Paleoclimatological perspective on the hydrometeorology of the Mekong Basin

NASA Astrophysics Data System (ADS)

Räsänen, T. A.; Lehr, C.; Mellin, I.; Ward, P. J.; Kummu, M.

2012-11-01

During recent decades the Mekong River has experienced substantial interannual variations between droughts and major floods. The causes of these variations have been sought in climate change and dam construction. However, so far little research has addressed whether these recent variations are significantly different to long-term variations in the past. Hence, the aim of our paper is to place the recent variations between droughts and floods into a historical and paleoclimatological context. To achieve this we analysed the Mekong's meteorological conditions over the period 1300-2005 with a basin scale approach by using the Monsoon Asia Drought Atlas (MADA), which is a Palmer Drought Severity Index (PDSI) dataset derived from tree-ring growth records. The correlation analyses, both in time and frequency domains, showed correlation between MADA and the Mekong's discharge over the period 1910-2005 which suggests that MADA can be used as proxy for the hydrometeorology of the Mekong Basin. We found that the meteorological conditions of the Mekong varied at multi-annual, decadal and centennial scales over the study period. We found two especially distinct features: firstly, multi-annual and decadal variation between prolonged wet and dry epochs; and secondly, epochs with higher or lower interannual variability between very dry and wet years. Furthermore we found two epochs with exceptionally large interannual variability, one at the beginning of 17th century and the other in the post 1950 epoch. Both epochs are characterized by distinct increases in variability between very wet and dry years. The variability in the post 1950 epoch is much higher compared to any of the other epochs included in this study. Thus, during recent decades the climate in the Mekong has exhibited features that have not been experienced for at least several centuries. These findings call for further climate research, particularly regarding increased climate variability, and resilient adaptation and development approaches in the basin.

Satellite orbit and data sampling requirements

NASA Technical Reports Server (NTRS)

Rossow, William

1993-01-01

Climate forcings and feedbacks vary over a wide range of time and space scales. The operation of non-linear feedbacks can couple variations at widely separated time and space scales and cause climatological phenomena to be intermittent. Consequently, monitoring of global, decadal changes in climate requires global observations that cover the whole range of space-time scales and are continuous over several decades. The sampling of smaller space-time scales must have sufficient statistical accuracy to measure the small changes in the forcings and feedbacks anticipated in the next few decades, while continuity of measurements is crucial for unambiguous interpretation of climate change. Shorter records of monthly and regional (500-1000 km) measurements with similar accuracies can also provide valuable information about climate processes, when 'natural experiments' such as large volcanic eruptions or El Ninos occur. In this section existing satellite datasets and climate model simulations are used to test the satellite orbits and sampling required to achieve accurate measurements of changes in forcings and feedbacks at monthly frequency and 1000 km (regional) scale.

Using Space Lidar Observations to Decompose Longwave Cloud Radiative Effect Variations Over the Last Decade

NASA Astrophysics Data System (ADS)

Vaillant de Guélis, Thibault; Chepfer, Hélène; Noel, Vincent; Guzman, Rodrigo; Winker, David M.; Plougonven, Riwal

2017-12-01

Measurements of the longwave cloud radiative effect (LWCRE) at the top of the atmosphere assess the contribution of clouds to the Earth warming but do not quantify the cloud property variations that are responsible for the LWCRE variations. The CALIPSO space lidar observes directly the detailed profile of cloud, cloud opacity, and cloud cover. Here we use these observations to quantify the influence of cloud properties on the variations of the LWCRE observed between 2008 and 2015 in the tropics and at global scale. At global scale, the method proposed here gives good results except over the Southern Ocean. We find that the global LWCRE variations observed over ocean are mostly due to variations in the opaque cloud properties (82%); transparent cloud columns contributed 18%. Variation of opaque cloud cover is the first contributor to the LWCRE evolution (58%); opaque cloud temperature is the second contributor (28%).

