of thermal conductivity in order to calculate the vertical heat flux from the measured temperature near the Earth's surface. The main model parameter—apparent thermal inertia—is calculated from the local seasonal extremums of temperature and albedo. We level the second factor by averaging mean annual heat fluxes in a latitudinal belt. The obtained mean heat fluxes significantly correlate with a difference between the insolation and optical depth of volcanic aerosol in the atmosphere, converted into a hindered heat flux. The calculated correlation smoothly increases with increasing latitude to 0.4-0.6, and the revealed latitudinal dependence is explained by the known effect of polar amplification.

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. .

Earth radiation budget measurements from satellites and their interpretation for climate modeling and studies

NASA Technical Reports Server (NTRS)

Vonderhaar, T. H.; Stephens, G. L.; Campbell, G. G.

1980-01-01

The annual and seasonal averaged Earth atmosphere radiation budgets derived from the most complete set of satellite observations available are presented. The budgets were derived from a composite of 48 monthly mean radiation budget maps. Annually and seasonally averaged radiation budgets are presented as global averages and zonal averages. The geographic distribution of the various radiation budget quantities is described. The annual cycle of the radiation budget was analyzed and the annual variability of net flux was shown to be largely dominated by the regular semi and annual cycles forced by external Earth-Sun geometry variations. Radiative transfer calculations were compared to the observed budget quantities and surface budgets were additionally computed with particular emphasis on discrepancies that exist between the present computations and previous surface budget estimates.

Eddy covariance measurement of CO2 flux to the atmosphere from a area of high volcanogenic emissions, Mammoth Mountain, California

USGS Publications Warehouse

Anderson, D.E.; Farrar, C.D.

2001-01-01

Three pilot studies were performed to assess application of the eddy covariance micrometeorological method in the measurement of carbon dioxide (CO2) flux of volcanic origin. The selected study area is one of high diffuse CO2 emission on Mammoth Mountain, CA. Because terrain and source characteristics make this a complex setting for this type of measurement, added consideration was given to source area and upwind fetch. Footprint analysis suggests that the eddy covariance measurements were representative of an upwind elliptical source area (3.8 ?? 103 m2) which can vary with mean wind direction, surface roughness, and atmospheric stability. CO2 flux averaged 8-16 mg m-2 s-1 (0.7-1.4 kg m-2 day-1). Eddy covariance measurements of flux were compared with surface chamber measurements made in separate studies [Geophys. Res. Lett. 25 (1998a) 1947; EOS Trans. 79 (1998) F941.] and were found to be similar. ?? 2001 Elsevier Science B.V. All rights reserved.

Evaluating Surface Flux Results from CERES-FLASHFlux

NASA Technical Reports Server (NTRS)

Wilber, Anne C.; Stackhouse, Paul W., Jr.; Kratz, David P.; Gupta, Shashi K.; Sawaengphokhai, Parnchai K.

2015-01-01

The Fast Longwave and Shortwave Radiative Flux (FLASHFlux) data product was developed to provide a rapid release version of the Clouds and Earth's Radiant Energy System (CERES) results, which could be made available to the research and applications communities within one week of the satellite observations by exchanging some accuracy for speed of processing. Unlike standard CERES products, FLASHFlux does not maintain a long-term consistent record. Therefore the latest algorithm changes and input data can be incorporated into processing. FLASHFlux released Version3A (January 2013) and Version 3B (August 2014) which include the latest meteorological product from Global Modeling and Assimilation Office (GMAO), GEOS FP-IT (5.9.1), the latest spectral response functions and gains for the CERES instruments, and aerosol climatology based on the latest MATCH data. Version 3B included a slightly updated calibration and some changes to the surface albedo over snow/ice. Typically FLASHFlux does not reprocess earlier versions when a new version is released. The combined record of Time Interpolated Space Averaged (TISA) surface flux results from Versions3A and 3B for July 2012 to October 2015 have been compared to the ground-based measurements. The FLASHFlux results are also compared to two other CERES gridded products, SYN1deg and EBAF surface fluxes.

Towards Improved High-Resolution Land Surface Hydrologic Reanalysis Using a Physically-Based Hydrologic Model and Data Assimilation

NASA Astrophysics Data System (ADS)

Shi, Y.; Davis, K. J.; Zhang, F.; Duffy, C.; Yu, X.

2014-12-01

A coupled physically based land surface hydrologic model, Flux-PIHM, has been developed by incorporating a land surface scheme into the Penn State Integrated Hydrologic Model (PIHM). The land surface scheme is adapted from the Noah land surface model. Flux-PIHM has been implemented and manually calibrated at the Shale Hills watershed (0.08 km2) in central Pennsylvania. Model predictions of discharge, point soil moisture, point water table depth, sensible and latent heat fluxes, and soil temperature show good agreement with observations. When calibrated only using discharge, and soil moisture and water table depth at one point, Flux-PIHM is able to resolve the observed 101 m scale soil moisture pattern at the Shale Hills watershed when an appropriate map of soil hydraulic properties is provided. A Flux-PIHM data assimilation system has been developed by incorporating EnKF for model parameter and state estimation. Both synthetic and real data assimilation experiments have been performed at the Shale Hills watershed. Synthetic experiment results show that the data assimilation system is able to simultaneously provide accurate estimates of multiple parameters. In the real data experiment, the EnKF estimated parameters and manually calibrated parameters yield similar model performances, but the EnKF method significantly decreases the time and labor required for calibration. The data requirements for accurate Flux-PIHM parameter estimation via data assimilation using synthetic observations have been tested. Results show that by assimilating only in situ outlet discharge, soil water content at one point, and the land surface temperature averaged over the whole watershed, the data assimilation system can provide an accurate representation of watershed hydrology. Observations of these key variables are available with national and even global spatial coverage (e.g., MODIS surface temperature, SMAP soil moisture, and the USGS gauging stations). National atmospheric reanalysis products, soil databases and land cover databases (e.g., NLDAS-2, SSURGO, NLCD) can provide high resolution forcing and input data. Therefore the Flux-PIHM data assimilation system could be readily expanded to other watersheds to provide regional scale land surface and hydrologic reanalysis with high spatial temporal resolution.

Impacts of sampling design and estimation methods on nutrient leaching of intensively monitored forest plots in the Netherlands.

PubMed

de Vries, W; Wieggers, H J J; Brus, D J

2010-08-05

Element fluxes through forest ecosystems are generally based on measurements of concentrations in soil solution at regular time intervals at plot locations sampled in a regular grid. Here we present spatially averaged annual element leaching fluxes in three Dutch forest monitoring plots using a new sampling strategy in which both sampling locations and sampling times are selected by probability sampling. Locations were selected by stratified random sampling with compact geographical blocks of equal surface area as strata. In each sampling round, six composite soil solution samples were collected, consisting of five aliquots, one per stratum. The plot-mean concentration was estimated by linear regression, so that the bias due to one or more strata being not represented in the composite samples is eliminated. The sampling times were selected in such a way that the cumulative precipitation surplus of the time interval between two consecutive sampling times was constant, using an estimated precipitation surplus averaged over the past 30 years. The spatially averaged annual leaching flux was estimated by using the modeled daily water flux as an ancillary variable. An important advantage of the new method is that the uncertainty in the estimated annual leaching fluxes due to spatial and temporal variation and resulting sampling errors can be quantified. Results of this new method were compared with the reference approach in which daily leaching fluxes were calculated by multiplying daily interpolated element concentrations with daily water fluxes and then aggregated to a year. Results show that the annual fluxes calculated with the reference method for the period 2003-2005, including all plots, elements and depths, lies only in 53% of the cases within the range of the average +/-2 times the standard error of the new method. Despite the differences in results, both methods indicate comparable N retention and strong Al mobilization in all plots, with Al leaching being nearly equal to the leaching of SO(4) and NO(3) with fluxes expressed in mol(c) ha(-1) yr(-1). This illustrates that Al release, which is the clearest signal of soil acidification, is mainly due to the external input of SO(4) and NO(3).

Sensitivity of Offshore Surface Fluxes and Sea Breezes to the Spatial Distribution of Sea-Surface Temperature

NASA Astrophysics Data System (ADS)

Lombardo, Kelly; Sinsky, Eric; Edson, James; Whitney, Michael M.; Jia, Yan

2018-03-01

A series of numerical sensitivity experiments is performed to quantify the impact of sea-surface temperature (SST) distribution on offshore surface fluxes and simulated sea-breeze dynamics. The SST simulations of two mid-latitude sea-breeze events over coastal New England are performed using a spatially-uniform SST, as well as spatially-varying SST datasets of 32- and 1-km horizontal resolutions. Offshore surface heat and buoyancy fluxes vary in response to the SST distribution. Local sea-breeze circulations are relatively insensitive, with minimal differences in vertical structure and propagation speed among the experiments. The largest thermal perturbations are confined to the lowest 10% of the sea-breeze column due to the relatively high stability of the mid-Atlantic marine atmospheric boundary layer (ABL) suppressing vertical mixing, resulting in the depth of the marine layer remaining unchanged. Minimal impacts on the column-averaged virtual potential temperature and sea-breeze depth translates to small changes in sea-breeze propagation speed. This indicates that the use of datasets with a fine-scale SST may not produce more accurate sea-breeze simulations in highly stable marine ABL regimes, though may prove more beneficial in less stable sub-tropical environments.

Ensemble simulations of the role of the stratosphere in the attribution of northern extratropical tropospheric ozone variability

NASA Astrophysics Data System (ADS)

Hess, P.; Kinnison, D.; Tang, Q.

2015-03-01

Despite the need to understand the impact of changes in emissions and climate on tropospheric ozone, the attribution of tropospheric interannual ozone variability to specific processes has proven difficult. Here, we analyze the stratospheric contribution to tropospheric ozone variability and trends from 1953 to 2005 in the Northern Hemisphere (NH) mid-latitudes using four ensemble simulations of the free running (FR) Whole Atmosphere Community Climate Model (WACCM). The simulations are externally forced with observed time-varying (1) sea-surface temperatures (SSTs), (2) greenhouse gases (GHGs), (3) ozone depleting substances (ODS), (4) quasi-biennial oscillation (QBO), (5) solar variability (SV) and (6) stratospheric sulfate surface area density (SAD). A detailed representation of stratospheric chemistry is simulated, including the ozone loss due to volcanic eruptions and polar stratospheric clouds. In the troposphere, ozone production is represented by CH4-NOx smog chemistry, where surface chemical emissions remain interannually constant. Despite the simplicity of its tropospheric chemistry, at many NH measurement locations, the interannual ozone variability in the FR WACCM simulations is significantly correlated with the measured interannual variability. This suggests the importance of the external forcing applied in these simulations in driving interannual ozone variability. The variability and trend in the simulated 1953-2005 tropospheric ozone from 30 to 90° N at background surface measurement sites, 500 hPa measurement sites and in the area average are largely explained on interannual timescales by changes in the 30-90° N area averaged flux of ozone across the 100 hPa surface and changes in tropospheric methane concentrations. The average sensitivity of tropospheric ozone to methane (percent change in ozone to a percent change in methane) from 30 to 90° N is 0.17 at 500 hPa and 0.21 at the surface; the average sensitivity of tropospheric ozone to the 100 hPa ozone flux (percent change in ozone to a percent change in the ozone flux) from 30 to 90° N is 0.19 at 500 hPa and 0.11 at the surface. The 30-90° N simulated downward residual velocity at 100 hPa increased by 15% between 1953 and 2005. However, the impact of this on the 30-90° N 100 hPa ozone flux is modulated by the long-term changes in stratospheric ozone. The ozone flux decreases from 1965 to 1990 due to stratospheric ozone depletion, but increases again by approximately 7% from 1990 to 2005. The first empirical orthogonal function of interannual ozone variability explains from 40% (at the surface) to over 80% (at 150 hPa) of the simulated ozone interannual variability from 30 to 90° N. This identified mode of ozone variability shows strong stratosphere-troposphere coupling, demonstrating the importance of the stratosphere in an attribution of tropospheric ozone variability. The simulations, with no change in emissions, capture almost 50% of the measured ozone change during the 1990s at a variety of locations. This suggests that a large portion of the measured change is not due to changes in emissions, but can be traced to changes in large-scale modes of ozone variability. This emphasizes the difficulty in the attribution of ozone changes, and the importance of natural variability in understanding the trends and variability of ozone. We find little relation between the El Niño-Southern Oscillation (ENSO) index and large-scale tropospheric ozone variability over the long-term record.

Quasi-analytical treatment of spatially averaged radiation transfer in complex terrain

NASA Astrophysics Data System (ADS)

LöWe, H.; Helbig, N.

2012-10-01

We provide a new quasi-analytical method to compute the subgrid topographic influences on the shortwave radiation fluxes and the effective albedo in complex terrain as required for large-scale meteorological, land surface, or climate models. We investigate radiative transfer in complex terrain via the radiosity equation on isotropic Gaussian random fields. Under controlled approximations we derive expressions for domain-averaged fluxes of direct, diffuse, and terrain radiation and the sky view factor. Domain-averaged quantities can be related to a type of level-crossing probability of the random field, which is approximated by long-standing results developed for acoustic scattering at ocean boundaries. This allows us to express all nonlocal horizon effects in terms of a local terrain parameter, namely, the mean-square slope. Emerging integrals are computed numerically, and fit formulas are given for practical purposes. As an implication of our approach, we provide an expression for the effective albedo of complex terrain in terms of the Sun elevation angle, mean-square slope, the area-averaged surface albedo, and the ratio of atmospheric direct beam to diffuse radiation. For demonstration we compute the decrease of the effective albedo relative to the area-averaged albedo in Switzerland for idealized snow-covered and clear-sky conditions at noon in winter. We find an average decrease of 5.8% and spatial patterns which originate from characteristics of the underlying relief. Limitations and possible generalizations of the method are discussed.

Impact of Land Model Calibration on Coupled Land-Atmosphere Prediction

NASA Technical Reports Server (NTRS)

Santanello, Joseph A., Jr.; Kumar, Sujay V.; Peters-Lidard, Christa D.; Harrison, Ken; Zhou, Shujia

2012-01-01

Land-atmosphere (L-A) interactions play a critical role in determining the diurnal evolution of both planetary boundary layer (PBL) and land surface heat and moisture budgets, as well as controlling feedbacks with clouds and precipitation that lead to the persistence of dry and wet regimes. Recent efforts to quantify the strength of L-A coupling in prediction models have produced diagnostics that integrate across both the land and PBL components of the system. In this study, we examine the impact of improved specification of land surface states, anomalies, and fluxes on coupled WRF forecasts during the summers of extreme dry and wet land surface conditions in the U.S. Southern Great Plains. The improved land initialization and surface flux parameterizations are obtained through calibration of the Noah land surface model using the new optimization and uncertainty estimation subsystem in NASA's Land Information System (LIS-OPT/UE). The impact of the calibration on the a) spinup of the land surface used as initial conditions, and b) the simulated heat and moisture states and fluxes of the coupled WRF simulations is then assessed. Changes in ambient weather and land-atmosphere coupling are evaluated along with measures of uncertainty propagation into the forecasts. In addition, the sensitivity of this approach to the period of calibration (dry, wet, average) is investigated. Results indicate that the offline calibration leads to systematic improvements in land-PBL fluxes and near-surface temperature and humidity, and in the process provide guidance on the questions of what, how, and when to calibrate land surface models for coupled model prediction.

Impact of highway construction on land surface energy balance and local climate derived from LANDSAT satellite data.

PubMed

Nedbal, Václav; Brom, Jakub

2018-08-15

Extensive construction of highways has a major impact on the landscape and its structure. They can also influence local climate and heat fluxes in the surrounding area. After the removal of vegetation due to highway construction, the amount of solar radiation energy used for plant evapotranspiration (latent heat flux) decreases, bringing about an increase in landscape surface temperature, changing the local climate and increasing surface run-off. In this study, we evaluated the impact of the D8 highway construction (Central Bohemia, Czech Republic) on the distribution of solar radiation energy into the various heat fluxes (latent, sensible and ground heat flux) and related surface functional parameters (surface temperature and surface wetness). The aim was to describe the severity of the impact and the distance from the actual highway in which it can be observed. LANDSAT multispectral satellite images and field meteorological measurements were used to calculate surface functional parameters and heat balance before and during the highway construction. Construction of a four-lane highway can influence the heat balance of the landscape surface as far as 90m in the perpendicular direction from the highway axis, i.e. up to 75m perpendicular from its edge. During a summer day, the decrease in evapotranspired water can reach up to 43.7m 3 per highway kilometre. This means a reduced cooling effect, expressed as the decrease in latent heat flux, by an average of 29.7MWh per day per highway kilometre and its surroundings. The loss of the cooling ability of the land surface by evaporation can lead to a rise in surface temperature by as much as 7°C. Thus, the results indicate the impact of extensive line constructions on the local climate. Copyright © 2018 Elsevier B.V. All rights reserved.

North Polar Radiative Flux Variability from 2002 Through 2014

NASA Technical Reports Server (NTRS)

Rutan, David; Rose, Fred; Doelling, David; Kato, Seiji; Smith, Bill, Jr.

2017-01-01

NASA's Clouds and the Earth's Radiant Energy System (CERES) project produces the SYN1Deg data product. SYN1deg provides global, 1deg gridded, hourly estimates of Top of Atmosphere (TOA) (CERES observations and calculations) and atmospheric and surface radiative flux (calculations). Examples of 12 year North Polar averages of some variables are shown to the right. Given recent interest in polar science we focus here on TOA and Surface validation of calculated irradiant fluxes. TOA upward longwave irradiance calculations match the CERES observations well both spatially and temporally with correlations remaining strong through PC 6. Compare SYN1Deg Calculations & Meteorological Teleconnections. TOA reflected shortwave irradiance calculations match the CERES observations well both spatially and temporally with correlations remaining string through PC 7. Comparing SYN1Deg calculations to teleconnection patterns requires expanding the area to 30N for EOF analyses. Correlating the Principal Components of various variables to teleconnection time series indicates which variable is most highly correlated with which teleconnection signal. The tables indicate the Pacific North American Oscillation is most correlated to the OLR EOF 1, and the North American Oscillation is correlated most closely to surface LW flux down EOF 1.

Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions

NASA Astrophysics Data System (ADS)

Schäfer, K.; Grant, R. H.; Emeis, S.; Raabe, A.; von der Heide, C.; Schmid, H. P.

2012-07-01

Measurements of land-surface emission rates of greenhouse and other gases at large spatial scales (10 000 m2) are needed to assess the spatial distribution of emissions. This can be readily done using spatial-integrating micro-meteorological methods like flux-gradient methods which were evaluated for determining land-surface emission rates of trace gases under stable boundary layers. Non-intrusive path-integrating measurements are utilized. Successful application of a flux-gradient method requires confidence in the gradients of trace gas concentration and wind, and in the applicability of boundary-layer turbulence theory; consequently the procedures to qualify measurements that can be used to determine the flux is critical. While there is relatively high confidence in flux measurements made under unstable atmospheres with mean winds greater than 1 m s-1, there is greater uncertainty in flux measurements made under free convective or stable conditions. The study of N2O emissions of flat grassland and NH3 emissions from a cattle lagoon involves quality-assured determinations of fluxes under low wind, stable or night-time atmospheric conditions when the continuous "steady-state" turbulence of the surface boundary layer breaks down and the layer has intermittent turbulence. Results indicate that following the Monin-Obukhov similarity theory (MOST) flux-gradient methods that assume a log-linear profile of the wind speed and concentration gradient incorrectly determine vertical profiles and thus flux in the stable boundary layer. An alternative approach is considered on the basis of turbulent diffusivity, i.e. the measured friction velocity as well as height gradients of horizontal wind speeds and concentrations without MOST correction for stability. It is shown that this is the most accurate of the flux-gradient methods under stable conditions.

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.

Inter-cusp Ion and Electron Transport in a Nstar-derivative Ion Thruster

NASA Technical Reports Server (NTRS)

Foster, John E.

2001-01-01

Diffusion of electrons and ions to anode surfaces between the magnetic cusps of a NASA Solar Electric Propulsion Technology Application Readiness ion thruster has been characterized. Ion flux measurements were made at the anode and at the screen grid electrode. The measurements indicated that the average ion current density at the anode and at the screen grid were approximately equal. Additionally, it was found that the electron flux to the anode between cusps is best described by the classical cross-field diffusion coefficient.

Ion and Electron Transport in an Nstar-derivative Ion Thruster. Revised

NASA Technical Reports Server (NTRS)

Foster, John E.

2001-01-01

Diffusion of electrons and ions to anode surfaces between the magnetic cusps of a NASA Solar Electric Propulsion Technology Application Readiness ion thruster has been characterized. Ion flux measurements were made at the anode and at the screen grid electrode. The measurements indicated that the average ion current density at the anode and at the screen grid were approximately equal. Additionally, it was found that the electron flux to the anode between cusps is best described by the classical cross-field diffusion coefficient.

Constraining the Sulfur Dioxide Degassing Flux from Turrialba Volcano, Costa Rica Using Unmanned Aerial System Measurements

NASA Technical Reports Server (NTRS)

Xi, Xin; Johnson, Matthew S.; Jeong, Seongeun; Fladeland, Matthew; Pieri, David; Diaz, Jorge Andres; Bland, Geoffrey L.

2016-01-01

Observed sulfur dioxide (SO2)mixing ratios onboard unmanned aerial systems (UAS) duringMarch 11-13, 2013 are used to constrain the three-day averaged SO2 degassing flux fromTurrialba volcanowithin a Bayesian inverse modeling framework. A mesoscale model coupled with Lagrangian stochastic particle backward trajectories is used to quantify the source-receptor relationships at very high spatial resolutions (i.e., b1 km). The model shows better performance in reproducing the near-surface meteorological properties and observed SO2 variations when using a first-order closure non-local planetary boundary layer (PBL) scheme. The optimized SO2 degassing fluxes vary from 0.59 +/- 0.37 to 0.83 +/- 0.33 kt d-1 depending on the PBL scheme used. These fluxes are in good agreement with ground-based gas flux measurements, and correspond to corrective scale factors of 8-12 to the posteruptive SO2 degassing rate in the AeroCom emission inventory. The maximum a posteriori solution for the SO2 flux is highly sensitive to the specification of prior and observational errors, and relatively insensitive to the SO2 loss term and temporal averaging of observations. Our results indicate relatively low degassing activity but sustained sulfur emissions from Turrialba volcano to the troposphere during March 2013. This study demonstrates the utility of low-cost small UAS platforms for volcanic gas composition and flux analysis.

A wind tunnel study of flows over idealised urban surfaces with roughness sublayer corrections

NASA Astrophysics Data System (ADS)

Ho, Yat-Kiu; Liu, Chun-Ho

2017-10-01

Dynamics in the roughness (RSLs) and inertial (ISLs) sublayers in the turbulent boundary layers (TBLs) over idealised urban surfaces are investigated analytically and experimentally. In this paper, we derive an analytical solution to the mean velocity profile, which is a continuous function applicable to both RSL and ISL, over rough surfaces in isothermal conditions. Afterwards, a modified mixing-length model for RSL/ISL transport is developed that elucidates how surface roughness affects the turbulence motions. A series of wind tunnel experiments are conducted to measure the vertical profiles of mean and fluctuating velocities, together with momentum flux over various configurations of surface-mounted ribs in cross flows using hot-wire anemometry (HWA). The analytical solution agrees well with the wind tunnel result that improves the estimate to mean velocity profile over urban surfaces and TBL dynamics as well. The thicknesses of RSL and ISL are calculated by monitoring the convergence/divergence between the temporally averaged and spatio-temporally averaged profiles of momentum flux. It is found that the height of RSL/ISL interface is a function of surface roughness. Examining the direct, physical influence of roughness elements on near-surface RSL flows reveals that the TBL flows over rough surfaces exhibit turbulence motions of two different length scales which are functions of the RSL and ISL structure. Conclusively, given a TBL, the rougher the surface, the higher is the RSL intruding upward that would thinner the ISL up to 50 %. Therefore, the conventional ISL log-law approximation to TBL flows over urban surfaces should be applied with caution.

Observational analysis of air-sea fluxes and sea water temperature offshore South China Sea

NASA Astrophysics Data System (ADS)

Bi, X.; Huang, J.; Gao, Z.; Liu, Y.

2017-12-01

This paper investigates the air-sea fluxes (momentum flux, sensible heat flux and latent heat flux) from eddy covariance method based on data collected at an offshore observation tower in the South China Sea from January 2009 to December 2016 and sea water temperature (SWT) on six different levels based on data collected from November 2011 to June 2013. The depth of water at the tower over the sea averages about 15 m. This study presents the in-situ measurements of continuous air-sea fluxes and SWT at different depths. Seasonal and diurnal variations in air-sea fluxes and SWT on different depths are examined. Results show that air-sea fluxes and all SWT changed seasonally; sea-land breeze circulation appears all the year round. Unlike winters where SWT on different depths are fairly consistent, the difference between sea surface temperature (SST) and sea temperature at 10 m water depth fluctuates dramatically and the maximum value reaches 7 °C during summer.

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

Smith, D.J.; Warner, J.A.; LeBarron, N.

Processes that use energetic ions for large substrates require that the time-averaged erosion effects from the ion flux be uniform across the surface. A numerical model has been developed to determine this flux and its effects on surface etching of a silica/photoresist combination. The geometry of the source and substrate is very similar to a typical deposition geometry with single or planetary substrate rotation. The model was used to tune an inert ion-etching process that used single or multiple Kaufman sources to less than 3% uniformity over a 30-cm aperture after etching 8 {micro}m of material. The same model canmore » be used to predict uniformity for ion-assisted deposition (IAD).« 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.

An alternative to the TEM (Transformed Eulerian Mean) equations

NASA Astrophysics Data System (ADS)

Gaßmann, Almut

2013-04-01

The TEM equations constitute a powerful means to get access to the residual circulation. However, due to their foundation on the wave perspective, they deliver only a zonally averaged picture without access to the three-dimensional structure or the local origins of the residual circulation. Therefore it is worth to investigate whether there are alternatives. The pathway followed here is to perform a transformation of the momentum and the potential temperature equation before taking the zonal mean. This is done by removing the steady state ideal wind solution vid = ?×?B-(?±P) from the equations (? - potential temperature, B - Bernoulli function, P - Ertel's potential vorticity EPV, ?± - density). The advantage of that approach is that the total EPV-flux does no longer contain an explicitly visible 'do-nothing-flux'. This flux, ?? ×?B, does only vanish when averaging on isentropic surfaces, but not on other isosurfaces. Here we find the reason why the conventional zonal mean on isentropes delivers a direct overturning cell on each hemisphere, whereas on other isosurfaces we obtain the typical three-cell structure with Headley, Ferrel, and polar cells. It will be demonstrated and made visible through idealized climate experiments with the ICON-IAP model that the zonal averages of the nonideal wind components vnid = v - vid and wnid = w - wid constitute similar direct overturning cells on non-isentropic surfaces as obtained with the TEM-generated v* and w*. It is also interesting to inspect fields of local nonideal wind components, the very origin of the residual circulation.

An approximate Riemann solver for thermal and chemical nonequilibrium flows

NASA Technical Reports Server (NTRS)

Prabhu, Ramadas K.

1994-01-01

Among the many methods available for the determination of inviscid fluxes across a surface of discontinuity, the flux-difference-splitting technique that employs Roe-averaged variables has been used extensively by the CFD community because of its simplicity and its ability to capture shocks exactly. This method, originally developed for perfect gas flows, has since been extended to equilibrium as well as nonequilibrium flows. Determination of the Roe-averaged variables for the case of a perfect gas flow is a simple task; however, for thermal and chemical nonequilibrium flows, some of the variables are not uniquely defined. Methods available in the literature to determine these variables seem to lack sound bases. The present paper describes a simple, yet accurate, method to determine all the variables for nonequilibrium flows in the Roe-average state. The basis for this method is the requirement that the Roe-averaged variables form a consistent set of thermodynamic variables. The present method satisfies the requirement that the square of the speed of sound be positive.

Mixing rates and vertical heat fluxes north of Svalbard from Arctic winter to spring

NASA Astrophysics Data System (ADS)

Meyer, Amelie; Fer, Ilker; Sundfjord, Arild; Peterson, Algot K.

2017-06-01

Mixing and heat flux rates collected in the Eurasian Basin north of Svalbard during the N-ICE2015 drift expedition are presented. The observations cover the deep Nansen Basin, the Svalbard continental slope, and the shallow Yermak Plateau from winter to summer. Mean quiescent winter heat flux values in the Nansen Basin are 2 W m-2 at the ice-ocean interface, 3 W m-2 in the pycnocline, and 1 W m-2 below the pycnocline. Large heat fluxes exceeding 300 W m-2 are observed in the late spring close to the surface over the Yermak Plateau. The data consisting of 588 microstructure profiles and 50 days of high-resolution under-ice turbulence measurements are used to quantify the impact of several forcing factors on turbulent dissipation and heat flux rates. Wind forcing increases turbulent dissipation seven times in the upper 50 m, and doubles heat fluxes at the ice-ocean interface. The presence of warm Atlantic Water close to the surface increases the temperature gradient in the water column, leading to enhanced heat flux rates within the pycnocline. Steep topography consistently enhances dissipation rates by a factor of four and episodically increases heat flux at depth. It is, however, the combination of storms and shallow Atlantic Water that leads to the highest heat flux rates observed: ice-ocean interface heat fluxes average 100 W m-2 during peak events and are associated with rapid basal sea ice melt, reaching 25 cm/d.

Annual emissions of mercury to the atmosphere from natural sources in Nevada and California

USGS Publications Warehouse

Coolbaugh, M.F.; Gustin, M.S.; Rytuba, J.J.

2002-01-01

The impact of natural source emissions on atmospheric mercury concentrations and the biogeochemical cycle of mercury is not known. To begin to assess this impact, mercury emissions to the atmosphere were scaled up for three areas naturally enriched in mercury: the Steamboat Springs geothermal area, Nevada, the New Idria mercury mining district, California, and the Medicine Lake volcano, California. Data used to scale up area emissions included mercury fluxes, measured in-situ using field flux chambers, from undisturbed and disturbed geologic substrates, and relationships between mercury emissions and geologic rock types, soil mercury concentrations, and surface heat flux. At select locations mercury fluxes were measured for 24 h and the data were used to adjust fluxes measured at different times of the day to give an average daily flux. This adjustment minimized daily temporal variability, which is observed for mercury flux because of light and temperature effects. Area emissions were scaled spatially and temporally with GIS software. Measured fluxes ranged from 0.3 to approximately 50 ng m-2 h-1 at undisturbed sites devoid of mercury mineralization, and to greater than 10,000 ng m-2 h-1 from substrates that were in areas of mercury mining. Area-averaged fluxes calculated for bare soil at Steamboat Springs, New Idria, and Medicine Lake of 181, 9.2, and 2 ng m-2 h-1, respectively, are greater than fluxes previously ascribed to natural non-point sources, indicating that these sources may be more significant contributors of mercury to the atmosphere than previously realized.

Investigation into aerodynamic and heat transfer of annular channel with inner and outer surface of the shape truncated cone and swirling fluid flow

NASA Astrophysics Data System (ADS)

Leukhin, Yu L.; Pankratov, E. V.; Karpov, S. V.

2017-11-01

We have carried out Investigation into aerodynamic and convective heat transfer of the annular channel. Inner or outer surface of annular channel has shape of blunt-nosed cone tapering to outlet end. Truncated cone connects to a cyclone swirling flow generator. Asymmetric and unsteady flow from the swirling generator in the shape of periodic process gives rise to the formation of secondary flows of the type Taylor-Görtler vortices. These vortices occupy the whole space of the annular channel, with the axes, which coincide with the motion direction of the major stream. Contraction of cross-sectional area of channel (in both cases 52%) causes a marked increase in total velocity of flow, primarily due to its axial component and promotes a more intensive vortex generation. Vortex structures have a significant influence on both average heat transfer and surface distribution. At cross-sections of the annular channel we observe similarity of curves describing distribution of total velocity about wall and heat flux density on the surface. The coordinates of maximum and minimum values of velocity and heat flux coincide. At the average cross-section channel of maximum value of heat transfer is greater than minimum of about by a factor of 2.7 times for outer heat transfer surface and about by a factor of 1.7 times for inner heat transfer surface. Taper channel has a much higher influence on heat transfer of the inner surface than the outer surface and manifests itself at lower values of dimensionless axial coordinate. For the investigated taper cone geometry of the annular channel the heat transfer coefficient of inner surface increases at the outlet section and exceeds value in comparison with straight-line section by 91 … 98%. Heat transfer of the outer cylinder in the same section increases only by 5 … 11%. The increase in average heat transfer over the surfaces is 36% and 4% respectively.

Release of Black Carbon From Thawing Permafrost Estimated by Sequestration Fluxes in the East Siberian Arctic Shelf Recipient

NASA Astrophysics Data System (ADS)

Salvadó, Joan A.; Bröder, Lisa; Andersson, August; Semiletov, Igor P.; Gustafsson, Örjan

2017-10-01

Black carbon (BC) plays an important role in carbon burial in marine sediments globally. Yet the sequestration of BC in the Arctic Ocean is poorly understood. Here we assess the concentrations, fluxes, and sources of soot BC (SBC)—the most refractory component of BC—in sediments from the East Siberian Arctic Shelf (ESAS), the World's largest shelf sea system. SBC concentrations in the contemporary shelf sediments range from 0.1 to 2.1 mg g-1 dw, corresponding to 2-12% of total organic carbon. The 210Pb-derived fluxes of SBC (0.42-11 g m-2 yr-1) are higher or in the same range as fluxes reported for marine surface sediments closer to anthropogenic emissions. The total burial flux of SBC in the ESAS ( 4,000 Gg yr-1) illustrates the great importance of this Arctic shelf in marine sequestration of SBC. The radiocarbon signal of the SBC shows more depleted yet also more uniform signatures (-721 to -896‰; average of -774 ± 62‰) than of the non-SBC pool (-304 to -728‰; average of -491 ± 163‰), suggesting that SBC is coming from an, on average, 5,900 ± 300 years older and more specific source than the non-SBC pool. We estimate that the atmospheric BC input to the ESAS is negligible ( 0.6% of the SBC burial flux). Statistical source apportionment modeling suggests that the ESAS sedimentary SBC is remobilized by thawing of two permafrost carbon (PF/C) systems: surface soil permafrost (topsoil/PF; 25 ± 8%) and Pleistocene ice complex deposits (ICD/PF; 75 ± 8%). The SBC contribution to the total mobilized permafrost carbon (PF/C) increases with increasing distance from the coast (from 5 to 14%), indicating that the SBC is more recalcitrant than other forms of translocated PF/C. These results elucidate for the first time the key role of permafrost thaw in the transport of SBC to the Arctic Ocean. With ongoing global warming, these findings have implications for the biogeochemical carbon cycle, increasing the size of this refractory carbon pool in the Arctic Ocean.

Aerosol Climate Effects: Local Radiative Forcing and Column Closure Experiments

NASA Technical Reports Server (NTRS)

Russell, P. B.; Bergstrom, Robert W.; Kinne, S. A.

2000-01-01

In an effort to reduce uncertainties in climate change predictions, experiments are being planned and conducted to measure anthropogenic aerosol properties and effects, including effects on radiative fields. The global average, direct anthropogenic aerosol effect on upwelling shortwave fluxes is estimated to be about +1/2 W/sq m, whereas errors in flux changes measured with airborne and spaceborne radiometers are 2 to 8 W/sq m or larger. This poses the question of whether flux changes expected in field experiments will be large enough to measure accurately. This paper obtains a new expression for the aerosol-induced change in upwelling flux, compares it to two-stream and adding-doubling (AD) results, and uses all three methods to estimate expected flux changes. The new expression accounts for the solar zenith angle dependences of aerosol transmission and reflection, as well as of surface albedo, all of which can have a strong effect in determining flux changes measured in field experiments. Despite its relative simplicity, the new expression gives results similar to previous two-stream results. Relative to AD results, it agrees within a few watts per square meter for the intermediate solar elevation angles where the flux changes peak (roughly 10 to 30 degrees), but it has negative errors for higher Sun and positive errors for lower Sun. All three techniques yield aerosol-induced changes in upwelling flux of +8 to +50 W/sq m for aerosol midvisible optical depths of 0.1 to 0.5. Because such aerosol optical depths occur frequently off the U.S. and European Atlantic coasts in summer, the flux changes they induce should be measurable by airborne, and possibly by spaceborne, radiometers, provided sufficient care is taken in experiment design (including measurements to separate aerosol radiative effects from those of absorbing gases). The expected flux changes are about 15 to 100 times larger than the global average flux change expected for the global average anthropogenic sulfate optical depth of 0.04. Reasons for the larger flux changes include the larger optical depths considered here (factor 2.5 to 12), plus restricting the measurements to cloud-free, daytime conditions over the ocean (factor 5 to 9).

Modelling Wind Effects on Subtidal Salinity in Apalachicola Bay, Florida

NASA Astrophysics Data System (ADS)

Huang, W.; Jones, W. K.; Wu, T. S.

2002-07-01

Salinity is an important factor for oyster and estuarine productivity in Apalachicola Bay. Observations of salinity at oyster reefs have indicated a high correlation between subtidal salinity variations and the surface winds along the bay axis in an approximately east-west direction. In this paper, we applied a calibrated hydrodynamic model to examine the surface wind effects on the volume fluxes in the tidal inlets and the subtidal salinity variations in the bay. Model simulations show that, due to the large size of inlets located at the east and west ends of this long estuary, surface winds have significant effects on the volume fluxes in the estuary inlets for the water exchanges between the estuary and ocean. In general, eastward winds cause the inflow from the inlets at the western end and the outflow from inlets at the eastern end of the bay. Winds at 15 mph speed in the east-west direction can induce a 2000 m3 s-1 inflow of saline seawater into the bay from the inlets, a rate which is about 2·6 times that of the annual average freshwater inflow from the river. Due to the varied wind-induced volume fluxes in the inlets and the circulation in the bay, the time series of subtidal salinity at oyster reefs considerably increases during strong east-west wind conditions in comparison to salinity during windless conditions. In order to have a better understanding of the characteristics of the wind-induced subtidal circulation and salinity variations, the researchers also connected model simulations under constant east-west wind conditions. Results show that the volume fluxes are linearly proportional to the east-west wind stresses. Spatial distributions of daily average salinity and currents clearly show the significant effects of winds on the bay.

Surface greenhouse gas fluxes downwind of a penguin colony in the maritime sub-Antarctic

NASA Astrophysics Data System (ADS)

Drewer, Julia; Braban, Christine F.; Tang, Y. Sim; Anderson, Margaret; Skiba, Ute M.; Dragosits, Ulrike; Trathan, Phil

2015-12-01

The relationship between ammonia (NH3) concentrations downwind from a penguin colony and local surface greenhouse gas (GHG) fluxes was investigated on the remote sub-Antarctic Bird Island (54°00‧S, 38°03‧W) during summer 2010 (November and December). A Macaroni penguin (Eudyptes chrysolophus) colony (40,000 pairs) at Goldcrest Point is a large point source of NH3 on the island and a measurement transect of 23 m, 36 m, 70 m, 143 m and 338 m was set up downwind from the colony. Atmospheric NH3 concentrations measured by passive diffusion samplers declined from 23 μg m-3 close to the colony to less than 1 μg m-3 338 m downwind. As increased nitrogen (N) deposition can affect soil carbon (C) and N cycling, it can therefore potentially influence GHG and nitric oxide (NO) emission rates. However, in this study, a clear correlation between surface GHG fluxes and atmospheric NH3 concentrations could not be established. Average fluxes for nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) over the entire transect and the eight week study period ranged from 7 to 23 μg N2O-N m-2 h-1, -5.5-245 μg CH4 m-2 h-1, and CO2 respiration rates averaged 2.2 μmol m-2 s-1. Laboratory studies using intact soil cores from the transect also did not show any significant correlation between atmospheric NH3 concentrations and N2O, NO, CH4 emissions or CO2 respiration rates. Overall, fluxes measured in the laboratory study reflected the high variability measured in the field. Large changes in soil depth along the transect, due to the topography of the island, possibly influenced fluxes more than NH3 concentration and seabirds appeared to have a more localised input (e.g. ground nesting birds). However, warmer temperatures might have a large potential to increase GHG fluxes in this ecosystem. This study confirms that GHG fluxes do occur in these ornithogenic ecosystems, however, the scale of the impact remains largely unquantified due to high uncertainties and high spatial variability.

Scaling of surface energy fluxes using remotely sensed data

NASA Astrophysics Data System (ADS)

French, Andrew Nichols

Accurate estimates of evapotranspiration (ET) across multiple terrains would greatly ease challenges faced by hydrologists, climate modelers, and agronomists as they attempt to apply theoretical models to real-world situations. One ET estimation approach uses an energy balance model to interpret a combination of meteorological observations taken at the surface and data captured by remote sensors. However, results of this approach have not been accurate because of poor understanding of the relationship between surface energy flux and land cover heterogeneity, combined with limits in available resolution of remote sensors. The purpose of this study was to determine how land cover and image resolution affect ET estimates. Using remotely sensed data collected over El Reno, Oklahoma, during four days in June and July 1997, scale effects on the estimation of spatially distributed ET were investigated. Instantaneous estimates of latent and sensible heat flux were calculated using a two-source surface energy balance model driven by thermal infrared, visible-near infrared, and meteorological data. The heat flux estimates were verified by comparison to independent eddy-covariance observations. Outcomes of observations taken at coarser resolutions were simulated by aggregating remote sensor data and estimated surface energy balance components from the finest sensor resolution (12 meter) to hypothetical resolutions as coarse as one kilometer. Estimated surface energy flux components were found to be significantly dependent on observation scale. For example, average evaporative fraction varied from 0.79, using 12-m resolution data, to 0.93, using 1-km resolution data. Resolution effects upon flux estimates were related to a measure of landscape heterogeneity known as operational scale, reflecting the size of dominant landscape features. Energy flux estimates based on data at resolutions less than 100 m and much greater than 400 m showed a scale-dependent bias. But estimates derived from data taken at about 400-m resolution (the operational scale at El Reno) were susceptible to large error due to mixing of surface types. The El Reno experiments show that accurate instantaneous estimates of ET require precise image alignment and image resolutions finer than landscape operational scale. These findings are valuable for the design of sensors and experiments to quantify spatially-varying hydrologic processes.

Estimates of surface humidity and latent heat fluxes over oceans from SSM/I data

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

Cho, S.H.; Atlas, R.M.; Shie, C.L.

1995-08-01

Monthly averages of daily latent heat fluxes over the oceans for February and August 1988 are estimated using a stability-dependent bulk scheme. Daily fluxes are computed from daily SSM/I (Special Sensor Microwave/Imager) wind speeds and EOF-retrieved SSM/I surface humidity, National Meteorological Center sea surface temperatures, and the European Centre for Medium-Range Weather Forecasts analyzed 2-m temperatures. Daily surface specific humidity (Q) is estimated from SSM/I precipitable water of total (W) and a 500-m bottom layer (W{sub B}) using an EOF (empirical orthogonal function) method. This method has six W-based categories of EOFs (independent of geographical locations) and is developed usingmore » 23 177 FGGE IIb humidity soundings over the global oceans. For 1200 FGGE IIb humidity soundings, the accuracy of EOF-retrieved Q is 0.75 g kg{sup -1} for the case without errors in W and W{sub B} and increases to 1.16 g kg{sup -1} for the case with errors in W and W{sub B}. Compared to 342 collocated radiosonde observations, the EOF-retrieved SSM/I Q has an accuracy of 1.7 g kg{sup -1}. The method improves upon the humidity retrieval of Liu and is competitive with that of Schulz et al. The SSM/I surface humidity and latent heat fluxes of these two months agree reasonably well with those of COADS (Comprehensive Ocean-Atmosphere Data Set). Compared to the COADS, the sea-air humidity difference of SSM/I has a positive bias of approximately 1-3 g kg{sup -1} (an overestimation of flux) over the wintertime eastern equatorial Pacific Ocean, it has a negative bias of about 1-2 g kg{sup -1} (an underestimation of flux). The results further suggest that the two monthly flux estimates, computed from daily and monthly mean data, do not differ significantly over the oceans. 35 refs., 12 figs., 4 tabs.« less

Temporal dynamics of CO2 fluxes and profiles over a Central European city

NASA Astrophysics Data System (ADS)

Vogt, R.; Christen, A.; Rotach, M. W.; Roth, M.; Satyanarayana, A. N. V.

2006-02-01

In Summer 2002 eddy covariance flux measurements of CO2 were performed over a dense urban surface. The month-long measurements were carried out in the framework of the Basel Urban Boundary Layer Experiment (BUBBLE). Two Li7500 open path analysers were installed at z/z H = 1.0 and 2.2 above a street canyon with z H the average building height of 14.6 m and z the height above street level. Additionally, profiles of CO2 concentration were sampled at 10 heights from street level up to 2 z H . The minimum and maximum of the average diurnal course of CO2 concentration at 2 z H were 362 and 423 ppmv in late afternoon and early morning, respectively. Daytime CO2 concentrations were not correlated to local sources, e.g. the minimum occurred together with the maximum in traffic load. During night-time CO2 is in general accumulated, except when inversion development is suppressed by frontal passages. CO2 concentrations were always decreasing with height and correspondingly, the fluxes on average always directed upward. At z/z H = 2.2 low values of about 3 µmol m-2 s-1 were measured during the second half of the night. During daytime average values reached up to 14 µmol m-2 s-1. The CO2 fluxes are well correlated with the traffic load, with their maxima occurring together in late afternoon. Daytime minimum CO2 concentrations fell below regional background values. Besides vertical mixing and entrainment, it is suggested that this is also due to advection of rural air with reduced CO2 concentration. Comparison with other urban observations shows a large range of differences among urban sites in terms of both CO2 fluxes and concentrations.

Surface flux processes and evolution of characteristic eddy scales above a young Middle Rio Grande forest

NASA Astrophysics Data System (ADS)

Cleverly, J. R.; Thibault, J. R.; Slusher, M.; Hipps, L.; Prueger, J.; Dahm, C. N.

2003-12-01

The extended drought throughout the Southwest has brought water budgets and policy decisions into public purview. It is often presumed that riparian restoration, i.e. removal of non-native species, presents a water salvage panacea. The cost of such operations can be prohibitive, making reliable estimates of phreatophytic ET a crucial piece of information. This study has taken a long-term approach to monitoring ET water flux from a variety of these forests. ET monitoring towers have been established at 5 sites along the Middle Rio Grande -- 2 over mature cottonwood forests, 2 over mature saltcedar forests, and 1 over a young mixed stand of Russian olive and willow. Because there is yet no infallible method for determining ET fluxes, eddy covariance technology provides the best method for evaluating those processes in the surface layer by provided data directly into surface layer similarity relationships. ET, energy, and carbon flux were measured during the 2003 growing season from towers using the 3-dimensional sonic eddy covariance (3SEC) method. Scalar flux sensors included a 3-D sonic anemometer, Krypton hygrometer, 12.7 μ m type E fine wire thermocouple (Campbell Scientific, Inc), and LI-7500 open-path IRGA (Licor, Inc). An averaging period of 30 min was chosen based as a period of low cospectral density. The following corrections were applied to these fluxes: coordinate rotation; correction of frequency-specific signal attenuation due to instrument separation, instrument line averaging, and signal path length (Massman 2000 & 2001); krypton hygrometer calibration as a function of humidity; oxygen contribution to the krypton hygrometer signal; and flux effects on measured densities (Webb et al 1980). These corrections reduced the closure error by 5 percent. Closure was then forced using the measured Bowen Ratio as the weighting factor. Measured ET, along with leaf area index, was reduced as much as 35 percent during the prolonged drought in the southwestern U.S. At the end of the season, younger cottonwood, willow, and Russian olive forests were developing severe chlorosis (< 100 mg m{-2} at some locations), and ET rates fell from 8.5 mm day-1 to 4.4 mm day-1 due to a record-breaking hot July. Evaluation of the 10-Hz raw data from the 3SEC system was performed using cospectral and wavelet time series analyses. Of particular interest are the low frequency harmonics between the turbulent scales and the spectral gap. Correlation of intermittent flux variations with variations in net radiation preceding summer monsoon precipitation illustrates the relative roles of vegetative homeostasis and advection in explaining remaining closure error following turbulence corrections. This time series analysis of physical turbulent Monin-Obukhov scales and surface fluxes illustrates the frequency-temporal relationships between surface processes, stomatal control, and mesoscale forcing events.

Investigation Of The Influence Of Temperature Inversions And Turbulence On Land-Atmosphere Interactions For Rolling Terrain

NASA Astrophysics Data System (ADS)

Osibanjo, Olabosipo O.

The objectives of this work are to calculate surface fluxes for rolling terrain using observational data collected during one week in September 2014 from a monitoring site in Echo, Oregon and to investigate the log law in the ABL. The site is located in the Columbia Basin with rolling terrain, irrigated farmland, and over 100 wind turbines. The 10 m tower was placed in a small valley depression to isolate nighttime temperature inversions. This thesis presents observations of momentum, sensible heat, moisture, and CO2 fluxes from data collected at a sampling frequency of 10Hz at four heights. Results show a strong correlation between temperature inversions and CO 2 flux. The log layer could not be achieved as the value of the estimated von Karman constant (˜0.62) is not close to that of the accepted value of 0.41. The impact of the irrigated farmland near the measurement site was observed in the latent heat flux, where the advection of moisture was evident in the tower moisture gradient. A strong relationship was also observed between fluxes of sensible heat, latent heat, CO2, and atmospheric stability. The average nighttime CO2 concentration observed was ˜407 ppm, and daytime ˜388 ppm compared to the 2013 global average CO2 concentration of 395 ppm. The maximum CO2 concentration (˜485 ppm) was observed on the strongest temperature inversion night. There are few uncertainties in the measurements. The manufacturer for the eddy covariance instruments (EC 150) quotes uncertainty of +/- 0.1°C for temperature between -0°C-40°C. Error bars were generated on the estimated surface sensible heat flux using the standard deviation and mean values. Under the most stable atmospheric conditions, uncertainty (assumed to be the variability in the flux estimates) was close to the minimum (˜+/- 5 W m-2). (Abstract shortened by ProQuest.).

High-resolution CO2 and CH4 flux inverse modeling combining GOSAT, OCO-2 and ground-based observations

NASA Astrophysics Data System (ADS)

Maksyutov, S. S.; Oda, T.; Saito, M.; Ito, A.; Janardanan Achari, R.; Sasakawa, M.; Machida, T.; Kaiser, J. W.; Belikov, D.; Valsala, V.; O'Dell, C.; Yoshida, Y.; Matsunaga, T.

2017-12-01

We develop a high-resolution CO2 and CH4 flux inversion system that is based on the Lagrangian-Eulerian coupled tracer transport model, and is designed to estimate surface fluxes from atmospheric CO2 and CH4 data observed by the GOSAT and OCO-2 satellites and by global in-situ networks, including observation in Siberia. We use the Lagrangian particle dispersion model (LPDM) FLEXPART to estimate the surface flux footprints for each observation at 0.1-degree spatial resolution for three days of transport. The LPDM is coupled to a global atmospheric tracer transport model (NIES-TM). The adjoint of the coupled transport model is used in an iterative optimization procedure based on either quasi-Newtonian algorithm or singular value decomposition. Combining surface and satellite data for use in inversion requires correcting for biases present in satellite observation data, that is done in a two-step procedure. As a first step, bi-weekly corrections to prior flux fields are estimated for the period of 2009 to 2015 from in-situ CO2 and CH4 data from global observation network, included in Obspack-GVP (for CO2), WDCGG (CH4) and JR-STATION datasets. High-resolution prior fluxes were prepared for anthropogenic emissions (ODIAC and EDGAR), biomass burning (GFAS), and the terrestrial biosphere. The terrestrial biosphere flux was constructed using a vegetation mosaic map and separate simulations of CO2 fluxes by the VISIT model for each vegetation type present in a grid. The prior flux uncertainty for land is scaled proportionally to monthly mean GPP by the MODIS product for CO2 and EDGAR emissions for CH4. Use of the high-resolution transport leads to improved representation of the anthropogenic plumes, often observed at continental continuous observation sites. OCO-2 observations are aggregated to 1 second averages, to match the 0.1 degree resolution of the transport model. Before including satellite observations in the inversion, the monthly varying latitude-dependent bias is estimated by comparing satellite observations with column abundance simulated with surface fluxes optimized by surface inversion. The bias-corrected GOSAT and OCO-2 data are then used in the inversion together with ground-based observations. Application of the bias correction to satellite data reduces the difference between the flux estimates based on ground-based and satellite observations.

Transient heat transfer behavior of water spray evaporative cooling on a stainless steel cylinder with structured surface for safety design application in high temperature scenario

NASA Astrophysics Data System (ADS)

Aamir, Muhammad; Liao, Qiang; Hong, Wang; Xun, Zhu; Song, Sihong; Sajid, Muhammad

2017-02-01

High heat transfer performance of spray cooling on structured surface might be an additional measure to increase the safety of an installation against any threat caused by rapid increase in the temperature. The purpose of present experimental study is to explore heat transfer performance of structured surface under different spray conditions and surface temperatures. Two cylindrical stainless steel samples were used, one with pyramid pins structured surface and other with smooth surface. Surface heat flux of 3.60, 3.46, 3.93 and 4.91 MW/m2 are estimated for sample initial average temperature of 600, 700, 800 and 900 °C, respectively for an inlet pressure of 1.0 MPa. A maximum cooling rate of 507 °C/s was estimated for an inlet pressure of 0.7 MPa at 900 °C for structured surface while for smooth surface maximum cooling rate of 356 °C/s was attained at 1.0 MPa for 700 °C. Structured surface performed better to exchange heat during spray cooling at initial sample temperature of 900 °C with a relative increase in surface heat flux by factor of 1.9, 1.56, 1.66 and 1.74 relative to smooth surface, for inlet pressure of 0.4, 0.7, 1.0 and 1.3 MPa, respectively. For smooth surface, a decreasing trend in estimated heat flux is observed, when initial sample temperature was increased from 600 to 900 °C. Temperature-based function specification method was utilized to estimate surface heat flux and surface temperature. Limited published work is available about the application of structured surface spray cooling techniques for safety of stainless steel structures at very high temperature scenario such as nuclear safety vessel and liquid natural gas storage tanks.

Numerical experiment on the flow field properties of a blunted body with a counterflowing jet in supersonic flows

NASA Astrophysics Data System (ADS)

Huang, Wei; Zhang, Rui-Rui; Yan, Li; Ou, Min; Moradi, R.

2018-06-01

The prediction of the drag and heat flux reduction characteristics is a very important issue in the conceptual design phase of the hypersonic vehicle. In this paper, the flow field properties around a blunted body with a counterflowing jet in the supersonic flow with the freestream Mach number being 3.98 were investigated numerically, and they are obtained by means of the two-dimensional axisymmetric Reynolds-averaged Navier-Stokes (RANS) equations coupled with the two equation standard k-ε turbulence model. The surface Stanton number distributions, as well as the surface static pressures, were extracted from the flow field structures in order to evaluate the drag and heat flux reduction characteristics. Further, the influences of the jet pressure ratio and the jet Mach number on the drag and heat flux reduction were analyzed based on the detailed code validation and grid independency analysis process. The obtained results show that the flow cell Reynolds number has a great impact on the heat flux prediction, and its best value is 5.0 for the case studied in the current study. However, the flow cell Reynolds number and the grid scale both have only a slight impact on the prediction of the surface static pressure distribution, as well as the turbulence model. The larger jet pressure ratio is beneficial for the drag and heat flux reduction, and the smaller jet Mach number is beneficial for the heat flux reduction. Further, the long penetration mode is beneficial for the drag reduction, but it is not beneficial for the heat flux reduction.

Water, Energy, and Carbon with Artificial Neural Networks (WECANN): a statistically based estimate of global surface turbulent fluxes and gross primary productivity using solar-induced fluorescence

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

Alemohammad, Seyed Hamed; Fang, Bin; Konings, Alexandra G.

A new global estimate of surface turbulent fluxes, latent heat flux (LE) and sensible heat flux ( H), and gross primary production (GPP) is developed using a machine learning approach informed by novel remotely sensed solar-induced fluorescence (SIF) and other radiative and meteorological variables. This is the first study to jointly retrieve LE, H, and GPP using SIF observations. The approach uses an artificial neural network (ANN) with a target dataset generated from three independent data sources, weighted based on a triple collocation (TC) algorithm. The new retrieval, named Water, Energy, and Carbon with Artificial Neural Networks (WECANN), provides estimatesmore » of LE, H, and GPP from 2007 to 2015 at 1° × 1° spatial resolution and at monthly time resolution. The quality of ANN training is assessed using the target data, and the WECANN retrievals are evaluated using eddy covariance tower estimates from the FLUXNET network across various climates and conditions. When compared to eddy covariance estimates, WECANN typically outperforms other products, particularly for sensible and latent heat fluxes. Analyzing WECANN retrievals across three extreme drought and heat wave events demonstrates the capability of the retrievals to capture the extent of these events. Uncertainty estimates of the retrievals are analyzed and the interannual variability in average global and regional fluxes shows the impact of distinct climatic events – such as the 2015 El Niño – on surface turbulent fluxes and GPP.« less

Water, Energy, and Carbon with Artificial Neural Networks (WECANN): a statistically based estimate of global surface turbulent fluxes and gross primary productivity using solar-induced fluorescence

DOE PAGES

Alemohammad, Seyed Hamed; Fang, Bin; Konings, Alexandra G.; ...

2017-09-20

A new global estimate of surface turbulent fluxes, latent heat flux (LE) and sensible heat flux ( H), and gross primary production (GPP) is developed using a machine learning approach informed by novel remotely sensed solar-induced fluorescence (SIF) and other radiative and meteorological variables. This is the first study to jointly retrieve LE, H, and GPP using SIF observations. The approach uses an artificial neural network (ANN) with a target dataset generated from three independent data sources, weighted based on a triple collocation (TC) algorithm. The new retrieval, named Water, Energy, and Carbon with Artificial Neural Networks (WECANN), provides estimatesmore » of LE, H, and GPP from 2007 to 2015 at 1° × 1° spatial resolution and at monthly time resolution. The quality of ANN training is assessed using the target data, and the WECANN retrievals are evaluated using eddy covariance tower estimates from the FLUXNET network across various climates and conditions. When compared to eddy covariance estimates, WECANN typically outperforms other products, particularly for sensible and latent heat fluxes. Analyzing WECANN retrievals across three extreme drought and heat wave events demonstrates the capability of the retrievals to capture the extent of these events. Uncertainty estimates of the retrievals are analyzed and the interannual variability in average global and regional fluxes shows the impact of distinct climatic events – such as the 2015 El Niño – on surface turbulent fluxes and GPP.« less

Global observation-based diagnosis of soil moisture control on land surface flux partition

NASA Astrophysics Data System (ADS)

Gallego-Elvira, Belen; Taylor, Christopher M.; Harris, Phil P.; Ghent, Darren; Veal, Karen L.; Folwell, Sonja S.

2016-04-01

Soil moisture plays a central role in the partition of available energy at the land surface between sensible and latent heat flux to the atmosphere. As soils dry out, evapotranspiration becomes water-limited ("stressed"), and both land surface temperature (LST) and sensible heat flux rise as a result. This change in surface behaviour during dry spells directly affects critical processes in both the land and the atmosphere. Soil water deficits are often a precursor in heat waves, and they control where feedbacks on precipitation become significant. State-of-the-art global climate model (GCM) simulations for the Coupled Model Intercomparison Project Phase 5 (CMIP5) disagree on where and how strongly the surface energy budget is limited by soil moisture. Evaluation of GCM simulations at global scale is still a major challenge owing to the scarcity and uncertainty of observational datasets of land surface fluxes and soil moisture at the appropriate scale. Earth observation offers the potential to test how well GCM land schemes simulate hydrological controls on surface fluxes. In particular, satellite observations of LST provide indirect information about the surface energy partition at 1km resolution globally. Here, we present a potentially powerful methodology to evaluate soil moisture stress on surface fluxes within GCMs. Our diagnostic, Relative Warming Rate (RWR), is a measure of how rapidly the land warms relative to the overlying atmosphere during dry spells lasting at least 10 days. Under clear skies, this is a proxy for the change in sensible heat flux as soil dries out. We derived RWR from MODIS Terra and Aqua LST observations, meteorological re-analyses and satellite rainfall datasets. Globally we found that on average, the land warmed up during dry spells for 97% of the observed surface between 60S and 60N. For 73% of the area, the land warmed faster than the atmosphere (positive RWR), indicating water stressed conditions and increases in sensible heat flux. Higher RWRs were observed for shorter vegetation and bare soil compared to tall, deep-rooted vegetation due to differences in both aerodynamic and hydrological properties. The variation of RWR with antecedent rainfall provides information on which evaporation regime a particular region lies in climatologically. Different drying stages for a given antecedent rainfall can thus be observed depending on land cover type. For instance, our results suggest that forests in a continental climate remain unstressed during a 10 day dry spell provided the previous month saw at least 95 mm of rain. Conversely, RWR values indicate that under similar conditions regions of grass/crop cover are water-stressed.

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.

Distribution, diffusive fluxes, and toxicity of heavy metals and PAHs in pore water profiles from the northern bays of Taihu Lake.

PubMed

Lei, Pei; Zhang, Hong; Shan, Baoqing; Zhang, Bozheng

2016-11-01

Pore water plays a more significant role than do sediments in pollutant cycling dynamics. Also, concentrations of pollutants in pore water provide important information about their bioavailability or eco-toxicity; however, very few studies have focused on this topic. In this study, four duplicate sediment cores from three typical northern bays as well as the central part of Taihu Lake were collected to investigate the distribution, diffusive fluxes, and toxicity of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in pore water profiles, which will be good in understanding the mobility and toxicity of these toxic pollutants and achieving better environmental management. The diffusive fluxes of heavy metals across the sediment-water interface was estimated through Fick's First Law, and the toxicity of heavy metals and PAHs in pore water was assessed by applying a water quality index (interstitial water toxicity criteria unit, IWCTU) and a hazard index (HI), respectively. The average concentrations of Cr, Cu, Ni, Pb, and Zn in surface pore water were 18.8, 23.4, 12.0, 13.5, and 42.5 μg L -1 , respectively. Also, concentrations of the selected heavy metals in both overlying water and pore water from Taihu Lake were all lower than the standard values of the environmental quality standards for surface water. The concentrations as the pore water depth increased, and the highest detected concentrations of heavy metals were recorded between 3 and 5 cm below the sediment surface. The average diffusive fluxes of these metals were 27.3, 24.8, 7.03, 7.81, and -3.32 μg (m 2 day) -1 , respectively, indicating export from sediment into overlying water, with the exception of Zn. There was a potential risk of toxicity, mainly from Pb and Cu, indicating that heavy metals in pore water had slight to moderate impact on sediment-dwelling organisms by values of the IWCTU and the Nemeraw index. The total PAH concentrations in pore water were higher than those in overlying water, and such gradient implies a potential flux of PAHs from pore water to overlying water. The average HI value of PAHs in surface pore water showed no or low ecological risk. While there may be occasional risk due to the HI values in some sites being greater than 1, the dominant contributors were carcinogenic PAHs. Because of their potential biological impact, heavy metals and PAHs and their comprehensive toxic effects in pore water should be given priority attention to keep the safety of Taihu Lake.

Effect of Sampling Depth on Air-Sea CO2 Flux Estimates in River-Stratified Arctic Coastal Waters

NASA Astrophysics Data System (ADS)

Miller, L. A.; Papakyriakou, T. N.

2015-12-01

In summer-time Arctic coastal waters that are strongly influenced by river run-off, extreme stratification severely limits wind mixing, making it difficult to effectively sample the surface 'mixed layer', which can be as shallow as 1 m, from a ship. During two expeditions in southwestern Hudson Bay, off the Nelson, Hayes, and Churchill River estuaries, we confirmed that sampling depth has a strong impact on estimates of 'surface' pCO2 and calculated air-sea CO2 fluxes. We determined pCO2 in samples collected from 5 m, using a typical underway system on the ship's seawater supply; from the 'surface' rosette bottle, which was generally between 1 and 3 m; and using a niskin bottle deployed at 1 m and just below the surface from a small boat away from the ship. Our samples confirmed that the error in pCO2 derived from typical ship-board versus small-boat sampling at a single station could be nearly 90 μatm, leading to errors in the calculated air-sea CO2 flux of more than 0.1 mmol/(m2s). Attempting to extrapolate such fluxes over the 6,000,000 km2 area of the Arctic shelves would generate an error approaching a gigamol CO2/s. Averaging the station data over a cruise still resulted in an error of nearly 50% in the total flux estimate. Our results have implications not only for the design and execution of expedition-based sampling, but also for placement of in-situ sensors. Particularly in polar waters, sensors are usually deployed on moorings, well below the surface, to avoid damage and destruction from drifting ice. However, to obtain accurate information on air-sea fluxes in these areas, it is necessary to deploy sensors on ice-capable buoys that can position the sensors in true 'surface' waters.

Measurements of Heat-Transfer and Friction Coefficients for Helium Flowing in a Tube at Surface Temperatures up to 5900 Deg R

NASA Technical Reports Server (NTRS)

Taylor, Maynard F.; Kirchgessner, Thomas A.

1959-01-01

Measurements of average heat transfer and friction coefficients and local heat transfer coefficients were made with helium flowing through electrically heated smooth tubes with length-diameter ratios of 60 and 92 for the following range of conditions: Average surface temperature from 1457 to 4533 R, Reynolds numbe r from 3230 to 60,000, heat flux up to 583,200 Btu per hr per ft2 of heat transfer area, and exit Mach numbe r up to 1.0. The results indicate that, in the turbulent range of Reynolds number, good correlation of the local heat transfer coefficients is obtained when the physical properties and density of helium are evaluated at the surface temperature. The average heat transfer coefficients are best correlated on the basis that the coefficient varies with [1 + (L/D))(sup -0,7)] and that the physical properties and density are evaluated at the surface temperature. The average friction coefficients for the tests with no heat addition are in complete agreement with the Karman-Nikuradse line. The average friction coefficients for heat addition are in poor agreement with the accepted line.

Methane emissions from Alaska in 2012 from CARVE airborne observations

PubMed Central

Chang, Rachel Y.-W.; Miller, Charles E.; Dinardo, Steven J.; Karion, Anna; Sweeney, Colm; Daube, Bruce C.; Henderson, John M.; Mountain, Marikate E.; Eluszkiewicz, Janusz; Miller, John B.; Bruhwiler, Lori M. P.; Wofsy, Steven C.

2014-01-01

We determined methane (CH4) emissions from Alaska using airborne measurements from the Carbon Arctic Reservoirs Vulnerability Experiment (CARVE). Atmospheric sampling was conducted between May and September 2012 and analyzed using a customized version of the polar weather research and forecast model linked to a Lagrangian particle dispersion model (stochastic time-inverted Lagrangian transport model). We estimated growing season CH4 fluxes of 8 ± 2 mg CH4⋅m−2⋅d−1 averaged over all of Alaska, corresponding to fluxes from wetlands of 56−13+22 mg CH4⋅m−2⋅d−1 if we assumed that wetlands are the only source from the land surface (all uncertainties are 95% confidence intervals from a bootstrapping analysis). Fluxes roughly doubled from May to July, then decreased gradually in August and September. Integrated emissions totaled 2.1 ± 0.5 Tg CH4 for Alaska from May to September 2012, close to the average (2.3; a range of 0.7 to 6 Tg CH4) predicted by various land surface models and inversion analyses for the growing season. Methane emissions from boreal Alaska were larger than from the North Slope; the monthly regional flux estimates showed no evidence of enhanced emissions during early spring or late fall, although these bursts may be more localized in time and space than can be detected by our analysis. These results provide an important baseline to which future studies can be compared. PMID:25385648

Methane emissions from Alaska in 2012 from CARVE airborne observations.

PubMed

Chang, Rachel Y-W; Miller, Charles E; Dinardo, Steven J; Karion, Anna; Sweeney, Colm; Daube, Bruce C; Henderson, John M; Mountain, Marikate E; Eluszkiewicz, Janusz; Miller, John B; Bruhwiler, Lori M P; Wofsy, Steven C

2014-11-25

We determined methane (CH4) emissions from Alaska using airborne measurements from the Carbon Arctic Reservoirs Vulnerability Experiment (CARVE). Atmospheric sampling was conducted between May and September 2012 and analyzed using a customized version of the polar weather research and forecast model linked to a Lagrangian particle dispersion model (stochastic time-inverted Lagrangian transport model). We estimated growing season CH4 fluxes of 8 ± 2 mg CH4⋅m(-2)⋅d(-1) averaged over all of Alaska, corresponding to fluxes from wetlands of 56(-13)(+22) mg CH4⋅m(-2)⋅d(-1) if we assumed that wetlands are the only source from the land surface (all uncertainties are 95% confidence intervals from a bootstrapping analysis). Fluxes roughly doubled from May to July, then decreased gradually in August and September. Integrated emissions totaled 2.1 ± 0.5 Tg CH4 for Alaska from May to September 2012, close to the average (2.3; a range of 0.7 to 6 Tg CH4) predicted by various land surface models and inversion analyses for the growing season. Methane emissions from boreal Alaska were larger than from the North Slope; the monthly regional flux estimates showed no evidence of enhanced emissions during early spring or late fall, although these bursts may be more localized in time and space than can be detected by our analysis. These results provide an important baseline to which future studies can be compared.

Effects of meridional flow variations on solar cycles 23 and 24

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

Upton, Lisa; Hathaway, David H., E-mail: lisa.a.upton@vanderbilt.edu, E-mail: lar0009@uah.edu, E-mail: david.hathaway@nasa.gov

2014-09-10

The faster meridional flow that preceded the solar cycle 23/24 minimum is thought to have led to weaker polar field strengths, producing the extended solar minimum and the unusually weak cycle 24. To determine the impact of meridional flow variations on the sunspot cycle, we have simulated the Sun's surface magnetic field evolution with our newly developed surface flux transport model. We investigate three different cases: a constant average meridional flow, the observed time-varying meridional flow, and a time-varying meridional flow in which the observed variations from the average have been doubled. Comparison of these simulations shows that the variationsmore » in the meridional flow over cycle 23 have a significant impact (∼20%) on the polar fields. However, the variations produced polar fields that were stronger than they would have been otherwise. We propose that the primary cause of the extended cycle 23/24 minimum and weak cycle 24 was the weakness of cycle 23 itself—with fewer sunspots, there was insufficient flux to build a big cycle. We also find that any polar counter-cells in the meridional flow (equatorward flow at high latitudes) produce flux concentrations at mid-to-high latitudes that are not consistent with observations.« less

The Galapagos Spreading Center at 86°W: A detailed geothermal field study

NASA Astrophysics Data System (ADS)

Green, Kenneth E.; von Herzen, Richard P.; Williams, David L.

1981-02-01

Appendix is available with entire article on microfiche. Orderfrom American Geophysical Union, 2000 Florida Avenue, N.W.,Washington, D.C. 20009. Document J80-013; $01.00. Payment mustaccompany order. We report here measurements of the heat flow field of the Galapagos Spreading Center on crust of age less than 1.0 m.y. The 443 measurements in an area of about 570 km2 reveal the general planform of the geothermal flux and permit the first truly areal estimate of the near-axis conductive heat flux. The intrusion process and associated hydrothermal circulation dominate the surface heat flow pattern, with circulation apparently continuing beyond the limits of our survey. The areal average of the conductive heat flux is 7.1 ± 0.8 HFU (295 ± 33 mW/m2), about one-third the heat flux predicted by plate models. The remaining heat is apparently removed by venting of hydrothermal waters at the spreading axis and through basalt outcrops and hydrothermal mounds off axis. The pattern of surface heat flux is lineated parallel to the axis and the strongly lineated topography. Sharp lateral gradients in the heat flow, greater than 10 HFU/km near escarpments and commonly expressed as high heat flow at the tops of the scarps and lower heat flow in the valleys, may indicate a local concentration of the circulation by surface fault systems and/or variable sediment thickness.

Fast Longwave and Shortwave Radiative Fluxes (FLASHFlux) From CERES and MODIS Measurements

NASA Astrophysics Data System (ADS)

Stackhouse, Paul; Gupta, Shashi; Kratz, David; Geier, Erika; Edwards, Anne; Wilber, Anne

The Clouds and the Earth's Radiant Energy System (CERES) project is currently producing highly accurate surface and top-of-atmosphere (TOA) radiation budget datasets from measurements taken by CERES broadband radiometers and a subset of imaging channels on the Moderate-resolution Imaging Spectroradiometer (MODIS) instrument operating onboard Terra and Aqua satellites. The primary objective of CERES is to produce highly accurate and stable time-series datasets of radiation budget parameters to meet the needs of climate change research. Accomplishing such accuracy and stability requires monitoring the calibration and stability of the instruments, maintaining constancy of processing algorithms and meteorological inputs, and extensively validating the products against independent measurements. Such stringent requirements inevitably delay the release of products to the user community by as much as six months to a year. While such delays are inconsequential for climate research, other applications like short-term and seasonal predictions, agricultural and solar energy research, ocean and atmosphere assimilation, and field experiment support could greatly benefit if CERES products were available quickly after satellite measurements. To meet the needs of the latter class of applications, FLASHFlux was developed and is being implemented at the NASA/LaRC. FLASHFlux produces reliable surface and TOA radiative parameters within a one week of satellite observations using CERES "quicklook" data stream and fast surface flux algorithms. Cloud properties used in flux computation are derived concurrently using MODIS channel radiances. In the process, a modest degree of accuracy is sacrificed in the interest of speed. All fluxes are derived initially on a CERES footprint basis. Daily average fluxes are then derived on a 1° x1° grid in the next stage of processing. To date, FLASHFlux datasets have been used in operational processing of CloudSat data, in support of a field experiment, and for the S'COOL education outreach program. In this presentation, examples will be presented of footprint level and gridded/daily averaged fluxes and their validation. FLASHFlux datasets are available to the science community at the LaRC Atmospheric Sciences Data Center (ASDC) at: eosweb.larc.nasa.gov/PRODOCS/flashflux/table flashflux.html.

Estimation of surface heat and moisture fluxes over a prairie grassland. II - Two-dimensional time filtering and site variability

NASA Technical Reports Server (NTRS)

Crosson, William L.; Smith, Eric A.

1992-01-01

The behavior of in situ measurements of surface fluxes obtained during FIFE 1987 is examined by using correlative and spectral techniques in order to assess the significance of fluctuations on various time scales, from subdiurnal up to synoptic, intraseasonal, and annual scales. The objectives of this analysis are: (1) to determine which temporal scales have a significant impact on areal averaged fluxes and (2) to design a procedure for filtering an extended flux time series that preserves the basic diurnal features and longer time scales while removing high frequency noise that cannot be attributed to site-induced variation. These objectives are accomplished through the use of a two-dimensional cross-time Fourier transform, which serves to separate processes inherently related to diurnal and subdiurnal variability from those which impact flux variations on the longer time scales. A filtering procedure is desirable before the measurements are utilized as input with an experimental biosphere model, to insure that model based intercomparisons at multiple sites are uncontaminated by input variance not related to true site behavior. Analysis of the spectral decomposition indicates that subdiurnal time scales having periods shorter than 6 hours have little site-to-site consistency and therefore little impact on areal integrated fluxes.

NAE Twin Otter operations in FIFE 1989

NASA Technical Reports Server (NTRS)

Macpherson, J. I.

1990-01-01

During the summer of 1989, the National Aeronautical Establishment (Canada) Twin Otter Atmospheric Research Aircraft was flow in support of the NASA sponsored First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment called FIFE-89. Airborne measurements of the fluxes of heat, momentum, water vapor and carbon dioxide were made during 16 flow-altitude flights over the FIFE project area in central Kansas. The Twin Otter operations in FIFE are documented and details are included on the instrumentation, software, flight procedures, atmospheric conditions and analysis methods. Comparisons of Twin Otter measured fluxes are made with those determined at several surface sites and with those made by other instrumented aircraft in the FIFE-87 measurements. Airborne flux measurements are related to run length, altitude, and environmental parameters such as vegetation type, temperature, and wind speed. One night flight was run in an attempt to measure the respiration component of the CO2 flux. The use of aircraft was studied for regional observations of fluxes and to relate these to satellite radiance measurements. Run average data are presented for all 285 flux runs flown by the Twin Otter in FIFE-89. This should serve as as a working reference for scientists utilizing Twin Otter data either directly of through the FIFE data archive.

Seven-Year SSM/I-Derived Global Ocean Surface Turbulent Fluxes

NASA Technical Reports Server (NTRS)

Chou, Shu-Hsien; Shie, Chung-Lin; Atlas, Robert M.; Ardizzone, Joe

2000-01-01

A 7.5-year (July 1987-December 1994) dataset of daily surface specific humidity and turbulent fluxes (momentum, latent heat, and sensible heat) over global oceans has been retrieved from the Special Sensor Microwave/Imager (SSM/I) data and other data. It has a spatial resolution of 2.0 deg.x 2.5 deg. latitude-longitude. The retrieved surface specific humidity is generally accurate over global oceans as validated against the collocated radiosonde observations. The retrieved daily wind stresses and latent heat fluxes show useful accuracy as verified by those measured by the RV Moana Wave and IMET buoy in the western equatorial Pacific. The derived turbulent fluxes and input variables are also found to agree generally with the global distributions of annual-and seasonal-means of those based on 4-year (1990-93) comprehensive ocean-atmosphere data set (COADS) with adjustment in wind speeds and other climatological studies. The COADS has collected the most complete surface marine observations, mainly from merchant ships. However, ship measurements generally have poor accuracy, and variable spatial coverages. Significant differences between the retrieved and COADS-based are found in some areas of the tropical and southern extratropical oceans, reflecting the paucity of ship observations outside the northern extratropical oceans. Averaged over the global oceans, the retrieved wind stress is smaller but the latent heat flux is larger than those based on COADS. The former is suggested to be mainly due to overestimation of the adjusted ship-estimated wind speeds (depending on sea states), while the latter is suggested to be mainly due to overestimation of ship-measured dew point temperatures. The study suggests that the SSM/I-derived turbulent fluxes can be used for climate studies and coupled model validations.

An update of Leighton's solar dynamo model

NASA Astrophysics Data System (ADS)

Cameron, R. H.; Schüssler, M.

2017-03-01

In 1969, Leighton developed a quasi-1D mathematical model of the solar dynamo, building upon the phenomenological scenario of Babcock published in 1961. Here we present a modification and extension of Leighton's model. Using the axisymmetric component (longitudinal average) of the magnetic field, we consider the radial field component at the solar surface and the radially integrated toroidal magnetic flux in the convection zone, both as functions of latitude. No assumptions are made with regard to the radial location of the toroidal flux. The model includes the effects of (I) turbulent diffusion at the surface and in the convection zone; (II) poleward meridional flow at the surface and an equatorward return flow affecting the toroidal flux; (III) latitudinal differential rotation and the near-surface layer of radial rotational shear; (iv) downward convective pumping of magnetic flux in the shear layer; and (v) flux emergence in the form of tilted bipolar magnetic regions treated as a source term for the radial surface field. While the parameters relevant for the transport of the surface field are taken from observations, the model condenses the unknown properties of magnetic field and flow in the convection zone into a few free parameters (turbulent diffusivity, effective return flow, amplitude of the source term, and a parameter describing the effective radial shear). Comparison with the results of 2D flux transport dynamo codes shows that the model captures the essential features of these simulations. We make use of the computational efficiency of the model to carry out an extended parameter study. We cover an extended domain of the 4D parameter space and identify the parameter ranges that provide solar-like solutions. Dipole parity is always preferred and solutions with periods around 22 yr and a correct phase difference between flux emergence in low latitudes and the strength of the polar fields are found for a return flow speed around 2 m s-1, turbulent diffusivity below about 80 km2s-1, and dynamo excitation not too far above the threshold (linear growth rate less than 0.1 yr-1).

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.

Global carbon assimilation system using a local ensemble Kalman filter with multiple ecosystem models

NASA Astrophysics Data System (ADS)

Zhang, Shupeng; Yi, Xue; Zheng, Xiaogu; Chen, Zhuoqi; Dan, Bo; Zhang, Xuanze

2014-11-01

In this paper, a global carbon assimilation system (GCAS) is developed for optimizing the global land surface carbon flux at 1° resolution using multiple ecosystem models. In GCAS, three ecosystem models, Boreal Ecosystem Productivity Simulator, Carnegie-Ames-Stanford Approach, and Community Atmosphere Biosphere Land Exchange, produce the prior fluxes, and an atmospheric transport model, Model for OZone And Related chemical Tracers, is used to calculate atmospheric CO2 concentrations resulting from these prior fluxes. A local ensemble Kalman filter is developed to assimilate atmospheric CO2 data observed at 92 stations to optimize the carbon flux for six land regions, and the Bayesian model averaging method is implemented in GCAS to calculate the weighted average of the optimized fluxes based on individual ecosystem models. The weights for the models are found according to the closeness of their forecasted CO2 concentration to observation. Results of this study show that the model weights vary in time and space, allowing for an optimum utilization of different strengths of different ecosystem models. It is also demonstrated that spatial localization is an effective technique to avoid spurious optimization results for regions that are not well constrained by the atmospheric data. Based on the multimodel optimized flux from GCAS, we found that the average global terrestrial carbon sink over the 2002-2008 period is 2.97 ± 1.1 PgC yr-1, and the sinks are 0.88 ± 0.52, 0.27 ± 0.33, 0.67 ± 0.39, 0.90 ± 0.68, 0.21 ± 0.31, and 0.04 ± 0.08 PgC yr-1 for the North America, South America, Africa, Eurasia, Tropical Asia, and Australia, respectively. This multimodel GCAS can be used to improve global carbon cycle estimation.

Measuring Convective Mass Fluxes Over Tropical Oceans

NASA Astrophysics Data System (ADS)

Raymond, David

2017-04-01

Deep convection forms the upward branches of all large-scale circulations in the tropics. Understanding what controls the form and intensity of vertical convective mass fluxes is thus key to understanding tropical weather and climate. These mass fluxes and the corresponding conditions supporting them have been measured by recent field programs (TPARC/TCS08, PREDICT, HS3) in tropical disturbances considered to be possible tropical storm precursors. In reality, this encompasses most strong convection in the tropics. The measurements were made with arrays of dropsondes deployed from high altitude. In some cases Doppler radar provided additional measurements. The results are in some ways surprising. Three factors were found to control the mass flux profiles, the strength of total surface heat fluxes, the column-integrated relative humidity, and the low to mid-tropospheric moist convective instability. The first two act as expected, with larger heat fluxes and higher humidity producing more precipitation and stronger lower tropospheric mass fluxes. However, unexpectedly, smaller (but still positive) convective instability produces more precipitation as well as more bottom-heavy convective mass flux profiles. Furthermore, the column humidity and the convective instability are anti-correlated, at least in the presence of strong convection. On spatial scales of a few hundred kilometers, the virtual temperature structure appears to be in dynamic balance with the pattern of potential vorticity. Since potential vorticity typically evolves on longer time scales than convection, the potential vorticity pattern plus the surface heat fluxes then become the immediate controlling factors for average convective properties. All measurements so far have taken place in regions with relatively flat sea surface temperature (SST) distributions. We are currently seeking funding for a measurement program in the tropical east Pacific, a region that exhibits strong SST gradients and correspondingly great diversity in the forms of convection. Given the strong boundary layer flows induced by the SST gradients in this region, we hope to determine whether the patterns of convective mass flux seen in other regions persist there.

A Climatology of Midlatitude Continental Clouds from the ARM SGP Site. Part II; Cloud Fraction and Surface Radiative Forcing

NASA Technical Reports Server (NTRS)

Xi, B.; Minnis, P.

2006-01-01

Data collected at the Department of Energy Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility (SCF) are analyzed to determine the monthly and hourly variations of cloud fraction and radiative forcing between January 1997 and December 2002. Cloud fractions are estimated for total cloud cover and for single-layered low (0-3 km), middle (3-6 km), and high clouds (more than 6 km) using ARM SCG ground-based paired lidar-radar measurements. Shortwave (SW) and longwave (LW) fluxes are derived from up- and down-looking standard precision spectral pyranometers and precision infrared radiometer measurements with uncertainties of approximately 10 Wm(exp -2). The annual averages of total, and single-layered low, middle and high cloud fractions are 0.49, 0.11, 0.03, and 0.17, respectively. Both total and low cloud amounts peak during January and February and reach a minimum during July and August, high clouds occur more frequently than other types of clouds with a peak in summer. The average annual downwelling surface SW fluxes for total and low clouds (151 and 138 Wm(exp-2), respectively) are less than those under middle and high clouds (188 and 201 Wm(exp -2), respectively), but the downwelling LW fluxes (349 and 356 Wm(exp -2)) underneath total and low clouds are greater than those from middle and high clouds (337 and 333 Wm(exp -2)). Low clouds produce the largest LW warming (55 Wm(exp -2) and SW cooling (-91 Wm(exp -2)) effects with maximum and minimum absolute values in spring and summer, respectively. High clouds have the smallest LW warming (17 Wm(exp -2)) and SW cooling (-37 Wm(exp -2)) effects at the surface. All-sky SW CRF decreases and LW CRF increases with increasing cloud fraction with mean slopes of -0.984 and 0.616 Wm(exp -2)%(exp -1), respectively. Over the entire diurnal cycle, clouds deplete the amount of surface insolation more than they add to the downwelling LW flux. The calculated CRFs do not appear to be significantly affected by uncertainties in data sampling and clear-sky screening. Traditionally, cloud radiative forcing includes, not only the radiative impact of the hydrometeors, but also the changes in the environment. Taken together over the ARM SCF, changes in humidity and surface albedo between clear and cloudy conditions offset approximately 20% of the NET radiative forcing caused by the cloud hydrometeors alone. Variations in water vapor, on average, account for 10% and 83% of the SW and LW CRFs, respectively, in total cloud cover conditions. The error analysis further reveals that the cloud hydrometeors dominate the SW CRF, while water vapor changes are most important for LW flux changes in cloudy skies. Similar studies over other locales are encouraged where water and surface albedo changes from clear to cloudy conditions may be much different than observed over the ARM SCF.

Simultaneous and multi-point measurement of ammonia emanating from human skin surface for the estimation of whole body dermal emission rate.

PubMed

Furukawa, Shota; Sekine, Yoshika; Kimura, Keita; Umezawa, Kazuo; Asai, Satomi; Miyachi, Hayato

2017-05-15

Ammonia is one of the members of odor gases and a possible source of odor in indoor environment. However, little has been known on the actual emission rate of ammonia from the human skin surface. Then, this study aimed to estimate the whole-body dermal emission rate of ammonia by simultaneous and multi-point measurement of emission fluxes of ammonia employing a passive flux sampler - ion chromatography system. Firstly, the emission fluxes of ammonia were non-invasively measured for ten volunteers at 13 sampling positions set in 13 anatomical regions classified by Kurazumi et al. The measured emission fluxes were then converted to partial emission rates using the surface body areas estimated by weights and heights of volunteers and partial rates of 13 body regions. Subsequent summation of the partial emission rates provided the whole body dermal emission rate of ammonia. The results ranged from 2.9 to 12mgh -1 with an average of 5.9±3.2mgh -1 per person for the ten healthy young volunteers. The values were much greater than those from human breath, and thus the dermal emission of ammonia was found more significant odor source than the breath exhalation in indoor environment. Copyright © 2017 Elsevier B.V. All rights reserved.

Visualization and Quality Control Web Tools for CERES Products

NASA Astrophysics Data System (ADS)

Mitrescu, C.; Doelling, D. R.

2017-12-01

The NASA CERES project continues to provide the scientific communities a wide variety of satellite-derived data products such as observed TOA broadband shortwave and longwave observed fluxes, computed TOA and Surface fluxes, as well as cloud, aerosol, and other atmospheric parameters. They encompass a wide range of temporal and spatial resolutions, suited to specific applications. CERES data is used mostly by climate modeling communities but also by a wide variety of educational institutions. To better serve our users, a web-based Ordering and Visualization Tool (OVT) was developed by using Opens Source Software such as Eclipse, java, javascript, OpenLayer, Flot, Google Maps, python, and others. Due to increased demand by our own scientists, we also implemented a series of specialized functions to be used in the process of CERES Data Quality Control (QC) such as 1- and 2-D histograms, anomalies and differences, temporal and spatial averaging, side-by-side parameter comparison, and others that made the process of QC far easier and faster, but more importantly far more portable. With the integration of ground site observed surface fluxes we further facilitate the CERES project to QC the CERES computed surface fluxes. An overview of the CERES OVT basic functions using Open Source Software, as well as future steps in expanding its capabilities will be presented at the meeting.

Development of Advanced Thermal and Environmental Barrier Coatings Using a High-Heat-Flux Testing Approach

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Miller, Robert A.

2003-01-01

The development of low conductivity, robust thermal and environmental barrier coatings requires advanced testing techniques that can accurately and effectively evaluate coating thermal conductivity and cyclic resistance at very high surface temperatures (up to 1700 C) under large thermal gradients. In this study, a laser high-heat-flux test approach is established for evaluating advanced low conductivity, high temperature capability thermal and environmental barrier coatings under the NASA Ultra Efficient Engine Technology (UEET) program. The test approach emphasizes the real-time monitoring and assessment of the coating thermal conductivity, which initially rises under the steady-state high temperature thermal gradient test due to coating sintering, and later drops under the cyclic thermal gradient test due to coating cracking/delamination. The coating system is then evaluated based on damage accumulation and failure after the combined steady-state and cyclic thermal gradient tests. The lattice and radiation thermal conductivity of advanced ceramic coatings can also be evaluated using laser heat-flux techniques. The external radiation resistance of the coating is assessed based on the measured specimen temperature response under a laser- heated intense radiation-flux source. The coating internal radiation contribution is investigated based on the measured apparent coating conductivity increases with the coating surface test temperature under large thermal gradient test conditions. Since an increased radiation contribution is observed at these very high surface test temperatures, by varying the laser heat-flux and coating average test temperature, the complex relation between the lattice and radiation conductivity as a function of surface and interface test temperature may be derived.

Surface Ocean pCO2 Seasonality and Sea-Air CO2 Flux Estimates for the North American East Coast

NASA Technical Reports Server (NTRS)

Signorini, Sergio; Mannino, Antonio; Najjar, Raymond G., Jr.; Friedrichs, Marjorie A. M.; Cai, Wei-Jun; Salisbury, Joe; Wang, Zhaohui Aleck; Thomas, Helmuth; Shadwick, Elizabeth

2013-01-01

Underway and in situ observations of surface ocean pCO2, combined with satellite data, were used to develop pCO2 regional algorithms to analyze the seasonal and interannual variability of surface ocean pCO2 and sea-air CO2 flux for five physically and biologically distinct regions of the eastern North American continental shelf: the South Atlantic Bight (SAB), the Mid-Atlantic Bight (MAB), the Gulf of Maine (GoM), Nantucket Shoals and Georges Bank (NS+GB), and the Scotian Shelf (SS). Temperature and dissolved inorganic carbon variability are the most influential factors driving the seasonality of pCO2. Estimates of the sea-air CO2 flux were derived from the available pCO2 data, as well as from the pCO2 reconstructed by the algorithm. Two different gas exchange parameterizations were used. The SS, GB+NS, MAB, and SAB regions are net sinks of atmospheric CO2 while the GoM is a weak source. The estimates vary depending on the use of surface ocean pCO2 from the data or algorithm, as well as with the use of the two different gas exchange parameterizations. Most of the regional estimates are in general agreement with previous studies when the range of uncertainty and interannual variability are taken into account. According to the algorithm, the average annual uptake of atmospheric CO2 by eastern North American continental shelf waters is found to be between 3.4 and 5.4 Tg C/yr (areal average of 0.7 to 1.0 mol CO2 /sq m/yr) over the period 2003-2010.

Diurnal cross-shore thermal exchange on a tropical forereef

NASA Astrophysics Data System (ADS)

Molina, L.; Pawlak, G.; Wells, J. R.; Monismith, S. G.; Merrifield, M. A.

2014-09-01

Observations of the velocity structure at the Kilo Nalu Observatory on the south shore of Oahu, Hawaii show that thermally driven baroclinic exchange is a dominant mechanism for cross-shore transport for this tropical forereef environment. Estimates of the exchange and net volume fluxes are comparable and show that the average residence time for the zone shoreward of the 12 m isobath is generally much less than 1 day. Although cross-shore wind stress influences the diurnal cross-shore exchange, surface heat flux is identified as the primary forcing mechanism from the phase relationships and from analysis of momentum and buoyancy balances for the record-averaged diurnal structure. Dynamic flow regimes are characterized based on a two-dimensional theoretical framework and the observations of the thermal structure at Kilo Nalu are shown to be in the unsteady temperature regime. Diurnal phasing and the cross-shore momentum balance suggest that turbulent stress divergence is an important driver of the baroclinic exchange. While the thermally driven exchange has a robust diurnal profile in the long term, there is high temporal variability on shorter time scales. Ensemble-averaged diurnal profiles indicate that the exchange is strongly modulated by surface heat flux, wind speed/direction, and alongshore velocity direction. The latter highlights the role of alongshore variability in the thermally driven exchange. Analysis of the thermal balance in the nearshore region indicates that the cross-shore exchange accounts for roughly 38% of the advective heat transport on a daily basis. This article was corrected on 10 OCT 2014. See the end of the full text for details.

[O3 dry deposition flux observation and soil resistance modeling over a bare soil in Nanjing area in autumn].

PubMed

Huang, Ji Qing; Zheng, You Fei; Xu, Jing Xin; Zhao, Hui; Yuan, Yue; Chu, Zhong Fang

2016-10-01

In this study, the concentration of O 3 and its deposition flux over a bare soil in Nanjing in autumn were observed by using an eddy covariance system with rapid ozone analyzer. We analyzed the correlation of ozone concentration, deposition flux, and meteorological conditions in order to explore the characteristics of the variations in ozone deposition flux and deposition velocity. We also compared flux and velocity by using modeled soil resistance with observations. The results showed that the diurnal variation of ozone concentration exhibited a single peak distribution, and it increased due to radiation enhancement from September 25th to October 28th, 2015. Ozone deposition flux over a bare soil in autumn was mainly affected by its concentration, with diurnal average values varying from -31.4 to -156.8 ng·s -1 ·m -2 (the negative sign indicated that the deposition direction was toward the ground). As a result of non-vegetation over a bare soil, the ozone deposition flux was significantly influenced by environmental factors. Diurnal average of deposition velocities varied in the range of 0.09-0.30 cm·s -1 . The turbulence exchange played a major role in the atmosphere transportation of ozone, and underlying surface condition was particularly important to O 3 dry deposition over the bare soil. Soil resistance (R s ) increased exponentially with air relative humidity (RH), and the equation was R s =89.981e 0.0246 RH . The parameterized ozone deposition velocities and fluxes were in good agreement with the measured values.

Blade motion and nutrient flux to the kelp, Eisenia arborea.

PubMed

Denny, Mark; Roberson, Loretta

2002-08-01

Marine algae rely on currents and waves to replenish the nutrients required for photosynthesis. The interaction of algal blades with flow often involves dynamic reorientations of the blade surface (pitching and flapping) that may in turn affect nutrient flux. As a first step toward understanding the consequences of blade motion, we explore the effect of oscillatory pitching on the flux to a flat plate and to two morphologies of the kelp Eisenia arborea. In slow flow (equivalent to a water velocity of 2.7 cm s(-1)), pitching increases the time-averaged flux to both kelp morphologies, but not to the plate. In fast flow (equivalent to 20 cm s(-1) in water), pitching has negligible effect on flux regardless of shape. For many aspects of flux, the flat plate is a reliable model for the flow-protected algal blade, but predictions made from the plate would substantially underestimate the flux to the flow-exposed blade. These measurements highlight the complexities of flow-related nutrient transport and the need to understand better the dynamic interactions among nutrient flux, blade motion, blade morphology, and water flow.

M dwarf energetic proton flux on exoplanets during flares: estimates using solar UV-proton relations

NASA Astrophysics Data System (ADS)

Youngblood, Allison, France; Kevin; Mason, James P.

2016-10-01

UV and X-ray stellar radiation impacts planetary atmospheres through heating and photochemistry, even regulating production of potential biomarkers. The surface conditions on M dwarf planets are not greatly affected by flares in the emission line-dominated far-UV spectra of M dwarfs (M < 0.5 Msun), however, theoretical investigations have largely ignored the additional influence of stellar energetic particles (SEPs) released during flares. Magnetospheric compression and atmospheric stripping by SEPs could allow life-damaging (or catalyzing) radiation to reach the planetary surface and cause atmospheric heating closer to the surface. For the sun, a relationship between >10 MeV proton flux and 1-8 Å irradiance has been established with data from the GOES satellites (Belov et al. 2005), however, only a few X-ray observations of M-dwarf flares covering the complete 1-8 Å bandpass exist. Current M dwarf SEP estimates (Segura et al. 2010) employ the Neupert effect to first estimate the average X-ray flux over a broad band (1-62 Å) from the observed near- and far-UV flare flux (Mitra-Kraev et al. 2005). To improve the quality of proton flux estimates, we have analyzed the GOES >10 MeV observed proton flux and SDO EVE's solar spectral irradiance measurements to define relationships between SEPs and extreme-UV emission lines with formation temperatures similar to far-UV lines directly accessible by the Hubble Space Telescope (HST). Under the necessary assumption that an M dwarf's SEP production mechanism is similar to the sun's, we estimate SEP fluxes during M-dwarf flares observed with HST as part of the MUSCLES (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems) Treasury Survey.

Bora event variability and the role of air-sea feedback

USGS Publications Warehouse

Pullen, J.; Doyle, J.D.; Haack, T.; Dorman, C.; Signell, R.P.; Lee, C.M.

2007-01-01

A two-way interacting high resolution numerical simulation of the Adriatic Sea using the Navy Coastal Ocean Model (NCOM) and Coupled Ocean/ Atmosphere Mesoscale Prediction System (COAMPS??) was conducted to improve forecast momentum and heat flux fields, and to evaluate surface flux field differences for two consecutive bora events during February 2003. (COAMPS?? is a registered trademark of the Naval Research Laboratory.) The strength, mean positions and extensions of the bora jets, and the atmospheric conditions driving them varied considerably between the two events. Bora 1 had 62% stronger heat flux and 51% larger momentum flux than bora 2. The latter displayed much greater diurnal variability characterized by inertial oscillations and the early morning strengthening of a west Adriatic barrier jet, beneath which a stronger west Adriatic ocean current developed. Elsewhere, surface ocean current differences between the two events were directly related to differences in wind stress curl generated by the position and strength of the individual bora jets. The mean heat flux bias was reduced by 72%, and heat flux RMSE reduced by 30% on average at four instrumented over-water sites in the two-way coupled simulation relative to the uncoupled control. Largest reductions in wind stress were found in the bora jets, while the biggest reductions in heat flux were found along the north and west coasts of the Adriatic. In bora 2, SST gradients impacted the wind stress curl along the north and west coasts, and in bora 1 wind stress curl was sensitive to the Istrian front position and strength. The two-way coupled simulation produced diminished surface current speeds of ???12% over the northern Adriatic during both bora compared with a one-way coupled simulation. Copyright 2007 by the American Geophysical Union.

Contributions of natural and anthropogenic sources to ambient ammonia in the Athabasca Oil Sands and north-western Canada

NASA Astrophysics Data System (ADS)

Whaley, Cynthia H.; Makar, Paul A.; Shephard, Mark W.; Zhang, Leiming; Zhang, Junhua; Zheng, Qiong; Akingunola, Ayodeji; Wentworth, Gregory R.; Murphy, Jennifer G.; Kharol, Shailesh K.; Cady-Pereira, Karen E.