Cyclic precipitation variation on the western Loess Plateau of China during the past four centuries

PubMed Central

Tan, Liangcheng; An, Zhisheng; Huh, Chih-An; Cai, Yanjun; Shen, Chuan-Chou; Shiau, Liang-Jian; Yan, Libin; Cheng, Hai; Edwards, R. Lawrence

2014-01-01

Precipitation variation on the Loess Plateau (LP) of China is not only important for rain-fed agriculture in this environmentally sensitive region, but also critical for the water and life securities over the whole Yellow River basin. Here we reconstruct high resolution precipitation variation on the western LP during the past 370 years by using two replicated, annually-laminated stalagmites. Spatial analysis suggests that the reconstruction can be also representative for the whole LP region. The precipitation variations show a significant quasi-50 year periodicity during the last 370 years, and have an important role in determining the runoff of the middle Yellow River. The main factor controlling the decadal scale variations and long-term trend in precipitation over this region is southerly water vapour transport associated with the Asian summer monsoon. The Pacific Decadal Oscillation is also an important influence on precipitation variation in this region, as it can affect the East Asian summer monsoon and the West Pacific Subtropical High. PMID:25223372

GISS GCMAM Modeled Climate Responses to Total and Spectral Solar Forcing on Decadal and Centennial Time Scales

NASA Astrophysics Data System (ADS)

Wen, Guoyong; Cahalan, Robert; Rind, David; Jonas, Jeffrey; Pilewskie, Peter; Harder, Jerry

2014-05-01

We examine the influence of the SORCE (Solar Radiation and Climate Experiment) SIM (Spectral Irradiance Monitor) observed spectral solar irradiance (SSI) variations on Earth's climate. We apply two reconstructed spectral solar forcing scenarios, one SIM based, the other based on the SATIRE (Spectral And Total Irradiance REconstruction) model, as inputs to the GISS (Goddard Institute for Space Studies) GCMAM (Global Climate Middle Atmosphere Model) to examine the climate responses on decadal and centennial time scales. We show that the atmosphere has different temperature, ozone, and dynamic responses to the two solar spectral forcing scenarios, even when the variations in TSI (Total Solar Irradiance) are the same. We find that solar variations under either scenario contribute a small fraction of the observed temperature increase since the industrial revolution. The trend of global averaged surface air temperature response to the SIM-based solar forcing is 0.02 °C/century, about half of the temperature trend to the SATIRE-based SSI. However the temporal variation of the surface air temperature for the SIM-based solar forcing scenario is much larger compared to its SATIRE counterpart. Further research is required to examine TSI and SSI variations in the ascending phase of solar cycle 24, to assess their implications for the solar influence on climate.

GISS GCMAM Modeled Climate Responses to Total and Spectral Solar Forcing on Decadal and Centennial Time Scales

NASA Astrophysics Data System (ADS)

Wen, G.; Cahalan, R. F.; Rind, D. H.; Jonas, J.; Pilewskie, P.; Harder, J. W.; Krivova, N.

2014-12-01

We examine the influence of the SORCE (Solar Radiation and Climate Experiment) SIM (Spectral Irradiance Monitor) observed spectral solar irradiance (SSI) variations on Earth's climate. We apply two reconstructed spectral solar forcing scenarios, one SIM based, the other based on the SATIRE (Spectral And Total Irradiance REconstruction) model, as inputs to the GISS (Goddard Institute for Space Studies) GCMAM (Global Climate Middle Atmosphere Model) to examine the climate responses on decadal and centennial time scales. We show that the atmosphere has different temperature, ozone, and dynamic responses to the two solar spectral forcing scenarios, even when the variations in TSI (Total Solar Irradiance) are the same. We find that solar variations under either scenario contribute a small fraction of the observed temperature increase since the industrial revolution. The trend of global averaged surface air temperature response to the SIM-based solar forcing is 0.02 °C/century, about half of the temperature trend to the SATIRE-based SSI. However the temporal variation of the surface air temperature for the SIM-based solar forcing scenario is much larger compared to its SATIRE counterpart. Further research is required to examine TSI and SSI variations in the ascending phase of solar cycle 24, to assess their implications for the solar influence on climate.

Trends and natural variability of North American spring onset as evaluated by a new gridded dataset of spring indices

USGS Publications Warehouse

Ault, Toby R.; Schwartz, Mark D.; Zurita-Milla, Raul; Weltzin, Jake F.; Betancourt, Julio L.