2018-02-01

Atmospheric ammonia (NH3) is a short-lived pollutant that plays an important role in aerosol chemistry and nitrogen deposition. Dominant NH3 emissions are from agriculture and forest fires, both of which are increasing globally. Even remote regions with relatively low ambient NH3 concentrations, such as northern Alberta and Saskatchewan in northern Canada, may be of interest because of industrial oil sands emissions and a sensitive ecological system. A previous attempt to model NH3 in the region showed a substantial negative bias compared to satellite and aircraft observations. Known missing sources of NH3 in the model were re-emission of NH3 from plants and soils (bidirectional flux) and forest fire emissions, but the relative impact of these sources on NH3 concentrations was unknown. Here we have used a research version of the high-resolution air quality forecasting model, GEM-MACH, to quantify the relative impacts of semi-natural (bidirectional flux of NH3 and forest fire emissions) and direct anthropogenic (oil sand operations, combustion of fossil fuels, and agriculture) sources on ammonia volume mixing ratios, both at the surface and aloft, with a focus on the Athabasca Oil Sands region during a measurement-intensive campaign in the summer of 2013. The addition of fires and bidirectional flux to GEM-MACH has improved the model bias, slope, and correlation coefficients relative to ground, aircraft, and satellite NH3 measurements significantly.By running the GEM-MACH-Bidi model in three configurations and calculating their differences, we find that averaged over Alberta and Saskatchewan during this time period an average of 23.1 % of surface NH3 came from direct anthropogenic sources, 56.6 % (or 1.24 ppbv) from bidirectional flux (re-emission from plants and soils), and 20.3 % (or 0.42 ppbv) from forest fires. In the NH3 total column, an average of 19.5 % came from direct anthropogenic sources, 50.0 % from bidirectional flux, and 30.5 % from forest fires. The addition of bidirectional flux and fire emissions caused the overall average net deposition of NHx across the domain to be increased by 24.5 %. Note that forest fires are very episodic and their contributions will vary significantly for different time periods and regions.This study is the first use of the bidirectional flux scheme in GEM-MACH, which could be generalized for other volatile or semi-volatile species. It is also the first time CrIS (Cross-track Infrared Sounder) satellite observations of NH3 have been used for model evaluation, and the first use of fire emissions in GEM-MACH at 2.5 km resolution.

STUDY OF RADON FLUX FROM SOIL IN BUDHAKEDAR REGION USING SRM.

PubMed

Bourai, A A; Aswal, Sunita; Kandari, Tushar; Kumar, Shiv; Joshi, Veena; Sahoo, B K; Ramola, R C

2016-10-01

In the present study, the radon flux rate of the soil is measured using portable radon monitor (scintillation radon monitor) in the Budhakedar region of District Tehri, India. The study area falls along a fault zone named Main Central Thrust, which is relatively rich in radium-bearing minerals. Radon flux rate from the soil is one of the most important factors for the evaluation of environmental radon levels. The earlier studies in the Budhakedar region shows a high level of radon (>4000 Bq m -3 ). Hence, it is important to measure the radon flux rate. The aim of the present study is to calculate the average estimate of the surface radon flux rate as well as the effective mass exhalation rate. A positive correlation of 0.54 was found between radon flux rate and radon mass exhalation rate. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Rapid electron transfer by the carbon matrix in natural pyrogenic carbon

PubMed Central

Sun, Tianran; Levin, Barnaby D. A.; Guzman, Juan J. L.; Enders, Akio; Muller, David A.; Angenent, Largus T.; Lehmann, Johannes

2017-01-01

Surface functional groups constitute major electroactive components in pyrogenic carbon. However, the electrochemical properties of pyrogenic carbon matrices and the kinetic preference of functional groups or carbon matrices for electron transfer remain unknown. Here we show that environmentally relevant pyrogenic carbon with average H/C and O/C ratios of less than 0.35 and 0.09 can directly transfer electrons more than three times faster than the charging and discharging cycles of surface functional groups and have a 1.5 V potential range for biogeochemical reactions that invoke electron transfer processes. Surface functional groups contribute to the overall electron flux of pyrogenic carbon to a lesser extent with greater pyrolysis temperature due to lower charging and discharging capacities, although the charging and discharging kinetics remain unchanged. This study could spur the development of a new generation of biogeochemical electron flux models that focus on the bacteria–carbon–mineral conductive network. PMID:28361882

The advantages, and challenges, in using multiple techniques in the estimation of surface water-groundwater fluxes.

NASA Astrophysics Data System (ADS)

Shanafield, M.; Cook, P. G.

2014-12-01

When estimating surface water-groundwater fluxes, the use of complimentary techniques helps to fill in uncertainties in any individual method, and to potentially gain a better understanding of spatial and temporal variability in a system. It can also be a way of preventing the loss of data during infrequent and unpredictable flow events. For example, much of arid Australia relies on groundwater, which is recharged by streamflow through ephemeral streams during flood events. Three recent surface water/groundwater investigations from arid Australian systems provide good examples of how using multiple field and analysis techniques can help to more fully characterize surface water-groundwater fluxes, but can also result in conflicting values over varying spatial and temporal scales. In the Pilbara region of Western Australia, combining streambed radon measurements, vertical heat transport modeling, and a tracer test helped constrain very low streambed residence times, which are on the order of minutes. Spatial and temporal variability between the methods yielded hyporheic exchange estimates between 10-4 m2 s-1 and 4.2 x 10-2 m2 s-1. In South Australia, three-dimensional heat transport modeling captured heterogeneity within 20 square meters of streambed, identifying areas of sandy soil (flux rates of up to 3 m d-1) and clay (flux rates too slow to be accurately characterized). Streamflow front modeling showed similar flux rates, but averaged over 100 m long stream segments for a 1.6 km reach. Finally, in central Australia, several methods are used to decipher whether any of the flow down a highly ephemeral river contributes to regional groundwater recharge, showing that evaporation and evapotranspiration likely accounts for all of the infiltration into the perched aquifer. Lessons learned from these examples demonstrate the influences of the spatial and temporal variability between techniques on estimated fluxes.

Continuous determination of land-atmosphere Hg0 exchange using a novel Relaxed Eddy Accumulation design

NASA Astrophysics Data System (ADS)

Osterwalder, Stefan; Fritsche, Johannes; Nilsson, Mats B.; Alewell, Christine; Bishop, Kevin

2015-04-01

The fate of anthropogenic emissions to the atmosphere is influenced by the exchange of elemental mercury (Hg0) with the earth surface. However, it remains challenging to quantify these exchanges which hold the key to a better understanding of mercury cycling at different scales, from the entire earth to specific environments. To better test hypotheses about land-atmosphere Hg interactions, we applied dynamic flux chambers (DFCs) for short term measurements and developed a novel Relaxed Eddy Accumulation (REA) design for continuous flux monitoring. Accurate determination of Hg0 fluxes has proven difficult due to the technical challenges presented by the small concentration differences (< 1 ng m-3) between updrafts and downdrafts. To address this we present a dual-intake, single analyzer REA system including a calibration module for periodic quality-control measurements with reference gases. To demonstrate the system performance, we present results from two contrasting environments: In February 2012 REA monitored a heterogeneous urban surface in the center of Basel, Switzerland where an average flux of 14 ng m-2 h-1 was detected with a distinct diurnal pattern. In May 2012, the REA monitored a boreal mire in northern Sweden with different turbulence regimes and Hg0 sink/source characteristics. During the snowmelt period in May 2012 the Hg0 flux averaged at 2 ng m-2 h-1. In order to better quantify inputs and outputs of Hg from boreal landscapes, we subsequently monitored the land-atmosphere exchange of Hg0 during a course of a year and compared the fluxes occasionally with DFC measurements. The amount of Hg0 volatilized from boreal mires was at a similar level as the annual export of Hg in stream water, identifying the mire as net source of Hg to neighboring environments. We believe that this dual-inlet, single detector approach is a significant innovation which can help realize the potential of REA for continuous, long-term determination of land-atmosphere Hg0 exchange.

Neoclassical toroidal plasma viscosity in the vicinity of the magnetic axis in tokamaks with broken symmetry

NASA Astrophysics Data System (ADS)

Shaing, K. C.; Lee, H.; Seol, J.; Aydemir, A. Y.

2015-08-01

Theory for neoclassical toroidal plasma viscosity in the low collisionality regime is extended to the vicinity of the magnetic axis in tokamaks with broken symmetry. The toroidal viscosity is induced by particles drifting off the perturbed magnetic surface under the influence of the symmetry breaking magnetic field. In the region away from the magnetic axis, the drift orbit dynamics is governed by the bounce averaged drift kinetic equation in the low collisionality regimes. In the vicinity of the magnetic axis, it is the drift kinetic equation, averaged over the trapped particle orbits, i.e., potato orbits, that governs the drift dynamics. The orbit averaged drift kinetic equation is derived when collision frequency is low enough for trapped particles to complete their potato trajectories. The resultant equation is solved in the 1 /ν regime to obtain transport fluxes and, thus, toroidal plasma viscosity through flux-force relation. Here, ν is the collision frequency. The viscosity does not vanish on the magnetic axis, and has the same scalings as that in the region away from magnetic axis, except that the fraction of bananas is replaced by the fraction of potatoes. It also has a weak radial dependence. Modeling of plasma flow velocity V for the case where the magnetic surfaces are broken is also discussed.

Energy flow and energy dissipation in a free surface.

NASA Astrophysics Data System (ADS)

Goldburg, Walter; Cressman, John

2005-11-01

Turbulent flows on a free surface are strongly compressible [1] and do not conserve energy in the absence of viscosity as bulk fluids do. Despite violation of assumptions essential to Kolmogorov's theory of 1941 (K41) [2, 3], surface flows show strong agreement with Kolmogorov scaling, though intermittency is larger there. Steady state turbulence is generated in a tank of water, and the spatially averaged energy flux is measured from the four-fifth's law at each instant of time. Likewise, the energy dissipation rate as measured from velocity gradients is also a random variable in this experiment. The energy flux - dissipation rate cross-correlation is measured to be correlated in incompressible bulk flows, but strongly anti-correlated on the surface. We argue that the reason for this discrepancy between surface and bulk flows is due to compressible effects present on the surface. [1] J. R. Cressman, J. Davoudi, W. I. Goldburg, and J. Schumacher, New Journal of Physics, 6, 53, 2004. [2] U. Frisch. Turbulence: The legacy of A. N. Kolmogorov, Cambridge University Press, Cambridge, 1995. [3] A. N. Kolmogorov, Doklady Akad. Nauk SSSR, 32, 16, 1941.

Utilization of point soil moisture measurements for field scale soil moisture averages and variances in agricultural landscapes

USDA-ARS?s Scientific Manuscript database

Soil moisture is a key variable in understanding the hydrologic processes and energy fluxes at the land surface. In spite of new technologies for in-situ soil moisture measurements and increased availability of remotely sensed soil moisture data, scaling issues between soil moisture observations and...

Temporal variability of methane fluxes in West Siberian taiga bogs and its implications for estimating regional methane emission

NASA Astrophysics Data System (ADS)

Sabrekov, Alexander; Ilyasov, Danil; Terentieva, Irina; Glagolev, Mikhail; Maksyutov, Shamil

2017-04-01

The West Siberia Lowland (WSL) is the biggest peatland area in Eurasia and is situated in the high latitudes experiencing enhanced rate of climate change. During 2015-16 summer periods, seasonal measurements of methane emission were made at the field station «Mukhrino» in the WSL middle taiga zone. The study was made at 3 wetland ecosystem types covering 80% of the taiga wetland area: i) waterlogged hollows or depressed areas with water level above the moss surface, ii) oligotrophic hollows or depressed parts of bogs with water level beneath the moss surface, iii) forested bogs with dwarf shrubs-sphagnum vegetation. Seven series of measurements were made by a static chamber method in 2016 and four series - in 2015. In 2015, we observed non-typical weather conditions including early dry spring and short cold rainy summer. Oppositely, weather conditions in 2016 were closer to average long-term with warmer drier summer. Significant difference between these years allowed analyzing the temporal variability and its sources. Average methane flux rates from forested bogs were 0.57 mgCH4/m2/h in 2016 and 0.33 mgCH4/m2/h in 2015. Seasonal dynamic during both years had similar concave downward shape. The highest fluxes were observed in June and were corresponded to the highest WTL, the main limiting factor of emission from forested bogs. The lowest fluxes in July were related to the low WTL combining with the highest temperature of upper methanotrophy layer. Average methane flux rates from oligotrophic hollows were 7.18 mgCH4/m2/h in 2016 and 4.28 mgCH4/m2/h in 2015. Seasonal dynamic of methane emission was indistinct in 2015. On the contrary, in 2016 it had regular seasonal pattern with peak emissions in July, which were four times higher than in 2015. WTL was not the limiting factor for CH4 emission from oligotrophic hollows, because even in the driest ones it was only 10 cm below the surface. Thus, the difference between peak emissions in 2015 and 2016 was mainly related to the temperature, which was considerably higher in 2016. Average methane flux rates from waterlogged hollows were 2.19 mgCH4/m2/h in 2016 and 4.07 mgCH4/m2/h in 2015. Seasonal dynamic had prominent shape in both years, however, peak emissions were observed in different months. Overall, patterns of emission in these ecosystems had more complicate nature and needs future investigations. Regional methane emission was estimated using new wetland map by Terentieva et al. (2016). Seasonal dynamic data for 2015-16 years gave the regional flux of 161 and 1257 ktCH4/yr for forested bogs and oligotrophic hollows, respectively. Similar values were obtained using not seasonal dynamic but only flux medians for 2015-16 years. However, the usage of old dataset gave only 32 and 841 ktCH4/yr for forested bogs and oligotrophic hollows, respectively. Thus, seasonal dynamics data had lower impact on regional methane emission estimate comparing to interannual variability data. Terentieva, I.E., Glagolev, M.V., Lapshina, E.D., Sabrekov, A.F., Maksyutov, S. Mapping of West Siberian taiga wetland complexes using Landsat imagery: implications for methane emissions // Biogeosciences. 2016. V. 13. № 16. P. 4615-4626.

Heat transfer characteristics within an array of impinging jets. Effects of crossflow temperature relative to jet temperature

NASA Technical Reports Server (NTRS)

Florschuetz, L. W.; Su, C. C.

1985-01-01

Spanwise average heat fluxes, resolved in the streamwise direction to one stream-wise hole spacing were measured for two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate. The jet flow, after impingement, was constrained to exit in a single direction along the channel formed by the jet orifice plate and heat transfer surface. The crossflow originated from the jets following impingement and an initial crossflow was present that approached the array through an upstream extension of the channel. The regional average heat fluxes are considered as a function of parameters associated with corresponding individual spanwise rows within the array. A linear superposition model was employed to formulate appropriate governing parameters for the individual row domain. The effects of flow history upstream of an individual row domain are also considered. The results are formulated in terms of individual spanwise row parameters. A corresponding set of streamwise resolved heat transfer characteristics formulated in terms of flow and geometric parameters characterizing the overall arrays is described.

Evaluating greenhouse gas emissions from hydropower complexes on large rivers in Eastern Washington

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

Arntzen, Evan V.; Miller, Benjamin L.; O'Toole, Amanda C.

2013-03-15

Water bodies, such as freshwater lakes, are known to be net emitters of carbon dioxide (CO2), and methane (CH4). In recent years, significant greenhouse gas (GHG) emissions from tropical, boreal, and mid-latitude reservoirs have been reported. At a time when hydropower is increasing worldwide, better understanding of seasonal and regional variation in GHG emissions is needed in order to develop a predictive understanding of such fluxes within man-made impoundments. We examined power-producing dam complexes within xeric temperate locations in the northwestern United States. Sampling environments on the Snake (Lower Monumental Dam Complex) and Columbia Rivers (Priest Rapids Dam Complex) includedmore » tributary, mainstem, embayment, forebay, and tailrace areas during winter and summer 2012. At each sampling location, GHG measurement pathways included surface gas flux, degassing as water passed through dams during power generation, ebullition within littoral embayments, and direct sampling of hyporheic pore-water. Measurements were also carried out in a free-flowing reach of the Columbia River to estimate unaltered conditions. Surface flux resulted in very low emissions, with reservoirs acting as a sink for CO2 (up to –262 mg m-2 d-1, which is within the range previously reported for similarly located reservoirs). Surface flux of methane remained below 1 mg CH4 m-2d-1, a value well below fluxes reported previously for temperate reservoirs. Water passing through hydroelectric projects acted as a sink for CO2 during winter and a small source during summer, with mean degassing fluxes of –117 and 4.5 t CO2 d-1, respectively. Degassing of CH4 was minimal, with mean fluxes of 3.1 × 10-6 and –5.6 × 10-4 t CH4 d-1 during winter and summer, respectively. Gas flux due to ebullition was greater in coves located within reservoirs than in coves within the free flowing Hanford Reach–and CH4 flux exceeded that of CO2. Methane emissions varied widely across sampling locations, ranging from 10.5 to 1039 mg CH4 m-2 d-1, with mean fluxes of 324 mg CH4 m-2 d-1in Lower Monumental Dam reservoir and 482 mg CH4 m-2d-1 in the Priest Rapids Dam reservoir. The magnitude of methane flux due to ebullition was unexpectedly high, and falls within the range recently reported for other temperate reservoirs around the world, further suggesting that this methane source should be considered in estimates of global greenhouse gas emissions. Methane flux from sediment pore-water within littoral embayments averaged 4.2 mg m-2 d-1 during winter and 8.1 mg m-2 d-1 during summer, with a peak flux of 19.8 mg m-2d-1 (at the same location where CH4 ebullition was also the greatest). Carbon dioxide flux from sediment pore-water averaged approximately 80 mg m-2d-1 with little difference between winter and summer. Similar to emissions from ebullition, flux from sediment pore-water was higher in reservoirs than in the free flowing reach.« less

Assessing Regional Scale Fluxes of Mass, Momentum, and Energy with Small Environmental Research Aircraft

NASA Astrophysics Data System (ADS)

Zulueta, Rommel Callejo

Natural ecosystems are rarely structurally or functionally homogeneous. This is true for the complex coastal regions of Magdalena Bay, Baja California Sur, Mexico, and the Barrow Peninsula on the Arctic Coastal Plain of Alaska. The coastal region of Magdalena Bay is comprised of the Pacific coastal ocean, eutrophic lagoon, mangroves, and desert ecosystems all adjacent and within a few kilometers, while the Barrow Peninsula is a mosaic of small ponds, thaw lakes, different aged vegetated thaw-lake basins ( VDTLBs ) and interstitial tundra which have been dynamically formed by both short- and long-term processes. We used a combination of tower- and small environmental research aircraft (SERA)-based eddy covariance measurements to characterize the spatial and temporal patterns of CO2, latent, and sensible heat fluxes along with MODIS NDVI, and land surface information, to scale the SERA-based CO2 fluxes up to the regional scale. In the first part of this research, the spatial variability in ecosystem fluxes from the Pacific coastal ocean, eutrophic lagoon, mangroves, and desert areas of northern Magdalena Bay were studied. SERA-derived average midday CO2 fluxes from the desert showed a slight uptake of -1.32 mumol CO2 m-2 s-1, the coastal ocean also showed uptake of -3.48 mumol CO2 m-2 s -1, and the lagoon mangroves showed the highest uptake of -8.11 mumol CO2 m-2 s-1. Additional simultaneous measurements of NDVI allowed simple linear modeling of CO2 flux as a function of NDVI for the mangroves of the Magdalena Bay region. In the second part of this research, the spatial variability of ecosystem fluxes across the 1802 km2 Barrow Peninsula region was studied. During typical 2006 summer conditions, the midday hourly CO2 flux over the region was -2.04 x 105 kgCO2 hr-1. The CO2 fluxes among the interstitial tundra, Ancient and Old VDTLBs, as well as between the Medium and Young VDTLBs were not significantly different. Combined, the interstitial tundra and Old and Ancient VDTLBs, represent ˜67% of the Barrow Peninsula surface area, accounting for ˜59% of the regional flux signal. Though the Medium and Young VDTLBs represent ˜11% of the surface area, they account for a large portion, ˜35%, of the total regional flux. The remaining ˜22% of the surface area are lakes and contributed the remaining ˜6% of the total regional flux. Previous studies treated vegetated areas of the region as a single surface type with measurements from a few study sites; doing so could underestimate the regional flux by ˜22%. The San Diego State University Sky Arrow 650TCN Environmental Research Aircraft proved to be an effective tool in characterizing land-atmosphere fluxes of energy, CO2 and water across heterogeneous landscapes at the scale of 1 km, and was capable of discriminating fluxes from the various ecosystem and land surface types a few kilometers distant. Here, we demonstrate that SERA-based approaches have the ability to cover large spatial scales while measuring the turbulent fluxes across a number of surfaces and combined with ground- and satellite-based measurements provide a valuable tool for both scaling and validation of regional-scale fluxes.

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.

Ocean Surface Observations of the Diurnal Cycle of Turbulence with ASIP

NASA Astrophysics Data System (ADS)

Ward, Brian; Sutherland, Graig; Reverdin, Gilles; Marie, Louis; Christensen, Kai; Brostrom, Goran; Harcourt, Ramsey; Breivik, Oyvind

2015-04-01

The STRASSE field experiment was conducted in August/September 2012 as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) campaign. The average conditions during STRASSE were low wind and high insolation, which are typical for the generation of near-surface diurnal warming. We deployed the Air-Sea Interaction Profiler (ASIP), an autonomous upwardly-rising microstructure instrument capable of resolving small-scale processes close to the air-sea interface. ASIP provides direct estimates of the dissipation rate of turbulent kinetic energy, temperature, salinity, and PAR at timescales suitable for the study of diurnal processes. In combination with the ASIP data, we had shipboard meteorological data for calculation of atmospheric forcing, and a surface mounted Lagrangian ADCP for determination of the near-surface velocity. There was a strong diurnal cycle of temperature and dissipation (from ASIP) and shear (from an ADCP). As air-sea fluxes are driven by turbulence immediately at the air-sea interface, the presence of this enhanced shear-induced turbulence will enhance fluxes.

Surface deformations as indicators of deep ebullition fluxes in a large northern peatland

USGS Publications Warehouse

Glaser, P.H.; Chanton, J.P.; Morin, P.; Rosenberry, D.O.; Siegel, D.I.; Ruud, O.; Chasar, L.I.; Reeve, A.S.

2004-01-01

Peatlands deform elastically during precipitation cycles by small (??3 cm) oscillations in surface elevation. In contrast, we used a Global Positioning System network to measure larger oscillations that exceeded 20 cm over periods of 4-12 hours during two seasonal droughts at a bog and fen site in northern Minnesota. The second summer drought also triggered 19 depressuring cycles in an overpressured stratum under the bog site. The synchronicity between the largest surface deformations and the depressuring cycles indicates that both phenomena are produced by the episodic release of large volumes of gas from deep semi-elastic compartments confined by dense wood layers. We calculate that the three largest surface deformations were associated with the release of 136 g CH4 m-2, which exceeds by an order of magnitude the annual average chamber fluxes measured at this site. Ebullition of gas from the deep peat may therefore be a large and previously unrecognized source of radiocarbon depleted methane emissions from northern peatlands. Copyright 2004 by the American Geophysical Union.

Evapotranspiration based on equilibrated relative humidity (ETRHEQ): Evaluation over the continental U.S.

NASA Astrophysics Data System (ADS)

Rigden, Angela J.; Salvucci, Guido D.

2015-04-01

A novel method of estimating evapotranspiration (ET), referred to as the ETRHEQ method, is further developed, validated, and applied across the U.S. from 1961 to 2010. The ETRHEQ method estimates the surface conductance to water vapor transport, which is the key rate-limiting parameter of typical ET models, by choosing the surface conductance that minimizes the vertical variance of the calculated relative humidity profile averaged over the day. The ETRHEQ method, which was previously tested at five AmeriFlux sites, is modified for use at common weather stations and further validated at 20 AmeriFlux sites that span a wide range of climates and limiting factors. Averaged across all sites, the daily latent heat flux RMSE is ˜26 W·m-2 (or 15%). The method is applied across the U.S. at 305 weather stations and spatially interpolated using ANUSPLIN software. Gridded annual mean ETRHEQ ET estimates are compared with four data sets, including water balance-derived ET, machine-learning ET estimates based on FLUXNET data, North American Land Data Assimilation System project phase 2 ET, and a benchmark product that integrates 14 global ET data sets, with RMSEs ranging from 8.7 to 12.5 cm·yr-1. The ETRHEQ method relies only on data measured at weather stations, an estimate of vegetation height derived from land cover maps, and an estimate of soil thermal inertia. These data requirements allow it to have greater spatial coverage than direct measurements, greater historical coverage than satellite methods, significantly less parameter specification than most land surface models, and no requirement for calibration.

Assessing recent air-sea freshwater flux changes using a surface temperature-salinity space framework

NASA Astrophysics Data System (ADS)

Grist, Jeremy P.; Josey, Simon A.; Zika, Jan D.; Evans, Dafydd Gwyn; Skliris, Nikolaos

2016-12-01

A novel assessment of recent changes in air-sea freshwater fluxes has been conducted using a surface temperature-salinity framework applied to four atmospheric reanalyses. Viewed in the T-S space of the ocean surface, the complex pattern of the longitude-latitude space mean global Precipitation minus Evaporation (PME) reduces to three distinct regions. The analysis is conducted for the period 1979-2007 for which there is most evidence for a broadening of the (atmospheric) tropical belt. All four of the reanalyses display an increase in strength of the water cycle. The range of increase is between 2% and 30% over the period analyzed, with an average of 14%. Considering the average across the reanalyses, the water cycle changes are dominated by changes in tropical as opposed to mid-high latitude precipitation. The increases in the water cycle strength, are consistent in sign, but larger than in a 1% greenhouse gas run of the HadGEM3 climate model. In the model a shift of the precipitation/evaporation cells to higher temperatures is more evident, due to the much stronger global warming signal. The observed changes in freshwater fluxes appear to be reflected in changes in the T-S distribution of the Global Ocean. Specifically, across the diverse range of atmospheric reanalyses considered here, there was an acceleration of the hydrological cycle during 1979-2007 which led to a broadening of the ocean's salinity distribution. Finally, although the reanalyses indicate that the warm temperature tropical precipitation dominated water cycle change, ocean observations suggest that ocean processes redistributed the freshening to lower ocean temperatures.

Interactions between aerosol absorption, thermodynamics, dynamics, and microphysics and their impacts on a multiple-cloud system

NASA Astrophysics Data System (ADS)

Lee, Seoung Soo; Li, Zhanqing; Mok, Jungbin; Ahn, Myoung-Hwan; Kim, Byung-Gon; Choi, Yong-Sang; Jung, Chang-Hoon; Yoo, Hye Lim

2017-12-01

This study investigates how the increasing concentration of black carbon aerosols, which act as radiation absorbers as well as agents for the cloud-particle nucleation, affects stability, dynamics and microphysics in a multiple-cloud system using simulations. Simulations show that despite increases in stability due to increasing concentrations of black carbon aerosols, there are increases in the averaged updraft mass fluxes (over the whole simulation domain and period). This is because aerosol-enhanced evaporative cooling intensifies convergence near the surface. This increase in the intensity of convergence induces an increase in the frequency of updrafts with the low range of speeds, leading to the increase in the averaged updraft mass fluxes. The increase in the frequency of updrafts induces that in the number of condensation entities and this leads to more condensation and cloud liquid that acts to be a source of the accretion of cloud liquid by precipitation. Hence, eventually, there is more accretion that offsets suppressed autoconversion, which results in negligible changes in cumulative precipitation as aerosol concentrations increase. The increase in the frequency of updrafts with the low range of speeds alters the cloud-system organization (represented by cloud-depth spatiotemporal distributions and cloud-cell population) by supporting more low-depth clouds. The altered organization in turn alters precipitation spatiotemporal distributions by generating more weak precipitation events. Aerosol-induced reduction in solar radiation that reaches the surface induces more occurrences of small-value surface heat fluxes, which in turn supports the more low-depth clouds and weak precipitation together with the greater occurrence of low-speed updrafts.

Atmospheric components of the surface energy budget over young sea ice: Results from the N-ICE2015 campaign

NASA Astrophysics Data System (ADS)

Walden, Von P.; Hudson, Stephen R.; Cohen, Lana; Murphy, Sarah Y.; Granskog, Mats A.

2017-08-01

The Norwegian young sea ice campaign obtained the first measurements of the surface energy budget over young, thin Arctic sea ice through the seasonal transition from winter to summer. This campaign was the first of its kind in the North Atlantic sector of the Arctic. This study describes the atmospheric and surface conditions and the radiative and turbulent heat fluxes over young, thin sea ice. The shortwave albedo of the snow surface ranged from about 0.85 in winter to 0.72-0.80 in early summer. The near-surface atmosphere was typically stable in winter, unstable in spring, and near neutral in summer once the surface skin temperature reached 0°C. The daily average radiative and turbulent heat fluxes typically sum to negative values (-40 to 0 W m-2) in winter but then transition toward positive values of up to nearly +60 W m-2 as solar radiation contributes significantly to the surface energy budget. The sensible heat flux typically ranges from +20-30 W m-2 in winter (into the surface) to negative values between 0 and -20 W m-2 in spring and summer. A winter case study highlights the significant effect of synoptic storms and demonstrates the complex interplay of wind, clouds, and heat and moisture advection on the surface energy components over sea ice in winter. A spring case study contrasts a rare period of 24 h of clear-sky conditions with typical overcast conditions and highlights the impact of clouds on the surface radiation and energy budgets over young, thin sea ice.

Troposphere-stratosphere (surface-55 km) monthly general circulation statistics for the Northern Hemisphere-four year averages

NASA Technical Reports Server (NTRS)

Wu, M. F.; Geller, M. A.; Olson, J. G.; Gelman, M. E.

1984-01-01

This report presents four year averages of monthly mean Northern Hemisphere general circulation statistics for the period from 1 December 1978 through 30 November 1982. Computations start with daily maps of temperature for 18 pressure levels between 1000 and 0.4 mb that were supplied by NOAA/NMC. Geopotential height and geostrophic wind are constructed using the hydrostatic and geostrophic formulae. Fields presented in this report are zonally averaged temperature, mean zonal wind, and amplitude and phase of the planetary waves in geopotential height with zonal wavenumbers 1-3. The northward fluxes of heat and eastward momentum by the standing and transient eddies along with their wavenumber decomposition and Eliassen-Palm flux propagation vectors and divergences by the standing and transient eddies along with their wavenumber decomposition are also given. Large annual and interannual variations are found in each quantity especially in the stratosphere in accordance with the changes in the planetary wave activity. The results are shown both in graphic and tabular form.

Confronting the WRF and RAMS mesoscale models with innovative observations in the Netherlands: Evaluating the boundary layer heat budget

NASA Astrophysics Data System (ADS)

Steeneveld, G. J.; Tolk, L. F.; Moene, A. F.; Hartogensis, O. K.; Peters, W.; Holtslag, A. A. M.

2011-12-01

The Weather Research and Forecasting Model (WRF) and the Regional Atmospheric Mesoscale Model System (RAMS) are frequently used for (regional) weather, climate and air quality studies. This paper covers an evaluation of these models for a windy and calm episode against Cabauw tower observations (Netherlands), with a special focus on the representation of the physical processes in the atmospheric boundary layer (ABL). In addition, area averaged sensible heat flux observations by scintillometry are utilized which enables evaluation of grid scale model fluxes and flux observations at the same horizontal scale. Also, novel ABL height observations by ceilometry and of the near surface longwave radiation divergence are utilized. It appears that WRF in its basic set-up shows satisfactory model results for nearly all atmospheric near surface variables compared to field observations, while RAMS needed refining of its ABL scheme. An important inconsistency was found regarding the ABL daytime heat budget: Both model versions are only able to correctly forecast the ABL thermodynamic structure when the modeled surface sensible heat flux is much larger than both the eddy-covariance and scintillometer observations indicate. In order to clarify this discrepancy, model results for each term of the heat budget equation is evaluated against field observations. Sensitivity studies and evaluation of radiative tendencies and entrainment reveal that possible errors in these variables cannot explain the overestimation of the sensible heat flux within the current model infrastructure.

Land surface models systematically overestimate the intensity, duration and magnitude of seasonal-scale evaporative droughts

DOE PAGES

Ukkola, A. M.; De Kauwe, M. G.; Pitman, A. J.; ...

2016-10-13

Land surface models (LSMs) must accurately simulate observed energy and water fluxes during droughts in order to provide reliable estimates of future water resources. We evaluated 8 different LSMs (14 model versions) for simulating evapotranspiration (ET) during periods of evaporative drought (Edrought) across six flux tower sites. Using an empirically defined Edrought threshold (a decline in ET below the observed 15th percentile), we show that LSMs simulated 58 Edrought days per year, on average, across the six sites, ~3 times as many as the observed 20 d. The simulated Edrought magnitude was ~8 times greater than observed and twice asmore » intense. Our findings point to systematic biases across LSMs when simulating water and energy fluxes under water-stressed conditions. The overestimation of key Edrought characteristics undermines our confidence in the models' capability in simulating realistic drought responses to climate change and has wider implications for phenomena sensitive to soil moisture, including heat waves.« less

An evaluation of a zero-heat-flux cutaneous thermometer in cardiac surgical patients.

PubMed

Eshraghi, Yashar; Nasr, Vivian; Parra-Sanchez, Ivan; Van Duren, Albert; Botham, Mark; Santoscoy, Thomas; Sessler, Daniel I

2014-09-01

Although core temperature can be measured invasively, there are currently no widely available, reliable, noninvasive thermometers for its measurement. We thus compared a prototype zero-heat-flux thermometer with simultaneous measurements from a pulmonary artery catheter. Specifically, we tested the hypothesis that zero-heat-flux temperatures are sufficiently accurate for routine clinical use. Core temperature was measured from the thermistor of a standard pulmonary artery catheter and with a prototype zero-heat-flux deep-tissue thermometer in 105 patients having nonemergent cardiac surgery. Zero-heat-flux probes were positioned on the lateral forehead and lateral neck. Skin surface temperature probes were attached to the forehead just adjacent to the zero-heat-flux probe. Temperatures were recorded at 1-minute intervals, excluding the period of cardiopulmonary bypass, and for the first 4 postoperative hours. Zero-heat-flux and pulmonary artery temperatures were compared with bias analysis; differences exceeding 0.5°C were considered to be potentially clinically important. The mean duration in the operating room was 279 ± 75 minutes, and the mean cross-clamp time was 118 ± 50 minutes. All subjects were monitored for an additional 4 hours in the intensive care unit. The average overall difference between forehead zero-heat-flux and pulmonary artery temperatures (i.e., forehead minus pulmonary artery) was -0.23°C (95% limits of agreement of ±0.82); 78% of the differences were ≤0.5°C. The average intraoperative temperature difference was -0.08°C (95% limits of agreement of ±0.88); 84% of the differences were ≤0.5°C. The average postoperative difference was -0.32°C (95% limits of agreement of ±0.75); 84% of the differences were ≤0.5°C. Bias and precision values for neck site were similar to the forehead values. Uncorrected forehead skin temperature showed an increasing negative bias as core temperature decreased. Core temperature can be noninvasively measured using the zero-heat-flux method. Bias was small, but precision was slightly worse than our designated 0.5°C limits compared with measurements from a pulmonary artery catheter.

Air-water exchange and dry deposition of polybrominated diphenyl ethers at a coastal site in Izmir Bay, Turkey.

PubMed

Cetin, Banu; Odabasi, Mustafa

2007-02-01

The air-water exchange of polybrominated diphenyl ethers (PBDEs), an emerging class of persistent organic pollutants (POPs), was investigated using paired air-water samples (n = 15) collected in July and December, 2005 from Guzelyali Port in Izmir Bay, Turkey. Total dissolved-phase water concentrations of PBDEs (sigma7PBDEs) were 212 +/- 65 and 87 +/- 57 pg L(-1) (average +/- SD) in summer and winter, respectively. BDE-209 was the most abundant congener in all samples, followed by BDE-99 and -47. Average ambient gas-phase sigma7PBDE concentrations were between 189 +/- 61 (summer) and 76 +/- 65 pg m(-3) (winter). Net air-water exchange fluxes ranged from -0.9 +/- 1.0 (BDE-28) (volatilization) to 11.1 +/- 5.4 (BDE-209) ng m(-2) day(-1) (deposition). The BDE-28 fluxes were mainly volatilization while the other congeners were deposited. Gas- and dissolved-phase concentrations were significantly correlated (P = 0.33-0.55, p < 0.05, except for BDE-209, r = 0.05, p > 0.05) indicating thatthe atmosphere controls the surface water PBDE levels in this coastal environment. Estimated particulate dry deposition fluxes ranged between 2.7 +/- 1.9 (BDE-154) and 116 +/- 84 ng m(-2) day(-1) (BDE-209) indicating that dry deposition is also a significant input to surface waters in the study area.

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.

Can we detect national-scale under-reporting of CO2 emissions using OCO-2 XCO2 observations in a carbon-weather data assimilation system?

NASA Astrophysics Data System (ADS)

Wuerth, S. M.; Fung, I. Y.; Anderson, J. L.; Raeder, K.

2016-12-01

A long-standing challenge in carbon cycle science is the inference of surface fluxes from atmospheric CO2 observations. Here we present initial results from our carbon-weather data assimilation system coupled to a mass-balance inversion . Our system combines the Community Atmosphere Model (CAM 5FV) with state-of-the-art ensemble data assimilation techniques from the Data Assimilation Research Testbed (DART), and assimilates OCO-2 XCO2 observations together with raw meteorological observations. The system uses a mass balance of the optimized atmospheric state to calculate CO2 sources and sinks throughout the globe. We present results from observing system simulation experiments (OSSE) aimed at comparing two different mass-balance approaches' abilities to detect under-reporting of national-scale CO2 emissions. In both experiments, we define a true state as the atmospheric state resulting from running CAM with a prognostic carbon cycle and CO2 emissions from CarbonTracker CT2015. Meteorological and OCO-2-like observations are harvested from this true state for assimilation. We create a hypothetical scenario in which fossil fuel CO2 emissions of a large emitter are scaled to half of their true values. Surface fluxes are then estimated using one of two approaches. The first approach computes, at every 6-hourly assimilation window, surface fluxes as the residual in the mass balance equation after divergence has been accounted for. The updated surface fluxes are then used as forcing in the ensuing CAM forecast. The second approach uses the initial false emissions for two weeks of model integration, then computes improved emissions by adding the time-averaged analysis increment in near-surface CO2 mixing ratio to the initial false emissions. The two weeks are re-run with these updated fluxes, and the process is then repeated for further refinement of fluxes. The advantages and disadvantages of the two approaches are discussed, and the system's ability to recover the true fluxes is assessed.

The roles of vertical mixing, solar radiation, and wind stress in a model simulation of the sea surface temperature seasonal cycle in the tropical Pacfic Ocean

NASA Technical Reports Server (NTRS)

Chen, Dake; Busalacchi, Antonio J.; Rothstein, Lewis M.

1994-01-01

The climatological seasonal cycle of sea surface temperature (SST) in the tropical Pacific is simulated using a newly developed upper ocean model. The roles of vertical mixing, solar radiation, and wind stress are investigated in a hierarchy of numerical experiments with various combinations of vertical mixing algorithms and surface-forcing products. It is found that the large SST annual cycle in the eastern equatorial Pacific is, to a large extent, controlled by the annually varying mixed layer depth which, in turn, is mainly determined by the competing effects of solar radiation and wind forcing. With the application of our hybrid vertical mixing scheme the model-simulated SST annual cycle is much improved in both amplitude and phase as compared to the case of a constant mixed layer depth. Beside the strong effects on vertical mixing, solar radiation is the primary heating term in the surface layer heat budget, and wind forcing influences SST by driving oceanic advective processes that redistribute heat in the upper ocean. For example, the SST seasonal cycle in the western Pacific basically follows the semiannual variation of solar heating, and the cycle in the central equatorial region is significantly affected by the zonal advective heat flux associated with the seasonally reversing South Equatorial Current. It has been shown in our experiments that the amount of heat flux modification needed to eliminate the annual mean SST errors in the model is, on average, no larger than the annual mean uncertainties among the various surface flux products used in this study. Whereas a bias correction is needed to account for remaining uncertainties in the annual mean heat flux, this study demonstrates that with proper treatment of mixed layer physics and realistic forcing functions the seasonal variability of SST is capable of being simulated successfully in response to external forcing without relying on a relaxation or damping formulation for the dominant surface heat flux contributions.

Annual cycles of deep-ocean biogeochemical export fluxes in subtropical and subantarctic waters, southwest Pacific Ocean

NASA Astrophysics Data System (ADS)

Nodder, Scott D.; Chiswell, Stephen M.; Northcote, Lisa C.

2016-04-01

The annual cycles of particle fluxes derived from moored sediment trap data collected during 2000-2012 in subtropical (STW) and subantarctic waters (SAW) east of New Zealand are presented. These observations are the most comprehensive export flux time series from temperate Southern Hemisphere latitudes to date. With high levels of variability, fluxes in SAW were markedly lower than in STW, reflecting the picophytoplankton-dominated communities in the iron-limited, high nutrient-low chlorophyll SAW. Austral spring chlorophyll blooms in surface STW were near synchronous with elevated fluxes of bio-siliceous, carbonate, and organic carbon-rich materials to the deep ocean, probably facilitated by diatom and/or coccolithophorid sedimentation. Lithogenic fluxes were also high in STW, compared to SAW, reflecting proximity to the New Zealand landmass. In contrast, the highest biogenic fluxes in SAW occurred in spring when surface chlorophyll concentrations were low, while highest annual chlorophyll concentrations were in summer with no associated flux increase. We hypothesize that the high spring export in SAW results from subsurface chlorophyll accumulation that is not evident from remote-sensing satellites. This material was also rich in biogenic silica, perhaps related to the preferential export of diatoms and other silica-producing organisms, such as silicoflagellates and radiolarians. Organic carbon fluxes in STW are similar to that of other mesotrophic to oligotrophic waters (˜6-7 mg C m-2 d-1), whereas export from SAW is below the global average (˜3 mg C m-2 d-1). Regional differences in flux across the SW Pacific and Tasman region reflect variations in physical processes and ecosystem structure and function.

BOREAS TF-10 NSA-YJP Tower Flux, Meteorological, and Porometry Data

NASA Technical Reports Server (NTRS)

McCaughey, J. Harry; Liblik, Laura; Hall, Forrest G. (Editor); Huemmrich, K. (Editor)

2000-01-01

The BOREAS TF-10 team collected tower flux and meteorological data at two sites, a fen and a young jack pine forest, near Thompson, Manitoba, Canada, as part of BOREAS. A preliminary data set was assembled in August 1993 while field testing the instrument packages, and at both sites data were collected from 15-Aug to 31-Aug. The main experimental period was in 1994, when continuous data were collected from the young jack pine site from 23-May to 20-Sep. Upon examination of the 1994 data set, it became clear that the behavior of the heat, water, and carbon dioxide fluxes throughout the whole growing season was an important scientific question, and that the 1994 data record was not sufficiently long to capture the character of the seasonal behavior of the fluxes. Thus, the young jack pine site was operated from 08-May to 07-Nov in 1996 in order to collect data from spring melt to autumn freeze-up. All variables are presented as 30-minute averages. Supporting data were also collected to describe the surface#s state and to provide the information, in association with the flux data, to build SVAT models. For the young jack pine site, these supporting data included stomatal conductance measurements. The data are stored in tabular ASCII files.

VOC emission rates over London and South East England obtained by airborne eddy covariance.

PubMed

Vaughan, Adam R; Lee, James D; Shaw, Marvin D; Misztal, Pawel K; Metzger, Stefan; Vieno, Massimo; Davison, Brian; Karl, Thomas G; Carpenter, Lucy J; Lewis, Alastair C; Purvis, Ruth M; Goldstein, Allen H; Hewitt, C Nicholas

2017-08-24

Volatile organic compounds (VOCs) originate from a variety of sources, and play an intrinsic role in influencing air quality. Some VOCs, including benzene, are carcinogens and so directly affect human health, while others, such as isoprene, are very reactive in the atmosphere and play an important role in the formation of secondary pollutants such as ozone and particles. Here we report spatially-resolved measurements of the surface-to-atmosphere fluxes of VOCs across London and SE England made in 2013 and 2014. High-frequency 3-D wind velocities and VOC volume mixing ratios (made by proton transfer reaction - mass spectrometry) were obtained from a low-flying aircraft and used to calculate fluxes using the technique of eddy covariance. A footprint model was then used to quantify the flux contribution from the ground surface at spatial resolution of 100 m, averaged to 1 km. Measured fluxes of benzene over Greater London showed positive agreement with the UK's National Atmospheric Emissions Inventory, with the highest fluxes originating from central London. Comparison of MTBE and toluene fluxes suggest that petroleum evaporation is an important emission source of toluene in central London. Outside London, increased isoprene emissions were observed over wooded areas, at rates greater than those predicted by a UK regional application of the European Monitoring and Evaluation Programme model (EMEP4UK). This work demonstrates the applicability of the airborne eddy covariance method to the determination of anthropogenic and biogenic VOC fluxes and the possibility of validating emission inventories through measurements.

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.

An Hα Imaging Survey of the Low-surface-brightness Galaxies Selected from the Fall Sky Region of the 40% ALFALFA H I Survey

NASA Astrophysics Data System (ADS)

Lei, Feng-Jie; Wu, Hong; Du, Wei; Zhu, Yi-Nan; Lam, Man-I.; Zhou, Zhi-Min; He, Min; Jin, Jun-Jie; Cao, Tian-Wen; Zhao, Pin-Song; Yang, Fan; Wu, Chao-Jian; Li, Hong-Bin; Ren, Juan-Juan

2018-03-01

We present the observed Hα flux and derived star formation rates (SFRs) for a fall sample of low-surface-brightness galaxies (LSBGs). The sample is selected from the fall sky region of the 40% ALFALFA H I Survey–SDSS DR7 photometric data, and all the Hα images were obtained using the 2.16 m telescope, operated by the National Astronomy Observatories, Chinese Academy of Sciences. A total of 111 LSBGs were observed and Hα flux was measured in 92 of them. Though almost all the LSBGs in our sample are H I-rich, their SFRs, derived from the extinction and filter-transmission-corrected Hα flux, are less than 1 M ⊙ yr‑1. LSBGs and star-forming galaxies have similar H I surface densities, but LSBGs have much lower SFRs and SFR surface densities than star-forming galaxies. Our results show that LSBGs deviate from the Kennicutt–Schmidt law significantly, which indicates that they have low star formation efficiency. The SFRs of LSBGs are close to average SFRs in Hubble time and support previous arguments that most of the LSBGs are stable systems and they tend to seldom contain strong interactions or major mergers in their star formation histories.

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

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.

Inverse Modeling of Hydrologic Parameters Using Surface Flux and Runoff Observations in the Community Land Model

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

Sun, Yu; Hou, Zhangshuan; Huang, Maoyi

2013-12-10

This study demonstrates the possibility of inverting hydrologic parameters using surface flux and runoff observations in version 4 of the Community Land Model (CLM4). Previous studies showed that surface flux and runoff calculations are sensitive to major hydrologic parameters in CLM4 over different watersheds, and illustrated the necessity and possibility of parameter calibration. Two inversion strategies, the deterministic least-square fitting and stochastic Markov-Chain Monte-Carlo (MCMC) - Bayesian inversion approaches, are evaluated by applying them to CLM4 at selected sites. The unknowns to be estimated include surface and subsurface runoff generation parameters and vadose zone soil water parameters. We find thatmore » using model parameters calibrated by the least-square fitting provides little improvements in the model simulations but the sampling-based stochastic inversion approaches are consistent - as more information comes in, the predictive intervals of the calibrated parameters become narrower and the misfits between the calculated and observed responses decrease. In general, parameters that are identified to be significant through sensitivity analyses and statistical tests are better calibrated than those with weak or nonlinear impacts on flux or runoff observations. Temporal resolution of observations has larger impacts on the results of inverse modeling using heat flux data than runoff data. Soil and vegetation cover have important impacts on parameter sensitivities, leading to the different patterns of posterior distributions of parameters at different sites. Overall, the MCMC-Bayesian inversion approach effectively and reliably improves the simulation of CLM under different climates and environmental conditions. Bayesian model averaging of the posterior estimates with different reference acceptance probabilities can smooth the posterior distribution and provide more reliable parameter estimates, but at the expense of wider uncertainty bounds.« less

Inverse modeling of hydrologic parameters using surface flux and runoff observations in the Community Land Model

NASA Astrophysics Data System (ADS)

Sun, Y.; Hou, Z.; Huang, M.; Tian, F.; Leung, L. Ruby

2013-12-01

This study demonstrates the possibility of inverting hydrologic parameters using surface flux and runoff observations in version 4 of the Community Land Model (CLM4). Previous studies showed that surface flux and runoff calculations are sensitive to major hydrologic parameters in CLM4 over different watersheds, and illustrated the necessity and possibility of parameter calibration. Both deterministic least-square fitting and stochastic Markov-chain Monte Carlo (MCMC)-Bayesian inversion approaches are evaluated by applying them to CLM4 at selected sites with different climate and soil conditions. The unknowns to be estimated include surface and subsurface runoff generation parameters and vadose zone soil water parameters. We find that using model parameters calibrated by the sampling-based stochastic inversion approaches provides significant improvements in the model simulations compared to using default CLM4 parameter values, and that as more information comes in, the predictive intervals (ranges of posterior distributions) of the calibrated parameters become narrower. In general, parameters that are identified to be significant through sensitivity analyses and statistical tests are better calibrated than those with weak or nonlinear impacts on flux or runoff observations. Temporal resolution of observations has larger impacts on the results of inverse modeling using heat flux data than runoff data. Soil and vegetation cover have important impacts on parameter sensitivities, leading to different patterns of posterior distributions of parameters at different sites. Overall, the MCMC-Bayesian inversion approach effectively and reliably improves the simulation of CLM under different climates and environmental conditions. Bayesian model averaging of the posterior estimates with different reference acceptance probabilities can smooth the posterior distribution and provide more reliable parameter estimates, but at the expense of wider uncertainty bounds.

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.