2015-01-01

Climate change is expected to modify the timing of seasonal transitions this century, impacting wildlife migrations, ecosystem function, and agricultural activity. Tracking seasonal transitions in a consistent manner across space and through time requires indices that can be used for monitoring and managing biophysical and ecological systems during the coming decades. Here a new gridded dataset of spring indices is described and used to understand interannual, decadal, and secular trends across the coterminous United States. This dataset is derived from daily interpolated meteorological data, and the results are compared with historical station data to ensure the trends and variations are robust. Regional trends in the first leaf index range from 20.8 to 21.6 days decade21, while first bloom index trends are between20.4 and 21.2 for most regions. However, these trends are modulated by interannual to multidecadal variations, which are substantial throughout the regions considered here. These findings emphasize the important role large-scale climate modes of variability play in modulating spring onset on interannual to multidecadal time scales. Finally, there is some potential for successful subseasonal forecasts of spring onset, as indices from most regions are significantly correlated with antecedent large-scale modes of variability.

Modeling Climate Responses to Spectral Solar Forcing on Centennial and Decadal Time Scales

NASA Technical Reports Server (NTRS)

Wen, G.; Cahalan, R.; Rind, D.; Jonas, J.; Pilewskie, P.; Harder, J.

2012-01-01

We report a series of experiments to explore clima responses to two types of solar spectral forcing on decadal and centennial time scales - one based on prior reconstructions, and another implied by recent observations from the SORCE (Solar Radiation and Climate Experiment) SIM (Spectral 1rradiance Monitor). We apply these forcings to the Goddard Institute for Space Studies (GISS) Global/Middle Atmosphere Model (GCMAM). that couples atmosphere with ocean, and has a model top near the mesopause, allowing us to examine the full response to the two solar forcing scenarios. We show different climate responses to the two solar forCing scenarios on decadal time scales and also trends on centennial time scales. Differences between solar maximum and solar minimum conditions are highlighted, including impacts of the time lagged reSponse of the lower atmosphere and ocean. This contrasts with studies that assume separate equilibrium conditions at solar maximum and minimum. We discuss model feedback mechanisms involved in the solar forced climate variations.

Rainfall Climatology over Asir Region, Saudi Arabia

NASA Astrophysics Data System (ADS)

Sharif, H.; Furl, C.; Al-Zahrani, M.

2012-04-01

Arid and semi-arid lands occupy about one-third of the land surface of the earth and support about one-fifth of the world population. The Asir area in Saudi Arabia is an example of these areas faced with the problem of maintaining sustainable water resources. This problem is exacerbated by the high levels of population growth, land use changes, increasing water demand, and climate variability. In this study, the characteristics of decade-scale variations in precipitation are examined in more detail for Asir region. The spatio-temporal distributions of rainfall over the region are analyzed. The objectives are to identify the sensitivity, magnitude, and range of changes in annual and seasonal evapotranspiration resulting from observed decade-scale precipitation variations. An additional objective is to characterize orographic controls on the space-time variability of rainfall. The rainfall data is obtained from more than 30 rain gauges spread over the region.

Recent variations in seasonality of temperature and precipitation in Canada, 1976-95

NASA Astrophysics Data System (ADS)

Whitfield, Paul H.; Bodtker, Karin; Cannon, Alex J.

2002-11-01

A previously reported analysis of rehabilitated monthly temperature and precipitation time series for several hundred stations across Canada showed generally spatially coherent patterns of variation between two decades (1976-85 and 1986-95). The present work expands that analysis to finer time scales and a greater number of stations. We demonstrate how the finer temporal resolution, at 5 day or 11 day intervals, increases the separation between clusters of recent variations in seasonal patterns of temperature and precipitation. We also expand the analysis by increasing the number of stations from only rehabilitated monthly data sets to rehabilitated daily sets, then to approximately 1500 daily observation stations. This increases the spatial density of data and allows a finer spatial resolution of patterns between the two decades. We also examine the success of clustering partial records, i.e. sites where the data record is incomplete. The intent of this study was to be consistent with previous work and explore how greater temporal and spatial detail in the climate data affects the resolution of patterns of recent climate variations. The variations we report for temperature and precipitation are taking place at different temporal and spatial scales. Further, the spatial patterns are much broader than local climate regions and ecozones, indicating that the differences observed may be the result of variations in atmospheric circulation.

ENSO/PDO-Like Variability of Tropical Ocean Surface Energy Fluxes Over the Satellite Era

NASA Technical Reports Server (NTRS)

Robertson, F. R.; Miller, Tim L.