Controls of Evapotranspiration and CO2 Fluxes from Scots Pine by Surface Conductance and Abiotic Factors

PubMed Central

Zha, Tianshan; Li, Chunyi; Kellomäki, Seppo; Peltola, Heli; Wang, Kai-Yun; Zhang, Yuqing

2013-01-01

Evapotranspiration (E) and CO2 flux (Fc) in the growing season of an unusual dry year were measured continuously over a Scots pine forest in eastern Finland, by eddy covariance techniques. The aims were to gain an understanding of their biological and environmental control processes. As a result, there were obvious diurnal and seasonal changes in E, Fc, surface conductance (gc), and decoupling coefficient (Ω), showing similar trends to those in radiation (PAR) and vapour pressure deficit (δ). The maximum mean daily values (24-h average) for E, Fc, gc, and Ω were 1.78 mmol m−2 s−1, −11.18 µmol m−2 s−1, 6.27 mm s−1, and 0.31, respectively, with seasonal averages of 0.71 mmol m−2 s−1, −4.61 µmol m−2 s−1, 3.3 mm s−1, and 0.16. E and Fc were controlled by combined biological and environmental variables. There was curvilinear dependence of E on gc and Fc on gc. Among the environmental variables, PAR was the most important factor having a positive linear relationship to E and curvilinear relationship to Fc, while vapour pressure deficit was the most important environmental factor affecting gc. Water use efficiency was slightly higher in the dry season, with mean monthly values ranging from 6.67 to 7.48 μmol CO2 (mmol H2O)−1 and a seasonal average of 7.06 μmol CO2 (μmol H2O)−1. Low Ω and its close positive relationship with gc indicate that evapotranspiration was sensitive to surface conductance. Mid summer drought reduced surface conductance and decoupling coefficient, suggesting a more biotic control of evapotranspiration and a physiological acclimation to dry air. Surface conductance remained low and constant under dry condition, supporting that a constant value of surface constant can be used for modelling transpiration under drought condition. PMID:23894401

Controls of evapotranspiration and CO2 fluxes from scots pine by surface conductance and abiotic factors.

PubMed

Zha, Tianshan; Li, Chunyi; Kellomäki, Seppo; Peltola, Heli; Wang, Kai-Yun; Zhang, Yuqing

2013-01-01

Evapotranspiration (E) and CO2 flux (Fc ) in the growing season of an unusual dry year were measured continuously over a Scots pine forest in eastern Finland, by eddy covariance techniques. The aims were to gain an understanding of their biological and environmental control processes. As a result, there were obvious diurnal and seasonal changes in E, Fc , surface conductance (gc ), and decoupling coefficient (Ω), showing similar trends to those in radiation (PAR) and vapour pressure deficit (δ). The maximum mean daily values (24-h average) for E, Fc , gc , and Ω were 1.78 mmol m(-2) s(-1), -11.18 µmol m(-2) s(-1), 6.27 mm s(-1), and 0.31, respectively, with seasonal averages of 0.71 mmol m(-2) s(-1), -4.61 µmol m(-2) s(-1), 3.3 mm s(-1), and 0.16. E and Fc were controlled by combined biological and environmental variables. There was curvilinear dependence of E on gc and Fc on gc . Among the environmental variables, PAR was the most important factor having a positive linear relationship to E and curvilinear relationship to Fc , while vapour pressure deficit was the most important environmental factor affecting gc . Water use efficiency was slightly higher in the dry season, with mean monthly values ranging from 6.67 to 7.48 μmol CO2 (mmol H2O)(-1) and a seasonal average of 7.06 μmol CO2 (μmol H2O)(-1). Low Ω and its close positive relationship with gc indicate that evapotranspiration was sensitive to surface conductance. Mid summer drought reduced surface conductance and decoupling coefficient, suggesting a more biotic control of evapotranspiration and a physiological acclimation to dry air. Surface conductance remained low and constant under dry condition, supporting that a constant value of surface constant can be used for modelling transpiration under drought condition.

The effects of surface evaporation parameterizations on climate sensitivity to solar constant variations

NASA Technical Reports Server (NTRS)

Chou, S.-H.; Curran, R. J.; Ohring, G.

1981-01-01

The effects of two different evaporation parameterizations on the sensitivity of simulated climate to solar constant variations are investigated by using a zonally averaged climate model. One parameterization is a nonlinear formulation in which the evaporation is nonlinearly proportional to the sensible heat flux, with the Bowen ratio determined by the predicted vertical temperature and humidity gradients near the earth's surface (model A). The other is the formulation of Saltzman (1968) with the evaporation linearly proportional to the sensible heat flux (model B). The computed climates of models A and B are in good agreement except for the energy partition between sensible and latent heat at the earth's surface. The difference in evaporation parameterizations causes a difference in the response of temperature lapse rate to solar constant variations and a difference in the sensitivity of longwave radiation to surface temperature which leads to a smaller sensitivity of surface temperature to solar constant variations in model A than in model B. The results of model A are qualitatively in agreement with those of the general circulation model calculations of Wetherald and Manabe (1975).

Percolation flux and Transport velocity in the unsaturated zone, Yucca Mountain, Nevada

USGS Publications Warehouse

Yang, I.C.

2002-01-01

The percolation flux for borehole USW UZ-14 was calculated from 14C residence times of pore water and water content of cores measured in the laboratory. Transport velocity is calculated from the depth interval between two points divided by the difference in 14C residence times. Two methods were used to calculate the flux and velocity. The first method uses the 14C data and cumulative water content data directly in the incremental intervals in the Paintbrush nonwelded unit and the Topopah Spring welded unit. The second method uses the regression relation for 14C data and cumulative water content data for the entire Paintbrush nonwelded unit and the Topopah Spring Tuff/Topopah Spring welded unit. Using the first method, for the Paintbrush nonwelded unit in boreholeUSW UZ-14 percolation flux ranges from 2.3 to 41.0 mm/a. Transport velocity ranges from 1.2 to 40.6 cm/a. For the Topopah Spring welded unit percolation flux ranges from 0.9 to 5.8 mm/a in the 8 incremental intervals calculated. Transport velocity ranges from 1.4 to 7.3 cm/a in the 8 incremental intervals. Using the second method, average percolation flux in the Paintbrush nonwelded unit for 6 boreholes ranges from 0.9 to 4.0 mm/a at the 95% confidence level. Average transport velocity ranges from 0.6 to 2.6 cm/a. For the Topopah Spring welded unit and Topopah Spring Tuff, average percolation flux in 5 boreholes ranges from 1.3 to 3.2 mm/a. Average transport velocity ranges from 1.6 to 4.0 cm/a. Both the average percolation flux and average transport velocity in the PTn are smaller than in the TS/TSw. However, the average minimum and average maximum values for the percolation flux in the TS/TSw are within the PTn average range. Therefore, differences in the percolation flux in the two units are not significant. On the other hand, average, average minimum, and average maximum transport velocities in the TS/TSw unit are all larger than the PTn values, implying a larger transport velocity for the TS/TSw although there is a small overlap.

Latent/sensible heat and water stress retrieval performances of the SPARSE dual-source energy balance model over irrigated and rainfed agricultural crops using eddy covariance, sap flow and extra-large aperture scintillometer data

NASA Astrophysics Data System (ADS)

Boulet, G.; Bahir, M.; Delogu, E.; Mougenot, B.; Bousbih, S.; Raimbault, B.; Fanise, P.; Saadi, S.; Chebbi, W.; Lili-Chabaane, Z.; Rivalland, V.; Lagouarde, J. P.; Olioso, A.

2016-12-01

The ability to monitor latent heat flux (LE) is relevant for applications requiring spatially-resolved estimates of moisture availability over large areas. Recently, a number of studies have focused on estimating surface energy fluxes via assimilation of land surface temperature (LST) observations into variational data assimilation (VDA) schemes. In this study, the performance of the combined-source variational data assimilation (CS-VDA) framework is assessed in detail using surface multitemporal heat fluxes collected at a Eucalypt forest savanna of Northern Australia. The CS VDA model treats the soil and vegetation as one medium. We extended previous studies, to a semi-arid ecosystem and included 1 and 3 hour global meteorological forcing data (GMD) rather than site-specific observations to drive CS VDA model. To implement the VDA model we relied on hourly water fluxes and meteorological measurements from an eddy covariance (EC) site located at our Australian study site. Using 1 and 3-hour average in-situ measurements, the mean difference between estimated and observed LE was ˜30%, which agreed with errors reported in the literature. We found that at least an 3 hour average meteorological data was required as input to the CS-VDA model, so 1-3-hourly temporal resolution MERRA-GMA and GLDAS, respectively, were used. We found that replacing local meteorological data with GMD reduced the performance of the LE estimation in comparison to in-situ measurements (GLDAS: RMSEdaily=98.52 W/m2, GMA: RMSEdaily=82.02 W/m2). Despite this, the model LE RMSE values at 8-day temporal scale (GMA: RMSE8-days=32.20 W/m2) was similar of those reported at this area by others models. This study provides the basis to produce an operational daily LE product using GMD dataset and LST remote sensing data within the CS-VDA algorithm.

Validation of a Solid Rocket Motor Internal Environment Model

NASA Technical Reports Server (NTRS)

Martin, Heath T.

2017-01-01

In a prior effort, a thermal/fluid model of the interior of Penn State University's laboratory-scale Insulation Test Motor (ITM) was constructed to predict both the convective and radiative heat transfer to the interior walls of the ITM with a minimum of empiricism. These predictions were then compared to values of total and radiative heat flux measured in a previous series of ITM test firings to assess the capabilities and shortcomings of the chosen modeling approach. Though the calculated fluxes reasonably agreed with those measured during testing, this exercise revealed means of improving the fidelity of the model to, in the case of the thermal radiation, enable direct comparison of the measured and calculated fluxes and, for the total heat flux, compute a value indicative of the average measured condition. By replacing the P1-Approximation with the discrete ordinates (DO) model for the solution of the gray radiative transfer equation, the radiation intensity field in the optically thin region near the radiometer is accurately estimated, allowing the thermal radiation flux to be calculated on the heat-flux sensor itself, which was then compared directly to the measured values. Though the fully coupling the wall thermal response with the flow model was not attempted due to the excessive computational time required, a separate wall thermal response model was used to better estimate the average temperature of the graphite surfaces upstream of the heat flux gauges and improve the accuracy of both the total and radiative heat flux computations. The success of this modeling approach increases confidence in the ability of state-of-the-art thermal and fluid modeling to accurately predict SRM internal environments, offers corrections to older methods, and supplies a tool for further studies of the dynamics of SRM interiors.

Use of 222Rn for estimation of greenhouse gases emissions at Russian territory

NASA Astrophysics Data System (ADS)

Berezina, E. V.; Elansky, N. F.

2009-04-01

It is well known that 222Rn is widely used as a tracer for studying different atmospheric processes including estimations of greenhouse gases emissions. Calculation of 222Rn fluxes from the soil into the atmosphere allows quantitative estimation of greenhouse gases emissions having the soil origin or sources of which are located near the surface. For accurate estimation of 222Rn fluxes detailed investigations of spatial and temporal variations of its concentrations are necessary. 222Rn concentrations data in the atmospheric surface layer over continental Russia from Moscow to Vladivostok obtained during the six TROICA (Transcontinental Observations Into the Chemistry of the Atmosphere) expeditions of the mobile laboratory along the Trans-Siberian railroad are analyzed. Spatial distribution, diurnal and seasonal variations of surface 222Rn concentrations along the Trans-Siberian railroad are investigated. According to the obtained data surface 222Rn concentration values above continental Russia vary from 0.5 to 75 Bq/m3 depending on meteorological conditions and geological features of the territory with the average value being 8.42 ± 0.10 Bq/m3. The average 222Rn concentration is maximum in the autumn expedition and minimum in the spring one. The factors mostly influencing 222Rn concentration variations are studied: surface temperature inversions, geological features of the territory, precipitations. 222Rn accumulation features in the atmospheric surface layer during night temperature inversions are analyzed. It was noted that during night temperature inversions the surface 222Rn concentration is 7 - 8 times more than the one during the nights without temperature inversions. Since atmospheric stratification determines accumulation and diurnal variations of many atmospheric pollutants as well as greenhouse gases its features are analyzed in detail. Surface temperature inversions were mainly observed from 18:00-19:00 to 06:00-07:00 in the warm season and from 16:00 to 08:00-09:00 in the cold season. During this time 222Rn accumulated in the surface atmospheric layer with its maximum concentration values being observed near sunrise. 222Rn fluxes from the soil into the atmosphere from Moscow to Vladivostok during surface temperature inversions are estimated taking into account geological factors. 222Rn accumulation layer depth in the lower atmosphere is calculated. Using the data of CO2, CH4 and 222Rn concentrations obtained in the expeditions we analyzed correlations between the greenhouse gases and 222Rn. There are significant positive correlations between CO2, CH4 and 222Rn concentrations during night temperature inversions especially in summer and in autumn. It indicates similar accumulation both 222Rn and the greenhouse gases in the surface layer during atmospheric stability. On the basis of the regressions between 222Rn, CO2 and CH4 concentrations the greenhouse gases night time fluxes in the surface layer from Moscow to Vladivostok are estimated using the calculated values of 222Rn fluxes. Acknowledgments. The work was supported by International Science and Technology Center (ISTC) under contract No. 2770 and by Russian Basic Research Foundation (project No. 08-05-13589, 07-05-12063 and 07-05-00428). The authors thank I. B. Belikov for preparation and carrying out the TROICA experiments.

Brazed graphite/refractory metal composites for first-wall protection elements

NASA Astrophysics Data System (ADS)

Šmid, I.; Croessmann, C. D.; Salmonson, J. C.; Whitley, J. B.; Kny, E.; Reheis, N.; Kneringer, G.; Nickel, H.

1991-03-01

The peak surface heat flux deposition on divertor elements of near term fusion devices is expected to exceed 10 MW/m 2. The needed reliability of brazed plasma interactive components, particularly under abnormal operating conditions with peak surface temperatures well beyond 1000°C, makes refractory metallic substrates and brazes with a high melting point very attractive. TZM, a high temperature alloy of molybdenum, and isotropic graphite, materials very closely matched in their thermal expansion, were brazed with four high-temperature brazes. The brazes used were Zr, 90Ni/10Ti, 90Cu/10Ti and 70Ag/27Cu/3Ti (nominal composition prior to brazing, wt%). The resulting composite tiles of 50 × 50 mm2 with a TZM thickness of 5 mm and a graphite thickness of 10 mm have been tested in high heat flux simulation for their thermal fatigue properties. Up to 600 loading cycles were carried out with an average heat flux of 10 MW/m 2 for 0.5 s pulses. The maximum surface temperature was 1100°C. In support of the experiment, the thermal response and temperature gradients of the samples were investigated using a finite element model.

Nitrous acid formation in a snow-free wintertime polluted rural area

NASA Astrophysics Data System (ADS)

Tsai, Catalina; Spolaor, Max; Fedele Colosimo, Santo; Pikelnaya, Olga; Cheung, Ross; Williams, Eric; Gilman, Jessica B.; Lerner, Brian M.; Zamora, Robert J.; Warneke, Carsten; Roberts, James M.; Ahmadov, Ravan; de Gouw, Joost; Bates, Timothy; Quinn, Patricia K.; Stutz, Jochen

2018-02-01

Nitrous acid (HONO) photolysis is an important source of hydroxyl radicals (OH) in the lower atmosphere, in particular in winter when other OH sources are less efficient. The nighttime formation of HONO and its photolysis in the early morning have long been recognized as an important contributor to the OH budget in polluted environments. Over the past few decades it has become clear that the formation of HONO during the day is an even larger contributor to the OH budget and additionally provides a pathway to recycle NOx. Despite the recognition of this unidentified HONO daytime source, the precise chemical mechanism remains elusive. A number of mechanisms have been proposed, including gas-phase, aerosol, and ground surface processes, to explain the elevated levels of daytime HONO. To identify the likely HONO formation mechanisms in a wintertime polluted rural environment we present LP-DOAS observations of HONO, NO2, and O3 on three absorption paths that cover altitude intervals from 2 to 31, 45, and 68 m above ground level (a.g.l.) during the UBWOS 2012 experiment in the Uintah Basin, Utah, USA. Daytime HONO mixing ratios in the 2-31 m height interval were, on average, 78 ppt, which is lower than HONO levels measured in most polluted urban environments with similar NO2 mixing ratios of 1-2 ppb. HONO surface fluxes at 19 m a.g.l., calculated using the HONO gradients from the LP-DOAS and measured eddy diffusivity coefficient, show clear upward fluxes. The hourly average vertical HONO flux during sunny days followed solar irradiance, with a maximum of (4.9 ± 0.2) × 1010 molec. cm-2 s-1 at noontime. A photostationary state analysis of the HONO budget shows that the surface flux closes the HONO budget, accounting for 63 ± 32 % of the unidentified HONO daytime source throughout the day and 90 ± 30 % near noontime. This is also supported by 1-D chemistry and transport model calculations that include the measured surface flux, thus clearly identifying chemistry at the ground as the missing daytime HONO source in this environment. Comparison between HONO surface flux, solar radiation, NO2 and HNO3 mixing ratios, and results from 1-D model runs suggest that, under high NOx conditions, HONO formation mechanisms related to solar radiation and NO2 mixing ratios, such as photo-enhanced conversion of NO2 on the ground, are most likely the source of daytime HONO. Under moderate to low NO2 conditions, photolysis of HNO3 on the ground seems to be the main source of HONO.

Recent Approaches to Modeling Transport of Mercury in Surface Water and Groundwater - Case Study in Upper East Fork Poplar Creek, Oak Ridge, TN - 13349

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

Bostick, Kent; Daniel, Anamary; Tachiev, Georgio

2013-07-01

In this case study, groundwater/surface water modeling was used to determine efficacy of stabilization in place with hydrologic isolation for remediation of mercury contaminated areas in the Upper East Fork Poplar Creek (UEFPC) Watershed in Oak Ridge, TN. The modeling simulates the potential for mercury in soil to contaminate groundwater above industrial use risk standards and to contribute to surface water contamination. The modeling approach is unique in that it couples watershed hydrology with the total mercury transport and provides a tool for analysis of changes in mercury load related to daily precipitation, evaporation, and runoff from storms. The modelmore » also allows for simulation of colloidal transport of total mercury in surface water. Previous models for the watershed only simulated average yearly conditions and dissolved concentrations that are not sufficient for predicting mercury flux under variable flow conditions that control colloidal transport of mercury in the watershed. The transport of mercury from groundwater to surface water from mercury sources identified from information in the Oak Ridge Environmental Information System was simulated using a watershed scale model calibrated to match observed daily creek flow, total suspended solids and mercury fluxes. Mercury sources at the former Building 81-10 area, where mercury was previously retorted, were modeled using a telescopic refined mesh with boundary conditions extracted from the watershed model. Modeling on a watershed scale indicated that only source excavation for soils/sediment in the vicinity of UEFPC had any effect on mercury flux in surface water. The simulations showed that colloidal transport contributed 85 percent of the total mercury flux leaving the UEFPC watershed under high flow conditions. Simulation of dissolved mercury transport from liquid elemental mercury and adsorbed sources in soil at former Building 81-10 indicated that dissolved concentrations are orders of magnitude below a target industrial groundwater concentration beneath the source and would not influence concentrations in surface water at Station 17. This analysis addressed only shallow concentrations in soil and the shallow groundwater flow path in soil and unconsolidated sediments to UEFPC. Other mercury sources may occur in bedrock and transport though bedrock to UEFPC may contribute to the mercury flux at Station 17. Generally mercury in the source areas adjacent to the stream and in sediment that is eroding can contribute to the flux of mercury in surface water. Because colloidally adsorbed mercury can be transported in surface water, actions that trap colloids and or hydrologically isolate surface water runoff from source areas would reduce the flux of mercury in surface water. Mercury in soil is highly adsorbed and transport in the groundwater system is very limited under porous media conditions. (authors)« less

Numerical modeling of the autumnal thermal bar

NASA Astrophysics Data System (ADS)

Tsydenov, Bair O.

2018-03-01

The autumnal riverine thermal bar of Kamloops Lake has been simulated using atmospheric data from December 1, 2015, to January 4, 2016. The nonhydrostatic 2.5D mathematical model developed takes into account the diurnal variability of the heat fluxes and wind on the lake surface. The average values for shortwave and longwave radiation and latent and sensible heat fluxes were 19.7 W/m2, - 95.9 W/m2, - 11.8 W/m2, and - 32.0 W/m2 respectively. Analysis of the wind regime data showed prevailing easterly winds and maximum speed of 11 m/s on the 8th and 19th days. Numerical experiments with different boundary conditions at the lake surface were conducted to evaluate effects of variable heat flux and wind stress. The results of modeling demonstrated that the variable heat flux affects the process of thermal bar evolution, especially during the lengthy night cooling. However, the wind had the greatest impact on the behavior of the autumnal thermal bar: The easterly winds contributed to an earlier appearance of the thermal bar, but the strong winds generating the intensive circulations (the velocity of the upper lake flow increased to 6 cm/s) may destroy the thermal bar front.

Concentrations and annual fluxes for selected water-quality constituents from the USGS National Stream Quality Accounting Network (NASQAN) 1996-2000

USGS Publications Warehouse

Kelly, Valerie J.; Hooper, Richard P.; Aulenbach, Brent T.; Janet, Mary

2001-01-01

This report contains concentrations and annual mass fluxes (loadings) for a broad range of water-quality constituents measured during 1996-2000 as part of the U.S. Geological Survey National Stream Quality Accounting Network (NASQAN). During this period, NASQAN operated a network of 40-42 stations in four of the largest river basins of the USA: the Colorado, the Columbia, the Mississippi (including the Missouri and Ohio), and the Rio Grande. The report contains surface-water quality data, streamflow data, field measurements (e.g. water temperature and pH), sediment-chemistry data, and quality-assurance data; interpretive products include annual and average loads, regression parameters for models used to estimate loads, sub-basin yield maps, maps depicting percent detections for censored constituents, and diagrams depicting flow-weighted average concentrations. Where possible, a regression model relating concentration to discharge and season was used for flux estimation. The interpretive context provided by annual loads includes identifying source and sink areas for constituents and estimating the loadings to receiving waters, such as reservoirs or the ocean.

Using a spatially-distributed hydrologic biogeochemistry model with a nitrogen transport module to study the spatial variation of carbon processes in a Critical Zone Observatory

DOE PAGES

Shi, Yuning; Eissenstat, David M.; He, Yuting; ...

2018-05-12

Terrestrial carbon processes are affected by soil moisture, soil temperature, nitrogen availability and solar radiation, among other factors. Most of the current ecosystem biogeochemistry models represent one point in space, and have limited characterization of hydrologic processes. Therefore these models can neither resolve the topographically driven spatial variability of water, energy, and nutrient, nor their effects on carbon processes. A spatially-distributed land surface hydrologic biogeochemistry model, Flux-PIHM-BGC, is developed by coupling the Biome-BGC model with a physically-based land surface hydrologic model, Flux-PIHM. In the coupled system, each Flux-PIHM model grid couples a 1-D Biome-BGC model. In addition, a topographic solarmore » radiation module and an advection-driven nitrogen transport module are added to represent the impact of topography on nutrient transport and solar energy distribution. Because Flux-PIHM is able to simulate lateral groundwater flow and represent the land surface heterogeneities caused by topography, Flux-PIHM-BGC is capable of simulating the complex interaction among water, energy, nutrient, and carbon in time and space. The Flux-PIHM-BGC model is tested at the Susquehanna/Shale Hills Critical Zone Observatory. Model results show that distributions of carbon and nitrogen stocks and fluxes are strongly affected by topography and landscape position, and tree growth is nitrogen limited. The predicted aboveground and soil carbon distributions generally agree with the macro patterns observed. Although the model underestimates the spatial variation, the predicted watershed average values are close to the observations. Lastly, the coupled Flux-PIHM-BGC model provides an important tool to study spatial variations in terrestrial carbon and nitrogen processes and their interactions with environmental factors, and to predict the spatial structure of the responses of ecosystems to climate change.« less

Component-specific dynamics of riverine mangrove CO2 efflux in the Florida coastal Everglades

USGS Publications Warehouse

Troxler, Tiffany G.; Barr, Jordan G.; Fuentes, Jose D.; Engel, Victor C.; Anderson, Gordon H.; Sanchez, Christopher; Lagomosino, David; Price, Rene; Davis, Stephen E.

2015-01-01

Carbon cycling in mangrove forests represents a significant portion of the coastal wetland carbon (C) budget across the latitudes of the tropics and subtropics. Previous research suggests fluctuations in tidal inundation, temperature and salinity can influence forest metabolism and C cycling. Carbon dioxide (CO2) from respiration that occurs from below the canopy is contributed from different components. In this study, we investigated variation in CO2 flux among different below-canopy components (soil, leaf litter, course woody debris, soil including pneumatophores, prop roots, and surface water) in a riverine mangrove forest of Shark River Slough estuary, Everglades National Park (Florida, USA). The range in CO2 flux from different components exceeded that measured among sites along the oligohaline-saline gradient. Black mangrove (Avicennia germinans) pneumatophores contributed the largest average CO2 flux. Over a narrow range of estuarine salinity (25–35 practical salinity units (PSU)), increased salinity resulted in lower CO2 flux to the atmosphere. Tidal inundation reduced soil CO2 flux overall but increased the partial pressure of CO2 (pCO2) observed in the overlying surface water upon flooding. Higher pCO2 in surface water is then subject to tidally driven export, largely as HCO3. Integration and scaling of CO2 flux rates to forest scale allowed for improved understanding of the relative contribution of different below-canopy components to mangrove forest ecosystem respiration (ER). Summing component CO2fluxes suggests a more significant contribution of below-canopy respiration to ER than previously considered. An understanding of below-canopy CO2 component fluxes and their contributions to ER can help to elucidate how C cycling will change with discrete disturbance events (e.g., hurricanes) and long-term change, including sea-level rise, and potential impact mangrove forests. As such, key controls on below-canopy ER must be taken into consideration when developing and modeling mangrove forest C budgets.

Using a spatially-distributed hydrologic biogeochemistry model with a nitrogen transport module to study the spatial variation of carbon processes in a Critical Zone Observatory

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

Shi, Yuning; Eissenstat, David M.; He, Yuting

Terrestrial carbon processes are affected by soil moisture, soil temperature, nitrogen availability and solar radiation, among other factors. Most of the current ecosystem biogeochemistry models represent one point in space, and have limited characterization of hydrologic processes. Therefore these models can neither resolve the topographically driven spatial variability of water, energy, and nutrient, nor their effects on carbon processes. A spatially-distributed land surface hydrologic biogeochemistry model, Flux-PIHM-BGC, is developed by coupling the Biome-BGC model with a physically-based land surface hydrologic model, Flux-PIHM. In the coupled system, each Flux-PIHM model grid couples a 1-D Biome-BGC model. In addition, a topographic solarmore » radiation module and an advection-driven nitrogen transport module are added to represent the impact of topography on nutrient transport and solar energy distribution. Because Flux-PIHM is able to simulate lateral groundwater flow and represent the land surface heterogeneities caused by topography, Flux-PIHM-BGC is capable of simulating the complex interaction among water, energy, nutrient, and carbon in time and space. The Flux-PIHM-BGC model is tested at the Susquehanna/Shale Hills Critical Zone Observatory. Model results show that distributions of carbon and nitrogen stocks and fluxes are strongly affected by topography and landscape position, and tree growth is nitrogen limited. The predicted aboveground and soil carbon distributions generally agree with the macro patterns observed. Although the model underestimates the spatial variation, the predicted watershed average values are close to the observations. Lastly, the coupled Flux-PIHM-BGC model provides an important tool to study spatial variations in terrestrial carbon and nitrogen processes and their interactions with environmental factors, and to predict the spatial structure of the responses of ecosystems to climate change.« less

Integrated thermal infrared imaging and Structure-from-Motion photogrametry to map apparent temperature and radiant hydrothermal heat flux at Mammoth Mountain, CA USA

USGS Publications Warehouse

Lewis, Aaron; George Hilley,; Lewicki, Jennifer L.

2015-01-01

This work presents a method to create high-resolution (cm-scale) orthorectified and georeferenced maps of apparent surface temperature and radiant hydrothermal heat flux and estimate the radiant hydrothermal heat emission rate from a study area. A ground-based thermal infrared (TIR) camera was used to collect (1) a set of overlapping and offset visible imagery around the study area during the daytime and (2) time series of co-located visible and TIR imagery at one or more sites within the study area from pre-dawn to daytime. Daytime visible imagery was processed using the Structure-from-Motion photogrammetric method to create a digital elevation model onto which pre-dawn TIR imagery was orthorectified and georeferenced. Three-dimensional maps of apparent surface temperature and radiant hydrothermal heat flux were then visualized and analyzed from various computer platforms (e.g., Google Earth, ArcGIS). We demonstrate this method at the Mammoth Mountain fumarole area on Mammoth Mountain, CA. Time-averaged apparent surface temperatures and radiant hydrothermal heat fluxes were observed up to 73.7 oC and 450 W m-2, respectively, while the estimated radiant hydrothermal heat emission rate from the area was 1.54 kW. Results should provide a basis for monitoring potential volcanic unrest and mitigating hydrothermal heat-related hazards on the volcano.

Carbon dioxide dynamics in a lake and a reservoir on a tropical island (Bali, Indonesia).

PubMed

Macklin, Paul A; Suryaputra, I Gusti Ngurah Agung; Maher, Damien T; Santos, Isaac R

2018-01-01

Water-to-air carbon dioxide fluxes from tropical lakes and reservoirs (artificial lakes) may be an important but understudied component of global carbon fluxes. Here, we investigate the seasonal dissolved carbon dioxide (CO2) dynamics in a lake and a reservoir on a tropical volcanic island (Bali, Indonesia). Observations were performed over four seasonal surveys in Bali's largest natural lake (Lake Batur) and largest reservoir (Palasari Reservoir). Average CO2 partial pressures in the natural lake and reservoir were 263.7±12.2 μatm and 785.0±283.6 μatm respectively, with the highest area-weighted partial pressures in the wet season for both systems. The strong correlations between seasonal mean values of dissolved oxygen (DO) and pCO2 in the natural lake (r2 = 0.92) suggest that surface water metabolism was an important driver of CO2 dynamics in this deep system. Radon (222Rn, a natural groundwater discharge tracer) explained up to 77% of the variability in pCO2 in the shallow reservoir, suggesting that groundwater seepage was the major CO2 driver in the reservoir. Overall, the natural lake was a sink of atmospheric CO2 (average fluxes of -2.8 mmol m-2 d-1) while the reservoir was a source of CO2 to the atmosphere (average fluxes of 7.3 mmol m-2 d-1). Reservoirs are replacing river valleys and terrestrial ecosystems, particularly throughout developing tropical regions. While the net effect of this conversion on atmospheric CO2 fluxes remains to be resolved, we speculate that reservoir construction will partially offset the CO2 sink provided by deep, volcanic, natural lakes and terrestrial environments.

Investigating the mechanisms responsible for the lack of surface energy balance closure in a central Amazonian tropical rainforest

DOE PAGES

Gerken, Tobias; Ruddell, Benjamin L.; Fuentes, Jose D.; ...

2017-04-29

This work investigates the diurnal and seasonal behavior of the energy balance residual (E) that results from the observed difference between available energy and the turbulent fluxes of sensible heat (H) and latent heat (LE) at the FLUXNET BR-Ma2 site located in the Brazilian central Amazon rainforest. The behavior of E is analyzed by extending the eddy covariance averaging length from 30 min to 4 h and by applying an Information Flow Dynamical Process Network to diagnose processes and conditions affecting E across different seasons. Results show that the seasonal turbulent flux dynamics and the Bowen ratio are primarily drivenmore » by net radiation (R n), with substantial sub-seasonal variability. The Bowen ratio increased from 0.25 in April to 0.4 at the end of September. Extension of the averaging length from 0.5 (94.6% closure) to 4 h and thus inclusion of longer timescale eddies and mesoscale processes closes the energy balance and lead to an increase in the Bowen ratio, thus highlighting the importance of additional H to E. Information flow analysis reveals that the components of the energy balance explain between 25 and 40% of the total Shannon entropy with higher values during the wet season than the dry season. Dry season information flow from the buoyancy flux to E are 30–50% larger than that from H, indicating the potential importance of buoyancy fluxes to closing E. While the low closure highlights additional sources not captured in the flux data and random measurement errors contributing to E, the findings of the information flow and averaging length analysis are consistent with the impact of mesoscale circulations, which tend to transport more H than LE, on the lack of closure.« less

Investigating the mechanisms responsible for the lack of surface energy balance closure in a central Amazonian tropical rainforest

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

Gerken, Tobias; Ruddell, Benjamin L.; Fuentes, Jose D.

This work investigates the diurnal and seasonal behavior of the energy balance residual (E) that results from the observed difference between available energy and the turbulent fluxes of sensible heat (H) and latent heat (LE) at the FLUXNET BR-Ma2 site located in the Brazilian central Amazon rainforest. The behavior of E is analyzed by extending the eddy covariance averaging length from 30 min to 4 h and by applying an Information Flow Dynamical Process Network to diagnose processes and conditions affecting E across different seasons. Results show that the seasonal turbulent flux dynamics and the Bowen ratio are primarily drivenmore » by net radiation (R n), with substantial sub-seasonal variability. The Bowen ratio increased from 0.25 in April to 0.4 at the end of September. Extension of the averaging length from 0.5 (94.6% closure) to 4 h and thus inclusion of longer timescale eddies and mesoscale processes closes the energy balance and lead to an increase in the Bowen ratio, thus highlighting the importance of additional H to E. Information flow analysis reveals that the components of the energy balance explain between 25 and 40% of the total Shannon entropy with higher values during the wet season than the dry season. Dry season information flow from the buoyancy flux to E are 30–50% larger than that from H, indicating the potential importance of buoyancy fluxes to closing E. While the low closure highlights additional sources not captured in the flux data and random measurement errors contributing to E, the findings of the information flow and averaging length analysis are consistent with the impact of mesoscale circulations, which tend to transport more H than LE, on the lack of closure.« less

Annual Cycles of Deep-ocean, Biogeochemical Export Fluxes and Biological Pump Processes in Subtropical and Subantarctic Waters, Southwest Pacific Ocean

NASA Astrophysics Data System (ADS)

Nodder, S.; Chiswell, S.; Northcote, L.

2016-02-01

One of the key aspects of the global carbon cycle is the efficiency and spatio-temporal variability of the biological pump. In this paper, the annual cycles of particle fluxes, derived from moored sediment trap data collected from 2000-12 in subtropical (STW) and subantarctic waters (SAW), east of New Zealand, are presented. These observations are the most comprehensive export flux time-series from temperate Southern Hemisphere latitudes to date. With high levels of variability, fluxes in SAW were markedly lower than in STW, reflecting the picophytoplankton-dominated communities in the iron-limited, high nutrient-low chlorophyll SAW. Austral spring chlorophyll blooms in surface STW were near-synchronous with elevated fluxes of bio-siliceous, carbonate and organic carbon-rich materials to the deep ocean, probably facilitated by diatom sedimentation. Lithogenic fluxes were also high in STW, compared to SAW, reflecting proximity to the New Zealand landmass. In contrast, the highest biogenic fluxes in SAW occurred in spring when surface chlorophyll concentrations were low, while highest annual chlorophyll concentrations were in summer with no associated flux increase. We hypothesize that the high spring export in SAW occurs from subsurface chlorophyll accumulations that are not evident from remote-sensing satellites. This material was also rich in biogenic silica, perhaps related to the preferential export of diatoms and other silica-producing organisms, such as silicoflagellates and radiolarians. Particle fluxes in STW are similar to that of other mesotrophic to oligotrophic waters ( 6-7 mgC m-2 d-1), whereas export from SAW is below global averages ( 3 mgC m-2 d-1), and is characterized by carbonate-dominated and prominent bio-siliceous deposition.

Air-Sea exchange of biogenic volatile organic compounds and the impact on aerosol particle size distributions

NASA Astrophysics Data System (ADS)

Kim, Michelle J.; Novak, Gordon A.; Zoerb, Matthew C.; Yang, Mingxi; Blomquist, Byron W.; Huebert, Barry J.; Cappa, Christopher D.; Bertram, Timothy H.

2017-04-01

We report simultaneous, underway eddy covariance measurements of the vertical flux of isoprene, total monoterpenes, and dimethyl sulfide (DMS) over the Northern Atlantic Ocean during fall. Mean isoprene and monoterpene sea-to-air vertical fluxes were significantly lower than mean DMS fluxes. While rare, intense monoterpene sea-to-air fluxes were observed, coincident with elevated monoterpene mixing ratios. A statistically significant correlation between isoprene vertical flux and short wave radiation was not observed, suggesting that photochemical processes in the surface microlayer did not enhance isoprene emissions in this study region. Calculations of secondary organic aerosol production rates (PSOA) for mean isoprene and monoterpene emission rates sampled here indicate that PSOA is on average <0.1 μg m-3 d-1. Despite modest PSOA, low particle number concentrations permit a sizable role for condensational growth of monoterpene oxidation products in altering particle size distributions and the concentration of cloud condensation nuclei during episodic monoterpene emission events from the ocean.

A comparison of UV surface brightness and HI surface densities for spiral galaxies

NASA Technical Reports Server (NTRS)

Federman, S. R.; Strom, C.

1990-01-01

Shaya and Federman (1987) suggested that the ambient ultraviolet flux at 1000 A permeating a spiral galaxy controls the neutral hydrogen (HI) surface density in the galaxy. They found that the atomic envelopes surrounding small molecular clouds, because of their great number, provide the major contribution to the HI surface density over the stellar disk. The increase in HI surface density with later Hubble types was ascribed to the stronger UV fields from more high-mass stars in later Hubble types. These hypotheses are based on the observations of nearby diffuse interstellar clouds, which show a sharp atomic-to-molecular transition (Savage et al. 1977), and on the theoretical framework introduced by Federman, Glassgold, and Kwan (1979). Atomic envelopes around interstellar clouds in the solar neighborhood arise when a steady state is reached between photodissociation of H2 and the formation of H2 on grains. The photodissociation process involves photons with wavelengths between 912 A and 1108 A. Shaya and Federman used H-alpha flux as an approximate measure for the far UV flux and made their comparisons based on averages over Hubble type. Here, researchers compare, on an individual basis, UV data obtained with space-borne and balloon-borne instruments for galaxies with measurements of HI surface density (Warmels 1988a, b). The comparisons substantiate the conclusion of Shaya and Federman that the far UV field controls the HI content of spiral galaxies.

A multi-model ensemble view of winter heat flux dynamics and the dipole mode in the Mediterranean Sea

NASA Astrophysics Data System (ADS)

Liguori, Giovanni; Di Lorenzo, Emanuele; Cabos, William

2017-02-01

Changes in surface heat fluxes affect several climate processes controlling the Mediterranean climate. These include the winter formation of deep waters, which is the primary driver of the Mediterranean Sea overturning circulation. Previous studies that characterize the spatial and temporal variability of surface heat flux anomalies over the basin reveal the existence of two statistically dominant patterns of variability: a monopole of uniform sign and an east-west dipole of opposite signs. In this work, we use the 12 regional climate model ensemble from the EU-FP6 ENSEMBLES project to diagnose the large-scale atmospheric processes that control the variability of heat fluxes over the Mediterranean Sea from interannual to decadal timescales (here defined as timescales > 6 year). Our findings suggest that while the monopole structure captures variability in the winter-to-winter domain-average net heat flux, the dipole pattern tracks changes in the Mediterranean climate that are connected to the East Atlantic/Western Russia (EA/WR) atmospheric teleconnection pattern. Furthermore, while the monopole exhibits significant differences in the spatial structure across the multi-model ensemble, the dipole pattern is very robust and more clearly identifiable in the anomaly maps of individual years. A heat budget analysis of the dipole pattern reveals that changes in winds associated with the EA/WR pattern exert dominant control through both a direct effect on the latent heat flux (i.e., wind speed) and an indirect effect through specific humidity (e.g., wind advection). A simple reconstruction of the heat flux variability over the deep-water formation regions of the Gulf of Lion and the Aegean Sea reveals that the combination of the monopole and dipole time series explains over 90 % of the heat flux variance in these regions. Given the important role that surface heat flux anomalies play in deep-water formation and the regional climate, improving our knowledge on the dynamics controlling the leading modes of heat flux variability may enhance our predictability of the climate of the Mediterranean area.

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.

Large area, surface discharge pumped, vacuum ultraviolet light source

DOEpatents

Sze, Robert C.; Quigley, Gerard P.

1996-01-01

Large area, surface discharge pumped, vacuum ultraviolet (VUV) light source. A contamination-free VUV light source having a 225 cm.sup.2 emission area in the 240-340 nm region of the electromagnetic spectrum with an average output power in this band of about 2 J/cm.sup.2 at a wall-plug efficiency of approximately 5% is described. Only ceramics and metal parts are employed in this surface discharge source. Because of the contamination-free, high photon energy and flux, and short pulse characteristics of the source, it is suitable for semiconductor and flat panel display material processing.

Turbulent flux variability and energy balance closure in the TERENO prealpine observatory: a hydrometeorological data analysis

NASA Astrophysics Data System (ADS)

Soltani, Mohsen; Mauder, Matthias; Laux, Patrick; Kunstmann, Harald

2017-07-01

The temporal multiscale variability of the surface heat fluxes is assessed by the analysis of the turbulent heat and moisture fluxes using the eddy covariance (EC) technique at the TERrestrial ENvironmental Observatories (TERENO) prealpine region. The fast and slow response variables from three EC sites located at Fendt, Rottenbuch, and Graswang are gathered for the period of 2013 to 2014. Here, the main goals are to characterize the multiscale variations and drivers of the turbulent fluxes, as well as to quantify the energy balance closure (EBC) and analyze the possible reasons for the lack of EBC at the EC sites. To achieve these goals, we conducted a principal component analysis (PCA) and a climatological turbulent flux footprint analysis. The results show significant differences in the mean diurnal variations of the sensible heat (H) and latent heat (LE) fluxes, because of variations in the solar radiation, precipitation patterns, soil moisture, and the vegetation fraction throughout the year. LE was the main consumer of net radiation. Based on the first principal component (PC1), the radiation and temperature components with a total mean contribution of 29.5 and 41.3%, respectively, were found to be the main drivers of the turbulent fluxes at the study EC sites. A general lack of EBC is observed, where the energy imbalance values amount 35, 44, and 35% at the Fendt, Rottenbuch, and Graswang sites, respectively. An average energy balance ratio (EBR) of 0.65 is obtained in the region. The best closure occurred in the afternoon peaking shortly before sunset with a different pattern and intensity between the study sites. The size and shape of the annual mean half-hourly turbulent flux footprint climatology was analyzed. On average, 80% of the flux footprint was emitted from a radius of approximately 250 m around the EC stations. Moreover, the overall shape of the flux footprints was in good agreement with the prevailing wind direction for all three TERENO EC sites.

Plasma power recycling at the divertor surface

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

Tang, Xian -Zhu; Guo, Zehua

With a divertor made of solid materials like carbon and tungsten, plasma ions are expected to be recycled at the divertor surface with a time-averaged particle recycling coefficient very close to unity in steady-state operation. This means that almost every plasma ion (hydrogen and helium) will be returned to the plasma, mostly as neutrals. The power flux deposited by the plasma on the divertor surface, on the other hand, can have varying recycling characteristics depending on the material choice of the divertor; the run-time atomic composition of the surface, which can be modified by material mix due to impurity migrationmore » in the chamber; and the surface morphology change over time. In general, a high-Z–material (such as tungsten) surface tends to reflect light ions and produce stronger power recycling, while a low-Z–material (such as carbon) surface tends to have a larger sticking coefficient for light ions and hence lower power recycling. Here, an explicit constraint on target plasma density and temperature is derived from the truncated bi-Maxwellian sheath model, in relation to the absorbed power load and power recycling coefficient at the divertor surface. Lastly, it is shown that because of the surface recombination energy flux, the attached plasma has a sharper response to power recycling in comparison to a detached plasma.« less

Plasma power recycling at the divertor surface

DOE PAGES

Tang, Xian -Zhu; Guo, Zehua

2016-12-03

With a divertor made of solid materials like carbon and tungsten, plasma ions are expected to be recycled at the divertor surface with a time-averaged particle recycling coefficient very close to unity in steady-state operation. This means that almost every plasma ion (hydrogen and helium) will be returned to the plasma, mostly as neutrals. The power flux deposited by the plasma on the divertor surface, on the other hand, can have varying recycling characteristics depending on the material choice of the divertor; the run-time atomic composition of the surface, which can be modified by material mix due to impurity migrationmore » in the chamber; and the surface morphology change over time. In general, a high-Z–material (such as tungsten) surface tends to reflect light ions and produce stronger power recycling, while a low-Z–material (such as carbon) surface tends to have a larger sticking coefficient for light ions and hence lower power recycling. Here, an explicit constraint on target plasma density and temperature is derived from the truncated bi-Maxwellian sheath model, in relation to the absorbed power load and power recycling coefficient at the divertor surface. Lastly, it is shown that because of the surface recombination energy flux, the attached plasma has a sharper response to power recycling in comparison to a detached plasma.« less

A new approach to three-dimensional neutron transport solution based on the method of characteristics and linear axial approximation

NASA Astrophysics Data System (ADS)

Zheng, Youqi; Choi, Sooyoung; Lee, Deokjung

2017-12-01

A new approach based on the method of characteristics (MOC) is proposed to solve the neutron transport equation. A new three-dimensional (3D) spatial discretization is applied to avoid the instability issue of the transverse leakage iteration of the traditional 2D/1D approach. In this new approach, the axial and radial variables are discretized in two different ways: the linear expansion is performed in the axial direction, then, the 3D solution of the angular flux is transformed to be the planar solution of 2D angular expansion moments, which are solved by the planar MOC sweeping. Based on the boundary and interface continuity conditions, the 2D expansion moment solution is equivalently transformed to be the solution of the axially averaged angular flux. Using the piecewise averaged angular flux at the top and bottom surfaces of 3D meshes, the planes are coupled to give the 3D angular flux distribution. The 3D CMFD linear system is established from the surface net current of every 3D pin-mesh to accelerate the convergence of power iteration. The STREAM code is extended to be capable of handling 3D problems based on the new approach. Several benchmarks are tested to verify its feasibility and accuracy, including the 3D homogeneous benchmarks and heterogeneous benchmarks. The computational sensitivity is discussed. The results show good accuracy in all tests. With the CMFD acceleration, the convergence is stable. In addition, a pin-cell problem with void gap is calculated. This shows the advantage compared to the traditional 2D/1D MOC methods.

A single-cell technique for the measurement of membrane potential, membrane conductance, and the efflux of rapidly penetrating solutes in Amphiuma erythrocytes.

PubMed

Stoner, L C; Kregenow, F M

1980-10-01

We describe a single-cell technique for measuring membrane potential, membrane resistance, and the efflux of rapidly penetrating solutes such as Cl and H2O. Erythrocytes from Amphiuma means were aspirated into a Sylgard (Dow Corning Corp.)-coated capillary. The aspirated cell separated a solution within the capillary from a solution in the bath. Each of these two solutions was contiguous with approximately 5% of the total membrane surface. Microelectrodes placed concentrically within the capillary permit the measurement of intracellular voltage, specific membrane resistance, and the electrical seal between the two solutions. The intracellular voltage averaged -17.7 mV (pH 7.6) and changed as either intra- or extracellular chloride was varied. The average specific membrane resistance measured by passing current across the exposed membrane surface was 110 ohm-cm2. 36Cl and tritiated H2O fluxes (0.84 +/- 0.05 x 10(-6) M . cm-2 . min-1 and 6.4 +/- 1.5 x 10(-3) M . cm-2 . min-1, respectively) were determined by noting the rate at which isotope leaves the cell and crosses the membrane exposed to the bath. Our measured values for the flux of 36Cl and tritiated H2O approximate reported values for free-floating cells. 36Cl efflux, in addition, is inhibited by 4-acetamido-4'-isothiocyano-stilbene 2,2'-disulfonic acid (SITS) and furosemide, known inhibitors of the anion exchange mechanism responsible for the rapid anion fluxes of red blood cells. One can also demonstrate directly that > 89% of 36Cl efflux is "electrically silent" by analyzing the flux in the presence of an imposed transcellular voltage.

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

Epithermal Neutron Evidence for a Diurnal Surface Hydration Process in the Moon's High Latitudes

NASA Technical Reports Server (NTRS)

McClanahan, T. P.; Mitrofanov, I. G.; Boynton, W. V.; Chin, G.; Parsons, A.; Starr, R. D.; Evans, L. G.; Sanin, A.; Litvak, M.; Livengood, T.

2015-01-01

We report evidence from epithermal neutron flux observations that show that the Moon's high latitude surfaces are being actively hydrated, dehydrated and rehydrated in a diurnal cycle. The near-surface hydration is indicated by an enhanced suppression of the lunar epithermal neutron leakage flux on the dayside of the dawn terminator on poleward-facing slopes (PFS). At 0600 to 0800 local-time, hydrogen concentrations within the upper 1 meter of PFS are observed to be maximized relative to equivalent equator-facing slopes (EFS). During the lunar day surface hydrogen concentrations diminish towards dusk and then rebuild overnight. Surface hydration is determined by differential comparison of the averaged EFS to PFS epithermal neutron count rates above +/- 75 deg latitude. At dawn the contrast bias towards PFS is consistent with at least 15 to 25 parts-per-million (ppm) hydrogen that dissipates by dusk. We review several lines of evidence derived from temperature and epithermal neutron data by a correlated analysis of observations from the Lunar Reconnaissance Orbiter's (LRO) Lunar Exploration Neutron Detector (LEND) that were mapped as a function of lunar local-time, Lunar Observing Laser Altimeter (LOLA) topography and Diviner (DLRE) surface temperature.

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.

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.

Eddy covariance flux measurements of gaseous elemental mercury using cavity ring-down spectroscopy.

PubMed

Pierce, Ashley M; Moore, Christopher W; Wohlfahrt, Georg; Hörtnagl, Lukas; Kljun, Natascha; Obrist, Daniel

2015-02-03

A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exchange between the Earth's surface and the atmosphere is important because gas exchange is important on a global scale. For example, surface GEM emissions from natural sources, legacy emissions, and re-emission of previously deposited anthropogenic pollution may exceed direct primary anthropogenic emissions. Using the EC technique for flux measurements requires subsecond measurements, which so far has not been feasible because of the slow time response of available instrumentation. The CRDS system measured GEM fluxes, which were compared to fluxes measured with the modified Bowen ratio (MBR) and a dynamic flux chamber (DFC). Measurements took place near Reno, NV, in September and October 2012 encompassing natural, low-mercury (Hg) background soils and Hg-enriched soils. During nine days of measurements with deployment of Hg-enriched soil in boxes within 60 m upwind of the EC tower, the covariance of GEM concentration and vertical wind speed was measured, showing that EC fluxes over an Hg-enriched area were detectable. During three separate days of flux measurements over background soils (without Hg-enriched soils), no covariance was detected, indicating fluxes below the detection limit. When fluxes were measurable, they strongly correlated with wind direction; the highest fluxes occurred when winds originated from the Hg-enriched area. Comparisons among the three methods showed good agreement in direction (e.g., emission or deposition) and magnitude, especially when measured fluxes originated within the Hg-enriched soil area. EC fluxes averaged 849 ng m(-2) h(-1), compared to DFC fluxes of 1105 ng m(-2) h(-1) and MBR fluxes of 1309 ng m(-2) h(-1). This study demonstrated that a CRDS system can be used to measure GEM fluxes over Hg-enriched areas, with a conservative detection limit estimate of 32 ng m(-2) h(-1).

Translation of Land Surface Model Accuracy and Uncertainty into Coupled Land-Atmosphere Prediction

NASA Technical Reports Server (NTRS)

Santanello, Joseph A.; Kumar, Sujay; Peters-Lidard, Christa D.; Harrison, Kenneth W.; Zhou, Shuija

2012-01-01

Land-atmosphere (L-A) Interactions playa critical role in determining the diurnal evolution of both planetary boundary layer (PBL) and land surface heat and moisture budgets, as well as controlling feedbacks with clouds and precipitation that lead to the persistence of dry and wet regimes. Recent efforts to quantify the strength of L-A coupling in prediction models have produced diagnostics that integrate across both the land and PBL components of the system. In this study, we examine the impact of improved specification of land surface states, anomalies, and fluxes on coupled WRF forecasts during the summers of extreme dry (2006) and wet (2007) land surface conditions in the U.S. Southern Great Plains. The improved land initialization and surface flux parameterizations are obtained through the use of a new optimization and uncertainty estimation module in NASA's Land Information System (US-OPT/UE), whereby parameter sets are calibrated in the Noah land surface model and classified according to a land cover and soil type mapping of the observation sites to the full model domain. The impact of calibrated parameters on the a) spinup of the land surface used as initial conditions, and b) heat and moisture states and fluxes of the coupled WRF Simulations are then assessed in terms of ambient weather and land-atmosphere coupling along with measures of uncertainty propagation into the forecasts. In addition, the sensitivity of this approach to the period of calibration (dry, wet, average) is investigated. Finally, tradeoffs of computational tractability and scientific validity, and the potential for combining this approach with satellite remote sensing data are also discussed.

A calculation of the radiation environment on the Martian surface

NASA Astrophysics Data System (ADS)

de Wet, Wouter C.; Townsend, Lawrence W.

2017-08-01

In this work, the radiation environment on the Martian surface, as produced by galactic cosmic radiation incident on the atmosphere, is modeled using the Monte Carlo radiation transport code, High Energy Transport Code-Human Exploration and Development in Space (HETC-HEDS). This work is performed in participation of the 2016 Mars Space Radiation Modeling Workshop held in Boulder, CO, and is part of a larger collaborative effort to study the radiation environment on the surface of Mars. Calculated fluxes for neutrons, protons, deuterons, tritons, helions, alpha particles, and heavier ions up to Fe are compared with measurements taken by Radiation Assessment Detector (RAD) instrument aboard the Mars Science Laboratory over a period of 2 months. The degree of agreement between measured and calculated surface flux values over the limited energy range of the measurements is found to vary significantly depending on the particle species or group. However, in many cases the fluxes predicted by HETC-HEDS fall well within the experimental uncertainty. The calculated results for alpha particles and the heavy ion groups Z = 3-5, Z = 6-8, Z = 9-13 and Z > 24 are in the best agreement, each with an average relative difference from measured data of less than 40%. Predictions for neutrons, protons, deuterons, tritons, Helium-3, and the heavy ion group Z = 14-24 have differences from the measurements, in some cases, greater than 50%. Future updates to the secondary light particle production methods in the nuclear model within HETC-HEDS are expected to improve light ion flux predictions.

Deriving a sea surface climatology of CO2 fugacity in support of air-sea gas flux studies

NASA Astrophysics Data System (ADS)

Goddijn-Murphy, L. M.; Woolf, D. K.; Land, P. E.; Shutler, J. D.; Donlon, C.

2014-07-01

Climatologies, or long-term averages, of essential climate variables are useful for evaluating models and providing a baseline for studying anomalies. The Surface Ocean Carbon Dioxide (CO2) Atlas (SOCAT) has made millions of global underway sea surface measurements of CO2 publicly available, all in a uniform format and presented as fugacity, fCO2. fCO2 is highly sensitive to temperature and the measurements are only valid for the instantaneous sea surface temperature (SST) that is measured concurrent with the in-water CO2 measurement. To create a climatology of fCO2 data suitable for calculating air-sea CO2 fluxes it is therefore desirable to calculate fCO2 valid for climate quality SST. This paper presents a method for creating such a climatology. We recomputed SOCAT's fCO2 values for their respective measurement month and year using climate quality SST data from satellite Earth observation and then extrapolated the resulting fCO2 values to reference year 2010. The data were then spatially interpolated onto a 1° × 1° grid of the global oceans to produce 12 monthly fCO2 distributions for 2010. The partial pressure of CO2 (pCO2) is also provided for those who prefer to use pCO2. The CO2 concentration difference between ocean and atmosphere is the thermodynamic driving force of the air-sea CO2 flux, and hence the presented fCO2 distributions can be used in air-sea gas flux calculations together with climatologies of other climate variables.

The effects of spatial heterogeneity and subsurface lateral transfer on evapotranspiration estimates in large scale Earth system models

NASA Astrophysics Data System (ADS)

Rouholahnejad, E.; Fan, Y.; Kirchner, J. W.; Miralles, D. G.

2017-12-01

Most Earth system models (ESM) average over considerable sub-grid heterogeneity in land surface properties, and overlook subsurface lateral flow. This could potentially bias evapotranspiration (ET) estimates and has implications for future temperature predictions, since overestimations in ET imply greater latent heat fluxes and potential underestimation of dry and warm conditions in the context of climate change. Here we quantify the bias in evaporation estimates that may arise from the fact that ESMs average over considerable heterogeneity in surface properties, and also neglect lateral transfer of water across the heterogeneous landscapes at global scale. We use a Budyko framework to express ET as a function of P and PET to derive simple sub-grid closure relations that quantify how spatial heterogeneity and lateral transfer could affect average ET as seen from the atmosphere. We show that averaging over sub-grid heterogeneity in P and PET, as typical Earth system models do, leads to overestimation of average ET. Our analysis at global scale shows that the effects of sub-grid heterogeneity will be most pronounced in steep mountainous areas where the topographic gradient is high and where P is inversely correlated with PET across the landscape. In addition, we use the Total Water Storage (TWS) anomaly estimates from the Gravity Recovery and Climate Experiment (GRACE) remote sensing product and assimilate it into the Global Land Evaporation Amsterdam Model (GLEAM) to correct for existing free drainage lower boundary condition in GLEAM and quantify whether, and how much, accounting for changes in terrestrial storage can improve the simulation of soil moisture and regional ET fluxes at global scale.

Surface radiation fluxes in transient climate simulations

NASA Astrophysics Data System (ADS)

Garratt, J. R.; O'Brien, D. M.; Dix, M. R.; Murphy, J. M.; Stephens, G. L.; Wild, M.

1999-01-01

Transient CO 2 experiments from five coupled climate models, in which the CO 2 concentration increases at rates of 0.6-1.1% per annum for periods of 75-200 years, are used to document the responses of surface radiation fluxes, and associated atmospheric properties, to the CO 2 increase. In all five models, the responses of global surface temperature and column water vapour are non-linear and fairly tightly constrained. Thus, global warming lies between 1.9 and 2.7 K at doubled, and between 3.1 and 4.1 K at tripled, CO 2, whilst column water vapour increases by between 3.5 and 4.5 mm at doubled, and between 7 and 8 mm at tripled, CO 2. Global cloud fraction tends to decrease by 1-2% out to tripled CO 2, mainly the result of decreases in low cloud. Global increases in column water, and differences in these increases between models, are mainly determined by the warming of the tropical oceans relative to the middle and high latitudes; these links are emphasised in the zonal profiles of warming and column water vapour increase, with strong water vapour maxima in the tropics. In all models the all-sky shortwave flux to the surface S↓ (global, annual average) changes by less than 5 W m -2 out to tripled CO 2, in some cases being essentially invariant in time. In contrast, the longwave flux to the surface L↓ increases significantly, by 25 W m -2 typically at tripled CO 2. The variations of S↓ and L↓ (clear-sky and all-sky fluxes) with increase in CO 2 concentration are generally non-linear, reflecting the effects of ocean thermal inertia, but as functions of global warming are close to linear in all five models. This is best illustrated for the clear-sky downwelling fluxes, and the net radiation. Regionally, as illustrated in zonal profiles and global distributions, greatest changes in both S↓ and L↓ are the result primarily of local maxima in warming and column water vapour increases.

Integral emission factors for methane determined using urban flux measurements and local-scale inverse models

NASA Astrophysics Data System (ADS)

Christen, Andreas; Johnson, Mark; Molodovskaya, Marina; Ketler, Rick; Nesic, Zoran; Crawford, Ben; Giometto, Marco; van der Laan, Mike

2013-04-01

The most important long-lived greenhouse gas (LLGHG) emitted during combustion of fuels is carbon dioxide (CO2), however also traces of the LLGHGs methane (CH4) and nitrous oxide (N2O) are released, the quantities of which depend largely on the conditions of the combustion process. Emission factors determine the mass of LLGHGs emitted per energy used (or kilometre driven for cars) and are key inputs for bottom-up emission modelling. Emission factors for CH4 are typically determined in the laboratory or on a test stand for a given combustion system using a small number of samples (vehicles, furnaces), yet associated with larger uncertainties when scaled to entire fleets. We propose an alternative, different approach - Can integrated emission factors be independently determined using direct micrometeorological flux measurements over an urban surface? If so, do emission factors determined from flux measurements (top-down) agree with up-scaled emission factors of relevant combustion systems (heating, vehicles) in the source area of the flux measurement? Direct flux measurements of CH4 were carried out between February and May, 2012 over a relatively densely populated, urban surface in Vancouver, Canada by means of eddy covariance (EC). The EC-system consisted of an ultrasonic anemometer (CSAT-3, Campbell Scientific Inc.) and two open-path infrared gas analyzers (Li7500 and Li7700, Licor Inc.) on a tower at 30m above the surface. The source area of the EC system is characterised by a relative homogeneous morphometry (5.3m average building height), but spatially and temporally varying emission sources, including two major intersecting arterial roads (70.000 cars drive through the 50% source area per day) and seasonal heating in predominantly single-family houses (natural gas). An inverse dispersion model (turbulent source area model), validated against large eddy simulations (LES) of the urban roughness sublayer, allows the determination of the spatial area that contributes to each measurement interval (30 min), which varies with wind direction and stability. A detailed geographic information system of the urban surface combined with traffic counts and building energy models makes it possible to statistically relate fluxes to vehicle density (km driven) and buildings (gas heated volume) - and ultimately quantify the contribution of space heating, transport sector and fugitive emissions to the total emitted CH4 from an urban environment. The measured fluxes of CH4 over the selected urban environment averaged to 22.8 mg CH4 m-2 day-1 during the study period. Compared with the simultaneously measured CO2 emissions, the contribution of CH4, however, accounts for only about 3% of the total LLGHG emissions from this particular urban surface. Traffic contributed 8.8 mg CH4 m-2 day-1, equivalent to 39% of the total CH4 flux. The determined emission factor for the typical fleet composition is 0.062 g CH4 per km driven which is higher than upscaled fleet emission factors (EPA) by a factor of two. This discrepancy can be partially explained through the slower city traffic with frequent idling (traffic congestion), fleet composition and cold starts. Emissions of CH4 by domestic space heating (55% of the total CH4 flux or 12.7 mg CH4 m-2 day-1) are also higher than estimated from upscaled emission factors. There is no evidence of substantial unknown sources such as soil processes, combustion of wood, and leakages from gas distribution pipes (residual: 6% or 1.3 mg CH4 m-2 day-1). The presented study is among the first direct measurements of CH4 emissions over an urban surface and demonstrates that flux measurements of greenhouse gases can be used to determine sources and emission factors in complex urban situations.

Modeling the Effect of Summertime Heating on Urban Runoff Temperature

NASA Astrophysics Data System (ADS)

Thompson, A. M.; Gemechu, A. L.; Norman, J. M.; Roa-Espinosa, A.

2007-12-01

Urban impervious surfaces absorb and store thermal energy, particularly during warm summer months. During a rainfall/runoff event, thermal energy is transferred from the impervious surface to the runoff, causing it to become warmer. As this higher temperature runoff enters receiving waters, it can be harmful to coldwater habitat. A simple model has been developed for the net energy flux at the impervious surfaces of urban areas to account for the heat transferred to runoff. Runoff temperature is determined as a function of the physical characteristics of the impervious areas, the weather, and the heat transfer between the moving film of runoff and the heated impervious surfaces that commonly exist in urban areas. Runoff from pervious surfaces was predicted using the Green- Ampt Mein-Larson infiltration excess method. Theoretical results were compared to experimental results obtained from a plot-scale field study conducted at the University of Wisconsin's West Madison Agricultural Research Station. Surface temperatures and runoff temperatures from asphalt and sod plots were measured throughout 15 rainfall simulations under various climatic conditions during the summers of 2004 and 2005. Average asphalt runoff temperatures ranged from 23.2°C to 37.1°C. Predicted asphalt runoff temperatures were in close agreement with measured values for most of the simulations (average RMSE = 4.0°C). Average pervious runoff temperatures ranged from 19.7° to 29.9°C and were closely approximated by the rainfall temperature (RMSE = 2.8°C). Predicted combined asphalt and sod runoff temperatures using a flow-weighted average were in close agreement with observed values (average RMSE = 3.5°C).

Neutral Solar Wind Generated by Lunar Exospheric Dust at the Terminator

NASA Technical Reports Server (NTRS)

Collier, Michael R.; Stubbs, Timothy J.

2007-01-01

We calculate the flux of neutral solar wind observed on the lunar surface at the terminator due to solar wind protons penetrating exospheric dust with: (1) grains larger that 0.1 microns and (2) grains larger than 0.01 microns. For grains larger than 0.1 microns, the ratio of the neutral solar wind to solar wind flux is estimated to be approx.10(exp -4)-10(exp -3) at solar wind speeds in excess of 800 km/s, but much lower (less than 10(exp -5) at average to low solar wind speeds. However, when the smaller grain sizes are considered, the ratio of the neutral solar wind flux to solar wind flux is estimated to be greater than or equal to 10(exp -5) at all speeds and at speeds in excess of 700 km/s reaches 10(exp -3)-10(exp -2). These neutral solar wind fluxes are easily measurable with current low energy neutral atom instrumentation. Observations of neutral solar wind from the surface of the Moon could provide a very sensitive determination of the distribution of very small dust grains in the lunar exosphere and would provide data complementary to optical measurements at ultraviolet and visible wavelengths. Furthermore, neutral solar wind, unlike its ionized counterpart, is .not held-off by magnetic anomalies, and may contribute to greater space weathering than expected in certain lunar locations.

Steady induction effects in geomagnetism. Part 1A: Steady motional induction of geomagnetic chaos

NASA Technical Reports Server (NTRS)

Voorhies, Coerte V.

1992-01-01

Geomagnetic effects of magnetic induction by hypothetically steady fluid motion and steady magnetic flux diffusion near the top of Earth's core are investigated using electromagnetic theory, simple magnetic earth models, and numerical experiments with geomagnetic field models. The problem of estimating a steady fluid velocity field near the top of Earth's core which induces the secular variation indicated by broad-scale models of the observed geomagnetic field is examined and solved. In Part 1, the steady surficial core flow estimation problem is solved in the context of the source-free mantle/frozen-flux core model. In the first paper (IA), the theory underlying such estimates is reviewed and some consequences of various kinematic and dynamic flow hypotheses are derived. For a frozen-flux core, fluid downwelling is required to change the mean square normal magnetic flux density averaged over the core-mantle boundary. For surficially geostrophic flow, downwelling implies poleward flow. The solution of the forward steady motional induction problem at the surface of a frozen-flux core is derived and found to be a fine, easily visualized example of deterministic chaos. Geomagnetic effects of statistically steady core surface flow may well dominate secular variation over several decades. Indeed, effects of persistent, if not steady, surficially geostrophic core flow are described which may help explain certain features of the present broad-scale geomagnetic field and perhaps paleomagnetic secular variation.

Effects of air filtration on concentration and deposition of gaseous and particulate air pollutants in open-top field chambers. [Ceanothus crassifolius Torr. , Pinus coulteri D. Don, P. ponderosa Dougl. ex P. C. Lawson

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

Bytnerowicz, A.; Olszyk, D.M.; Dawson, P.J.

Concentrations of gaseous and particulate air pollutants, and deposition fluxes of NO{sup {minus}}{sub 3}, SO{sup {minus}2}{sub 4}, and NH{sup +}{sub 4} ions to branches of California lilac (Ceanothus crassifolius Torr.), Coulter pine (Pinus coulteri D. Don.), ponderosa pine (P. ponderosa Dougl. ex P. C. Lawson), nylon filters, and paper filters were measured in open-top field chambers with different filtration materials and in chamberless outside plots. Additionally, concentrations of O{sub 3}, NO{sub 2}, NO, SO{sub 2} and total S compounds also were determined in the chambers. Effects of different air filtrations were more evident for deposition fluxes to plant and surrogatemore » surfaces. On the average, in the CHARCOAL chambers, deposition fluxes of NO{sup {minus}}{sub 3}, SO{sup 2{minus}}{sub 4}, and NH{sup +}{sub 4} to the surfaces were reduced to 21, 38, and 26% of the outside values, respectively. In the DUST 1 DUST 2 chambers, deposition fluxes of NO{sup {minus}}{sub 3}, SO{sup 2{minus}}{sub 4}, and NH{sup +}{sub 4} were reduced to about 50, 56, and 75% of the outside levels, respectively. Deposition fluxes of the studied ions to plants were much lower than to nylon and paper filters.« less

Research Note:Effects of human activities on the Yangtze River suspended sediment flux into the estuary in the last century

NASA Astrophysics Data System (ADS)

Yang, S. L.; Shi, Z.; Zhao, H. Y.; Li, P.; Dai, S. B.; Gao, A.

The surface erosion area in the Yangtze River basin increased from 364×103 km2 in the 1950s to 707×103 km2 in 2001 due to a great increase in population. Based on the regression relationship between surface erosion area and population, the surface erosion area was predicted to be about 280×103 km2 at the beginning of the 20th century. The sediment yield, which increased by about 30% during the first six decades of the 20th century, was closely related to the surface erosion area in this river basin. The Yangtze annual suspended sediment flux into the estuary was about 395×106 t a-1 at the beginning of the century, and this gradually increased to an average of 509×106 t a-1 in the 1960s. The increase in the suspended sediment flux into the estuary was accelerated in the 1950s and the 1960s due to the rapid increase in population and land use immediately after the Second World War and the Liberation War. After the riverine suspended sediment flux reached its maximum in the 1960s, it decreased to <206×106 t a-1 in 2003. Construction of dams was found to be the principal cause for this decreasing trend because, during the same period, (a) the riverine water discharge did not show a decreasing trend, (b) water diversion was not influential and (c) sedimentation in lakes and canals of the middle and lower reaches did not increase. The total storage capacity of reservoirs has increased dramatically over the past half century. The amount of sediment trapped in reservoirs has increased to more than half a billion t a-1. As a result, the suspended sediment flux into the estuary dramatically decreased, even though the sediment yield from many areas of the basin increased in recent decades. Human activities gradually increased the suspended sediment flux into the estuary before the 1960s and then rapidly decreased it. The last century was a period when the Yangtze suspended sediment flux into the estuary was dramatically affected by human activities.

Investigating carbon flux variability in subtropical peat soils of the Everglades using hydrogeophysical methods

NASA Astrophysics Data System (ADS)

Comas, Xavier; Wright, William

2014-08-01

The spatial and temporal variability in accumulation and release of greenhouse gases (mainly methane and carbon dioxide) to the atmosphere from peat soils remains very uncertain. The use of near-surface geophysical methods such as ground penetrating radar (GPR) has proven useful during the last decade to expand scales of measurement as related to in situ gas distribution and dynamics beyond traditional methods (i.e., gas chambers). However, this approach has focused exclusively on boreal peatlands, while no studies in subtropical systems like the Everglades using these techniques exist. In this paper GPR is combined with gas traps, time-lapse cameras, gas chromatography, and surface deformation measurements to explore biogenic gas dynamics (mainly gas buildup and release) in two locations in the Everglades. Similar to previous studies in northern peatlands, our data in the Everglades show a statistically significant correlation between the following: (1) GPR-estimated gas content and gas fluxes, (2) GPR-estimated gas content and surface deformation, and (3) atmospheric pressure and both GPR-estimated gas content and gas flux. From these results several gas-releasing events ranging between 33.8 and 718.8 mg CH4 m-2 d-1 were detected as identified by the following: (1) decreases in GPR-estimated gas content within the peat matrix, (2) increases in gas fluxes captured by gas traps and time-lapse cameras, and (3) decreases in surface deformation. Furthermore, gas-releasing events corresponded to periods of high atmospheric pressure. Changes in gas accumulation and release were attributed to differences in seasonality and peat soil type between sites. These results suggest that biogenic gas releases in the Everglades are spatially and temporarily variable. For example, flux events measured at hourly scales were up to threefold larger when compared to daily fluxes, therefore suggesting that flux measurements decline when averaged over longer time spans. This research therefore questions what the appropriate spatial and temporal scale of measurement is necessary to properly capture the dynamics of biogenic gas release in subtropical peat soils.

On the applicability of surrogate-based Markov chain Monte Carlo-Bayesian inversion to the Community Land Model: Case studies at flux tower sites: SURROGATE-BASED MCMC FOR CLM

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

Huang, Maoyi; Ray, Jaideep; Hou, Zhangshuan

2016-07-04

The Community Land Model (CLM) has been widely used in climate and Earth system modeling. Accurate estimation of model parameters is needed for reliable model simulations and predictions under current and future conditions, respectively. In our previous work, a subset of hydrological parameters has been identified to have significant impact on surface energy fluxes at selected flux tower sites based on parameter screening and sensitivity analysis, which indicate that the parameters could potentially be estimated from surface flux observations at the towers. To date, such estimates do not exist. In this paper, we assess the feasibility of applying a Bayesianmore » model calibration technique to estimate CLM parameters at selected flux tower sites under various site conditions. The parameters are estimated as a joint probability density function (PDF) that provides estimates of uncertainty of the parameters being inverted, conditional on climatologically-average latent heat fluxes derived from observations. We find that the simulated mean latent heat fluxes from CLM using the calibrated parameters are generally improved at all sites when compared to those obtained with CLM simulations using default parameter sets. Further, our calibration method also results in credibility bounds around the simulated mean fluxes which bracket the measured data. The modes (or maximum a posteriori values) and 95% credibility intervals of the site-specific posterior PDFs are tabulated as suggested parameter values for each site. Analysis of relationships between the posterior PDFs and site conditions suggests that the parameter values are likely correlated with the plant functional type, which needs to be confirmed in future studies by extending the approach to more sites.« less

On the applicability of surrogate-based MCMC-Bayesian inversion to the Community Land Model: Case studies at Flux tower sites

DOE PAGES

Huang, Maoyi; Ray, Jaideep; Hou, Zhangshuan; ...

2016-06-01

The Community Land Model (CLM) has been widely used in climate and Earth system modeling. Accurate estimation of model parameters is needed for reliable model simulations and predictions under current and future conditions, respectively. In our previous work, a subset of hydrological parameters has been identified to have significant impact on surface energy fluxes at selected flux tower sites based on parameter screening and sensitivity analysis, which indicate that the parameters could potentially be estimated from surface flux observations at the towers. To date, such estimates do not exist. In this paper, we assess the feasibility of applying a Bayesianmore » model calibration technique to estimate CLM parameters at selected flux tower sites under various site conditions. The parameters are estimated as a joint probability density function (PDF) that provides estimates of uncertainty of the parameters being inverted, conditional on climatologically average latent heat fluxes derived from observations. We find that the simulated mean latent heat fluxes from CLM using the calibrated parameters are generally improved at all sites when compared to those obtained with CLM simulations using default parameter sets. Further, our calibration method also results in credibility bounds around the simulated mean fluxes which bracket the measured data. The modes (or maximum a posteriori values) and 95% credibility intervals of the site-specific posterior PDFs are tabulated as suggested parameter values for each site. As a result, analysis of relationships between the posterior PDFs and site conditions suggests that the parameter values are likely correlated with the plant functional type, which needs to be confirmed in future studies by extending the approach to more sites.« less

On the applicability of surrogate-based MCMC-Bayesian inversion to the Community Land Model: Case studies at Flux tower sites

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

Huang, Maoyi; Ray, Jaideep; Hou, Zhangshuan

The Community Land Model (CLM) has been widely used in climate and Earth system modeling. Accurate estimation of model parameters is needed for reliable model simulations and predictions under current and future conditions, respectively. In our previous work, a subset of hydrological parameters has been identified to have significant impact on surface energy fluxes at selected flux tower sites based on parameter screening and sensitivity analysis, which indicate that the parameters could potentially be estimated from surface flux observations at the towers. To date, such estimates do not exist. In this paper, we assess the feasibility of applying a Bayesianmore » model calibration technique to estimate CLM parameters at selected flux tower sites under various site conditions. The parameters are estimated as a joint probability density function (PDF) that provides estimates of uncertainty of the parameters being inverted, conditional on climatologically average latent heat fluxes derived from observations. We find that the simulated mean latent heat fluxes from CLM using the calibrated parameters are generally improved at all sites when compared to those obtained with CLM simulations using default parameter sets. Further, our calibration method also results in credibility bounds around the simulated mean fluxes which bracket the measured data. The modes (or maximum a posteriori values) and 95% credibility intervals of the site-specific posterior PDFs are tabulated as suggested parameter values for each site. As a result, analysis of relationships between the posterior PDFs and site conditions suggests that the parameter values are likely correlated with the plant functional type, which needs to be confirmed in future studies by extending the approach to more sites.« less

On the applicability of surrogate-based Markov chain Monte Carlo-Bayesian inversion to the Community Land Model: Case studies at flux tower sites

NASA Astrophysics Data System (ADS)

Huang, Maoyi; Ray, Jaideep; Hou, Zhangshuan; Ren, Huiying; Liu, Ying; Swiler, Laura

2016-07-01

The Community Land Model (CLM) has been widely used in climate and Earth system modeling. Accurate estimation of model parameters is needed for reliable model simulations and predictions under current and future conditions, respectively. In our previous work, a subset of hydrological parameters has been identified to have significant impact on surface energy fluxes at selected flux tower sites based on parameter screening and sensitivity analysis, which indicate that the parameters could potentially be estimated from surface flux observations at the towers. To date, such estimates do not exist. In this paper, we assess the feasibility of applying a Bayesian model calibration technique to estimate CLM parameters at selected flux tower sites under various site conditions. The parameters are estimated as a joint probability density function (PDF) that provides estimates of uncertainty of the parameters being inverted, conditional on climatologically average latent heat fluxes derived from observations. We find that the simulated mean latent heat fluxes from CLM using the calibrated parameters are generally improved at all sites when compared to those obtained with CLM simulations using default parameter sets. Further, our calibration method also results in credibility bounds around the simulated mean fluxes which bracket the measured data. The modes (or maximum a posteriori values) and 95% credibility intervals of the site-specific posterior PDFs are tabulated as suggested parameter values for each site. Analysis of relationships between the posterior PDFs and site conditions suggests that the parameter values are likely correlated with the plant functional type, which needs to be confirmed in future studies by extending the approach to more sites.

Water Vapor Exchange in a Costa Rican Lower Montane Tropical Forest

NASA Astrophysics Data System (ADS)

Andrews, R.; Miller, G. R.; Cahill, A. T.; Moore, G. W.; Aparecido, L. M. T.

2015-12-01

Because of high canopy interception in tropical forests, evaporation from wet canopy surfaces makes up a sizeable portion of the total water vapor flux. The modeling complexities presented by changing canopy wetness, along with a scarcity of land-atmosphere flux exchange data from tropical forests, means evapotranspiration (ET) processes have been poorly represented in the tropics in land-surface modeling schemes. To better understand tropical forest ET, we will evaluate the influence of canopy wetness and various micrometeorological data on ET partitioning and total ET flux. We have collected flux data from a lower montane forest in Costa Rica at a newly established AmeriFlux site, which notably has the highest mean annual precipitation of any site in the network. The site features a 39-m canopy tower, equipped with two eddy covariance systems (LI-7200, LI-COR), a CO2/H2O atmospheric profile system (AP200, Campbell Scientific), leaf wetness sensors (LWS, Decagon Devices), sap flow sensors, and a soil respiration chamber (LI-8100A, LI-COR) as well as an array of other micrometeorological sensors. At the site, total ET is driven primarily by available energy, and to a lesser extent, by vapor pressure deficit. Average daily latent energy fluxes peak at values of 160, 75, and 35 W m-2 for dry, partially wet, and wet canopy conditions respectively. Correlations between latent energy flux and all other variables are strongest for drier canopy conditions. Complex relationships between canopy wetness and tropical forest ET cause the environmental controls on these fluxes to be significantly different from those in other biomes. As a result, a new modeling paradigm is needed to more accurately model ET differences between tropical forests and other vegetation types.

Determination of monthly mean humidity in the atmospheric surface layer over oceans from satellite data

NASA Technical Reports Server (NTRS)

Liu, W. T.; Niiler, P. P.

1984-01-01

A simple statistical technique is described to determine monthly mean marine surface-layer humidity, which is essential in the specification of surface latent heat flux, from total water vapor in the atmospheric column measured by space-borne sensors. Good correlation between the two quantities was found in examining the humidity soundings from radiosonde reports of mid-ocean island stations and weather ships. The relation agrees with that obtained from satellite (Seasat) data and ship reports averaged over 2 deg areas and a 92-day period in the North Atlantic and in the tropical Pacific. The results demonstrate that, by using a local regression in the tropical Pacific, total water vapor can be used to determine monthly mean surface layer humidity to an accuracy of 0.4 g/kg. With a global regression, determination to an accuracy of 0.8 g/kg is possible. These accuracies correspond to approximately 10 to 20 W/sq m in the determination of latent heat flux with the bulk parameterization method, provided that other required parameters are known.

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.

Winds over the ocean as measured by the scatterometer on Seasat

NASA Technical Reports Server (NTRS)

Pierson, W. J.

1981-01-01

An analysis is presented of the relative accuracy of Seasat scatterometer measurements of the wind speeds and directions at 19.5 m altitude as compared to ground truth measurements taken by surface ships and instrumented buoys. Attention is given to the JASIN, QE II, and GOASEX surface data. The validity of 2-30 min averages taken from surface stations spread out over a wide area and serving as a basis for defining wind field averages over the 50 km resolution of SASS is examined. Satisfactory wind speeds were found to be available from SASS readings in the wind speed range 6-14 m/sec. The use of 25 SASS readings around a grid point was determined to reduce scatter to 0.25 m/sec when used in numerical weather prediction modeling. Improvements to the SASS techniques by the Seasat successor, NOSS, are discussed, and inclusion of momentum, heat, and water turbulent fluxes by NOSS is noted.

The cycling and sea-air exchange of mercury in the waters of the Eastern Mediterranean during the 2010 MED-OCEANOR cruise campaign.

PubMed

Fantozzi, L; Manca, G; Ammoscato, I; Pirrone, N; Sprovieri, F

2013-03-15

An oceanographic cruise campaign on-board the Italian research vessel Urania was carried out from the 26th of August to the 13th of September 2010 in the Eastern Mediterranean. The campaign sought to investigate the mercury cycle at coastal and offshore locations in different weather conditions. The experimental activity focused on measuring mercury speciation in both seawater and in air, and using meteorological parameters to estimate elemental mercury exchange at the sea-atmosphere interface. Dissolved gaseous mercury (DGM), unfiltered total mercury (UTHg) and filtered total mercury (FTHg) surface concentrations ranged from 16 to 114, 300 to 18,760, and 230 to 10,990pgL(-1), respectively. The highest DGM, UTHg and FTHg values were observed close to Augusta (Sicily), a highly industrialized area of the Mediterranean region, while the lowest values were recorded at offshore stations. DGM vertical profiles partially followed the distribution of sunlight, as a result of the photoinduced transformations of elemental mercury in the surface layers of the water column. However, at some stations, we observed higher DGM concentrations in samples taken from the bottom of the water column, suggesting biological mercury production processes or the presence of tectonic activity. Moreover, two days of continuous measurement at one location demonstrated that surface DGM concentration is affected by solar radiation and atmospheric turbulence intensity. Atmospheric measurements of gaseous elemental mercury (GEM) showed an average concentration (1.6ngm(-3)) close to the background level for the northern hemisphere. For the first time this study used a numerical scheme based on a two-thin film model with a specific parameterization for mercury to estimate elemental mercury flux. The calculated average mercury flux during the entire cruise was 2.2±1.5ngm(-2)h(-1). The analysis of flux data highlights the importance of the wind speed on the mercury evasion from sea surfaces. Copyright © 2012 Elsevier B.V. All rights reserved.

Tidal truncation and barotropic convergence in a channel network tidally driven from opposing entrances

USGS Publications Warehouse

Warner, J.C.; Schoellhamer, D.; Schladow, G.

2003-01-01

Residual circulation patterns in a channel network that is tidally driven from entrances on opposite sides are controlled by the temporal phasing and spatial asymmetry of the two forcing tides. The Napa/Sonoma Marsh Complex in San Francisco Bay, CA, is such a system. A sill on the west entrance to the system prevents a complete tidal range at spring tides that results in tidal truncation of water levels. Tidal truncation does not occur on the east side but asymmetries develop due to friction and off-channel wetland storage. The east and west asymmetric tides meet in the middle to produce a barotropic convergence zone that controls the transport of water and sediment. During spring tides, tidally averaged water-surface elevations are higher on the truncated west side. This creates tidally averaged fluxes of water and sediment to the east. During neap tides, the water levels are not truncated and the propagation speed of the tides controls residual circulation, creating a tidally averaged flux in the opposite direction. ?? 2003 Elsevier Science B.V. All rights reserved.

Interannual Variability of Tropical Ocean Evaporation: A Comparison of Microwave Satellite and Assimilation Results

NASA Technical Reports Server (NTRS)

Robertson, Franklin R.; Wick, Gary; Bosilovich, Michael G.

2005-01-01

Remote sensing methodologies for turbulent heat fluxes over oceans depend on driving bulk formulations of fluxes with measured surface winds and estimated near surface thermodynamics from microwave sensors of the Special Sensor Microwave Imager (SSM/I) heritage. We will review recent work with a number of SSM/I-based algorithms and investigate the ability of current data sets to document global, tropical ocean-averaged evaporation changes in association with El Nino and La Nina SST changes. We show that in addition to interannual signals, latent heat flux increases over the period since late 1987 range from approx. .1 to .6 mm/ day are present; these represent trends 2 to 3 times larger than the NCEP Reanalysis. Since atmospheric storage cannot account for the difference, and since compensating evapotranspiration changes over land are highly unlikely to be this large, these evaporation estimates cannot be reconciled with ocean precipitation records such as those produced by the Global Precipitation Climatology Project, GPCP. The reasons for the disagreement include less than adequate intercalibration between SSM/I sensors providing winds and water vapor for driving the algorithms, biases due to the assumption that column integrated water vapor mirrors near surface water vapor variations, and other factors as well. The reanalyses have their own problems with spin-up during assimilation, lack of constraining input data at the ocean surface, and amplitude of synoptic transients.

Nuclear physics of reverse electron flow at pulsar polar caps

NASA Astrophysics Data System (ADS)

Jones, P. B.

2010-01-01

Protons produced in electromagnetic showers formed by the reverse electron flux are usually the largest component of the time-averaged polar cap open magnetic flux line current in neutron stars with positive corotational charge density. Although the electric field boundary conditions in the corotating frame are time independent, instabilities on both medium and short time-scales cause the current to alternate between states in which either protons or positrons and ions form the major component. These properties are briefly discussed in relation to nulling and microstructure in radio pulsars, pair production in an outer gap and neutron stars with high surface temperatures.

An overview of results from the GEWEX radiation flux assessment

NASA Astrophysics Data System (ADS)

Raschke, E.; Stackhouse, P.; Kinne, S.; Contributors from Europe; the USA

2013-05-01

Multi-annual radiative flux averages of the International Cloud Climatology Project (ISCCP), of the GEWEX - Surface Radiation Budget Project (SRB) and of the Clouds and Earth Radiative Energy System (CERES) are compared and analyzed to characterize the Earth's radiative budget, assess differences and identify possible causes. These satellite based data-sets are also compared to results of a median model, which represents 20 climate models, that participated in the 4th IPCC assessment. Consistent distribution patterns and seasonal variations among the satellite data-sets demonstrate their scientific value, which would further increase if the datasets would be reanalyzed with more accurate and consistent ancillary data.

[Distributions and air-sea fluxes of dissolved nitrous oxide in the Yangtze River estuary and its adjacent marine area in spring and summer].

PubMed

Wang, Lan; Zhang, Gui-ling; Sun, Ming-shuang; Ren, Jing-ling

2014-12-01

Distributions and air-sea fluxes of nitrous oxide (N2O) in the seawaters of the Yangtze River estuary and its adjacent marine area were investigated during two cruises in March and July 2012. Dissolved N2O concentrations in surface waters ranged from 9.34 to 49.08 nmol x L(-1) with an average of (13.27 ± 6.40) nmol x L(-1) in spring and ranged from 7.27 to 27.81 nmol x L(-1) with an average of (10.62 ± 5.03) nmol x L(-1) in summer. There was no obvious difference between surface and bottom N2O concentrations. N2O concentrations in both surface and bottom waters decreased along the freshwater plume from the river mouth to the open sea. High values of dissolved N2O were found in turbidity maximum zone, which suggests that maximal turbidity enhances nitrification. Temperature had dual effects on dissolved N2O concentrations. N2O saturations in surface waters ranged from 86.9% to 351.3% with an average of (111.5 ± 41.4)% in spring and ranged from 111.7% to 396.0% with an average of (155.9 ± 68.4)% in summer. N2O were over-saturated at most stations. The sea-to-air fluxes of N2O were estimated to be (3.2 ± 10.9), (5.5 ± 19.3) and (12.2 ±52.3) μmol x (m2 x d)(-1) in spring and (7.3 ± 12.4), (12.7 ± 20.4) and (20.4 ± 35.9) μmol x (m2 x d)(-1) in summer using the LM86, W92 and RC01 relationships, respectively. The annual emissions of N2O from the Yangtze River estuary and its adjacent marine area were estimated to be 0.6 x 10(-2) Tg x a(-1) (LM86), 1.1 x 10(-2) Tg x a(-1) (W92) and 2.0 x 10(-2) Tg x a(-1) (RC01). Although the area of the Yangtze River estuary and its adjacent marine area only accounts for 0.02% of the total area of the world's oceans, their emission of N2O accounts for 0.06% of global oceanic N2O emission, indicating that the Yangtze River estuary and its adjacent marine area is an active area to produce and emit N2O.

Role of surface heat fluxes underneath cold pools

PubMed Central

Garelli, Alix; Park, Seung‐Bu; Nie, Ji; Torri, Giuseppe; Kuang, Zhiming

2016-01-01

Abstract The role of surface heat fluxes underneath cold pools is investigated using cloud‐resolving simulations with either interactive or horizontally homogenous surface heat fluxes over an ocean and a simplified land surface. Over the ocean, there are limited changes in the distribution of the cold pool temperature, humidity, and gust front velocity, yet interactive heat fluxes induce more cold pools, which are smaller, and convection is then less organized. Correspondingly, the updraft mass flux and lateral entrainment are modified. Over the land surface, the heat fluxes underneath cold pools drastically impact the cold pool characteristics with more numerous and smaller pools, which are warmer and more humid and accompanied by smaller gust front velocities. The interactive fluxes also modify the updraft mass flux and reduce convective organization. These results emphasize the importance of interactive surface fluxes instead of prescribed flux boundary conditions, as well as the formulation of surface heat fluxes, when studying convection. PMID:27134320

Factors Controlling Diffusive CO2 Transport and Production in the Cedarburg Bog, Saukville, Wisconsin

NASA Astrophysics Data System (ADS)

Joynt, E.; Grundl, T.; Han, W. S.; Gulbranson, E. L.

2016-12-01

Wetlands are vital components of the carbon cycle containing an estimated 20-30% of the global soil carbon store. The Cedarburg Bog of southeastern Wisconsin contains multiple wetland types, including the southernmost string bog found in North America. Carbon dioxide (CO2) behavior in wetland systems respond to multiple interdependent variables that are collectively not well understood. Modeling CO2 behavior in wetland environments requires a detailed representation of these variables. In 2014 a LI-COR 8100A automated soil gas flux system was installed in the string bog, measuring CO2 concentration and flux. Groundwater data, soil temperature, and weather data (temperature, pressure, precipitation, etc.) were included to reveal correlations between soil CO2 flux/concentration and external forces. In 2015 field data were complemented with soil moisture data and depth profiles of pore water chemistry and stable carbon isotopes from peat and soil gas to discern source and evolution of CO2 at depth. Initial gaseous δ13C(CO2) average -18‰ and deplete overnight suggesting increasing microbial metabolic efficiency. δ13C soil microbial biomass measure roughly -21‰ to -22‰. LI-COR data show diurnal and seasonal trends; CO2 concentration builds overnight while flux increases during the day. CO2 flux magnitude and CO2 concentration range peak in mid-summer, but frequency of increased CO2 flux events varies seasonally each year. Flux averages 7.55 mgCO2/min-m2 during the day but reaches 530 mgCO2/min-m2. Increased atmospheric and soil temperatures and decreasing atmospheric pressure prelude increasing CO2 flux intensity, though correlation strengths vary. Water level may influence CO2 flux, but observations suggest a mobile peat surface with the water table. 2016 imagery from trail cameras will determine extent of peat/well casing movement with water level changes. Further interpretation of data trends will utilize HYDRUS-1D to quantify relationships under changing environmental conditions.

Effects of Mesoscale Eddies in the Active Mixed Layer: Test of the Parametrisation in Eddy Resolving Simulations

NASA Technical Reports Server (NTRS)

Luneva, M. V.; Clayson, C. A.; Dubovikov, Mikhail

2015-01-01

In eddy resolving simulations, we test a mixed layer mesoscale parametrisation, developed recently by Canuto and Dubovikov [Ocean Model., 2011, 39, 200-207]. With no adjustable parameters, the parametrisation yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy (EKE). We compare terms of the parametrisation diagnosed from coarse-grained fields with the eddy mesoscale fluxes diagnosed directly from the high resolution model. An expression for the EKE in terms of mean fields has also been found to get a closed parametrisation in terms of the mean fields only. In 40 numerical experiments we simulated two types of flows: idealised flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1-2 degrees and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are positively correlated with the parametrisation with higher (0.5-0.74) correlations at the experiments with larger baroclinic radius Rossby. After being averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations are consistent with the parametrisation for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parametrisation unless vertical turbulent mixing in the upper layer becomes strong enough in comparison with mesoscale advection. In the latter case, numerical simulations demonstrate that the deviation of the fluxes from the parametrisation is controlled by dimensionless parameter estimating the ratio of vertical turbulent mixing term to mesoscale advection. An analysis using a modified omega-equation reveals that the effects of the vertical mixing of vorticity is responsible for the two-three fold amplification of vertical mesoscale flux. Possible physical mechanisms, responsible for the amplification of vertical mesoscale flux are discussed.

Improved Estimates of Temporally Coherent Internal Tides and Energy Fluxes from Satellite Altimetry

NASA Technical Reports Server (NTRS)

Ray, Richard D.; Chao, Benjamin F. (Technical Monitor)

2002-01-01

Satellite altimetry has opened a surprising new avenue to observing internal tides in the open ocean. The tidal surface signatures are very small, a few cm at most, but in many areas they are robust, owing to averaging over many years. By employing a simplified two dimensional wave fitting to the surface elevations in combination with climatological hydrography to define the relation between the surface height and the current and pressure at depth, we may obtain rough estimates of internal tide energy fluxes. Initial results near Hawaii with Topex/Poseidon (T/P) data show good agreement with detailed 3D (three dimensional) numerical models, but the altimeter picture is somewhat blurred owing to the widely spaced T/P tracks. The resolution may be enhanced somewhat by using data from the ERS-1 (ESA (European Space Agency) Remote Sensing) and ERS-2 satellite altimeters. The ERS satellite tracks are much more closely spaced (0.72 deg longitude vs. 2.83 deg for T/P), but the tidal estimates are less accurate than those for T/P. All altimeter estimates are also severely affected by noise in regions of high mesoscale variability, and we have obtained some success in reducing this contamination by employing a prior correction for mesoscale variability based on ten day detailed sea surface height maps developed by Le Traon and colleagues. These improvements allow us to more clearly define the internal tide surface field and the corresponding energy fluxes. Results from throughout the global ocean will be presented.

Logistic characteristics of phonon transport in silicon thin film: the S-curve

NASA Astrophysics Data System (ADS)

Yilbas, B. S.; Mansoor, S. Bin

2013-10-01

The logistic characteristics of the averaged heat flux are investigated across the thin film incorporating the S-curve. Temporal behaviour of the heat flux vector is computed using the Boltzmann transport equation. The dispersion relations are introduced to account for the frequency dependent phonon transport across the film. The influence of film width on the characteristics of the averaged heat flux is also examined. It is found that temporal behaviour of the averaged heat flux follows the S-curve. The S-curve characteristics change for different film widths. The time to reach 95% steady value of the averaged heat flux is short for the film with small widths, which is attributed to the ballistic behaviour of phonons in the film.

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.

Turbulent Flow and Sand Dune Dynamics: Identifying Controls on Aeolian Sediment Transport

NASA Astrophysics Data System (ADS)

Weaver, C. M.; Wiggs, G.

2007-12-01

Sediment transport models are founded on cubic power relationships between the transport rate and time averaged flow parameters. These models have achieved limited success and recent aeolian and fluvial research has focused on the modelling and measurement of sediment transport by temporally varying flow conditions. Studies have recognised turbulence as a driving force in sediment transport and have highlighted the importance of coherent flow structures in sediment transport systems. However, the exact mechanisms are still unclear. Furthermore, research in the fluvial environment has identified the significance of turbulent structures for bedform morphology and spacing. However, equivalent research in the aeolian domain is absent. This paper reports the findings of research carried out to characterise the importance of turbulent flow parameters in aeolian sediment transport and determine how turbulent energy and turbulent structures change in response to dune morphology. The relative importance of mean and turbulent wind parameters on aeolian sediment flux was examined in the Skeleton Coast, Namibia. Measurements of wind velocity (using sonic anemometers) and sand transport (using grain impact sensors) at a sampling frequency of 10 Hz were made across a flat surface and along transects on a 9 m high barchan dune. Mean wind parameters and mass sand flux were measured using cup anemometers and wedge-shaped sand traps respectively. Vertical profile data from the sonic anemometers were used to compute turbulence and turbulent stress (Reynolds stress; instantaneous horizontal and vertical fluctuations; coherent flow structures) and their relationship with respect to sand transport and evolving dune morphology. On the flat surface time-averaged parameters generally fail to characterise sand transport dynamics, particularly as the averaging interval is reduced. However, horizontal wind speed correlates well with sand transport even with short averaging times. Quadrant analysis revealed that turbulent events with a positive horizontal component, such as sweeps and outward interactions, were responsible for the majority of sand transport. On the dune surface results demonstrate the development and modification of turbulence and sediment flux in key regions: toe, crest and brink. Analysis suggests that these modifications are directly controlled by streamline curvature and flow acceleration. Conflicting models of dune development, morphology and stability arise when based upon either the dynamics of measured turbulent flow or mean flow.

Experimental Study of Aligned and Staggered Wind Farms in a Convective Boundary Layer

NASA Astrophysics Data System (ADS)

Markfort, Corey; Zhang, Wei; Porte-Agel, Fernando

2011-11-01

Wind farm-atmosphere interaction is complicated by turbine configuration and thermal effects on momentum and kinetic energy fluxes. Wind farms of finite length have been modeled as increased surface roughness or as a sparse canopy; however it is not clear which approach is more appropriate. Experiments were conducted in a thermally controlled boundary layer wind tunnel, using a custom x-wire/cold wire and surface heat flux sensors, to understand the effect of aligned versus staggered turbine configurations on momentum absorption and flow adjustment in a convective boundary layer (CBL). Results for experiments of a large farm show the span-wise averaged flow statistics exhibit similar turbulent transport properties to that of canopy flows. The wake adjusts within and grows over the farm more quickly for a staggered compared to an aligned farm. Using canopy flow scaling, we show that the flow equilibrates faster and the overall momentum absorption is higher in a staggered compared to an aligned farm. Wake recovery behind a single turbine is facilitated by buoyancy in a CBL (Zhang et al. under review). We find a similar effect in wind farms resulting in reduced effective roughness and momentum absorption. We also find a reduction of surface heat flux for both wind farms, but greater for the staggered farm.

Mapping land water and energy balance relations through conditional sampling of remote sensing estimates of atmospheric forcing and surface states

NASA Astrophysics Data System (ADS)

Farhadi, Leila; Entekhabi, Dara; Salvucci, Guido

2016-04-01

In this study, we develop and apply a mapping estimation capability for key unknown parameters that link the surface water and energy balance equations. The method is applied to the Gourma region in West Africa. The accuracy of the estimation method at point scale was previously examined using flux tower data. In this study, the capability is scaled to be applicable with remotely sensed data products and hence allow mapping. Parameters of the system are estimated through a process that links atmospheric forcing (precipitation and incident radiation), surface states, and unknown parameters. Based on conditional averaging of land surface temperature and moisture states, respectively, a single objective function is posed that measures moisture and temperature-dependent errors solely in terms of observed forcings and surface states. This objective function is minimized with respect to parameters to identify evapotranspiration and drainage models and estimate water and energy balance flux components. The uncertainty of the estimated parameters (and associated statistical confidence limits) is obtained through the inverse of Hessian of the objective function, which is an approximation of the covariance matrix. This calibration-free method is applied to the mesoscale region of Gourma in West Africa using multiplatform remote sensing data. The retrievals are verified against tower-flux field site data and physiographic characteristics of the region. The focus is to find the functional form of the evaporative fraction dependence on soil moisture, a key closure function for surface and subsurface heat and moisture dynamics, using remote sensing data.