2008-01-01

Recent variations of tropical climate on interannual to near-decadal scales have provided a useful target for studying the nature of climate feedback processes. A strong warm / cold ENSO couplet (e.g. 1997-2000) along with several subsequent weaker events are prominent interannual signals that are part of an apparent longer term strengthening of the Walker circulation during the mid to late 1990's with some weakening thereafter. Decadal scale changes in tropical SST structure during the 1990s are accompanied by focusing of precipitation over the Indo-Pacific warm pool and an increase in tropical ocean evaporation of order 1.0 % /decade. Associated with ENSO and PDO-like tropical SST changes are surface freshwater and radiative fluxes which have important implications for heat and energy transport variations. In this study we examine how surface fluxes attending interannual to decadal SST fluctuations, e.g. precipitation (GPCP, TRMM), turbulent fluxes (OAFlux), and radiative fluxes (ERBE/CERES, SRB) are coupled. Using these data we analyze vertically-integrated divergence of moist static energy, divMSE, and its dry static energy and latent energy components. We examine consistency between these data sets and explore relationships between SST variations, flux changes and modulation of tropical Walker and Hadley circulations. Strong signatures ofMSE flux transport linking ascending and descending regions of tropical circulations are found. Relative strengths of these fluxes and transports are interpreted as a measure of efficiency in the overall process of tropical heat balance during episodes of warm or cold tropical SST.

The decadal-scale variation of the South Asian summer monsoon onset and its connection with the PDO

NASA Astrophysics Data System (ADS)

Watanabe, T.; Yamazaki, K.

2013-12-01

The summer Asian monsoon shows the abrupt increase of precipitation on the onset phase. It is an interesting and important problem when the summer monsoon onset occurs because natural resources, such as water and renewable energy agricultural product, are influenced by the variation of the summer Asian monsoon. Some researchers suggested the advance of the Asian summer monsoon onset in recent decades. We investigated the variation of the Asian monsoon onset using the long-term onset data over Kerala, a state in the southwest region of India, for 1948-2011. We discuss three main questions: 1) how is the variation of the monsoon onset date in the long-term period, 2) how the variation of the onset date is related to variations of atmospheric circulation and SST, and 3) what is the mechanism of such variation. Our main method is composite analysis using monthly-mean data. Though the onset date over Kerala shows the trend toward the early onset in recent three decades, such a trend is not observed in the whole period. It is noteworthy that the onset over Kerala shows the interannual variation on a multi-decadal scale. As regards the early onset years of Kerala, the summer monsoon onset is early over the following regions: the region from the southern Arabian Sea to southwestern India, the region from the southern Bay of Bengal to the Indochina Peninsula and the western North Pacific Ocean. On the other hand, the onset is late over southern China, Taiwan and the northern Philippine Sea. In early onset years of Kerala, the sea surface temperature over the northern Pacific Ocean is very similar to the negative PDO. The stationary wave train related with the negative PDO reaches into the Central Asia region, generates warm anomaly there and hence intensifies the land-sea thermal contrast there, which promotes the summer monsoon onset over South and Southeast Asia. Though the correlation between the onset over Kerala and the PDO is weak before 1976, it becomes high after 1976. The change in the correlation seems to be related to the change of the wave train path. The wave train which propagates from the northern Pacific Ocean to the western Russia can propagate southwards and southeastwards more easily in the period of 1976-2002 than the period of 1958-1975.

A note on Bjerkne's hypothesis for North Atlantic variability

NASA Astrophysics Data System (ADS)

Bryan, Kirk; Stouffer, Ron

1991-01-01

On decadal time-scales the historical surface temperature record over land in the Northern Hemisphere is dominated by polar amplified variations. These variations are coherent with SST anomalies concentrated in the Northwest Atlantic, but extending with lesser amplitude into the North Pacific as well. Bierknes suggested that multi-year SST anomalies in the subpolar North Atlantic were due to irregular changes in the intensity of the thermohaline circulation. In support of the Bjerknes hypothesis there is evidence that winter overturning in the Labrador Sea was suppressed for a brief period from 1967-1969 by a cap of relative fresh water at the surface. Cause and effect are unclear, but this event was associated with a marked cooling of the entire Northern Hemisphere. The difference in SST averaged over the Northern Hemisphere oceans and SST averaged over the Southern Hemisphere oceans from the equator to 40°S is coherent with Sahel summer rainfall on decadal time scales. Empirical evidence is supported by numerical experiments with the British Meteorological Office atmospheric climate model which simulate augmented monsoonal rainfall in the Sahel region of Africa in response to realistic warm SST anomalies in the Northwest Atlantic. A coupled ocean-atmosphere global model exhibits two equilibrium climate states. One has an active thermohaline circulation in the North Atlantic and the other does not. The two climate states provide an extreme example which illustrates the type of large scale air sea interaction Bjerknes visualized as a mechanism for North Atlantic climate variability on decadal time-scales.