Jet Surface Interaction-Scrubbing Noise

NASA Technical Reports Server (NTRS)

Khavaran, Abbas

2013-01-01

Generation of sound due to scrubbing of a jet flow past a nearby solid surface is investigated within the framework of the generalized acoustic analogy theory. The analysis applies to the boundary layer noise generated at and near a wall, and excludes the scattered noise component that is produced at the leading or the trailing edge. While compressibility effects are relatively unimportant at very low Mach numbers, frictional heat generation and thermal gradient normal to the surface could play important roles in generation and propagation of sound in high speed jets of practical interest. A general expression is given for the spectral density of the far-field sound as governed by the variable density Pridmore- Brown equation. The propagation Green's function should be solved numerically starting with the boundary conditions on the surface and subject to specified mean velocity and temperature profiles between the surface and the observer. The equivalent sources of aerodynamic sound are associated with non-linear momentum flux and enthalpy flux terms that appear in the linearized Navier-Stokes equations. These multi-pole sources should be modeled and evaluated with input from a Reynolds-Averaged Navier-Stokes (RANS) solver with an appropriate turbulence model.

Thermal modeling of grinding for process optimization and durability improvements

NASA Astrophysics Data System (ADS)

Hanna, Ihab M.

Both thermal and mechanical aspects of the grinding process are investigated in detail in an effort to predict grinding induced residual stresses. An existing thermal model is used as a foundation for computing heat partitions and temperatures in surface grinding. By numerically processing data from IR temperature measurements of the grinding zone; characterizations are made of the grinding zone heat flux. It is concluded that the typical heat flux profile in the grinding zone is triangular in shape, supporting this often used assumption found in the literature. Further analyses of the computed heat flux profiles has revealed that actual grinding zone contact lengths exceed geometric contact lengths by an average of 57% for the cases considered. By integrating the resulting heat flux profiles; workpiece energy partitions are computed for several cases of dry conventional grinding of hardened steel. The average workpiece energy partition for the cases considered was 37%. In an effort to more accurately predict grinding zone temperatures and heat fluxes, refinements are made to the existing thermal model. These include consideration of contact length extensions due to local elastic deformations, variations of the assumed contact area ratio as a function of grinding process parameters, consideration of coolant latent heat of vaporization and its effect on heat transfer beyond the coolant boiling point, and incorporation of coolant-workpiece convective heat flux effects outside the grinding zone. The result of the model refinements accounting for contact length extensions and process-dependant contact area ratios is excellent agreement with IR temperature measurements over a wide range of grinding conditions. By accounting for latent heat of vaporization effects, grinding zone temperature profiles are shown to be capable of reproducing measured profiles found in the literature for cases on the verge of thermal surge conditions. Computed peak grinding zone temperatures for the aggressive grinding examples given are 30--50% lower than those computed using the existing thermal model formulation. By accounting for convective heat transfer effects outside the grinding zone, it is shown that while surface temperatures in the wake of the grinding zone may be significantly affected under highly convective conditions, computed residual stresses are less sensitive to such conditions. Numerical models are used to evaluate both thermally and mechanically induced stress fields in an elastic workpiece, while finite element modeling is used to evaluate residual stresses for workpieces with elastic-plastic material properties. Modeling of mechanical interactions at the local grit-workpiece length scale is used to create the often measured effect of compressive surface residual stress followed by a subsurface tensile peak. The model is shown to be capable of reproducing trends found in the literature of surface residual stresses which are compressive for low temperature grinding conditions, with surface stresses increasing linearly and becoming tensile with increasing temperatures. Further modifications to the finite element model are made to allow for transiently varying inputs for more complicated grinding processes of industrial components such as automotive cam lobes.

Synchronization Experiments With A Global Coupled Model of Intermediate Complexity

NASA Astrophysics Data System (ADS)

Selten, Frank; Hiemstra, Paul; Shen, Mao-Lin

2013-04-01

In the super modeling approach an ensemble of imperfect models are connected through nudging terms that nudge the solution of each model to the solution of all other models in the ensemble. The goal is to obtain a synchronized state through a proper choice of connection strengths that closely tracks the trajectory of the true system. For the super modeling approach to be successful, the connections should be dense and strong enough for synchronization to occur. In this study we analyze the behavior of an ensemble of connected global atmosphere-ocean models of intermediate complexity. All atmosphere models are connected to the same ocean model through the surface fluxes of heat, water and momentum, the ocean is integrated using weighted averaged surface fluxes. In particular we analyze the degree of synchronization between the atmosphere models and the characteristics of the ensemble mean solution. The results are interpreted using a low order atmosphere-ocean toy model.

Maintenance of Surface Current Balance by Field-Aligned Thermoelectric Currents at Astronomical Bodies: Cassini at Rhea

NASA Astrophysics Data System (ADS)

Teolis, B. D.

2014-12-01

Cassini spacecraft magnetic field data at Saturn's moon Rhea reveal a field-aligned electric current system in the flux tube, which forms to satisfy the requirement to balance ion and electron currents on the moon's sharp surface. Unlike induction currents at bodies surrounded by significant atmospheres, Rhea's flux tube current system is not driven by motion through the plasma, but rather thermoelectrically, by heat flow into the object. In addition to Rhea, the requirements for the current system are easily satisfied at many plasma absorbing bodies: (1) a difference of average ion and electron gyroradii radii, and (2) a "sharp" body of any size, i.e., without a significant thick atmosphere. This type of current system is therefore expected to occur generally, e.g. at other airless planetary satellites, asteroids, and even spacecraft; and accordingly, represents a fundamental aspect of the physics of the interaction of astrophysical objects with space plasmas.

Spatial and seasonal dynamics of surface soil carbon in the Luquillo Experimental Forest, Puerto Rico.

Treesearch

Hongqing Wang; Joseph D. Cornell; Charles A.S. Hall; David P. Marley

2002-01-01

We developed a spatially-explicit version of the CENTURY soil model to characterize the storage and flux of soil organic carbon (SOC, 0–30 cm depth) in the Luquillo Experimental Forest (LEF), Puerto Rico as a function of climate, vegetation, and soils. The model was driven by monthly estimates of average air temperature, precipitation, and potential evapotranspiration...

Comparison of performances between IPM and SPM motors with rotor eccentricity

NASA Astrophysics Data System (ADS)

Hwang, C. C.; Chang, C. M.; Cheng, S. P.; Chan, C. K.; Pan, C. T.; Chang, T. Y.

2004-11-01

Rotor eccentricity in two three-phase, 6-pole, 36-slot interior permanent magnet- and surface-mounted synchronous motors are investigated and compared by means of a transient finite element model. Magnet flux density, EMF, cogging torque and average torque generated by the model are presented for the cases of static rotor eccentricity. These results are compared with those obtained from a symmetric rotor case.

A high flux pulsed source of energetic atomic oxygen. [for spacecraft materials ground testing

NASA Technical Reports Server (NTRS)

Krech, Robert H.; Caledonia, George E.

1986-01-01

The design and demonstration of a pulsed high flux source of nearly monoenergetic atomic oxygen are reported. In the present test setup, molecular oxygen under several atmospheres of pressure is introduced into an evacuated supersonic expansion nozzle through a pulsed molecular beam valve. A 10J CO2 TEA laser is focused to intensities greater than 10 to the 9th W/sq cm in the nozzle throat, generating a laser-induced breakdown with a resulting 20,000-K plasma. Plasma expansion is confined by the nozzle geometry to promote rapid electron-ion recombination. Average O-atom beam velocities from 5-13 km/s at fluxes up to 10 to the 18th atoms/pulse are measured, and a similar surface oxygen enrichment in polyethylene samples to that obtained on the STS-8 mission is found.

Role of surface heat fluxes underneath cold pools

DOE PAGES

Gentine, Pierre; Garelli, Alix; Park, Seung -Bu; ...

2016-01-05

In this paper, the role of surface heat fluxes underneath cold pools is investigated using cloud–resolving simulations with either interactive or horizontally homogenous surface heat fluxes over an ocean and a simplified land surface. Over the ocean, there are limited changes in the distribution of the cold pool temperature, humidity, and gust front velocity, yet interactive heat fluxes induce more cold pools, which are smaller, and convection is then less organized. Correspondingly, the updraft mass flux and lateral entrainment are modified. Over the land surface, the heat fluxes underneath cold pools drastically impact the cold pool characteristics with more numerousmore » and smaller pools, which are warmer and more humid and accompanied by smaller gust front velocities. The interactive fluxes also modify the updraft mass flux and reduce convective organization. These results emphasize the importance of interactive surface fluxes instead of prescribed flux boundary conditions, as well as the formulation of surface heat fluxes, when studying convection.« less

Large area, surface discharge pumped, vacuum ultraviolet light source

DOEpatents

Sze, R.C.; Quigley, G.P.

1996-12-17

Large area, surface discharge pumped, vacuum ultraviolet (VUV) light source is disclosed. A contamination-free VUV light source having a 225 cm{sup 2} emission area in the 240-340 nm region of the electromagnetic spectrum with an average output power in this band of about 2 J/cm{sup 2} at a wall-plug efficiency of approximately 5% is described. Only ceramics and metal parts are employed in this surface discharge source. Because of the contamination-free, high photon energy and flux, and short pulse characteristics of the source, it is suitable for semiconductor and flat panel display material processing. 3 figs.

Mercury's helium exosphere after Mariner 10's third encounter

NASA Technical Reports Server (NTRS)

Curtis, S. A.; Hartle, R. E.

1977-01-01

From Mariner 10 third encounter UV data, a value of .00045 was calculated as the fraction of the solar wind He++ flux intercepted and captured by Mercury's magnetosphere if the observed He atmosphere is maintained by the solar wind. If an internal source for He prevails, the corresponding upper bound for the global outgassing rate is estimated to be 4.5 x 10 to the 22nd power per sec. A surface temperature distribution was used which satisfies the heat equation over Mercury's entire surface using Mariner 10 determined mean surface thermal characteristics. The means stand off distance of Mercury's magnetopause averaged over Mercury's orbit was also used.

Impact of Multiple Scattering on Longwave Radiative Transfer Involving Clouds

DOE PAGES

Kuo, Chia-Pang; Yang, Ping; Huang, Xianglei; ...

2017-12-13

General circulation models (GCMs) are extensively used to estimate the influence of clouds on the global energy budget and other aspects of climate. Because radiative transfer computations involved in GCMs are costly, it is typical to consider only absorption but not scattering by clouds in longwave (LW) spectral bands. In this study, the flux and heating rate biases due to neglecting the scattering of LW radiation by clouds are quantified by using advanced cloud optical property models, and satellite data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, Clouds and the Earth's Radiant Energy System (CERES), and Moderatemore » Resolution Imaging Spectrometer (MODIS) merged products (CCCM). From the products, information about the atmosphere and clouds (microphysical and buck optical properties, and top and base heights) is used to simulate fluxes and heating rates. One-year global simulations for 2010 show that the LW scattering decreases top-of-atmosphere (TOA) upward flux and increases surface downward flux by 2.6 and 1.2 W/m 2, respectively, or approximately 10% and 5% of the TOA and surface LW cloud radiative effect, respectively. Regional TOA upward flux biases are as much as 5% of global averaged outgoing longwave radiation (OLR). LW scattering causes approximately 0.018 K/d cooling at the tropopause and about 0.028 K/d heating at the surface. Furthermore, over 40% of the total OLR bias for ice clouds is observed in 350–500 cm -1. Overall, the radiative effects associated with neglecting LW scattering are comparable to the counterpart due to doubling atmospheric CO 2 under clear-sky conditions.« less

Comparison of surface sensible and latent heat fluxes over the Tibetan Plateau from reanalysis and observations

NASA Astrophysics Data System (ADS)

Xie, Jin; Yu, Ye; Li, Jiang-lin; Ge, Jun; Liu, Chuan

2018-02-01

Surface sensible and latent heat fluxes (SH and LE) over the Tibetan Plateau (TP) have been under research since 1950s, especially for recent several years, by mainly using observation, reanalysis, and satellite data. However, the spatiotemporal changes are not consistent among different studies. This paper focuses on the spatiotemporal variation of SH and LE over the TP from 1981 to 2013 using reanalysis data sets (ERA-Interim, JRA-55, and MERRA) and observations. Results show that the spatiotemporal changes from the three reanalysis data sets are significantly different and the probable causes are discussed. Averaged for the whole TP, both SH and LE from MERRA are obviously higher than the other two reanalysis data sets. ERA-Interim shows a significant downward trend for SH and JRA-55 shows a significant increase of LE during the 33 years with other data sets having no obvious changes. By comparing the heat fluxes and some climate factors from the reanalysis with observations, it is found that the differences of heat fluxes among the three reanalysis data sets are closely related to their differences in meteorological conditions as well as the different parameterizations for surface transfer coefficients. In general, the heat fluxes from the three reanalysis have a better representation in the western TP than that in the eastern TP under inter-annual scale. While in terms of monthly variation, ERA-Interim may have better applicability in the eastern TP with dense vegetation conditions, while SH of JRA-55 and LE of MERRA are probably more representative for the middle and western TP with poor vegetation conditions.

Carbon dioxide and methane emissions from the Yukon River system

USGS Publications Warehouse

Striegl, Robert G.; Dornblaser, Mark M.; McDonald, Cory P.; Rover, Jennifer R.; Stets, Edward G.

2012-01-01

Carbon dioxide (CO2) and methane (CH4) emissions are important, but poorly quantified, components of riverine carbon (C) budgets. This is largely because the data needed for gas flux calculations are sparse and are spatially and temporally variable. Additionally, the importance of C gas emissions relative to lateral C exports is not well known because gaseous and aqueous fluxes are not commonly measured on the same rivers. We couple measurements of aqueous CO2 and CH4 partial pressures (pCO2, pCH4) and flux across the water-air interface with gas transfer models to calculate subbasin distributions of gas flux density. We then combine those flux densities with remote and direct observations of stream and river water surface area and ice duration, to calculate C gas emissions from flowing waters throughout the Yukon River basin. CO2emissions were 7.68 Tg C yr−1 (95% CI: 5.84 −10.46), averaging 750 g C m−2 yr−1 normalized to water surface area, and 9.0 g C m−2 yr−1 normalized to river basin area. River CH4 emissions totaled 55 Gg C yr−1 or 0.7% of the total mass of C emitted as CO2 plus CH4 and ∼6.4% of their combined radiative forcing. When combined with lateral inorganic plus organic C exports to below head of tide, C gas emissions comprised 50% of total C exported by the Yukon River and its tributaries. River CO2 and CH4 derive from multiple sources, including groundwater, surface water runoff, carbonate equilibrium reactions, and benthic and water column microbial processing of organic C. The exact role of each of these processes is not yet quantified in the overall river C budget.

Modeling decadal timescale interactions between surface water and ground water in the central Everglades, Florida, USA

USGS Publications Warehouse

Harvey, J.W.; Newlin, J.T.; Krupa, S.L.

2006-01-01

Surface-water and ground-water flow are coupled in the central Everglades, although the remoteness of this system has hindered many previous attempts to quantify interactions between surface water and ground water. We modeled flow through a 43,000 ha basin in the central Everglades called Water Conservation Area 2A. The purpose of the model was to quantify recharge and discharge in the basin's vast interior areas. The presence and distribution of tritium in ground water was the principal constraint on the modeling, based on measurements in 25 research wells ranging in depth from 2 to 37 m. In addition to average characteristics of surface-water flow, the model parameters included depth of the layer of 'interactive' ground water that is actively exchanged with surface water, average residence time of interactive ground water, and the associated recharge and discharge fluxes across the wetland ground surface. Results indicated that only a relatively thin (8 m) layer of the 60 m deep surfical aquifer actively exchanges surface water and ground water on a decadal timescale. The calculated storage depth of interactive ground water was 3.1 m after adjustment for the porosity of peat and sandy limestone. Modeling of the tritium data yielded an average residence time of 90 years in interactive ground water, with associated recharge and discharge fluxes equal to 0.01 cm d -1. 3H/3He isotopic ratio measurements (which correct for effects of vertical mixing in the aquifer with deeper, tritium-dead water) were available from several wells, and these indicated an average residence time of 25 years, suggesting that residence time was overestimated using tritium measurements alone. Indeed, both residence time and storage depth would be expected to be overestimated due to vertical mixing. The estimate of recharge and discharge (0.01 cm d-1) that resulted from tritium modeling therefore is still considered reliable, because the ratio of residence time and storage depth (used to calculated recharge and discharge) is much less sensitive to vertical mixing compared with residence time alone. We conclude that a small but potentially significant component of flow through the Everglades is recharged to the aquifer and stored there for years to decades before discharged back to surface water. Long-term storage of water and solutes in the ground-water system beneath the wetlands has implications for restoration of Everglades water quality.

Modeling decadal timescale interactions between surface water and ground water in the central Everglades, Florida, USA

NASA Astrophysics Data System (ADS)

Harvey, Judson W.; Newlin, Jessica T.; Krupa, Steven L.

2006-04-01

Surface-water and ground-water flow are coupled in the central Everglades, although the remoteness of this system has hindered many previous attempts to quantify interactions between surface water and ground water. We modeled flow through a 43,000 ha basin in the central Everglades called Water Conservation Area 2A. The purpose of the model was to quantify recharge and discharge in the basin's vast interior areas. The presence and distribution of tritium in ground water was the principal constraint on the modeling, based on measurements in 25 research wells ranging in depth from 2 to 37 m. In addition to average characteristics of surface-water flow, the model parameters included depth of the layer of 'interactive' ground water that is actively exchanged with surface water, average residence time of interactive ground water, and the associated recharge and discharge fluxes across the wetland ground surface. Results indicated that only a relatively thin (8 m) layer of the 60 m deep surfical aquifer actively exchanges surface water and ground water on a decadal timescale. The calculated storage depth of interactive ground water was 3.1 m after adjustment for the porosity of peat and sandy limestone. Modeling of the tritium data yielded an average residence time of 90 years in interactive ground water, with associated recharge and discharge fluxes equal to 0.01 cm d -1. 3H/ 3He isotopic ratio measurements (which correct for effects of vertical mixing in the aquifer with deeper, tritium-dead water) were available from several wells, and these indicated an average residence time of 25 years, suggesting that residence time was overestimated using tritium measurements alone. Indeed, both residence time and storage depth would be expected to be overestimated due to vertical mixing. The estimate of recharge and discharge (0.01 cm d -1) that resulted from tritium modeling therefore is still considered reliable, because the ratio of residence time and storage depth (used to calculated recharge and discharge) is much less sensitive to vertical mixing compared with residence time alone. We conclude that a small but potentially significant component of flow through the Everglades is recharged to the aquifer and stored there for years to decades before discharged back to surface water. Long-term storage of water and solutes in the ground-water system beneath the wetlands has implications for restoration of Everglades water quality.

Characterization of extreme air-sea turbulent fluxes

NASA Astrophysics Data System (ADS)

Gulev, Sergey; Belyaev, Konstantin

2017-04-01

Extreme ocean-atmosphere turbulent fluxes play a critical role in the convective processes in the mid and subpolar latitudes and may also affect a variety of atmospheric processes, such as generation and re-intensification of extreme cyclones in the areas of the mid latitude storm tracks. From the ocean dynamics perspective, specifically for quantifying extreme vertical mixing, characterization of the extreme fluxes requires, besides estimation of the extreme events, also consideration of the relative extremeness of surface fluxes and their timing, e.g. the duration of periods of high surface fluxes. In order to comprehensively characterize extreme turbulent fluxes at sea surface we propose a formalism based upon probability density distributions of surface turbulent fluxes and flux-related variables. Individual absolute flux extremes were derived using Modified Fisher-Tippett (MFT) distribution of turbulent fluxes. Then, we extend this distribution to the fractional distribution, characterizing the fraction of time-integrated turbulent heat flux provided by the fluxes exceeding a given percentile. Finally, we consider the time durations during which fluxes of a given intensity provide extreme accumulations of heat loss from the surface. For estimation of these characteristics of surface fluxes we use fluxes recomputed from the state variables available from modern era reanalyses (ERA-Interim, MERRA and CFSR) for the period from 1979 onwards. Applications of the formalism to the VOS (Voluntary Observing Ship) - based surface fluxes are also considered. We discuss application of the new metrics of mesoscale and synoptic variability of surface fluxes to the dynamics of mixed layer depth in the North Atlantic.

Annual cycles of mass flux and isotopic composition of pteropod shells settling into the deep Sargasso sea

NASA Astrophysics Data System (ADS)

Jasper, John P.; Deuser, Werner G.

1993-04-01

Mass fluxes and stable isotopic compositions ( δ18O and δ13C) pteropod shells collected during a 6-year series of 2-month sediment-trap deployments in the deep (3.2 km) Sargasso Sea provide information on annual population changes, habitat depths and life spans of thecosome pteropods (Euthecosomata). The flux of pteropod shells responds to the annual cycle of primary production in the upper ocean. Flux maxima of the shells (> 1 mm) of eight species occur from late winter through autumn. Seasonal changes in the hydrography of the upper water column are quite accurately recorded in the δ18O variations of six perennial species, which generally confirm the distinction between non-migratory ( Creseis acicula, Creseis virgula conica, and Diacria quadridentata) and diurnally migratory taxa ( Styliola subula, Cuvierina columnella, and Clio pyramidata). Isotopic records of C. acicula and C. virgula conica are consistent with shell formation above 50 m. The records of the migratory species reflect what appear to be average calcification depths of 50-75 m. Average annual δ13C variations reveal the annual cycles of primary production and stratification of near-surface waters. Adult life spans of the species studied appear to be no more than a few months. The results of this study should be useful in paleoceanographic reconstructions based on isotopic measurements of sedimentary pteropod shells.

The neutron guide upgrade of the TOSCA spectrometer

NASA Astrophysics Data System (ADS)

Pinna, Roberto S.; Rudić, Svemir; Parker, Stewart F.; Armstrong, Jeff; Zanetti, Matteo; Škoro, Goran; Waller, Simon P.; Zacek, Daniel; Smith, Clive A.; Capstick, Matthew J.; McPhail, David J.; Pooley, Daniel E.; Howells, Gareth D.; Gorini, Giuseppe; Fernandez-Alonso, Felix

2018-07-01

The primary flightpath of the TOSCA indirect geometry neutron spectrometer has been upgraded with a high-m 14.636 m (including 0.418 m of air gaps) neutron guide composed of ten sections in order to boost the neutron flux at the sample position. The upgraded incident neutron beam has been characterised with the help of the time-of-flight neutron monitor; the beam profile and the gain in the neutron flux data are presented. At an average proton current-on-target of 160 μA and proton energy of 800 MeV (ISIS Target Station 1; at the time of the measurements) we have found that the wavelength-integrated neutron flux (from 0.28 Å to 4.65 Å) at the position of the TOSCA instrument sample (spatially averaged across a 3.0 × 3.0 cm2 surface centred around the (0,0) position) is approximately 2.11 × 107 neutrons cm-2 s-1 while the gain in the neutron flux is as much as 46-fold for neutrons with a wavelength of 2.5 Å. The instrument's excellent spectral resolution and low spectral background have been preserved upon the upgrade. The much improved count rate allows faster measurements where useful data of hydrogen rich samples can be recorded within minutes, as well as experiments involving smaller samples that were not possible in the past.

Precision Requirements for Space-based XCO2 Data

NASA Technical Reports Server (NTRS)

Miller, C. E.; Crisp, D.; DeCola, P. C.; Olsen, S. C.; Randerson, J. T.; Rayner, P.; Jacob, D.J.; Jones, D.; Suntharalingam, P.

2005-01-01

Precision requirements have been determined for the column-averaged CO2 dry air mole fraction (X(sub CO2)) data products to be delivered by the Orbiting Carbon Observatory (OCO). These requirements result from an assessment of the amplitude and spatial gradients in X(sub CO2), the relationship between X(sub CO2) precision and surface CO2 flux uncertainties calculated from inversions of the X(sub CO2) data, and the effects of X,,Z biases on CO2 flux inversions. Observing system simulation experiments and synthesis inversion modeling demonstrate that the OCO mission design and sampling strategy provide the means to achieve the X(sub CO2) precision requirements. The impact of X(sub CO2) biases on CO2 flux uncertainties depend on their spatial and temporal extent since CO2 sources and sinks are inferred from regional-scale X(sub CO2) gradients. Simulated OCO sampling of the TRACE-P CO2 fields shows the ability of X(sub CO2) data to constrain CO2 flux inversions over Asia and distinguish regional fluxes from India and China.

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.

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.

Impact of Calibrated Land Surface Model Parameters on the Accuracy and Uncertainty of Land-Atmosphere Coupling in WRF Simulations

NASA Technical Reports Server (NTRS)

Santanello, Joseph A., Jr.; Kumar, Sujay V.; Peters-Lidard, Christa D.; Harrison, Ken; Zhou, Shujia

2012-01-01

Land-atmosphere (L-A) interactions play a critical role in determining the diurnal evolution of both planetary boundary layer (PBL) and land surface temperature and moisture budgets, as well as controlling feedbacks with clouds and precipitation that lead to the persistence of dry and wet regimes. Recent efforts to quantify the strength of L-A coupling in prediction models have produced diagnostics that integrate across both the land and PBL components of the system. In this study, we examine the impact of improved specification of land surface states, anomalies, and fluxes on coupled WRF forecasts during the summers of extreme dry (2006) and wet (2007) land surface conditions in the U.S. Southern Great Plains. The improved land initialization and surface flux parameterizations are obtained through the use of a new optimization and uncertainty estimation module in NASA's Land Information System (LIS-OPT/UE), whereby parameter sets are calibrated in the Noah land surface model and classified according to a land cover and soil type mapping of the observation sites to the full model domain. The impact of calibrated parameters on the a) spinup of the land surface used as initial conditions, and b) heat and moisture states and fluxes of the coupled WRF simulations are then assessed in terms of ambient weather and land-atmosphere coupling along with measures of uncertainty propagation into the forecasts. In addition, the sensitivity of this approach to the period of calibration (dry, wet, average) is investigated. Finally, tradeoffs of computational tractability and scientific validity, and the potential for combining this approach with satellite remote sensing data are also discussed.

Measurement of local high-level, transient surface heat flux

NASA Technical Reports Server (NTRS)

Liebert, Curt H.

1988-01-01

This study is part of a continuing investigation to develop methods for measuring local transient surface heat flux. A method is presented for simultaneous measurements of dual heat fluxes at a surface location by considering the heat flux as a separate function of heat stored and heat conducted within a heat flux gage. Surface heat flux information is obtained from transient temperature measurements taken at points within the gage. Heat flux was determined over a range of 4 to 22 MW/sq m. It was concluded that the method is feasible. Possible applications are for heat flux measurements on the turbine blade surfaces of space shuttle main engine turbopumps and on the component surfaces of rocket and advanced gas turbine engines and for testing sensors in heat flux gage calibrators.

COMBINED ANALYSIS OF THORIUM AND FAST NEUTRON DATA AT THE LUNAR SURFACE

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

O. GASNAULT; W. FELDMAN; ET AL

2001-01-01

The global distribution of the radioactive elements (U, K, Th) at the lunar surface is an important parameter for an understanding of lunar evolution, because they have provided continuous heat over the lifetime of the Moon. Today, only the thorium distribution is available for the whole lunar surface [1]. Another key parameter that characterize the surface of the Moon is the presence of mare basalts. These basalts are concentrated on the nearside and are represented by materials with high-Fe content, sometimes associated with high-Ti. We demonstrated elsewhere that the fast neutron measurement made by Lunar Prospector is representative of themore » average soil atomic mass [2]. is primarily dominated by Fe and Ti in basaltic terranes, and therefore the map of the fast neutrons provides a good delineation of mare basalts. We focus here on the correlated variations of thorium abundances and fast neutron fluxes averaged over areas of 360 km in diameter, in an attempt to provide a better understanding of the thorium emplacement on the surface of the Moon.« less

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.

3-D density imaging with muon flux measurements from underground galleries

NASA Astrophysics Data System (ADS)

Lesparre, N.; Cabrera, J.; Marteau, J.

2017-03-01

Atmospheric muon flux measurements provide information on subsurface density distribution. In this study, muon flux was measured underground, in the Tournemire experimental platform (France). The objective was to image the medium between the galleries and the surface and evaluate the feasibility to detect the presence of discontinuities, for example, produced by secondary subvertical faults or by karstic networks. Measurements were performed from three different sites with a partial overlap of muon trajectories, offering the possibility to seek density variations at different depths. The conversion of the measured muon flux to average density values showed global variations further analysed through a 3-D nonlinear inversion procedure. Main results are the presence of a very low density region at the level of the upper aquifer, compatible with the presence of a karstic network hosting local cavities, and the absence of secondary faults. We discuss the validity of the present results and propose different strategies to improve the accuracy of such measurements and analysis.

STRATIFIED COMPOSITION EFFECTS ON PLANETARY NEUTRON FLUX

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

O. GASNAULT; ET AL

2001-01-01

All the bodies of the solar system that are directly irradiated by the galactic cosmic rays, emit enough neutrons to allow a measurement from space. These leakage neutron fluxes are indexes of the surface composition, depending on the energy of the neutrons [1]. Recent work propose geochemical interpretations of these fluxes: the thermal energy range is sensitive to iron, titanium, rare earth elements and thorium [2, 3], the epithermal energy range is sensitive to hydrogen, samarium and gadolinium [2] and the fast energy range is representative of the average soil atomic mass [4]. Nevertheless these studies make the hypothesis ofmore » a composition uniform within the footprint of the spectrometer and independent of depth. We show in this abstract that a stratified composition could change significantly the flux intensity and complicate the interpretation of the measurements. The neutron leakage flux is a competition between production effects (sensitive at high energy) and diffusion-capture effects (mostly sensitive at low energy). On one hand, it happens to be that the elements which produce the higher number of neutrons in typical lunar compositions are iron and titanium, which have also large cross section of absorption with the neutrons. On the other hand, the maximum of neutron intensity does not occur at the surface but at about 180 g cm{sup {minus}2} in depth. Therefore, if we have an iron- and/or titanium-rich soil (important production of neutrons) with a top layer having less iron and/or titanium (i.e. more transparent to the neutrons), we can expect an enhancement of the flux compared to a uniform composition.« less

Characterization of land surface energy fluxes in a tropical lowland rice paddy

NASA Astrophysics Data System (ADS)

Chatterjee, Dibyendu; Tripathi, Rahul; Chatterjee, Sumanta; Debnath, Manish; Shahid, Mohammad; Bhattacharyya, Pratap; Swain, Chinmaya Kumar; Tripathy, Rojalin; Bhattacharya, Bimal K.; Nayak, Amaresh Kumar

2018-04-01

A field experiment was conducted in 2015 to study the land surface energy fluxes from tropical lowland rice paddy in eastern India with an objective to determine the mass, momentum, and energy exchange rates between rice paddies and the atmosphere. All the land surface energy fluxes were measured by eddy covariance (EC) system (make Campbell Scientific) in dry season (DS, 1-125 Julian days), dry fallow (DF, 126-181 Julian days), wet season (WS, 182-324 Julian days), and wet fallow (WF, 325-365 Julian days). The rice was cultivated in dry season (January-May) and wet season (July-November) in low wet lands and the ground is kept fallow during the remainder of the year. Results showed that albedo varied from 0.09 to 0.24 and showed positive value from morning 6:00 h until evening 18:00 h. Mean soil temperature (T g) was highest in DF, while the skin temperature (T s) was highest in WS. Average Bowen ratio (B) ranged from 0.21 to 0.64 and large variation in B was observed during the fallow periods as compared to the cropping seasons. The magnitude of aerodynamic, canopy, and climatological resistances increased with the progress of cropping season and their magnitudes decreased during the end of both cropping seasons and found minimum during the fallow periods. At a constant vapor pressure deficit (VPD) at 0.16, 0.18, 0.15, and 0.43 kPa, latent heat flux (LE) initially increased, but later it tended to level off with an increase in VPD. The actual evapotranspiration (ETa) during both the cropping seasons was higher than the fallow period. This study can be used as a source of default values for many land surface energy fluxes which are required in various meteorological or air-quality models for rice paddies. A larger imbalance of energy was observed during the wet season as the energy is stored and perhaps advected in the fresh water.

Regional N2O fluxes in Amazonia derived from aircraft vertical profiles

NASA Astrophysics Data System (ADS)

D'Amelio, M. T. S.; Gatti, L. V.; Miller, J. B.; Tans, P.

2009-08-01

Nitrous oxide (N2O) is the third most important anthropogenic greenhouse gas. Globally, the main sources of N2O are nitrification and denitrification in soils. About two thirds of the soil emissions occur in the tropics and approximately 20% originate in wet rainforest ecosystems, like the Amazon forest. The work presented here involves aircraft vertical profiles of N2O from the surface to 4 km over two sites in the Eastern and Central Amazon: Tapajós National Forest (SAN) and Cuieiras Biologic Reserve (MAN), and the estimation of N2O fluxes for regions upwind of these sites. To our knowledge, these regional scale N2O measurements in Amazonia are unique and represent a new approach to looking regional scale emissions. The fluxes upwind of MAN exhibited little seasonality, and the annual mean was 2.1±1.0 mg N2O m-2 day-1, higher than that for fluxes upwind of SAN, which averaged 1.5±1.6 mg N2O m-2 day-1. The higher rainfall around the MAN site could explain the higher N2O emissions. For fluxes from the coast to SAN seasonality is present for all years, with high fluxes in the months of March through May, and in November through December. The first peak of N2O flux is strongly associated with the wet season. The second peak of high N2O flux recorded at SAN occurs during the dry season and can not be easily explained. However, about half of the dry season profiles exhibit significant correlations with CO, indicating a larger than expected source of N2O from biomass burning. The average CO:N2O ratio for all profiles sampled during the dry season is 94±77 mol CO:mol N2O and suggests a larger biomass burning contribution to the global N2O budget than previously reported.

A new class of draw solutions for minimizing reverse salt flux to improve forward osmosis desalination.

PubMed

Nguyen, Hau Thi; Nguyen, Nguyen Cong; Chen, Shiao-Shing; Ngo, Huu Hao; Guo, Wenshan; Li, Chi-Wang

2015-12-15

The applications of forward osmosis (FO) have been hindered because of the lack of an optimal draw solution. The reverse salt flux from the draw solution not only reduces the water flux but also increases the cost of draw solute replenishment. Therefore, in this study, Tergitol NP7 and NP9 with a long straight carbon chain and low critical micelle concentration (CMC) were coupled with highly charged ethylenediaminetetraacetic acid (EDTA) as an innovative draw solution to minimize reverse salt diffusion in FO for the first time. The results showed that the lowest reverse salt flux of 0.067 GMH was observed when 0.1M EDTA-2Na coupled with 15mM NP7 was used as a draw solution and deionized water was used as a feed solution in FO mode (active layer facing with the feed solution). This is due to the hydrophobic interaction between the tails of NP7 and the FO membrane, thus creating layers on the membrane surface and constricting the FO membrane pores. Moreover, 1M EDTA-2Na coupled with 15mM NP7 is promising as an optimal draw solution for brackish water and sea water desalination. Average water fluxes of 7.68, 6.78, and 5.95 LMH were achieved when brackish water was used as a feed solution (5, 10, and 20g/L NaCl), and an average water flux of 3.81 LMH was achieved when sea water was used as a feed solution (35g/L NaCl). The diluted draw solution was recovered using a nanofiltration (NF-TS80) membrane with a high efficiency of 95% because of the high charge and large size of the draw solution. Copyright © 2015 Elsevier B.V. All rights reserved.

Dynamics of Permafrost Associated Methane Hydrate in Response to Climate Change

NASA Astrophysics Data System (ADS)

You, K.; Flemings, P. B.

2014-12-01

The formation and melting of methane hydrate and ice are intertwined in permafrost regions. A shortage of methane supply leads to formation of hydrate only at depth, below the base of permafrost. We consider a system with the ground surface initially at 0 oC with neither ice nor hydrate present. We abruptly decrease the temperature from 0 to -10 oC to simulate the effect of marine regression/ global cooling. A low methane supply rate of 0.005 kg m-2 yr-1 from depth leads to distinct ice and hydrate layers: a 100 m continuous hydrate layer is present beneath 850 m at 80 k.y.. However, a high methane supply rate of 0.1 kg m-2 yr-1 leads to 50 m ice-bonded methane hydrate at the base of permafrost, and the hydrate layer distributes between the depth of 350 and 700 m at 80 k.y.. We apply our model to illuminate future melting of hydrate at Mallik, a known Arctic hydrate accumulation. We assume a 600 m thick ice saturated (average 90%) layer extending downward from the ground surface. We increase the surface temperature linearly from -6 to 0 oC for 300 yr and then keep the surface temperature at 0 oC to reflect future climate warming caused by doubling of CO2. Hydrate melting is initiated at the base of the hydrate layer after 15 k.y.. Methane gas starts to vent to the atmosphere at 38 k.y. with an average flux of ~ 0.35 g m-2 yr-1. If the 600 m thick average ice saturation is decreased to half (45%) (or to zero), methane gas starts to vent to the atmosphere at 29 k.y. (or at 20 k.y.) with the same average flux. These results are found by a newly-developed fully-coupled multiphase multicomponent fluid flow and heat transport model. Our thermodynamic equilibrium-based model emphasizes the role of salinity in both ice and hydrate dynamics.

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.

Zircons reveal magma fluxes in the Earth's crust.

PubMed

Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

2014-07-24

Magma fluxes regulate the planetary thermal budget, the growth of continents and the frequency and magnitude of volcanic eruptions, and play a part in the genesis and size of magmatic ore deposits. However, because a large fraction of the magma produced on the Earth does not erupt at the surface, determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large-scale geological processes. Here we show that age distributions of zircons, a mineral often present in crustal magmatic rocks, in combination with thermal modelling, provide an accurate means of retrieving magma fluxes. The characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the Earth's crust. Our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems. Analysis of existing age population data sets using our method suggests that porphyry-type deposits, plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes. We anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions, and to determine the main factors controlling the distribution of resources on our planet.

Seasonal flux and assemblage composition of planktic foraminifera from the northern Gulf of Mexico, 2008–14

USGS Publications Warehouse

Reynolds, Caitlin E.; Richey, Julie N.

2016-07-28

The U.S. Geological Survey anchored a sediment trap in the northern Gulf of Mexico in January 2008 to collect seasonal time-series data on the flux and assemblage composition of live planktic foraminifers. This report provides an update of the previous time-series data to include continuous results from January 2013 through May 2014. Ten taxa constituted ~95 percent of both the 2013 and 2014 assemblages: Globigerinoides ruber (pink and white varieties), Globigerinoides sacculifer, Globigerina calida, Globigerinella aequilateralis, Globorotalia menardii group [The Gt. menardii group includes Gt. menardii, Gt. tumida, and Gt. ungulata], Orbulina universa, Globorotalia truncatulinoides, Pulleniatina spp., and Neogloboquadrina dutertrei. In 2013, the mean daily flux was 177 tests per square meter per day (m−2 day−1), with maximum fluxes of >1,200 tests m−2 day−1 during the middle of February and minimum fluxes of <13 tests m−2 day−1 during the beginning of November. In 2014, the mean daily flux was 189 tests m−2 day−1, with maximum fluxes of >900 tests m−2 day−1 at the end of January and minimum fluxes of <30 tests m−2 day−1 at the beginning of January. Globorotalia truncatulinoides showed a clear preference for the winter, consistent with data from 2008 to 2012. Globigerinoides ruber (white) flux data for 2012 (average 23 tests m−2 day−1) were consistent with data from 2011 (average 30 tests m−2 day−1) and 2010 (average 29 tests m−2 day−1) and showed a steady threefold increase since 2009 (average 11 tests m−2 day−1) and a tenfold increase from the 2008 flux (3 tests m−2 day−1). The flux data from 2013 (average 15 tests m−2 day−1) and 2014 (average 8 tests m−2 day−1) showed decline from the previous 3 years.

Convective sources of trajectories traversing the tropical tropopause layer

NASA Astrophysics Data System (ADS)

Tissier, Ann-Sophie; Legras, Bernard

2016-03-01

Transit properties across the tropical tropopause layer are studied using extensive forward and backward Lagrangian diabatic trajectories between cloud tops and the reference surface 380 K. After dividing the tropical domain into 11 subregions according to the distribution of land and convection, we estimate the contribution of each region to the upward mass flux across the 380 K surface and to the vertical distribution of convective sources and transit times over the period 2005-2008. The good agreement between forward and backward statistics is the basis of the results presented here. It is found that about 85 % of the tropical parcels at 380 K originate from convective sources throughout the year. From November to April, the sources are dominated by the warm pool which accounts for up to 70 % of the upward flux. During boreal summer, the Asian monsoon region is the largest contributor with similar contributions from the maritime and continental parts of the region; however, the vertical distributions and transit times associated with these two subregions are very different. Convective sources are generally higher over the continental part of the Asian monsoon region, with shorter transit times. We estimate the monthly averaged upward mass flux on the 380 K surface and show that the contribution from convective outflow accounts for 80 % on average and explains most of its seasonal variations. The largest contributor to the convective flux is the South Asian Pacific region (warm pool) at 39 % throughout the year followed by oceanic regions surrounding continental Asia at 18 % and Africa at 10.8 %. Continental Asian lowlands account for 8 %. The Tibetan Plateau is a minor overall contributor (0.8 %), but transport from convective sources in this region is very efficient due to its central location beneath the Asian upper level anticyclone. The core results are robust to uncertainties in data and methods, but the vertical source distributions and transit times exhibit some sensitivity to the representations of cloud tops and heating rates. The main sensitivity is to the radiative heating rates which vary among reanalyses.

PES Surface Modification Using Green Chemistry: New Generation of Antifouling Membranes.

PubMed

Nady, Norhan

2016-04-18

A major limitation in using membrane-based separation processes is the loss of performance due to membrane fouling. This drawback can be addressed thanks to surface modification treatments. A new and promising surface modification using green chemistry has been recently investigated. This modification is carried out at room temperature and in aqueous medium using green catalyst (enzyme) and nontoxic modifier, which can be safely labelled "green surface modification". This modification can be considered as a nucleus of new generation of antifouling membranes and surfaces. In the current research, ferulic acid modifier and laccase bio-catalyst were used to make poly(ethersulfone) (PES) membrane less vulnerable to protein adsorption. The blank and modified PES membranes are evaluated based on e.g., their flux and protein repellence. Both the blank and the modified PES membranes (or laminated PES on silicon dioxide surface) are characterized using many techniques e.g., SEM, EDX, XPS and SPM, etc. The pure water flux of the most modified membranes was reduced by 10% on average relative to the blank membrane, and around a 94% reduction in protein adsorption was determined. In the conclusions section, a comparison between three modifiers-ferulic acid, and two other previously used modifiers (4-hydroxybenzoic acid and gallic acid)-is presented.

PES Surface Modification Using Green Chemistry: New Generation of Antifouling Membranes

PubMed Central

Nady, Norhan

2016-01-01

A major limitation in using membrane-based separation processes is the loss of performance due to membrane fouling. This drawback can be addressed thanks to surface modification treatments. A new and promising surface modification using green chemistry has been recently investigated. This modification is carried out at room temperature and in aqueous medium using green catalyst (enzyme) and nontoxic modifier, which can be safely labelled “green surface modification”. This modification can be considered as a nucleus of new generation of antifouling membranes and surfaces. In the current research, ferulic acid modifier and laccase bio-catalyst were used to make poly(ethersulfone) (PES) membrane less vulnerable to protein adsorption. The blank and modified PES membranes are evaluated based on e.g., their flux and protein repellence. Both the blank and the modified PES membranes (or laminated PES on silicon dioxide surface) are characterized using many techniques e.g., SEM, EDX, XPS and SPM, etc. The pure water flux of the most modified membranes was reduced by 10% on average relative to the blank membrane, and around a 94% reduction in protein adsorption was determined. In the conclusions section, a comparison between three modifiers—ferulic acid, and two other previously used modifiers (4-hydroxybenzoic acid and gallic acid)—is presented. PMID:27096873

Turbulence and Radiation in Stratocumulus-Topped Marine Boundary Layers: A Case Study from VOCALS-REx

DOE PAGES

Ghate, Virendra P.; Albrecht, Bruce A.; Miller, Mark A.; ...

2014-01-13

Observations made during a 24-h period as part of the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study Regional Experiment (VOCALS-REx) are analyzed to study the radiation and turbulence associated with the stratocumulus-topped marine boundary layer (BL). The first 14 h exhibited a well-mixed (coupled) BL with an average cloud-top radiative flux divergence of ~130 W m 22; the BL was decoupled during the last 10 h with negligible radiative flux divergence. The averaged radiative cooling very close to the cloud top was -9.04 K h -1 in coupled conditions and -3.85 K h -1 in decoupled conditions. Thismore » is the first study that combined data from a vertically pointing Doppler cloud radar and a Doppler lidar to yield the vertical velocity structure of the entire BL. The averaged vertical velocity variance and updraft mass flux during coupled conditions were higher than those during decoupled conditions at all levels by a factor of 2 or more. The vertical velocity skewness was negative in the entire BL during coupled conditions, whereas it was weakly positive in the lower third of the BL and negative above during decoupled conditions. A formulation of velocity scale is proposed that includes the effect of cloud-top radiative cooling in addition to the surface buoyancy flux. When scaled by the velocity scale, the vertical velocity variance and coherent downdrafts had similar magnitude during the coupled and decoupled conditions. Finally, the coherent updrafts that exhibited a constant profile in the entire BL during both the coupled and decoupled conditions scaled well with the convective velocity scale to a value of ~0.5.« less

Net summertime emission of ammonia from corn and triticale fields

NASA Astrophysics Data System (ADS)

Richter, Undine; Smith, Jeremy; Brümmer, Christian

2016-04-01

Recent advancements in laser spectrometry offer new opportunities to investigate ecosystem-atmosphere exchange of environmentally relevant trace gases. In this study, we used a quantum cascade laser (QCL) absorption spectrometer to continuously measure high-frequency concentrations of ammonia and the net exchange between an agricultural site and the atmosphere based on the eddy-covariance approach. The footprint was split into two main sectors, one planted with corn (Zea mays) and the other one with triticale. Ammonia concentrations were highly variable between 2 and almost 100 ppb with an average value of 8.1 ppb during the observation period from April to September 2015. While both deposition and emission of ammonia was observed, the total campaign exchange resulted in a loss of 3.3 kg NH3-N ha-1. Highest average emission fluxes of 65 ng N m-2 s-1 were recorded after fertilization at the beginning of the campaign in April and May. Afterwards the exchange of ammonia with the atmosphere decreased considerably, but the site remained on average a consistent source with sporadic lower peaks and an average flux of 13 ng N m-2 s-1. While management in the form of fertilization was the main driver for ammonia concentration and exchange at the site, biophysical controls from temperature, wind regime, and surface wetness are also presented.

Biogeochemical flux and phytoplankton succession: A year-long sediment trap record in the Australian sector of the Subantarctic Zone

NASA Astrophysics Data System (ADS)

Wilks, Jessica V.; Rigual-Hernández, Andrés S.; Trull, Thomas W.; Bray, Stephen G.; Flores, José-Abel; Armand, Leanne K.

2017-03-01

The Subantarctic Zone (SAZ) plays a crucial role in global carbon cycling as a significant sink for atmospheric CO2. In the Australian sector, the SAZ exports large quantities of organic carbon from the surface ocean, despite lower algal biomass accumulation in surface waters than other Southern Ocean sectors. We present the first analysis of diatom and coccolithophore assemblages and seasonality, as well as the first annual quantification of bulk organic components of captured material at the base of the mixed layer (500 m depth) in the SAZ. Sediment traps were moored in the SAZ southwest of Tasmania as part of the long-term SAZ Project for one year (September 2003 to September 2004). Annual mass flux at 500 m and 2000 m was composed mainly of calcium carbonate, while biogenic silica made up on average <10% of material captured in the traps. Organic carbon flux was estimated at 1.1 g m-2 y-1 at 500 m, close to the estimated global mean carbon flux. Low diatom fluxes and high fluxes of coccoliths were consistent with low biogenic silica and high calcium carbonate fluxes, respectively. Diatoms and coccoliths were identified to species level. Diatom and coccolithophore sinking assemblages reflected some seasonal ecological succession. A theoretical scheme of diatom succession in live assemblages is compared to successional patterns presented in sediment traps. This study provides a unique, direct measurement of the biogeochemical fluxes and their main biological carbon vectors just below the winter mixed layer depth at which effective sequestration of carbon occurs. Comparison of these results with previous sediment trap deployments at the same site at deeper depths (i.e. 1000, 2000 and 3800 m) documents the changes particle fluxes experience in the lower "twilight zone" where biological processes and remineralisation of carbon reduce the efficiency of carbon sequestration.

Flux-transport Dynamos Driven by a Tachocline α -effect; a Solution to Magnetic Parity Selection in the Sun

NASA Astrophysics Data System (ADS)

Dikpati, M.; Gilman, P. A.

2001-05-01

We propose here an α Ω flux-transport dynamo driven by a tachocline α -effect, produced by the global hydrodynamic instability of tachocline differential rotation as calculated using a shallow-water model (Dikpati & Gilman, 2001, ApJ, Mar.20 issue). Growing, unstable shallow-water modes propagating longitudinally in the tachocline create alternate vortices which correlate with upward/downward radial motion of top boundary, associated with convergence/divergence of the disturbance flow to produce a longitude-averaged net kinetic helicity, and hence an α -effect. We show that a flux-transport dynamo driven by a tachocline α -effect is equally successful as a Babcock-Leighton flux-transport dynamo (Dikpati & Charbonneau 1999, ApJ, 518, 508) in reproducing many large-scale solar cycle features, including the most difficult feature of phase relationship between the subsurface toroidal field and surface radial field. In view of the success of flux-transport dynamos, whether the α -effect is at the surface or in the tachocline, we argue that the solar dynamo should be considered to involve three basic processes, rather than two (α -effect and Ω -effect only). The third important process is the advective transport of flux by meridional circulation. In reality, both α -effects (Babcock-Leighton type and tachocline α -effect) are likely to exist, but it is hard to estimate their relative magnitudes. We show, by extending the simulation in a full spherical shell model that a flux-transport dynamo driven by a tachocline α -effect selects toroidal field that is antisymmetric about the equator, while a Babcock-Leighton flux-transport dynamo selects symmetric toroidal field. Since our present Sun selects antisymmetric toroidal fields, we argue that the flux-transport solar dynamo is primarily driven by a tachocline α -effect. Acknowledgements: This work is supported by NASA grants W-19752 and S-10145-X. National Center for Atmospheric Research is sponsored by National Science Foundation.

28-ka History of Sea Surface Temperature, Primary Productivity and Planktonic Community Variability in the Western Arabian Sea

NASA Astrophysics Data System (ADS)

Pourmand, A.; Marcantonio, F.; Bianchi, T.

2006-12-01

Uranium-series radionuclides and organic compounds, which represent major groups of planktonic organisms, have been measured in western Arabian Sea sediments that span the past 28 ka. Variability of the Indian Ocean monsoons and their influence on primary productivity, sea surface temperature (SST), and planktonic community structure has been investigated. The average alkenone-derived SST for the glacial was ~3°C lower than that measured for the Holocene. We also identify, for the first time, an interval of exceptionally low SSTs between 19-18.1 ka BP (15.3°C at 18.5 ka). During this time, the low SSTs coincide with high cumulative biomarker fluxes (CBF). We propose that intensification of winter northeast monsoon winds during the glacial period resulted in cold SSTs, deep convective mixing, and enhanced primary productivity. Following the last termination, and within the Holocene, SSTs vary by ~2°C with high CBFs occurring at times of relatively warmer SSTs. The fluxes of dinoflagellates and zooplankton relative to the total flux of organisms remain constant throughout the record. However, transitioning from the glacial to the Holocene, diatom fluxes comparatively increase relative to the total flux of organisms, while those of coccolithophorids decrease. Considering that the Indian Ocean monsoons are an important component of the global climate system, a shift in the planktonic ecosystem structure in the Arabian Sea may have important implications for the global biogeochemical cycle of carbon.

Interspecific variation in SO/sub 2/ flux: leaf surface versus internal flux, and components of leaf conductance. [Pisum sativum L. , Lycopersicon esculentum Mill. Flacca, Geranium carolinianum L. , Diplacus aurantiacus (Curtis) Jeps

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

Olszyk, D.M.; Tingey, D.T.

The objective of this study was to clarify the relationships among stomatal, residual, and epidermal conductances in determining the flux of SO/sub 2/ air pollution to leaves. Variations in leaf SO/sub 2/ and H/sub 2/O vapor fluxes were determined using four plant species: Pisum sativum L. (garden pea), Lycopersicon esculentum Mill. flacca (mutant of tomato), Geranium carolinianum L. (wild geranium), and Diplacus aurantiacus (Curtis) Jeps. (a native California shrub). Fluxes were measured using the mass-balance approach during exposure to 4.56 micromoles per cubic meter (0.11 microliters per liter) SO/sub 2/ for 2 hours in a controlled environmental chamber. Flux throughmore » adaxial and abaxial leaf surfaces with closed stomata ranged from 1.9 to 9.4 nanomoles per square meter per second for SO/sub 2/, and 0.3 to 1.3 millimoles per square meter per second for H/sub 2/O vapor. Flux of SO/sub 2/ into leaves through stomata ranged from approx.0 to 8.5 (dark) and 3.8 to 16.0 (light) millimoles per square meter per second. Flux of H/sub 2/O vapor from leaves through stomata ranged from approx.0 to 0.6 (dark) to 0.4 to 0.9 (light) millimole per square meter per second. Lycopersicon had internal flux rates for both SO/sub 2/ and H/sub 2/O vapor over twice as high as for the other species. Stomatal conductance based on H/sub 2/O vapor flux averaged from 0.07 to 0.13 mole per square meter per second among the four species. Internal conductance of SO/sub 2/ as calculated from SO/sub 2/ flux was from 0.04 mole per square meter per second lower to 0.06 mole per square meter per second higher than stomatal conductance. For Pisum, Geranium, and Diplacus stomatal conductance was the same or slightly higher than internal conductance, indicating that, in general, SO/sub 2/ flux could be predicted from stomatal conductance for H/sub 2/O vapor.« less

Large-Eddy Simulation of Shallow Cumulus over Land: A Composite Case Based on ARM Long-Term Observations at Its Southern Great Plains Site

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

Zhang, Yunyan; Klein, Stephen A.; Fan, Jiwen

Based on long-term observations by the Atmospheric Radiation Measurement program at its Southern Great Plains site, a new composite case of continental shallow cumulus (ShCu) convection is constructed for large-eddy simulations (LES) and single-column models. The case represents a typical daytime nonprecipitating ShCu whose formation and dissipation are driven by the local atmospheric conditions and land surface forcing and are not influenced by synoptic weather events. The case includes early morning initial profiles of temperature and moisture with a residual layer; diurnally varying sensible and latent heat fluxes, which represent a domain average over different land surface types; simplified large-scalemore » horizontal advective tendencies and subsidence; and horizontal winds with prevailing direction and average speed. Observed composite cloud statistics are provided for model evaluation. The observed diurnal cycle is well reproduced by LES; however, the cloud amount, liquid water path, and shortwave radiative effect are generally underestimated. LES are compared between simulations with an all-or-nothing bulk microphysics and a spectral bin microphysics. The latter shows improved agreement with observations in the total cloud cover and the amount of clouds with depths greater than 300 m. When compared with radar retrievals of in-cloud air motion, LES produce comparable downdraft vertical velocities, but a larger updraft area, velocity, and updraft mass flux. Both observations and LES show a significantly larger in-cloud downdraft fraction and downdraft mass flux than marine ShCu.« less

Large-Eddy Simulation of Shallow Cumulus over Land: A Composite Case Based on ARM Long-Term Observations at Its Southern Great Plains Site

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

Zhang, Yunyan; Klein, Stephen A.; Fan, Jiwen

Based on long-term observations by the Atmospheric Radiation Measurement program at its Southern Great Plains site, a new composite case of continental shallow cumulus (ShCu) convection is constructed for large-eddy simulations (LES) and single-column models. The case represents a typical daytime non-precipitating ShCu whose formation and dissipation are driven by the local atmospheric conditions and land-surface forcing, and are not influenced by synoptic weather events. The case includes: early-morning initial profiles of temperature and moisture with a residual layer; diurnally-varying sensible and latent heat fluxes which represent a domain average over different land-surface types; simplified large-scale horizontal advective tendencies andmore » subsidence; and horizontal winds with prevailing direction and average speed. Observed composite cloud statistics are provided for model evaluation. The observed diurnal cycle is well-reproduced by LES, however the cloud amount, liquid water path, and shortwave radiative effect are generally underestimated. LES are compared between simulations with an all-or-nothing bulk microphysics and a spectral bin microphysics. The latter shows improved agreement with observations in the total cloud cover and the amount of clouds with depths greater than 300 meters. When compared with radar retrievals of in-cloud air motion, LES produce comparable downdraft vertical velocities, but a larger updraft area, velocity and updraft mass flux. Finally, both observation and LES show a significantly larger in-cloud downdraft fraction and downdraft mass flux than marine ShCu.« less

Large-Eddy Simulation of Shallow Cumulus over Land: A Composite Case Based on ARM Long-Term Observations at Its Southern Great Plains Site

DOE PAGES

Zhang, Yunyan; Klein, Stephen A.; Fan, Jiwen; ...

2017-09-19

Based on long-term observations by the Atmospheric Radiation Measurement program at its Southern Great Plains site, a new composite case of continental shallow cumulus (ShCu) convection is constructed for large-eddy simulations (LES) and single-column models. The case represents a typical daytime non-precipitating ShCu whose formation and dissipation are driven by the local atmospheric conditions and land-surface forcing, and are not influenced by synoptic weather events. The case includes: early-morning initial profiles of temperature and moisture with a residual layer; diurnally-varying sensible and latent heat fluxes which represent a domain average over different land-surface types; simplified large-scale horizontal advective tendencies andmore » subsidence; and horizontal winds with prevailing direction and average speed. Observed composite cloud statistics are provided for model evaluation. The observed diurnal cycle is well-reproduced by LES, however the cloud amount, liquid water path, and shortwave radiative effect are generally underestimated. LES are compared between simulations with an all-or-nothing bulk microphysics and a spectral bin microphysics. The latter shows improved agreement with observations in the total cloud cover and the amount of clouds with depths greater than 300 meters. When compared with radar retrievals of in-cloud air motion, LES produce comparable downdraft vertical velocities, but a larger updraft area, velocity and updraft mass flux. Finally, both observation and LES show a significantly larger in-cloud downdraft fraction and downdraft mass flux than marine ShCu.« less

Experimental study of the surface thermal signature of gravity currents: application to the assessment of lava flow effusion rate

NASA Astrophysics Data System (ADS)

Garel, F.; Kaminski, E.; Tait, S.; Limare, A.

2011-12-01

During an effusive volcanic eruption, the crisis management is mainly based on the prediction of lava flows advance and its velocity. As the spreading of lava flows is mainly controlled by its rheology and the eruptive mass flux, the key question is how to evaluate them during the eruption (rather than afterwards.) A relationship between the heat flux lost by the lava at its surface and the eruption rate is likely to exist, based on the first-order argument that higher eruption rates should correspond to larger power radiated by a lava flow. The semi-empirical formula developed by Harris and co-workers (e.g. Harris et al., Bull. Volc. 2007) is currently used to estimate lava flow rate from satellite surveys yielding the surface temperatures and area of the lava flow field. However, this approach is derived from a static thermal budget of the lava flow and does not explicitly model the time-evolution of the surface thermal signal. Here we propose laboratory experiments and theoretical studies of the cooling of a viscous axisymmetric gravity current fed at constant flux rate. We first consider the isoviscous case, for which the spreading is well-know. The experiments using silicon oil and the theoretical model both reveal the establishment of a steady surface thermal structure after a transient time. The steady state is a balance between surface cooling and heat advection in the flow. The radiated heat flux in the steady regime, a few days for a basaltic lava flow, depends mainly on the effusion rate rather than on the viscosity. In this regime, one thermal survey of the radiated power could provide a consistent estimate of the flow rate if the external cooling conditions (wind) are reasonably well constrained. We continue to investigate the relationship between the thermal radiated heat flux and the effusion rate by using in the experiments fluids with temperature-dependent viscosity (glucose syrup) or undergoing solidification while cooling (PEG wax). We observe a transient evolution of the radiated heat flux closely related to the variations of the flow area. The study of experiments with time-variable effusion rates finally gives first leads on the inertia of the thermal surface structure. This is to be related to the time-period over which the thermal proxy averages the actual effusion rate, hence to the acquisition frequency appropriate for a thermal monitoring of effusive volcanic eruptions.

Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa

NASA Astrophysics Data System (ADS)

Matsumoto, Toru; Hasegawa, S.; Nakao, S.; Sakai, M.; Yurimoto, H.

2018-03-01

We investigated impact crater structures on regolith particles from asteroid Itokawa using scanning electron microscopy. We observed the surfaces of 51 Itokawa particles, ranging from 15 μm to 240 μm in size. Craters with average diameters ranging from 10 nm to 2.8 μm were identified on 13 Itokawa particles larger than 80 μm. We examined the abundance, spatial distribution, and morphology of approximately 900 craters on six Itokawa particles. Craters with sizes in excess of 200 nm are widely dispersed, with spatial densities from 2.6 μm2 to 4.5 μm2; a fraction of the craters was locally concentrated with a density of 0.1 μm2. The fractal dimension of the cumulative crater diameters ranges from 1.3 to 2.3. Craters of several tens of nanometers in diameter exhibit pit and surrounding rim structures. Craters of more than 100 nm in diameter commonly have melted residue at their bottom. These morphologies are similar to those of submicrometer-sized craters on lunar regolith. We estimated the impactor flux on Itokawa regolith-forming craters, assuming that the craters were accumulated during direct exposure to the space environment for 102 to 104 yr. The range of impactor flux onto Itokawa particles is estimated to be at least one order of magnitude higher than the interplanetary dust flux and comparable to the secondary impact flux on the Moon. This indicates that secondary ejecta impacts are probably the dominant cratering process in the submicrometer range on Itokawa regolith particles, as well as on the lunar surface. We demonstrate that secondary submicrometer craters can be produced anywhere in centimeter- to meter-sized depressions on Itokawa's surface through primary interplanetary dust impacts. If the surface unevenness on centimeter to meter scales is a significant factor determining the abundance of submicrometer secondary cratering, the secondary impact flux could be independent of the overall shapes or sizes of celestial bodies, and the secondary impact flux could have similar values on Itokawa and the Moon.

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.

Space-Time Controls on Carbon Sequestration Over Large-Scale Amazon Basin

NASA Technical Reports Server (NTRS)

Smith, Eric A.; Cooper, Harry J.; Gu, Jiujing; Grose, Andrew; Norman, John; daRocha, Humberto R.; Starr, David O. (Technical Monitor)

2002-01-01

A major research focus of the LBA Ecology Program is an assessment of the carbon budget and the carbon sequestering capacity of the large scale forest-pasture system that dominates the Amazonia landscape, and its time-space heterogeneity manifest in carbon fluxes across the large scale Amazon basin ecosystem. Quantification of these processes requires a combination of in situ measurements, remotely sensed measurements from space, and a realistically forced hydrometeorological model coupled to a carbon assimilation model, capable of simulating details within the surface energy and water budgets along with the principle modes of photosynthesis and respiration. Here we describe the results of an investigation concerning the space-time controls of carbon sources and sinks distributed over the large scale Amazon basin. The results are derived from a carbon-water-energy budget retrieval system for the large scale Amazon basin, which uses a coupled carbon assimilation-hydrometeorological model as an integrating system, forced by both in situ meteorological measurements and remotely sensed radiation fluxes and precipitation retrieval retrieved from a combination of GOES, SSM/I, TOMS, and TRMM satellite measurements. Brief discussion concerning validation of (a) retrieved surface radiation fluxes and precipitation based on 30-min averaged surface measurements taken at Ji-Parana in Rondonia and Manaus in Amazonas, and (b) modeled carbon fluxes based on tower CO2 flux measurements taken at Reserva Jaru, Manaus and Fazenda Nossa Senhora. The space-time controls on carbon sequestration are partitioned into sets of factors classified by: (1) above canopy meteorology, (2) incoming surface radiation, (3) precipitation interception, and (4) indigenous stomatal processes varied over the different land covers of pristine rainforest, partially, and fully logged rainforests, and pasture lands. These are the principle meteorological, thermodynamical, hydrological, and biophysical control paths which perturb net carbon fluxes and sequestration, produce time-space switching of carbon sources and sinks, undergo modulation through atmospheric boundary layer feedbacks, and respond to any discontinuous intervention on the landscape itself such as produced by human intervention in converting rainforest to pasture or conducting selective/clearcut logging operations.

Sediment transport on the Palos Verdes shelf over seasonal to decadal time scales

USGS Publications Warehouse

Wiberg, P.L.; Drake, D.E.; Harris, C.K.; Noble, M.

2002-01-01

We combine direct observations, longer-term wave data, and model calculations to characterize resuspension and transport of fine-grained, effluent-affected sediment on the Palos Verdes shelf. Near-bed waves, currents, and suspended sediment concentrations were monitored during the winter of 1992-93 with a bottom tripod and current-meter mooring at a 63-m-deep site. Wave conditions that winter were moderate (??? 2 year recurrence interval), and mean current was alongshelf to the northwest; currents were not significantly correlated with wave conditions. Seven wave events during the winter (December-March) produced near-bed wave orbital velocities at the study site in excess of 14 cm s-1, the observed threshold for significant resuspension. Three of these events occurred during the bottom tripod deployment and are characterized by the highest persistent suspended sediment concentrations in the tripod record. Suspended sediment flux was alongshelf to the northwest for 5 of the 6 wave events for which current data were available; one event occurred during low southeast currents. Measured suspended sediment concentration and grain size generally agree with values that were calculated using a shelf sediment transport model with no adjustment of parameters from values determined for two muddy sites on the northern California shelf. We extend our seasonal observations to a period of almost 2 decades by applying the observed thresholds for wave-driven resuspension to near-bed wave conditions calculated from NDBC Buoy 46025 surface wave data. An average of 10 resuspension events per year, with an average duration of 1.6 days, were identified at a water depth of 60 m; the number of events dropped to 3 per year at 90 m, beyond the shelf break. For the majority of these events, calculated net suspended sediment flux is toward the northwest (alongshelf) at an average rate of 140 kg m-1 h-1; about a third of the events have net southeastward flux at an average rate of 30 kg m-1 h-1. The calculated thickness of the resuspended surface layer of the bed was less than 1 cm for all events at 60 m. ?? 2002 Elsevier Science Ltd. All rights reserved.

Uncertainties in Surface Layer Modeling

NASA Astrophysics Data System (ADS)

Pendergrass, W.

2015-12-01

A central problem for micrometeorologists has been the relationship of air-surface exchange rates of momentum and heat to quantities that can be predicted with confidence. The flux-gradient profile developed through Monin-Obukhov Similarity Theory (MOST) provides an integration of the dimensionless wind shear expression where is an empirically derived expression for stable and unstable atmospheric conditions. Empirically derived expressions are far from universally accepted (Garratt, 1992, Table A5). Regardless of what form of these relationships might be used, their significance over any short period of time is questionable since all of these relationships between fluxes and gradients apply to averages that might rarely occur. It is well accepted that the assumption of stationarity and homogeneity do not reflect the true chaotic nature of the processes that control the variables considered in these relationships, with the net consequence that the levels of predictability theoretically attainable might never be realized in practice. This matter is of direct relevance to modern prognostic models which construct forecasts by assuming the universal applicability of relationships among averages for the lower atmosphere, which rarely maintains an average state. Under a Cooperative research and Development Agreement between NOAA and Duke Energy Generation, NOAA/ATDD conducted atmospheric boundary layer (ABL) research using Duke renewable energy sites as research testbeds. One aspect of this research has been the evaluation of legacy flux-gradient formulations (the ϕ functions, see Monin and Obukhov, 1954) for the exchange of heat and momentum. At the Duke Energy Ocotillo site, NOAA/ATDD installed sonic anemometers reporting wind and temperature fluctuations at 10Hz at eight elevations. From these observations, ϕM and ϕH were derived from a two-year database of mean and turbulent wind and temperature observations. From this extensive measurement database, using a methodology proposed by Kanenasu, Wesely and Hicks (1979), the overall dependence of ϕM and ϕH on is characterized. Results indicate considerable scatter with the familiar relationships, such as Paulson (1970), best describing the averages; however it is the scatter that largely defines the attainable levels of predictability.

Sediment Flux of Particulate Organic Phosphorus in the Open Black Sea

NASA Astrophysics Data System (ADS)

Parkhomenko, A. V.; Kukushkin, A. S.

2018-03-01

The interannual variation of the monthly average (weighted average) concentrations of particulate organic phosphorus (PPOM) in the photosynthetic layer, oxycline, redox zone, and H2S zone in the open Black Sea is estimated based on long-term observation data. The suspension sedimentation rates from the studied layers are assessed using model calculations and published data. The annual variation of PPOM sediment fluxes from the photosynthetic layer, oxycline, redox zone, and upper H2S zone to the anaerobic zone of the sea and the correspondingly annual average values are estimated for the first time. A regular decrease in the PPOM annual average flux with depth in the upper active layer is demonstrated. A correlation between the annual average values of PPOM sediment flux from the photosynthetic layer and ascending phosphate flux to this layer is shown, which suggests their balance in the open sea. The results are discussed in terms of the phosphorus biogeochemical cycle and the concept of new and regenerative primary production in the open Black Sea.

The global mean energy balance under cloud-free conditions

NASA Astrophysics Data System (ADS)

Wild, Martin; Hakuba, Maria; Folini, Dois; Ott, Patricia; Long, Charles

2017-04-01

A long standing problem of climate models is their overestimation of surface solar radiation not only under all-sky, but also under clear-sky conditions (Wild et al. 1995, Wild et al. 2006). This overestimation reduced over time in consecutive model generations due to the simulation of stronger atmospheric absorption. Here we analyze the clear sky fluxes of the latest climate model generation from the Coupled Model Intercomparison Project Phase 5 (CMIP5) against an expanded and updated set of direct observations from the Baseline Surface Radiation Network (BSRN). Clear sky climatologies from these sites have been composed based on the Long and Ackermann (2000) clear sky detection algorithm (Hakuba et al. 2017), and sampling issues when comparing with model simulated clear sky fluxes have been analyzed in Ott (2017). Overall, the overestimation of clear sky insolation in the CMIP5 models is now merely 1-2 Wm-2 in the multimodel mean, compared to 4 Wm-2 in CMIP3 and 6 Wm-2 in AMIPII (Wild et al. 2006). Still a considerable spread in the individual model biases is apparent, ranging from -2 Wm-2 to 10 Wm-2 when averaged over 53 globally distributed BSRN sites. This bias structure is used to infer best estimates for present day global mean clear sky insolation, following an approach developped in Wild et al. (2013, 2015, Clim. Dyn.) for all sky fluxes. Thereby the flux biases in the various models are linearly related to their respective global means. A best estimate can then be inferred from the linear regression at the intersect where the bias against the surface observations becomes zero. This way we obtain a best estimate of 247 Wm-2 for the global mean insolation at the Earth surface under cloud free conditions, and a global mean absorbed solar radiation of 214 Wm-2 in the cloud-free atmosphere, assuming a global mean surface albedo of 13.5%. Combined with a best estimate for the net influx of solar radiation at the Top of Atmosphere under cloud free conditions from CERES EBAF of 286 Wm-2, this leaves an amount of 72 Wm-2 absorbed solar radiation in the cloud free atmosphere. The 72 Wm-2 closely match our best estimate for the global mean cloud-free atmospheric absorption in Wild et al. JGR (2006) based on older models and their biases against much fewer direct observation. This indicates that the estimate of global mean solar absorption in the cloud free atmosphere slightly above 70 Wm-2 is fairly robust. In comparison, the global mean solar absorption under all sky conditions was estimated in Wild et al. (2015) at 80 Wm-2 based on the same approach. The difference between the all- and clear-sky absorption represents the cloud radiative effect on the atmospheric absorption, and is thus estimated here to be around 8 Wm-2. This is similar in magnitude to the 11 Wm-2 derived by Hakuba et al. (2017) when averaged over the atmospheric cloud effect determined at 36 BSRN station. We applied the same methodology also for the longwave fluxes. Thereby we obtained a best estimate for the global mean clear sky downward longwave flux at the Earth surface of 214 Wm-2. Together with a surface and TOA upward longwave flux of 398 Wm-2 and 266 Wm-2, respectively, this leaves an atmospheric longwave divergence under clear sky conditions of 182 Wm-2. Selected related references: Hakuba, M. Z., Folini, D., Wild, M., Long, C. N., Schaepman-Strub, G., and Stephens, G.L., 2017: Cloud Effects on Atmospheric Solar Absorption in Light of Most Recent Surface and Satellite Measurements. AIP Conf. Proc. (in press). Ott, P., 2017: Master Thesis at ETH Zurich (in prep.). Wild, M., Ohmura, A., Gilgen, H., and Roeckner, E., 1995: Validation of GCM simulated radiative fluxes using surface observations. J. Climate, 8, 1309-1324. Wild, M., Long, C.N., and Ohmura, A., 2006: Evaluation of clear-sky solar fluxes in GCMs participating in AMIP and IPCC-AR4 from a surface perspective. J. Geophys. Res., 111, D01104, doi:10.1029/2005JD006118. Wild, M., Folini, D., Schär, C., Loeb, N., Dutton, E.G., and König-Langlo, G., 2013: The global energy balance from a surface perspective. Climate Dynamics, 40, 3107-3134. Wild, M., Folini, D., Hakuba, M., Schär, C., Seneviratne, S.I., Kato, S., Rutan, D., Ammann, C., Wood, E.F., and König-Langlo, G., 2015: The energy balance over land and oceans: An assessment based on direct observations and CMIP5 climate models, Climate Dynamics, 3393-3429, 44, DOI 10.1007/s00382-014-2430-z.

Estimation of regional surface CO2 fluxes with GOSAT observations using two inverse modeling approaches

NASA Astrophysics Data System (ADS)

Maksyutov, Shamil; Takagi, Hiroshi; Belikov, Dmitry A.; Saeki, Tazu; Zhuravlev, Ruslan; Ganshin, Alexander; Lukyanov, Alexander; Yoshida, Yukio; Oshchepkov, Sergey; Bril, Andrey; Saito, Makoto; Oda, Tomohiro; Valsala, Vinu K.; Saito, Ryu; Andres, Robert J.; Conway, Thomas; Tans, Pieter; Yokota, Tatsuya

2012-11-01

Inverse estimation of surface C02 fluxes is performed with atmospheric transport model using ground-based and GOSAT observations. The NIES-retrieved C02 column mixing (Xc02) and column averaging kernel are provided by GOSAT Level 2 product v. 2.0 and PPDF-DOAS method. Monthly mean C02 fluxes for 64 regions are estimated together with a global mean offset between GOSAT data and ground-based data. We used the fixed-lag Kalman filter to infer monthly fluxes for 42 sub-continental terrestrial regions and 22 oceanic basins. We estimate fluxes and compare results obtained by two inverse modeling approaches. In basic approach adopted in GOSAT Level4 product v. 2.01, we use aggregation of the GOSAT observations into monthly mean over 5x5 degree grids, fluxes are estimated independently for each region, and NIES atmospheric transport model is used for forward simulation. In the alternative method, the model-observation misfit is estimated for each observation separately and fluxes are spatially correlated using EOF analysis of the simulated flux variability similar to geostatistical approach, while transport simulation is enhanced by coupling with a Lagrangian transport model Flexpart. Both methods use using the same set of prior fluxes and region maps. Daily net ecosystem exchange (NEE) is predicted by the Vegetation Integrative Simulator for Trace gases (VISIT) optimized to match seasonal cycle of the atmospheric C02 . Monthly ocean-atmosphere C02 fluxes are produced with an ocean pC02 data assimilation system. Biomass burning fluxes were provided by the Global Fire Emissions Database (GFED); and monthly fossil fuel C02 emissions are estimated with ODIAC inventory. The results of analyzing one year of the GOSAT data suggest that when both GOSAT and ground-based data are used together, fluxes in tropical and other remote regions with lower associated uncertainties are obtained than in the analysis using only ground-based data. With version 2.0 of L2 Xc02 the fluxes appear reasonable for many regions and seasons, however there is a need for improving the L2 bias correction, data filtering and the inverse modeling method to reduce estimated flux anomalies visible in some areas. We also observe that application of spatial flux correlations with EOF­ based approach reduces flux anomalies.

Modelling nitrate from land-surface to wells-perforations under Mediterranean agricultural land: success, failure, and future scenarios

NASA Astrophysics Data System (ADS)

Levy, Yehuda; Chefetz, Benny; Shapira, Roi; Kurtzman, Daniel

2017-04-01

Contamination of groundwater resources by nitrate due to leaching under agricultural land is probably the most troublesome agriculture-related water contamination, worldwide. Deep soil sampling (10 m) were used for calibrating vertical flow and nitrogen-transport numerical models of the unsaturated zone, under different agricultural land uses. Vegetables fields (potato and strawberries) and deciduous (persimmon) orchards in the Sharon area overlaying the coastal aquifer of Israel, were examined. Average nitrate-nitrogen fluxes below vegetables fields were 210-290 kg ha-1 a-1 and under deciduous orchards were 110-140 kg ha-1 a-1. The output water and nitrate-nitrogen fluxes of the unsaturated zone models were used as input for a three dimensional flow and nitrate-transport model in the aquifer under an area of 13.3 square kilometers of agricultural land. The area was subdivided to 4 agricultural land-uses: vegetables, deciduous, citrus orchards and non-cultivated. Fluxes of water and nitrate-nitrogen below citrus orchards were taken from a previous study in this area (Kurtzman et al., 2013, j. Contam. Hydrol.). The groundwater flow model was calibrated to well heads only by changing the hydraulic conductivity while transient recharge fluxes were constraint to the bottom-fluxes of the unsaturated zone flow models. The nitrate-transport model in the aquifer, which was fed at the top by the nitrate fluxes of the unsaturated zone models, succeeded in reconstructing the average nitrate concentration in the wells. On the other hand, this transport model failed in calculating the high concentrations in the most contaminated wells and the large spatial variability of nitrate-concentrations in the aquifer. In order to reconstruct the spatial variability and enable predictions nitrate-fluxes from the unsaturated zone were multiplied by local multipliers. This action was rationalized by the fact that the high concentrations in some wells cannot be explained by regular agricultural activity, and are probably a result of some malfunction in the well area. Prediction of the nitrate concentration 40 years to the future with 3 nitrogen-fertilization scenarios showed the following: 1) under "business as usual" fertilization scenario, the NO3 concentration will increase in average by 19 mg l-1; 2) In reducing 25% of the nitrogen fertilization mass scenario, the nitrate concentration in the aquifer will stabilize; 3) In reducing 50% of the nitrogen fertilization mass scenario, the concentration will decrease in average by 18 mg l-1.

Anticorrelation of X-ray bright points with sunspot number, 1970-1978

NASA Technical Reports Server (NTRS)

Golub, L.; Davis, J. M.; Krieger, A. S.

1979-01-01

Soft X-ray observations of the solar corona over the period 1970-1978 show that the number of small short-lived bipolar magnetic features (X-ray bright points) varies inversely with the sunspot index. During the entire period from 1973 to 1978 most of the magnetic flux emerging at the solar surface appeared in the form of bright points. In 1970, near the peak of solar cycle 20, the contributions from bright points and from active regions appear to be approximately equal. These observations strongly support an earlier suggestion that the solar cycle may be characterized as an oscillator in wave-number space with relatively little variation in the average total rate of flux emergence.

SToRM: A Model for Unsteady Surface Hydraulics Over Complex Terrain

USGS Publications Warehouse

Simoes, Francisco J.

2014-01-01

A two-dimensional (depth-averaged) finite volume Godunov-type shallow water model developed for flow over complex topography is presented. The model is based on an unstructured cellcentered finite volume formulation and a nonlinear strong stability preserving Runge-Kutta time stepping scheme. The numerical discretization is founded on the classical and well established shallow water equations in hyperbolic conservative form, but the convective fluxes are calculated using auto-switching Riemann and diffusive numerical fluxes. The model’s implementation within a graphical user interface is discussed. Field application of the model is illustrated by utilizing it to estimate peak flow discharges in a flooding event of historic significance in Colorado, U.S.A., in 2013.

Linking lowermost mantle structure, core-mantle boundary heat flux and mantle plume formation

NASA Astrophysics Data System (ADS)

Li, Mingming; Zhong, Shijie; Olson, Peter

2018-04-01

The dynamics of Earth's lowermost mantle exert significant control on the formation of mantle plumes and the core-mantle boundary (CMB) heat flux. However, it is not clear if and how the variation of CMB heat flux and mantle plume activity are related. Here, we perform geodynamic model experiments that show how temporal variations in CMB heat flux and pulses of mantle plumes are related to morphologic changes of the thermochemical piles of large-scale compositional heterogeneities in Earth's lowermost mantle, represented by the large low shear velocity provinces (LLSVPs). We find good correlation between the morphologic changes of the thermochemical piles and the time variation of CMB heat flux. The morphology of the thermochemical piles is significantly altered during the initiation and ascent of strong mantle plumes, and the changes in pile morphology cause variations in the local and the total CMB heat flux. Our modeling results indicate that plume-induced episodic variations of CMB heat flux link geomagnetic superchrons to pulses of surface volcanism, although the relative timing of these two phenomena remains problematic. We also find that the density distribution in thermochemical piles is heterogeneous, and that the piles are denser on average than the surrounding mantle when both thermal and chemical effects are included.

Factors controlling temporal variability of near-ground atmospheric 222Rn concentration over Central Europe

NASA Astrophysics Data System (ADS)

Zimnoch, M.; Wach, P.; Chmura, L.; Gorczyca, Z.; Rozanski, K.; Godlowska, J.; Mazur, J.; Kozak, K.; Jeričević, A.

2014-02-01

Specific activity of 222Rn in near-ground atmosphere has been measured quasi-continuously from January 2005 to December 2009 at two continental sites in Europe: Heidelberg (south-west Germany) and Krakow (southern Poland). Atmosphere was sampled at ca. 30 m and 20 m, respectively, above the local ground. Both stations were equipped with identical instrumentation. Regular observations of 222Rn were supplemented by measurements of surface fluxes of this gas in Krakow urban area, using two entirely different approaches. Atmospheric 222Rn concentrations varied at both sites in a wide range, from less than 2 Bq m-3 to approximately 40 Bq m-3 in Krakow and ca. 35 Bq m-3 in Heidelberg. Averaged over entire observation period, the 222Rn content in Krakow was approximately 30 % higher when compared to Heidelberg (5.86 ± 0.09 Bq -3 and 4.50 ± 0.07 Bq m-3, respectively). Distinct seasonality of 222Rn signal was visible in both presented time series, with higher values recorded generally during late summer and autumn. The surface 222Rn fluxes in Krakow also revealed a distinct seasonality, with broad maximum observed during summer and early autumn and minimum during the winter. Averaged over 5 yr observation period, the night-time surface 222Rn flux was equal 46.8 ± 2.4 Bq m-2 h-1. Although the atmospheric 222Rn levels at Heidelberg and Krakow appeared to be controlled primarily by local factors, it was possible to evaluate the "continental effect" in atmospheric 222Rn content between both sites, related to the gradual build-up of 222Rn concentration in the air masses travelling between Heidelberg and Krakow. The mean value of this load was equal 0.78 ± 0.12 Bq m-3. The measured minimum 222Rn concentrations at both sites and the difference between them was interpreted in the framework of a simple box model coupled with HYSPLIT analysis of air mass trajectories. Best fit of experimental and model data was obtained for the average 222Rn flux over the European continent equal 52 Bq m-2 h-1, the mean transport velocity of the air masses within convective mixed layer of PBL on their route from the Atlantic coast to Heidelberg and Krakow equal 3.5 m s-1, the mean rate constant of 222Rn removal across the top of PBL equal to the 222Rn decay constant and the mean height of the convective mixed layer height equal 1600 m.

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.

Calculation of surface and top of atmosphere radiative fluxes from physical quantities based on ISCCP data sets. 1: Method and sensitivity to input data uncertainties

NASA Technical Reports Server (NTRS)

Zhang, Y.-C.; Rossow, W. B.; Lacis, A. A.

1995-01-01

The largest uncertainty in upwelling shortwave (SW) fluxes (approximately equal 10-15 W/m(exp 2), regional daily mean) is caused by uncertainties in land surface albedo, whereas the largest uncertainty in downwelling SW at the surface (approximately equal 5-10 W/m(exp 2), regional daily mean) is related to cloud detection errors. The uncertainty of upwelling longwave (LW) fluxes (approximately 10-20 W/m(exp 2), regional daily mean) depends on the accuracy of the surface temperature for the surface LW fluxes and the atmospheric temperature for the top of atmosphere LW fluxes. The dominant source of uncertainty is downwelling LW fluxes at the surface (approximately equal 10-15 W/m(exp 2)) is uncertainty in atmospheric temperature and, secondarily, atmospheric humidity; clouds play little role except in the polar regions. The uncertainties of the individual flux components and the total net fluxes are largest over land (15-20 W/m(exp 2)) because of uncertainties in surface albedo (especially its spectral dependence) and surface temperature and emissivity (including its spectral dependence). Clouds are the most important modulator of the SW fluxes, but over land areas, uncertainties in net SW at the surface depend almost as much on uncertainties in surface albedo. Although atmospheric and surface temperature variations cause larger LW flux variations, the most notable feature of the net LW fluxes is the changing relative importance of clouds and water vapor with latitude. Uncertainty in individual flux values is dominated by sampling effects because of large natrual variations, but uncertainty in monthly mean fluxes is dominated by bias errors in the input quantities.

CERES EBAF Info

Atmospheric Science Data Center

2014-01-24

... fluxes, where TOA net flux is constrained to ocean heat storage. - Surface: Computed surface clear-sky and all-sky fluxes consistent with the EBAF-TOA fluxes. Data Products:  EBAF-TOA EBAF-Surface ...

Ground Boundary Conditions for Thermal Convection Over Horizontal Surfaces at High Rayleigh Numbers

NASA Astrophysics Data System (ADS)

Hanjalić, K.; Hrebtov, M.

2016-07-01

We present "wall functions" for treating the ground boundary conditions in the computation of thermal convection over horizontal surfaces at high Rayleigh numbers using coarse numerical grids. The functions are formulated for an algebraic-flux model closed by transport equations for the turbulence kinetic energy, its dissipation rate and scalar variance, but could also be applied to other turbulence models. The three-equation algebraic-flux model, solved in a T-RANS mode ("Transient" Reynolds-averaged Navier-Stokes, based on triple decomposition), was shown earlier to reproduce well a number of generic buoyancy-driven flows over heated surfaces, albeit by integrating equations up to the wall. Here we show that by using a set of wall functions satisfactory results are found for the ensemble-averaged properties even on a very coarse computational grid. This is illustrated by the computations of the time evolution of a penetrative mixed layer and Rayleigh-Bénard (open-ended, 4:4:1 domain) convection, using 10 × 10 × 100 and 10 × 10 × 20 grids, compared also with finer grids (e.g. 60 × 60 × 100), as well as with one-dimensional treatment using 1 × 1 × 100 and 1 × 1 × 20 nodes. The approach is deemed functional for simulations of a convective boundary layer and mesoscale atmospheric flows, and pollutant transport over realistic complex hilly terrain with heat islands, urban and natural canopies, for diurnal cycles, or subjected to other time and space variations in ground conditions and stratification.

Scale - dependent effects on the surface energy fluxes modelling in Iberian oak-savanna (dehesa) using the Two-Source Energy Balance (TSEB)

NASA Astrophysics Data System (ADS)

Andreu, Ana; Nieto, Hector; Gómez-Giráldez, Pedro; González-Dugo, Maria P.

2017-04-01

Iberian semi-arid oak-savannas (dehesas) are complex ecosystems where bare soil and different layers of vegetation (grass/scrubs/trees) are distributed following heterogeneous patterns. An assumption of the two source energy balance models is that the effective source/sink for turbulent flux exchange at the surface(canopy/soil) is described by a bulk radiometric surface temperature (TRAD) and resistance. Therefore, the agreement of the TRAD used as an input to these models, with the "bulk" concept (determined by the spatial resolution), will influence the final energy fluxes estimations. The representativeness of the field-ground measurements, the spatial resolution of sensors, the averaging and the up-scaling of TRAD and the ecosystem vegetation parameters, will be crucial for the precision of the results, more than in homogeneous landscapes. The aim of this study is to analyze the scale-effects derived from TSEB application, comparing the observed energy fluxes and the estimated ones obtained from multiple TRAD data sources of different nature: tree/grass/soil ground-based observations, tower footprint, hyperspectral reflectance imagery acquired with an airborne platform, medium (Landsat) and low spatial resolution satellite data (Sentinel 3, MODIS), and how the up-scaling of the vegetation structural characteristics contribute to the discrepancies. The study area selected for this purpose is a dehesa site (Santa Clotilde, Cordoba), which present canopy mosaics (oak, annual grasses and bushes) differing in phenology, physiology and functioning, and bare soil, all of them influencing the turbulent and radiative exchanges.

Latitude Variation of the Subsurface Lunar Temperature: Lunar Prospector Thermal Neutrons

NASA Astrophysics Data System (ADS)

Little, R. C.; Feldman, W. C.; Maurice, S.; Genetay, I.; Lawrence, D. J.; Lawson, S. L.; Gasnault, O.; Barraclough, B. L.; Elphic, R. C.; Prettyman, T. H.; Binder, A. B.

2001-05-01

Planetary thermal neutron fluxes provide a sensitive proxy for mafic and feldspathic terranes, and are also necessary for translating measured gamma-ray line strengths to elemental abundances. Both functions require a model for near surface temperatures and a knowledge of the dependence of thermal neutron flux on temperature. We have explored this dependence for a representative sample of lunar soil compositions and surface temperatures using MCNP. For all soil samples, the neutron density is found to be independent of temperature, in accord with neutron moderation theory. The thermal neutron flux, however, does vary with temperature in a way that depends on D, the ratio of macroscopic absorption to energy-loss cross sections of soil compositions. The weakest dependence is for the largest D (which corresponds to the Apollo 17 high Ti basalt in our soil selection), and the largest dependence is for the lowest D (which corresponds to ferroan anorthosite, [FAN] in our selection). For the lunar model simulated, the depth at which the thermal neutron population is most sensitive to temperature is ~30 g/cm**2. These simulations were compared with the flux of thermal neutrons measured using the Lunar Prospector neutron spectrometer over the lunar highlands using a sub-surface temperature profile that varies with latitude, L, as (Cos L)**0.25. The fit is excellent. The best fitting equatorial temperature is determined to be, Teq=224+/-40 K. This temperature range brackets the average temperature measured below the thermal wave at the equator, Tmeas = 252+/-3K [Langseth and Keihm, 1977]. The present result represents the first measurement of subsurface temperature from orbit using neutrons.

Sources of Sodium in the Lunar Exosphere: Modeling Using Ground-Based Observations of Sodium Emission and Spacecraft Data of the Plasma

NASA Technical Reports Server (NTRS)

Sarantos, Menelaos; Killen, Rosemary M.; Sharma, A. Surjalal; Slavin, James A.

2009-01-01

Observations of the equatorial lunar sodium emission are examined to quantify the effect of precipitating ions on source rates for the Moon's exospheric volatile species. Using a model of exospheric sodium transport under lunar gravity forces, the measured emission intensity is normalized to a constant lunar phase angle to minimize the effect of different viewing geometries. Daily averages of the solar Lyman alpha flux and ion flux are used as the input variables for photon-stimulated desorption (PSD) and ion sputtering, respectively, while impact vaporization due to the micrometeoritic influx is assumed constant. Additionally, a proxy term proportional to both the Lyman alpha and to the ion flux is introduced to assess the importance of ion-enhanced diffusion and/or chemical sputtering. The combination of particle transport and constrained regression models demonstrates that, assuming sputtering yields that are typical of protons incident on lunar soils, the primary effect of ion impact on the surface of the Moon is not direct sputtering but rather an enhancement of the PSD efficiency. It is inferred that the ion-induced effects must double the PSD efficiency for flux typical of the solar wind at 1 AU. The enhancement in relative efficiency of PSD due to the bombardment of the lunar surface by the plasma sheet ions during passages through the Earth's magnetotail is shown to be approximately two times higher than when it is due to solar wind ions. This leads to the conclusion that the priming of the surface is more efficiently carried out by the energetic plasma sheet ions.

Upper Atmosphere Heating From Ocean-Generated Acoustic Wave Energy

DOE PAGES

Bowman, D. C.; Lees, J. M.

2018-04-27

We present that colliding sea surface waves generate the ocean microbarom, an acoustic signal that may transmit significant energy to the upper atmosphere. Previous estimates of acoustic energy flux from the ocean microbarom and mountain-wind interactions are on the order of 0.01 to 1 mW/m 2, heating the thermosphere by tens of Kelvins per day. We captured upgoing ocean microbarom waves with a balloon-borne infrasound microphone; the maximum acoustic energy flux was approximately 0.05 mW/m 2. This is about half the average value reported in previous ground-based microbarom observations spanning 8 years. The acoustic flux from the microbarom episode describedmore » here may have heated the thermosphere by several Kelvins per day while the source persisted. Lastly, we suggest that ocean wave models could be used to parameterize acoustically generated heating of the upper atmosphere based on sea state.« less

Analysis of data from Viking RPA's

NASA Technical Reports Server (NTRS)

Hanson, W. B.

1981-01-01

Measurements of the martian ionosphere performed by Viking Retarding Potential Analyzer (RPA) are reported. Viking RPA measurements of low energy electron fluxes out to 16,000 km above the Mars surface are discussed including both energy spectra and periods of continuous monitoring of the total flux above 15 ev. The mean electron current at energies greater than ev increases montonically by nearly two orders of magnitude from about 9000 km down to 700 km, but no clear signature of the bow shock is seen. The total wave power in the 2 sec measurement intervals for this current does, however, show a broad peak near 1700 km altitude. These variations in the low energy electron fluxes are related to whistler mode oscillations in the solar wind plasma. It is concluded that there may be a highly turbulent shock structure that masks a clear signature of the bow shock in the time averaged data.

Integrated analysis of the effects of agricultural management on nitrogen fluxes at landscape scale.

PubMed

Kros, J; Frumau, K F A; Hensen, A; de Vries, W

2011-11-01

The integrated modelling system INITIATOR was applied to a landscape in the northern part of the Netherlands to assess current nitrogen fluxes to air and water and the impact of various agricultural measures on these fluxes, using spatially explicit input data on animal numbers, land use, agricultural management, meteorology and soil. Average model results on NH(3) deposition and N concentrations in surface water appear to be comparable to observations, but the deviation can be large at local scale, despite the use of high resolution data. Evaluated measures include: air scrubbers reducing NH(3) emissions from poultry and pig housing systems, low protein feeding, reduced fertilizer amounts and low-emission stables for cattle. Low protein feeding and restrictive fertilizer application had the largest effect on both N inputs and N losses, resulting in N deposition reductions on Natura 2000 sites of 10% and 12%, respectively. Copyright © 2011 Elsevier Ltd. All rights reserved.

Upper Atmosphere Heating From Ocean-Generated Acoustic Wave Energy

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

Bowman, D. C.; Lees, J. M.

We present that colliding sea surface waves generate the ocean microbarom, an acoustic signal that may transmit significant energy to the upper atmosphere. Previous estimates of acoustic energy flux from the ocean microbarom and mountain-wind interactions are on the order of 0.01 to 1 mW/m 2, heating the thermosphere by tens of Kelvins per day. We captured upgoing ocean microbarom waves with a balloon-borne infrasound microphone; the maximum acoustic energy flux was approximately 0.05 mW/m 2. This is about half the average value reported in previous ground-based microbarom observations spanning 8 years. The acoustic flux from the microbarom episode describedmore » here may have heated the thermosphere by several Kelvins per day while the source persisted. Lastly, we suggest that ocean wave models could be used to parameterize acoustically generated heating of the upper atmosphere based on sea state.« less

BOREAS TF-11 CO2 and CH4 Flux Data from the SSA-Fen

NASA Technical Reports Server (NTRS)

Valentine, David W.; Hall, Forrest G. (Editor); Conrad, Sara (Editor)

2000-01-01

The BOREAS TF-11 team collected several data sets in its efforts to fully describe the flux and site characteristics at the SSA-Fen site. This data set contains fluxes of methane and carbon dioxide at the SSA-Fen site measured using static chambers. The measurements were conducted as part of a 2 x 2 factorial experiment in which we added carbon (300 g/sq m as wheat straw) and nitrogen (6 g/sq m as urea) to four replicate locations in the vicinity of the TF-11 tower. In addition to siting and treatment variables, it reports air temperature and water table height relative to the average peat surface during each measurement. The data set covers the period from the first week of June 1994 through the second week of September 1994. The data are stored in tabular ASCII files.

Effects of PCB Substrate Surface Finish, Flux, and Phosphorus Content on Ionic Contamination

NASA Astrophysics Data System (ADS)

Bacior, M.; Sobczak, N.; Siewiorek, A.; Kudyba, A.; Homa, M.; Nowak, R.; Dziula, M.; Masłoń, S.

2015-02-01

The ionic contamination on printed circuit boards (PCB) having different surface finishes was examined using ionograph. The study was performed at the RT on three types of PCBs covered with: (i) hot air solder leveling (HASL LF), (ii) electroless nickel immersion gold (ENIG), and (iii) organic surface protectant (OSP), all on Cu substrates, as well as two types of fluxes, namely EF2202 and RF800. In the group of boards without soldered components, the lowest average value of contamination was for the ENIG 18 µm surface (0.01 μg NaCl/cm2). Boards with soldered components were more contaminated (from 0.29 μg NaCl/cm2 for the HASL LF 18 µm surface). After spraying boards with fluxing agents, the values of contaminants were the highest. The influence of phosphorus content in Ni-P layer of ENIG finish on ionic contamination was examined. In the group of PCBs with Au coating, the smallest amount of surface contaminants (0.32 μg NaCl/cm2) was for Ni-2-5%P layer. PCBs with Ni-11%P layer were higher contaminated (0.47 μg NaCl/cm2), and another with Ni-8%P layer had 0.81 μg NaCl/cm2. PCBs without Au coating, had the lowest contamination (0.48 μg NaCl/cm2) at phosphorous content equal 11%P. Higher contamination (0.67 μg NaCl/cm2) was at 2-5%P, up to 1.98 μg NaCl/cm2 for 8% of P. Boards with Au finish have lower value of contamination than identical boards without Au layer thus contributing to better reliability of electronic assemblies, since its failures due to current leakage and corrosion can be caused by contaminants.

Representation of the Geosynchronous Plasma Environment in Spacecraft Charging Calculations

NASA Technical Reports Server (NTRS)

Davis, V. A.; Mandell, M. J.; Thomsen, M. F.

2006-01-01

Historically, our ability to predict and postdict spacecraft surface charging has been limited by the characterization of the plasma environment. One difficulty lies in the common practice of fitting the plasma data to a Maxwellian or Double Maxwellian distribution function, which may not represent the data well for charging purposes. We use electron and ion flux spectra measured by the Los Alamos National Laboratory (LANL) Magnetospheric Plasma Analyzer (MPA) to examine how the use of different spectral representations of the charged particle environment in computations of spacecraft potentials during magnetospheric substorms affects the accuracy of the results. We calculate the spacecraft potential using both the measured fluxes and several different fits to these fluxes. These measured fluxes have been corrected for the difference between the measured and calculated potential. The potential computed using the measured fluxes and the best available material properties of graphite carbon, with a secondary electron escape fraction of 81%, is within a factor of three of the measured potential for 87% of the data. Potentials calculated using a Kappa function fit to the incident electron flux distribution function and a Maxwellian function fit to the incident ion flux distribution function agree with measured potentials nearly as well as do potentials calculated using the measured fluxes. Alternative spectral representations gave less accurate estimates of potential. The use of all the components of the net flux, along with spacecraft specific average material properties, gives a better estimate of the spacecraft potential than the high energy flux alone.

Characterization of structural response to hypersonic boundary-layer transition

DOE PAGES

Riley, Zachary B.; Deshmukh, Rohit; Miller, Brent A.; ...