Unforced decadal fluctuations in a coupled model of the atmosphere and ocean mixed layer

NASA Technical Reports Server (NTRS)

Barnett, T. P.; Del Genio, A. D.; Ruedy, R. A.

1992-01-01

Global average temperature in a 100-year control run of a model used for greenhouse gas response simulations showed low-frequency natural variability comparable in magnitude to that observed over the last 100 years. The model variability was found to be barotropic in the atmosphere, and located in the tropical strip with largest values near the equator in the Pacific. The model variations were traced to complex, low-frequency interactions between the meridional sea surface temperature gradients in the eastern equatorial Pacific, clouds at both high and low levels, and features of the tropical atmospheric circulation. The variations in these and other model parameters appear to oscillate between two limiting climate states. The physical scenario accounting for the oscillations on decadal time scales is almost certainly not found in the real world on shorter time scales due to limited resolution and the omission of key physics (e.g., equatorial ocean dynamics) in the model. The real message is that models with dynamical limitations can still produce significant long-term variability. Only a thorough physical diagnosis of such simulations and comparisons with decadal-length data sets will allow one to decide if faith in the model results is, or is not, warranted.

Mesoscale to Synoptic Scale Cloud Variability

NASA Technical Reports Server (NTRS)

Rossow, William B.

1998-01-01

The atmospheric circulation and its interaction with the oceanic circulation involve non-linear and non-local exchanges of energy and water over a very large range of space and time scales. These exchanges are revealed, in part, by the related variations of clouds, which occur on a similar range of scales as the atmospheric motions that produce them. Collection of comprehensive measurements of the properties of the atmosphere, clouds and surface allows for diagnosis of some of these exchanges. The use of a multi-satellite-network approach by the International Satellite Cloud Climatology Project (ISCCP) comes closest to providing complete coverage of the relevant range space and time scales over which the clouds, atmosphere and ocean vary. A nearly 15-yr dataset is now available that covers the range from 3 hr and 30 km to decade and planetary. This paper considers three topics: (1) cloud variations at the smallest scales and how they may influence radiation-cloud interactions, and (2) cloud variations at "moderate" scales and how they may cause natural climate variability, and (3) cloud variations at the largest scales and how they affect the climate. The emphasis in this discussion is on the more mature subject of cloud-radiation interactions. There is now a need to begin similar detailed diagnostic studies of water exchange processes.

Forcing of Climate Variations by Mev-gev Particles

NASA Technical Reports Server (NTRS)

Tinsley, Brian A.

1990-01-01

Changes in ionization production in the lower stratosphere by a few percent during Forbush decreases have been shown to correlate well with changes in winter tropospheric dynamics by a similar relatively small amount. Changes in ionization production by tens of percent on the decadal time scale have been shown to be correlated with changes in winter storm frequencies by tens of percent in the western North Atlantic. Changes in total solar irradiance or solar UV do not have time variations to match the tropospheric variations on the day to day time scales discussed here. Forcing related to magnetic activity is not supported. Thus solar wind/MeV-GeV particle changes appear to be the only viable forcing function for these day to day variations. If solar wind/particle forcing of a few percent amplitude can produce short term weather responses, then observed changes by tens of percent on the decadal and centennial time scale could produce climate changes on these longer time scales. The changes in circulation involved would produce regional climate changes, as observed. At present the relations between stratospheric ionization, electric fields and chemistry and aerosol and cloud microphysics are as poorly known as the relations between the latter and storm feedback processes. However, the capability for investigating these relationships now exists and has recently been most successfully used for elucidating the stratospheric chemistry and cloud microphysics associated with the Antarctic ozone hole. The economic benefits of being able to predict winter severity on an interannual basis, and the extent to which climate change related to solar variability will add to or substract from the greenhouse effect, should be more than adequate to justify support for research in this area.

Terrestrial Waters and Sea Level Variations on Interannual Time Scale

NASA Technical Reports Server (NTRS)

Llovel, W.; Becker, M.; Cazenave, A.; Jevrejeva, S.; Alkama, R.; Decharme, B.; Douville, H.; Ablain, M.; Beckley, B.