2016-05-24

The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This paper phenomenologically explores this interaction using a fundamental two-dimensional aerothermoelastic model under the assumption of an aluminum panel with simple supports. Specifically, an existing model is extended to examine the impact of transition onset location, transition length, and transitional overshoot in heat flux and fluctuating pressure on the structural response of surface panels. Transitional flow conditions are found to yield significantly increased thermal gradients, and theymore » can result in higher maximum panel temperatures compared to turbulent flow. Results indicate that overshoot in heat flux and fluctuating pressure reduces the flutter onset time and increases the strain energy accumulated in the panel. Furthermore, overshoot occurring near the midchord can yield average temperatures and peak displacements exceeding those experienced by the panel subject to turbulent flow. Lastly, these results suggest that fully turbulent flow does not always conservatively predict the thermo-structural response of surface panels.« less

Tracking near-surface atmospheric conditions using an infrasound network.

PubMed

Marcillo, O; Johnson, J B

2010-07-01

Continuous volcanic infrasound signal was recorded on a three-microphone network at Kilauea in July 2008 and inverted for near-surface horizontal winds. Inter-station phase delays, determined by signal cross-correlation, vary by up to 4% and are attributable to variable atmospheric conditions. The results suggest two predominant weather regimes during the study period: (1) 6-9 m/s easterly trade winds and (2) lower-intensity 2-5 m/s mountain breezes from Mauna Loa. The results demonstrate the potential of using infrasound for tracking local averaged meteorological conditions, which has implications for modeling plume dispersal and quantifying gas flux.

Airborne boundary layer flux measurements of trace species over Canadian boreal forest and northern wetland regions

NASA Technical Reports Server (NTRS)

Ritter, John A.; Barrick, John D. W.; Watson, Catherine E.; Sachse, Glen W.; Gregory, Gerald L.; Anderson, Bruce E.; Woerner, Mary A.; Collins, James E., Jr.

1994-01-01

Airborne heat, moisture, O3, CO, and CH4 flux measurements were obtained over the Hudson Bay lowlands (HBL) and northern boreal forest regions of Canada during July - August 1990. The airborne flux measurements were an integral part of the NASA/Arctic Boundary Layer Expedition (ABLE) 3B field experiment executed in collaboration with the Canadian Northern Wetlands Study (NOWES). Airborne CH4 flux measurements were taken over a large portion of the HBL. The surface level flux of CH4 was obtained from downward extrapolations of multiple-level CH4 flux measurements. Methane source strengths ranged from -1 to 31 mg m(exp -2)/d, with the higher values occurring in relatively small, isolated areas. Similar measurements of the CH4 source strength in the boreal forest region of Schefferville, Quebec, ranged from 6 to 27 mg m(exp -2)/d and exhibited a diurnal dependence. The CH4 source strengths found during the ABLE 3B expedition were much lower than the seasonally averaged source strength of 51 mg m(exp -2)/d found for the Yukon-Kuskokwim delta region of Alaska during the previous ABLE 3A study. Large positive CO fluxes (0.31 to 0.53 parts per billion by volume (ppbv) m/s) were observed over the inland, forested regions of the HBL study area, although the mechanism for the generation of these fluxes was not identified. Repetitive measurements along the same ground track at various times of day near the Schefferville site also suggested a diurnal dependence for CO emissions. Measurements of surface resistance to the uptake of O3 (1.91 to 0.80 s/cm) for the HBL areas investigated were comparable to those observed near the Schefferville site (3.40 to 1.10 s/cm). Surface resistance values for the ABLE 3B study area were somewhat less than those observed over the Yukon-Kuskokwim delta during the previous ABLE 3A study. The budgets for heat, moisture, O3, CO, and CH4 were evaluated. The residuals from these budget studies indicated, for the cases selected, a moderate net photochemical production of O3 present in the boundary layer over the HBL that coincided with an in situ destruction of CO, although the mechanism responsible for the destruction of CO was not identified. Results from the O3 budget analysis indicate the importance of in situ photochemical production and its possible dominance over surface deposition to the local O3 budget at the Schefferville site. Measurements of the in situ production of O3 indicated a direct relationship between the presence of biomass burning or large-scale pollution effects. Residuals from budget calculations for conserved quantities (heat, moisture, and CH4) were compared with their respective surface fluxes to provide a measure of the internal self-consistency of the flux measurements.

Continental Heat Gain in the Global Climate System

NASA Astrophysics Data System (ADS)

Smerdon, J. E.; Beltrami, H.; Pollack, H. N.; Huang, S.

2001-12-01

Observed increases in 20th century surface-air temperatures are one consequence of a net energy flux into all major components of the Earth climate system including the atmosphere, ocean, cryosphere, and lithosphere. Levitus et al. [2001] have estimated the heat gained by the atmosphere, ocean and cryosphere as 18.2x1022 J, 6.6x1021 J, and 8.1x1021 J, respectively, over the past half-century. However the heat gain of the lithosphere via a heat flux across the solid surface of the continents (30% of the Earth's surface) was not addressed in the Levitus analysis. Here we calculate that final component of Earth's changing energy budget, using ground-surface temperature reconstructions for the continents [Huang et al., 2000]. These reconstructions have shown a warming of at least 0.5 K in the 20th century and were used to determine the flux estimates presented here. In the last half-century, the interval of time considered by Levitus et al., there was an average flux of 40 mW/m2 across the land surface into the subsurface, leading to 9.2x1021 J absorbed by the ground. This amount of heat is significantly less than the energy transferred into the oceans, but of the same magnitude as the energy absorbed by the atmosphere or cryosphere. The heat inputs into all the major components of the climate system - atmosphere, ocean, cryosphere, lithosphere - conservatively sum to more than 20x1022 J during the last half-century, and reinforce the conclusion that the warming in this interval has been truly global. Huang, S., Pollack, H.N., and Shen, P.-Y. 2000. Temperature trends over the past five centuries reconstructed from borehole temperatures. Nature. 403. 756-758 Levitus, S., Antonov, J., Wang, J., Delworth, T. L., Dixon, K. and Broccoli, A. 2001. Anthropogenic warming of the Earth's climate system. Science, 292, 267-270

Large-scale variability of wind erosion mass flux rates at Owens Lake 1. Vertical profiles of horizontal mass fluxes of wind-eroded particles with diameter greater than 50 μm

USGS Publications Warehouse

Gillette, Dale A.; Fryrear, D.W.; Xiao, Jing Bing; Stockton, Paul; Ono, Duane; Helm, Paula J.; Gill, Thomas E; Ley, Trevor

1997-01-01

A field experiment at Owens (dry) Lake, California, tested whether and how the relative profiles of airborne horizontal mass fluxes for >50-μm wind-eroded particles changed with friction velocity. The horizontal mass flux at almost all measured heights increased proportionally to the cube of friction velocity above an apparent threshold friction velocity for all sediment tested and increased with height except at one coarse-sand site where the relative horizontal mass flux profile did not change with friction velocity. Size distributions for long-time-averaged horizontal mass flux samples showed a saltation layer from the surface to a height between 30 and 50 cm, above which suspended particles dominate. Measurements from a large dust source area on a line parallel to the wind showed that even though the saltation flux reached equilibrium ∼650 m downwind of the starting point of erosion, weakly suspended particles were still input into the atmosphere 1567 m downwind of the starting point; thus the saltating fraction of the total mass flux decreased after 650 m. The scale length difference and ratio of 70/30 suspended mass flux to saltation mass flux at the farthest down wind sampling site confirm that suspended particles are very important for mass budgets in large source areas and that saltation mass flux can be a variable fraction of total horizontal mass flux for soils with a substantial fraction of <100-μm particles.

Carbon dioxide fluxes from an urban area in Beijing

NASA Astrophysics Data System (ADS)

Song, Tao; Wang, Yuesi

2012-03-01

A better understanding of urban carbon dioxide (CO 2) emissions is important for quantifying urban contributions to the global carbon budget. From January to December 2008, CO 2 fluxes were measured, by eddy covariance at 47 m above ground on a meteorological tower in a high-density residential area in Beijing. The results showed that the urban surface was a net source of CO 2 in the atmosphere. Diurnal flux patterns were similar to those previously observed in other cities and were largely influenced by traffic volume. Carbon uptake by both urban vegetation during the growing season and the reduction of fuel consumption for domestic heating resulted in less-positive daily fluxes in the summer. The average daily flux measured in the summer was 0.48 mg m - 2 s - 1 , which was 82%, 35% and 36% lower than those in the winter, spring and autumn, respectively. The reduction of vehicles on the road during the 29th Olympic and Paralympic Games had a significant impact on CO 2 flux. The flux of 0.40 mg m - 2 s - 1 for September 2008 was approximately 0.17 mg m - 2 s - 1 lower than the flux for September 2007. Annual CO 2 emissions from the study site were estimated at 20.6 kg CO 2 m - 2 y - 1 , considerably higher than yearly emissions obtained from other urban and suburban landscapes.

Revisiting the global surface energy budgets with maximum-entropy-production model of surface heat fluxes

NASA Astrophysics Data System (ADS)

Huang, Shih-Yu; Deng, Yi; Wang, Jingfeng

2017-09-01

The maximum-entropy-production (MEP) model of surface heat fluxes, based on contemporary non-equilibrium thermodynamics, information theory, and atmospheric turbulence theory, is used to re-estimate the global surface heat fluxes. The MEP model predicted surface fluxes automatically balance the surface energy budgets at all time and space scales without the explicit use of near-surface temperature and moisture gradient, wind speed and surface roughness data. The new MEP-based global annual mean fluxes over the land surface, using input data of surface radiation, temperature data from National Aeronautics and Space Administration-Clouds and the Earth's Radiant Energy System (NASA CERES) supplemented by surface specific humidity data from the Modern-Era Retrospective Analysis for Research and Applications (MERRA), agree closely with previous estimates. The new estimate of ocean evaporation, not using the MERRA reanalysis data as model inputs, is lower than previous estimates, while the new estimate of ocean sensible heat flux is higher than previously reported. The MEP model also produces the first global map of ocean surface heat flux that is not available from existing global reanalysis products.

Development of a locally mass flux conservative computer code for calculating 3-D viscous flow in turbomachines

NASA Technical Reports Server (NTRS)

Walitt, L.

1982-01-01

The VANS successive approximation numerical method was extended to the computation of three dimensional, viscous, transonic flows in turbomachines. A cross-sectional computer code, which conserves mass flux at each point of the cross-sectional surface of computation was developed. In the VANS numerical method, the cross-sectional computation follows a blade-to-blade calculation. Numerical calculations were made for an axial annular turbine cascade and a transonic, centrifugal impeller with splitter vanes. The subsonic turbine cascade computation was generated in blade-to-blade surface to evaluate the accuracy of the blade-to-blade mode of marching. Calculated blade pressures at the hub, mid, and tip radii of the cascade agreed with corresponding measurements. The transonic impeller computation was conducted to test the newly developed locally mass flux conservative cross-sectional computer code. Both blade-to-blade and cross sectional modes of calculation were implemented for this problem. A triplet point shock structure was computed in the inducer region of the impeller. In addition, time-averaged shroud static pressures generally agreed with measured shroud pressures. It is concluded that the blade-to-blade computation produces a useful engineering flow field in regions of subsonic relative flow; and cross-sectional computation, with a locally mass flux conservative continuity equation, is required to compute the shock waves in regions of supersonic relative flow.

Carbon Dioxide Emissions from Reservoirs in the Lower Jordan Watershed

PubMed Central

Alshboul, Zeyad; Lorke, Andreas

2015-01-01

We have analyzed monthly hydrological, meteorological and water quality data from three irrigation and drinking water reservoirs in the lower Jordan River basin and estimated the atmospheric emission rates of CO2. The data were collected between 2006 and 2013 and show that the reservoirs, which differ in size and age, were net sources of CO2. The estimated surface fluxes were comparable in magnitude to those reported for hydroelectric reservoirs in the tropical and sub-tropical zones. Highest emission rates were observed for a newly established reservoir, which was initially filled during the sampling period. In the two older reservoirs, CO2 partial pressures and fluxes were significantly decreasing during the observation period, which could be related to simultaneously occurring temporal trends in water residence time and chemical composition of the water. The results indicate a strong influence of water and reservoir management (e.g. water consumption) on CO2 emission rates, which is affected by the increasing anthropogenic pressure on the limited water resources in the study area. The low wind speed and relatively high pH favored chemical enhancement of the CO2 gas exchange at the reservoir surfaces, which caused on average a four-fold enhancement of the fluxes. A sensitivity analysis indicates that the uncertainty of the estimated fluxes is, besides pH, mainly affected by the poorly resolved wind speed and resulting uncertainty of the chemical enhancement factor. PMID:26588241

Carbon Dioxide Emissions from Reservoirs in the Lower Jordan Watershed.

PubMed

Alshboul, Zeyad; Lorke, Andreas

2015-01-01

We have analyzed monthly hydrological, meteorological and water quality data from three irrigation and drinking water reservoirs in the lower Jordan River basin and estimated the atmospheric emission rates of CO2. The data were collected between 2006 and 2013 and show that the reservoirs, which differ in size and age, were net sources of CO2. The estimated surface fluxes were comparable in magnitude to those reported for hydroelectric reservoirs in the tropical and sub-tropical zones. Highest emission rates were observed for a newly established reservoir, which was initially filled during the sampling period. In the two older reservoirs, CO2 partial pressures and fluxes were significantly decreasing during the observation period, which could be related to simultaneously occurring temporal trends in water residence time and chemical composition of the water. The results indicate a strong influence of water and reservoir management (e.g. water consumption) on CO2 emission rates, which is affected by the increasing anthropogenic pressure on the limited water resources in the study area. The low wind speed and relatively high pH favored chemical enhancement of the CO2 gas exchange at the reservoir surfaces, which caused on average a four-fold enhancement of the fluxes. A sensitivity analysis indicates that the uncertainty of the estimated fluxes is, besides pH, mainly affected by the poorly resolved wind speed and resulting uncertainty of the chemical enhancement factor.

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.

Determining suitability of Large Aperture Scintillometer for validating remote sensing based evapotranspiration maps

NASA Astrophysics Data System (ADS)

Paul, G.; Gowda, P. H.; Howell, T. A.; Basu, S.; Colaizzi, P. D.; Marek, T.

2013-12-01

Scintillation method is a relatively new technique for measuring the sensible heat and water fluxes over land surfaces. Path integrating capabilities of scintillometer over heterogeneous landscapes make it a potential tool for comparing the energy fluxes derived from remote sensing based energy balance algorithms. For this reason, scintillometer-derived evapotranspiration (ET) fluxes are being used to evaluate remote sensing based energy balance algorithms for their ability to estimate ET fluxes. However, LAS' (Large Aperture Scintillometer) ability to derive ET fluxes is not thoroughly tested. The objective of this study was to evaluate LAS- and Surface Energy Balance System (SEBS)-derived fluxes against lysimetric data to determine LAS' suitability for validating remote sensing based evapotranspiration (ET) maps. The study was conducted during the Bushland Evapotranspiration and Agricultural Remote sensing EXperiment - 2008 (BEAREX-08) at the USDA-ARS Conservation and Production Research Laboratory (CPRL), Bushland, Texas. SEBS was coded in a GIS environment to retrieve ET fluxes from the high resolution imageries acquired using airborne multispectral sensors. The CPRL has four large weighing lysimeters (3 m long x 3 m wide x 2.4 m deep), each located in the middle of approximately 5 ha fields, arranged in a block pattern. The two lysimeter fields located on the east (NE and SE) were managed under irrigated conditions, and the other two lysimeters on the west (NW and SW) were under dryland management. Each lysimeter field was equipped with an automated weather station that provided measurements for net radiation (Rn), Ts, soil heat flux (Go), Ta, relative humidity, and wind speed. During BEAREX08, the NE and SE fields were planted to cotton on May 21, and the NW and SW dryland lysimeters fields were planted to cotton on June 5. One LAS each was deployed across two large dryland lysimeter fields (NW and SW) and two large irrigated lysimeter fields (NE and SE). The structural parameter of refractive index of air was measured at 1-min interval and averaged at 15-min, and synchronized with weather station. The source area (footprint) of the surface energy fluxes were computed using a footprint model. ET fluxes were derived using LAS-estimated H as a residual from the energy balance equation. Comparison of SEBS- and LAS-derived ET fluxes were made against lysimetric data and performance of each method was discussed to determine the suitability of LAS for evaluating accuracy of remote sensing based ET maps.

Experimental drought in a tropical rain forest increases soil carbon dioxide losses to the atmosphere

USGS Publications Warehouse

Cleveland, C.C.; Wieder, W.R.; Reed, S.C.; Townsend, A.R.

2010-01-01

Climate models predict precipitation changes for much of the humid tropics, yet few studies have investigated the potential consequences of drought on soil carbon (C) cycling in this important biome. In wet tropical forests, drought could stimulate soil respiration via overall reductions in soil anoxia, but previous research suggests that litter decomposition is positively correlated with high rainfall fluxes that move large quantities of dissolved organic matter (DOM) from the litter layer to the soil surface. Thus, reduced rainfall could also limit C delivery to the soil surface, reducing respiration rates. We conducted a throughfall manipulation experiment to investigate how 25% and 50% reductions in rainfall altered both C movement into soils and the effects of those DOM fluxes on soil respiration rates. In response to the experimental drought, soil respiration rates increased in both the -25% and -50% treatments. Throughfall fluxes were reduced by 26% and 55% in the-25% and-50% treatments, respectively. However, total DOM fluxes leached from the litter did not vary between treatments, because the concentrations of leached DOM reaching the soil surface increased in response to the simulated drought. Annual DOM concentrations averaged 7.7 ?? 0.8, 11.2 ?? 0.9, and 15.8 ?? 1.2 mg C/L in the control, -25%, and -50% plots, respectively, and DOM concentrations were positively correlated with soil respiration rates. A laboratory incubation experiment confirmed the potential importance of DOM concentration on soil respiration rates, suggesting that this mechanism could contribute to the increase in CO2 fluxes observed in the reduced rainfall plots. Across all plots, the data suggested that soil CO2 fluxes were partially regulated by the magnitude and concentration of soluble C delivered to the soil, but also by soil moisture and soil oxygen availability. Together, our data suggest that declines in precipitation in tropical rain forests could drive higher CO2 fluxes to the atmosphere both via increased soil O2 availability and through responses to elevated DOM concentrations. ?? 2010 by the Ecological Society of America.

Experimental drought in a tropical rain forest increases soil carbon dioxide losses to the atmosphere

USGS Publications Warehouse

Cleveland, Cory C.; Wieder, William R.; Reed, Sasha C.; Townsend, Alan R.

2010-01-01

Climate models predict precipitation changes for much of the humid tropics, yet few studies have investigated the potential consequences of drought on soil carbon (C) cycling in this important biome. In wet tropical forests, drought could stimulate soil respiration via overall reductions in soil anoxia, but previous research suggests that litter decomposition is positively correlated with high rainfall fluxes that move large quantities of dissolved organic matter (DOM) from the litter layer to the soil surface. Thus, reduced rainfall could also limit C delivery to the soil surface, reducing respiration rates. We conducted a throughfall manipulation experiment to investigate how 25% and 50% reductions in rainfall altered both C movement into soils and the effects of those DOM fluxes on soil respiration rates. In response to the experimental drought, soil respiration rates increased in both the -25% and -50% treatments. Throughfall fluxes were reduced by 26% and 55% in the -25% and -50% treatments, respectively. However, total DOM fluxes leached from the litter did not vary between treatments, because the concentrations of leached DOM reaching the soil surface increased in response to the simulated drought. Annual DOM concentrations averaged 7.7 ± 0.8, 11.2 ± 0.9, and 15.8 ± 1.2 mg C/L in the control, -25%, and -50% plots, respectively, and DOM concentrations were positively correlated with soil respiration rates. A laboratory incubation experiment confirmed the potential importance of DOM concentration on soil respiration rates, suggesting that this mechanism could contribute to the increase in CO2 fluxes observed in the reduced rainfall plots. Across all plots, the data suggested that soil CO2 fluxes were partially regulated by the magnitude and concentration of soluble C delivered to the soil, but also by soil moisture and soil oxygen availability. Together, our data suggest that declines in precipitation in tropical rain forests could drive higher CO2 fluxes to the atmosphere both via increased soil O2 availability and through responses to elevated DOM concentrations.

Direct Aerosol Radiative Forcing: Calculations and Measurements from the Tropospheric

NASA Technical Reports Server (NTRS)

Russell, P. B.; Hignett, P.; Stowe, L. L.; Livingston, J. M.; Kinne, S.; Wong, J.; Chan, K. Roland (Technical Monitor)

1997-01-01

Radiative forcing is defined as the change in the net (downwelling minus upwelling) radiative flux at a given level in the atmosphere. This net flux is the radiative power density available to drive climatic processes in the earth-atmosphere system below that level. Recent research shows that radiative forcing by aerosol particles is a major source of uncertainty in climate predictions. To reduce those uncertainties, TARFOX was designed to determine direct (cloud-free) radiative forcing by the aerosols in one of the world's major industrial pollution plumes--that flowing from the east coast of the US over the Atlantic Ocean. TARFOX measured a variety of aerosol radiative effects (including direct forcing) while simultaneously measuring the chemical, physical, and optical properties of the aerosol particles causing those effects. The resulting data sets permit a wide variety of tests of the consistency, or closure, among the measurements and the models that link them. Because climate predictions use the same or similar model components, closure tests help to assess and reduce prediction uncertainties. In this work we use the TARFOX-determined aerosol, gas, and surface properties to compute radiative forcing for a variety of aerosol episodes, with inadvisable optical depths ranging from 0.07 to 0.6. We calculate forcing by several techniques with varying degrees of sophistication, in part to test the range of applicability of simplified techniques--which are often the only ones feasible in climate predictions by general circulation models (GCMs). We then compare computed forcing to that determined from: (1) Upwelling and downwelling fluxes (0.3-0.7 mm and 0.7-3.0 mm) measured by radiometers on the UK MRF C-130. and (2) Daily average cloud-free absorbed solar and emitted thermal radiative flux at the top of the atmosphere derived from the AVHRR radiometer on the NOAA- 14 satellite. The calculations and measurements all yield aerosol direct radiative forcing in the range -50 to -190 W sq m per unit inadvisable optical depth. The magnitudes are about 15 to 100 times larger than the global-average direct forcing expected for the global-average sulfate aerosol optical depth of 0.04. The reasons for the larger forcing in TARFOX include the relatively large optical depths and the focus on cloud-free, daytime conditions over the dark ocean surface. These are the conditions that produce the actual major radiative forcing events that contribute to any global-average climate effect. Detailed comparisons of calculated and measured forcings for specific events are used for more refined tests of closure.

The SeaFlux Turbulent Flux Dataset Version 1.0 Documentation

NASA Technical Reports Server (NTRS)

Clayson, Carol Anne; Roberts, J. Brent; Bogdanoff, Alec S.

2012-01-01

Under the auspices of the World Climate Research Programme (WCRP) Global Energy and Water cycle EXperiment (GEWEX) Data and Assessment Panel (GDAP), the SeaFlux Project was created to investigate producing a high-resolution satellite-based dataset of surface turbulent fluxes over the global oceans. The most current release of the SeaFlux product is Version 1.0; this represents the initial release of turbulent surface heat fluxes, associated near-surface variables including a diurnally varying sea surface temperature.

Intraseasonal Oscillations over South America: A Study with a Regional Climate Model

NASA Technical Reports Server (NTRS)

Chen, Baode; Chao, Winston

2003-01-01

The National Center for Atmospheric Research (NCAR) regional climate model version 2 (RegCM2) is used to investigate the observed characteristics of intraseasonal oscillations over South America. Our study is mainly concentrated on an intraseaonal mode, which is observed to account for a large portion of the intraseasonal variation, to have a standing feature and to be independent of the MJO. The NCEPDOE AMIP-II reanalysis is utilized to provide initial and lateral boundary conditions for the RegCM2 based upon the OOZ, 062, 122 and 182 data.Our results indicate that the intraseasonal oscillation still exists with time- averaged lateral boundary condition, which prevents the MJO and other outside disturbances from entering the model's domain, suggesting a locally forced oscillation responsible for ths intraseasonal mode independent of the MJO. Further experiments show that the annual and daily variabilities and a radiative-convective interaction are not essential to the locally forced intraseasonal oscillation. The intraseasonal oscillations over Amazon in our model essentially result from interactions among atmospheric continental- scale circulation, surface radiation, surface sensible and latent heat fluxes, and cumulus convection. The wavelet analyses of various surface energy fluxes and surface energy budget also verify that the primary cause of intraseasonal oscillation is the interaction of land surface processes with the atmosphere.

Geometric stabilization of the electrostatic ion-temperature-gradient driven instability. I. Nearly axisymmetric systems

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

Zocco, A.; Plunk, G. G.; Xanthopoulos, P.

The effects of a non-axisymmetric (3D) equilibrium magnetic field on the linear ion-temperature-gradient (ITG) driven mode are investigated. We consider the strongly driven, toroidal branch of the instability in a global (on the magnetic surface) setting. Previous studies have focused on particular features of non-axisymmetric systems, such as strong local shear or magnetic ripple, that introduce inhomogeneity in the coordinate along the magnetic field. In contrast, here we include non-axisymmetry explicitly via the dependence of the magnetic drift on the field line label α, i.e., across the magnetic field, but within the magnetic flux surface. We consider the limit wheremore » this variation occurs on a scale much larger than that of the ITG mode, and also the case where these scales are similar. Close to axisymmetry, we find that an averaging effect of the magnetic drift on the flux surface causes global (on the surface) stabilization, as compared to the most unstable local mode. In the absence of scale separation, we find destabilization is also possible, but only if a particular resonance occurs between the magnetic drift and the mode, and finite Larmor radius effects are neglected. We discuss the relative importance of surface global effects and known radially global effects.« less

Multi-scale observations of the variability of magmatic CO2 emissions, Mammoth Mountain, CA, USA

NASA Astrophysics Data System (ADS)

Lewicki, J. L.; Hilley, G. E.

2014-09-01

One of the primary indicators of volcanic unrest at Mammoth Mountain is diffuse emission of magmatic CO2, which can effectively track this unrest if its variability in space and time and relationship to near-surface meteorological and hydrologic phenomena versus those occurring at depth beneath the mountain are understood. In June-October 2013, we conducted accumulation chamber soil CO2 flux surveys and made half-hourly CO2 flux measurements with automated eddy covariance and accumulation chamber (auto-chamber) instrumentation at the largest area of diffuse CO2 degassing on Mammoth Mountain (Horseshoe Lake tree kill; HLTK). Estimated CO2 emission rates for HLTK based on 20 June, 30 July, and 24-25 October soil CO2 flux surveys were 165, 172, and 231 t d- 1, respectively. The average (June-October) CO2 emission rate estimated for this area was 123 t d- 1 based on an inversion of 4527 eddy covariance CO2 flux measurements and corresponding modeled source weight functions. Average daily eddy covariance and auto-chamber CO2 fluxes consistently declined over the four-month observation time. Wavelet analysis of auto-chamber CO2 flux and environmental parameter time series was used to evaluate the periodicity of, and local correlation between these variables in time-frequency space. Overall, CO2 emissions at HLTK were highly dynamic, displaying short-term (hourly to weekly) temporal variability related to meteorological and hydrologic changes, as well as long-term (monthly to multi-year) variations related to migration of CO2-rich magmatic fluids beneath the volcano. Accumulation chamber soil CO2 flux surveys were also conducted in the four additional areas of diffuse CO2 degassing on Mammoth Mountain in July-August 2013. Summing CO2 emission rates for all five areas yielded a total for the mountain of 311 t d- 1, which may suggest that emissions returned to 1998-2009 levels, following an increase from 2009 to 2011.

Multi-scale observations of the variability of magmatic CO2 emissions, Mammoth Mountain, CA, USA

USGS Publications Warehouse

Lewicki, Jennifer L.; Hilley, George E.

2014-01-01

One of the primary indicators of volcanic unrest at Mammoth Mountain is diffuse emission of magmatic CO2, which can effectively track this unrest if its variability in space and time and relationship to near-surface meteorological and hydrologic phenomena versus those occurring at depth beneath the mountain are understood. In June–October 2013, we conducted accumulation chamber soil CO2 flux surveys and made half-hourly CO2 flux measurements with automated eddy covariance and accumulation chamber (auto-chamber) instrumentation at the largest area of diffuse CO2 degassing on Mammoth Mountain (Horseshoe Lake tree kill; HLTK). Estimated CO2 emission rates for HLTK based on 20 June, 30 July, and 24–25 October soil CO2 flux surveys were 165, 172, and 231 t d− 1, respectively. The average (June–October) CO2 emission rate estimated for this area was 123 t d− 1 based on an inversion of 4527 eddy covariance CO2 flux measurements and corresponding modeled source weight functions. Average daily eddy covariance and auto-chamber CO2 fluxes consistently declined over the four-month observation time. Wavelet analysis of auto-chamber CO2 flux and environmental parameter time series was used to evaluate the periodicity of, and local correlation between these variables in time–frequency space. Overall, CO2 emissions at HLTK were highly dynamic, displaying short-term (hourly to weekly) temporal variability related to meteorological and hydrologic changes, as well as long-term (monthly to multi-year) variations related to migration of CO2-rich magmatic fluids beneath the volcano. Accumulation chamber soil CO2 flux surveys were also conducted in the four additional areas of diffuse CO2 degassing on Mammoth Mountain in July–August 2013. Summing CO2 emission rates for all five areas yielded a total for the mountain of 311 t d− 1, which may suggest that emissions returned to 1998–2009 levels, following an increase from 2009 to 2011.

The seasonal cycle of diabatic heat storage in the Pacific Ocean

USGS Publications Warehouse

White, Warren B.; Cayan, D.R.; Niiler, P.P.; Moisan, J.; Lagerloef, G.; Bonjean, F.; Legler, D.

2005-01-01

This study quantifies uncertainties in closing the seasonal cycle of diabatic heat storage (DHS) over the Pacific Ocean from 20??S to 60??N through the synthesis of World Ocean Circulation Experiment (WOCE) reanalysis products from 1993 to 1999. These products are DHS from Scripps Institution of Oceanography (SIO); near-surface geostrophic and Ekman currents from Earth and Space Research (ESR); and air-sea heat fluxes from Comprehensive Ocean-Atmosphere Data Set (COADS), National Centers for Environmental Prediction (NCEP), and European Center for Mid-Range Weather Forecasts (ECMWF). With these products, we compute residual heat budget components by differencing long-term monthly means from the long-term annual mean. This allows the seasonal cycle of the DHS tendency to be modeled. Everywhere latent heat flux residuals dominate sensible heat flux residuals, shortwave heat flux residuals dominate longwave heat flux residuals, and residual Ekman heat advection dominates residual geostrophic heat advection, with residual dissipation significant only in the Kuroshio-Oyashio current extension. The root-mean-square (RMS) of the differences between observed and model residual DHS tendencies (averaged over 10??latitude-by-20??longitude boxes) is <20 W m-2 in the interior ocean and <100 W m-2 in the Kuroshio-Oyashio current extension. This reveals that the residual DHS tendency is driven everywhere by some mix of residual latent heat flux, shortwave heat flux, and Ekman heat advection. Suppressing bias errors in residual air-sea turbulent heat fluxes and Ekman heat advection through minimization of the RMS differences reduces the latter to <10 W m-2 over the interior ocean and <25 W m -2 in the Kuroshio-Oyashio current extension. This reveals air-sea temperature and specific humidity differences from in situ surface marine weather observations to be a principal source of bias error, overestimated over most of ocean but underestimated near the Intertropical Convergence Zone. ?? 2005 Elsevier Ltd. All rights reserved.

Thermal and petrologic constraints on lower crustal melt accumulation under the Salton Sea Geothermal Field

NASA Astrophysics Data System (ADS)

Karakas, Ozge; Dufek, Josef; Mangan, Margaret T.; Wright, Heather M.; Bachmann, Olivier

2017-06-01

In the Salton Sea region of southern California (USA), concurrent magmatism, extension, subsidence, and sedimentation over the past 0.5 to 1.0 Ma have led to the creation of the Salton Sea Geothermal Field (SSGF)-the second largest and hottest geothermal system in the continental United States-and the small-volume rhyolite eruptions that created the Salton Buttes. In this study, we determine the flux of mantle-derived basaltic magma that would be required to produce the elevated average heat flow and sustain the magmatic roots of rhyolite volcanism observed at the surface of the Salton Sea region. We use a 2D thermal model to show that a lower-crustal, partially molten mush containing < 20- 40% interstitial melt develops over a ∼105-yr timescale for basalt fluxes of 0.008 to 0.010 m3 /m2 /yr (∼0.0008 to ∼0.001 km3/yr injection rate) given extension rates at or below the current value of ∼0.01 m/yr (Brothers et al., 2009). These regions of partial melt are a natural consequence of a thermal regime that scales with average surface heat flow in the Salton Trough, and are consistent with seismic observations. Our results indicate limited melting and assimilation of pre-existing rocks in the lower crust. Instead, we find that basalt fractionation in the lower crust produces derivative melts of andesitic to dacitic composition. Such melts are then expected to ascend and accumulate in the upper crust, where they further evolve to give rise to small-volume rhyolite eruptions (Salton Buttes) and fuel local spikes in surface heat flux as currently seen in the SSGF. Such upper crustal magma evolution, with limited assimilation of hydrothermally altered material, is required to explain the slight decrease in δ18 O values of zircons (and melts) that have been measured in these rhyolites.

Decadal trends in regional CO2 fluxes estimated from atmospheric inversions

NASA Astrophysics Data System (ADS)

Saeki, T.; Patra, P. K.

2016-12-01

Top-down approach (or atmospheric inversion) using atmospheric transport models and CO2 observations are an effective way to optimize surface fluxes at subcontinental scales and monthly time intervals. We used the CCSR/NIES/FRCGC AGCM-based Chemistry Transport Model (JAMSTEC's ACTM) and atmospheric CO2 concentrations at NOAA, CSIRO, JMA, NIES, NIES-MRI sites from Obspack GLOBALVIEW-CO2 data product (2013) for estimating CO2 fluxes for the period of 1990-2011. Carbon fluxes were estimated for 84 partitions (54 lands + 30 oceans) of the globe by using a Bayesian synthesis inversion framework. A priori fluxes are (1) atmosphere-ocean exchange from Takahashi et al. (2009), (2) 3-hourly terrestrial biosphere fluxes (annually balanced) from CASA model, and (3) fossil fuel fluxes from CDIAC global totals and EDGAR4.2 spatial distributions. Four inversion cases have been tested with 1) 21 sites (sites which have real data fraction of 90 % or more for 1989-2012), 2) 21 sites + CONTRAIL data, 3) 66 sites (over 70 % coverage), and 4) 157 sites. As a result of time-dependent inversions, mean total flux (excluding fossil fuel) for the period 1990-2011 is estimated to be -3.09 ±0.16 PgC/yr (mean and standard deviation of the four cases), where land (incl. biomass burning and land use change) and ocean absorb an average rate of -1.80 ±0.18 and -1.29 ±0.08 PgC/yr, respectively. The average global total sink from 1991-2000 to 2001-2010 increases by about 0.5 PgC/yr, mainly due to the increase in northern and tropical land sinks (Africa, Boreal Eurasia, East Asia and Europe), while ocean sinks show no clear trend. Inversion with CONTRAIL data estimates large positive flux anomalies in late 1997 associated with the 1997/98 El-Nino, while inversion without CONTARIL data between Japan and Australia fails to estimate such large anomalies. Acknowledgements. This work is supported by the Environment Research and Technology Development Fund (2-1401) of the Ministry of the Environment, Japan. We thank all measurement groups for submitting CO2 concentration data to the obspack-GLOBALVIEW product.

Effects of warming and nitrogen fertilization on GHG flux in the permafrost region of an alpine meadow

NASA Astrophysics Data System (ADS)

Chen, Xiaopeng; Wang, Genxu; Zhang, Tao; Mao, Tianxu; Wei, Da; Hu, Zhaoyong; Song, Chunlin

2017-05-01

The limited number of in situ measurements of greenhouse gas (GHG) flux during soil freeze-thaw cycles in permafrost regions limits our ability to accurately predict how the alpine ecosystem carbon sink or source function will vary under future warming and increased nitrogen (N) deposition. An alpine meadow in the permafrost region of the Qinghai-Tibet Plateau was selected, and a simulated warming with N fertilization experiment was carried out to investigate the key GHG fluxes (ecosystem respiration [Re], CH4 and N2O) in the early (EG), mid (MG) and late (LG) growing seasons. The results showed that: (i) warming (4.5 °C) increased the average seasonal Re, CH4 uptake and N2O emission by 73.5%, 65.9% and 431.6%, respectively. N fertilization (4 g N m-2) alone had no significant effect on GHG flux; the interaction of warming and N fertilization enhanced CH4 uptake by 10.3% and N2O emissions by 27.2% than warming, while there was no significant effect on the Re; (ii) the average seasonal fluxes of Re, CH4 and N2O were MG > LG > EG, and Re and CH4 uptake were most sensitive to the soil freezing process instead of soil thawing process; (iii) surface soil temperature was the main driving factor of the Re and CH4 fluxes, and the N2O flux was mainly affected by daily rainfall; (iv) in the growing season, warming increased greenhouse warming potential (GWP) of the alpine meadow by 74.5%, the N fertilization decreased GWP of the warming plots by 13.9% but it was not statistically significant. These results indicate that (i) relative to future climate warming (or permafrost thawing), there could be a hysteresis of GHG flux in the alpine meadow of permafrost region; (ii) under the scenario of climate warming, increasing N deposition has limited impacts on the feedback of GHG flux of the alpine meadow.

Multitemporal ALSM change detection, sediment delivery, and process mapping at an active earthflow

USGS Publications Warehouse

DeLong, Stephen B.; Prentice, Carol S.; Hilley, George E.; Ebert, Yael

2012-01-01

Remote mapping and measurement of surface processes at high spatial resolution is among the frontiers in Earth surface process research. Remote measurements that allow meter-scale mapping of landforms and quantification of landscape change can revolutionize the study of landscape evolution on human timescales. At Mill Gulch in northern California, USA, an active earthflow was surveyed in 2003 and 2007 by airborne laser swath mapping (ALSM), enabling meter-scale quantification of landscape change. We calculate four-year volumetric flux from the earthflow and compare it to long-term catchment average erosion rates from cosmogenic radionuclide inventories from adjacent watersheds. We also present detailed maps of changing features on the earthflow, from which we can derive velocity estimates and infer dominant process. These measurements rely on proper digital elevation model (DEM) generation and a simple surface-matching technique to align the multitemporal data in a manner that eliminates systematic error in either dataset. The mean surface elevation of the earthflow and an opposite slope that was directly influenced by the earthflow decreased 14 ± 1 mm/yr from 2003 to 2007. By making the conservative assumption that these features were the dominant contributor of sediment flux from the entire Mill Gulch drainage basin during this time interval, we calculate a minimum catchment-averaged erosion rate of 0·30 ± 0·02 mm/yr. Analysis of beryllium-10 (10Be) concentrations in fluvial sand from nearby Russian Gulch and the South Fork Gualala River provide catchment averaged erosion rates of 0·21 ± 0·04 and 0·23 ± 0·03 mm/yr respectively. From translated landscape features, we can infer surface velocities ranging from 0·5 m/yr in the wide upper ‘source’ portion of the flow to 5 m/yr in the narrow middle ‘transport’ portion of the flow. This study re-affirms the importance of mass wasting processes in the sediment budgets of uplifting weak lithologies.

Geometrical correction factors for heat flux meters

NASA Technical Reports Server (NTRS)

Baumeister, K. J.; Papell, S. S.

1974-01-01

General formulas are derived for determining gage averaging errors of strip-type heat flux meters used in the measurement of one-dimensional heat flux distributions. The local averaging error e(x) is defined as the difference between the measured value of the heat flux and the local value which occurs at the center of the gage. In terms of e(x), a correction procedure is presented which allows a better estimate for the true value of the local heat flux. For many practical problems, it is possible to use relatively large gages to obtain acceptable heat flux measurements.

The impact of reforestation in the northeast United States on precipitation and surface temperature

NASA Astrophysics Data System (ADS)

Clark, Allyson

Since the 1920s, forest coverage in the northeastern United States has recovered from disease, clearing for agricultural and urban development, and the demands of the timber industry. Such a dramatic change in ground cover can influence heat and moisture fluxes to the atmosphere, as measured in altered landscapes in Australia, Israel, and the Amazon. In this study, the impacts of recent reforestation in the northeastern United States on summertime precipitation and surface temperature were quantified by comparing average modern values to 1950s values. Weak positive (negative) relationships between reforestation and average monthly precipitation and daily minimum temperatures (average daily maximum surface temperature) were found. There was no relationship between reforestation and average surface temperature. Results of the observational analysis were compared with results obtained from reforestation scenarios simulated with the BUGS5 global climate model. The single difference between the model runs was the amount of forest coverage in the northeast United States; three levels of forest were defined - a grassland state, with 0% forest coverage, a completely forested state, with approximately 100% forest coverage, and a control state, with forest coverage closely resembling modern forest coverage. The three simulations were compared, and had larger magnitude average changes in precipitation and in all temperature variables. The difference in magnitudes between the model simulations observations was much larger than the difference in the amount of reforestation in each case. Additionally, unlike in observations, a negative relationship was found between average daily minimum temperature and amount of forest coverage, implying that additional factors influence temperature and precipitation in the real world that are not accounted for in the model.

Chemical weathering in a tropical watershed, Luquillo Mountains, Puerto Rico: I. Long-term versus short-term weathering fluxes

USGS Publications Warehouse

White, A.F.; Blum, A.E.; Schulz, M.S.; Vivit, D.V.; Stonestrom, David A.; Larsen, M.; Murphy, S.F.; Eberl, D.

1998-01-01

The pristine Rio Icacos watershed in the Luquillo Mountains in eastern Puerto Rico has the fastest documented weathering rate of silicate rocks on the Earth's surface. A regolith propagation rate of 58 m Ma-1 calculated from iso-volumetric saprolite formation from quartz diorite, is comparable to the estimated denudation rate (25-50 Ma-1) but is an order of magnitude faster than the global average weathering rate (6 Ma-1). Weathering occurs in two distinct environments; plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith. These environments produce distinctly different water chemistries, with K, Mg, and Si increasing linearly with depth in saprolite porewaters and with stream waters dominated by Ca, Na, and Si. Such differences are atypical of less intense weathering in temperate watersheds. Porewater chemistry in the shallow regolith is controlled by closed-system recycling of inorganic nutrients such as K. Long-term elemental fluxes through the regolith (e.g., Si = 1.7 ?? 10-8 moles m-2 s-1) are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface (200 Ma). Mass losses attributed to solute fluxes are determined using a step-wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water. Pressure heads decrease with depth in the shallow regolith (-2.03 m H2O m-1), indicating that both increasing capillary tension and graviometric potential control porewater infiltration. Interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr-1 at average field moisture saturation which is comparable with LiBr tracer tests and with base discharge from the watershed. Short term weathering fluxes calculated from solute chemistries and infiltration rates (e.g., Si = 1.4 ?? 10-8 moles m-2 s-1) are compared to watershed flux rates (e.g., Si = 2.7 ?? 10-8 moles m-2 s-1). Consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation, temperature, and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the Luquillo Mountains of Puerto Rico. This has important ramifications for tropical environments and global climate change. Copyright ?? 1998 Elsevier Science Ltd.

A Regional CO2 Observing System Simulation Experiment Using ASCENDS Observations and WRF-STILT Footprints

NASA Technical Reports Server (NTRS)

Wang, James S.; Kawa, S. Randolph; Eluszkiewicz, Janusz; Collatz, G. J.; Mountain, Marikate; Henderson, John; Nehrkorn, Thomas; Aschbrenner, Ryan; Zaccheo, T. Scott

2012-01-01

Knowledge of the spatiotemporal variations in emissions and uptake of CO2 is hampered by sparse measurements. The recent advent of satellite measurements of CO2 concentrations is increasing the density of measurements, and the future mission ASCENDS (Active Sensing of CO2 Emissions over Nights, Days and Seasons) will provide even greater coverage and precision. Lagrangian atmospheric transport models run backward in time can quantify surface influences ("footprints") of diverse measurement platforms and are particularly well suited for inverse estimation of regional surface CO2 fluxes at high resolution based on satellite observations. We utilize the STILT Lagrangian particle dispersion model, driven by WRF meteorological fields at 40-km resolution, in a Bayesian synthesis inversion approach to quantify the ability of ASCENDS column CO2 observations to constrain fluxes at high resolution. This study focuses on land-based biospheric fluxes, whose uncertainties are especially large, in a domain encompassing North America. We present results based on realistic input fields for 2007. Pseudo-observation random errors are estimated from backscatter and optical depth measured by the CALIPSO satellite. We estimate a priori flux uncertainties based on output from the CASA-GFED (v.3) biosphere model and make simple assumptions about spatial and temporal error correlations. WRF-STILT footprints are convolved with candidate vertical weighting functions for ASCENDS. We find that at a horizontal flux resolution of 1 degree x 1 degree, ASCENDS observations are potentially able to reduce average weekly flux uncertainties by 0-8% in July, and 0-0.5% in January (assuming an error of 0.5 ppm at the Railroad Valley reference site). Aggregated to coarser resolutions, e.g. 5 degrees x 5 degrees, the uncertainty reductions are larger and more similar to those estimated in previous satellite data observing system simulation experiments.

Variations of solar, interplanetary, and geomagnetic parameters with solar magnetic multipole fields during Solar Cycles 21-24

NASA Astrophysics Data System (ADS)

Kim, Bogyeong; Lee, Jeongwoo; Yi, Yu; Oh, Suyeon

2015-01-01

In this study we compare the temporal variations of the solar, interplanetary, and geomagnetic (SIG) parameters with that of open solar magnetic flux from 1976 to 2012 (from Solar Cycle 21 to the early phase of Cycle 24) for a purpose of identifying their possible relationships. By the open flux, we mean the average magnetic field over the source surface (2.5 solar radii) times the source area as defined by the potential field source surface (PFSS) model of the Wilcox Solar Observatory (WSO). In our result, most SIG parameters except the solar wind dynamic pressure show rather poor correlations with the open solar magnetic field. Good correlations are recovered when the contributions from individual multipole components are counted separately. As expected, solar activity indices such as sunspot number, total solar irradiance, 10.7 cm radio flux, and solar flare occurrence are highly correlated with the flux of magnetic quadrupole component. The dynamic pressure of solar wind is strongly correlated with the dipole flux, which is in anti-phase with Solar Cycle (SC). The geomagnetic activity represented by the Ap index is correlated with higher order multipole components, which show relatively a slow time variation with SC. We also found that the unusually low geomagnetic activity during SC 23 is accompanied by the weak open solar fields compared with those in other SCs. It is argued that such dependences of the SIG parameters on the individual multipole components of the open solar magnetic flux may clarify why some SIG parameters vary in phase with SC and others show seemingly delayed responses to SC variation.

Specification of electron radiation environment at GEO and MEO for surface charging estimates

NASA Astrophysics Data System (ADS)

Ganushkina, N.; Dubyagin, S.; Mateo Velez, J. C.; Liemohn, M. W.

2017-12-01

A series of anomalies at GEO have been attributed to electrons of energy below 100 keV, responsible for surface charging. The process at play is charge deposition on covering insulating surfaces and is directly linked to the space environment at a time scale of a few tens of seconds. Even though modern satellites benefited from the analysis of past flight anomalies and losses, it appears that surface charging remains a source of problems. Accurate specification of the space environment at different orbits is of a key importance. We present the operational model for low energy (< 200 keV) electrons in the inner magnetosphere, Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM). This model has been operating online since March 2013 (http://fp7-spacecast.eu and imptam.fmi.fi) and it is driven by the real time solar wind and IMF parameters and by the real time Dst index. The presented model provides the low energy electron flux at all L-shells and at all satellite orbits, when necessary. IMPTAM is used to simulate the fluxes of low energy electrons inside the Earth's magnetosphere at the time of severe events measured on LANL satellites at GEO. There is no easy way to say what will be the flux of keV electrons at MEO when surface charging events are detected at GEO than to use a model. The maximal electron fluxes obtained at MEO (L = 4.6) within a few tens of minutes hours following the LANL events at GEO have been extracted to feed a database of theoretical/numerical worst-case environments for surface charging at MEO. All IMPTAM results are instantaneous, data have not been average. In order to validate the IMPTAM output at MEO, we conduct the statistical analysis of measured electron fluxes onboard Van Allen Probes (ECT HOPE (20 eV-45 keV) and ECT MagEIS (30 - 300 keV) at distances of 4.6 Re. IMPTAM e- flux at MEO is used as input to SPIS, the Spacecraft Plasma Interaction System Software toolkit for spacecraft-plasma interactions and spacecraft charging modelling (http://dev.spis.org/projects/spine/home/spis). The research leading to these results was funded by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement No 606716 SPACESTORM and by the European Union's Horizon 2020 research and innovation programme under grant agreement No 637302 PROGRESS.

Stable near-surface ocean salinity stratifications due to evaporation observed during STRASSE

NASA Astrophysics Data System (ADS)

Asher, William E.; Jessup, Andrew T.; Clark, Dan

2014-05-01

Under conditions with a large solar flux and low wind speed, a stably stratified warm layer forms at the ocean surface. Evaporation can then lead to an increase in salinity in the warm layer. A large temperature gradient will decrease density enough to counter the density increase caused by the salinity increase, forming a stable positive salinity anomaly at the surface. If these positive salinity anomalies are large in terms of the change in salinity from surface to the base of the gradient, if their areal coverage is a significant fraction of the satellite footprint, and if they persist long enough to be in the satellite field of view, they could be relevant for calibration and validation of L-band microwave salinity measurements. A towed, surface-following profiler was deployed from the N/O Thalassa during the Subtropical Atlantic Surface Salinity Experiment (STRASSE). The profiler measured temperature and conductivity in the surface ocean at depths of 10, 50, and 100 cm. The measurements show that positive salinity anomalies are common at the ocean surface for wind speeds less than 4 m s-1 when the average daily insolation is >300 W m-2 and the sea-to-air latent heat flux is greater than zero. A semiempirical model predicts the observed dependence of measured anomalies on environmental conditions. However, the model results and the field data suggest that these ocean surface salinity anomalies are not large enough in terms of the salinity difference to significantly affect microwave radiometric measurements of salinity.

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.