2011-01-01

On decadal to multi-decadal time scales, thermal expansion of sea waters and land ice loss are the main contributors to sea level variations. However, modification of the terrestrial water cycle due to climate variability and direct anthropogenic forcing may also affect sea level. For the past decades, variations in land water storage and corresponding effects on sea level cannot be directly estimated from observations because these are almost non-existent at global continental scale. However, global hydrological models developed for atmospheric and climatic studies can be used for estimating total water storage. For the recent years (since mid-2002), terrestrial water storage change can be directly estimated from observations of the GRACE space gravimetry mission. In this study, we analyse the interannual variability of total land water storage, and investigate its contribution to mean sea level variability at interannual time scale. We consider three different periods that, each, depend on data availability: (1) GRACE era (2003-2009), (2) 1993-2003 and (3) 1955-1995. For the GRACE era (period 1), change in land water storage is estimated using different GRACE products over the 33 largest river basins worldwide. For periods 2 and 3, we use outputs from the ISBA-TRIP (Interactions between Soil, Biosphere, and Atmosphere-Total Runoff Integrating Pathways) global hydrological model. For each time span, we compare change in land water storage (expressed in sea level equivalent) to observed mean sea level, either from satellite altimetry (periods 1 and 2) or tide gauge records (period 3). For each data set and each time span, a trend has been removed as we focus on the interannual variability. We show that whatever the period considered, interannual variability of the mean sea level is essentially explained by interannual fluctuations in land water storage, with the largest contributions arising from tropical river basins.

Spatiotemporal evolution of the chlorophyll a trend in the North Atlantic Ocean.

PubMed

Zhang, Min; Zhang, Yuanling; Shu, Qi; Zhao, Chang; Wang, Gang; Wu, Zhaohua; Qiao, Fangli

2018-01-15

Analyses of the chlorophyll a concentration (chla) from satellite ocean color products have suggested the decadal-scale variability of chla linked to the climate change. The decadal-scale variability in chla is both spatially and temporally non-uniform. We need to understand the spatiotemporal evolution of chla in decadal or multi-decadal timescales to better evaluate its linkage to climate variability. Here, the spatiotemporal evolution of the chla trend in the North Atlantic Ocean for the period 1997-2016 is analyzed using the multidimensional ensemble empirical mode decomposition method. We find that this variable trend signal of chla shows a dipole pattern between the subpolar gyre and along the Gulf Stream path, and propagation along the opposite direction of the North Atlantic Current. This propagation signal has an overlapping variability of approximately twenty years. Our findings suggest that the spatiotemporal evolution of chla during the two most recent decades is part of the multidecadal variations and possibly regulated by the changes of Atlantic Meridional Overturning Circulation, whereas the mechanisms of such evolution patterns still need to be explored. Copyright © 2017 Elsevier B.V. All rights reserved.

Contingent Pacific-Atlantic Ocean influence on multicentury wildfire synchrony over western North America.

PubMed

Kitzberger, Thomas; Brown, Peter M; Heyerdahl, Emily K; Swetnam, Thomas W; Veblen, Thomas T

2007-01-09

Widespread synchronous wildfires driven by climatic variation, such as those that swept western North America during 1996, 2000, and 2002, can result in major environmental and societal impacts. Understanding relationships between continental-scale patterns of drought and modes of sea surface temperatures (SSTs) such as El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) may explain how interannual to multidecadal variability in SSTs drives fire at continental scales. We used local wildfire chronologies reconstructed from fire scars on tree rings across western North America and independent reconstructions of SST developed from tree-ring widths at other sites to examine the relationships of multicentury patterns of climate and fire synchrony. From 33,039 annually resolved fire-scar dates at 238 sites (the largest paleofire record yet assembled), we examined forest fires at regional and subcontinental scales. Since 1550 CE, drought and forest fires covaried across the West, but in a manner contingent on SST modes. During certain phases of ENSO and PDO, fire was synchronous within broad subregions and sometimes asynchronous among those regions. In contrast, fires were most commonly synchronous across the West during warm phases of the AMO. ENSO and PDO were the main drivers of high-frequency variation in fire (interannual to decadal), whereas the AMO conditionally changed the strength and spatial influence of ENSO and PDO on wildfire occurrence at multidecadal scales. A current warming trend in AMO suggests that we may expect an increase in widespread, synchronous fires across the western U.S. in coming decades.

Geomagnetic field declination: from decadal to centennial scales

NASA Astrophysics Data System (ADS)

Dobrica, Venera; Demetrescu, Crisan; Mandea, Mioara

2018-04-01

Declination annual mean time series longer than 1 century provided by 24 geomagnetic observatories worldwide, together with 5 Western European reconstructed declination series over the last 4 centuries, have been analyzed in terms of the frequency constituents of the secular variation at inter-decadal and sub-centennial timescales of 20-35 and 70-90 years. Observatory and reconstructed time series have been processed by several types of filtering, namely Hodrick-Prescott, running averages, and Butterworth. The Hodrick-Prescott filtering allows us to separate a quasi-oscillation at a decadal timescale, which is assumed to be related to external variations and called the 11-year constituent, from a long-term trend. The latter has been decomposed into two other oscillations called inter-decadal and sub-centennial constituents by applying a Butterworth filtering with cutoffs at 30 and 73 years, respectively. The analysis shows that the generally accepted geomagnetic jerks occur around extrema in the time derivative of the trend and coincide with extrema in the time derivative of the 11-year constituent. The sub-centennial constituent is traced back to 1600 in the five 400-year-long time series and seems to be a major constituent of the secular variation, geomagnetic jerks included.

Tropical cyclone-related socio-economic losses in the western North Pacific region

NASA Astrophysics Data System (ADS)

Welker, C.; Faust, E.

2013-01-01

The western North Pacific (WNP) is the area of the world most frequently affected by tropical cyclones (TCs). However, little is known about the socio-economic impacts of TCs in this region, probably because of the limited relevant loss data. Here, loss data from Munich RE's NatCatSERVICE database is used, a high-quality and widely consulted database of natural disasters. In the country-level loss normalisation technique we apply, the original loss data are normalised to present-day exposure levels by using the respective country's nominal gross domestic product at purchasing power parity as a proxy for wealth. The main focus of our study is on the question of whether the decadal-scale TC variability observed in the Northwest Pacific region in recent decades can be shown to manifest itself economically in an associated variability in losses. It is shown that since 1980 the frequency of TC-related loss events in the WNP exhibited, apart from seasonal and interannual variations, interdecadal variability with a period of about 22 yr - driven primarily by corresponding variations of Northwest Pacific TCs. Compared to the long-term mean, the number of loss events was found to be higher (lower) by 14% (9%) in the positive (negative) phase of the decadal-scale WNP TC frequency variability. This was identified for the period 1980-2008 by applying a wavelet analysis technique. It was also possible to demonstrate the same low-frequency variability in normalised direct economic losses from TCs in the WNP region. The identification of possible physical mechanisms responsible for the observed decadal-scale Northwest Pacific TC variability will be the subject of future research, even if suggestions have already been made in earlier studies.

Impact of warming events on reef-scale temperature variability as captured in two Little Cayman coral Sr/Ca records

NASA Astrophysics Data System (ADS)

von Reumont, J.; Hetzinger, S.; Garbe-Schönberg, D.; Manfrino, C.; Dullo, W.-Chr.

2016-03-01

The rising temperature of the world's oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events. The susceptibility of corals to temperature stress varies on local and regional scales. Insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature (SST) products often do not resolve reef-scale variations. Here we use 42 years (1970-2012) of coral Sr/Ca data to reconstruct seasonal- to decadal-scale SST variations in two adjacent but distinct reef environments at Little Cayman, Cayman Islands. Our results indicate that two massive Diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events. Coral Sr/Ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations (>33°C). Surprisingly, coral Sr/Ca from the deeper fore reef is strongly affected by thermal stress events, although seasonal temperature extremes and mean SSTs at this site are reduced compared to the lagoon. The shallow lagoon coral showed decadal variations in Sr/Ca, supposedly related to the modulation of lagoonal temperature through varying tidal water exchange, influenced by the 18.6 year lunar nodal cycle. Our results show that reef-scale SST variability can be much larger than suggested by satellite SST measurements. Thus, using coral SST proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs.

Interannual and Decadal Variability of Summer Rainfall over South America

NASA Technical Reports Server (NTRS)

Zhou, Jiayu; Lau, K.-M.

1999-01-01

Using the CPC (Climate Prediction Center) Merged Analysis of Precipitation product along with the Goddard Earth Observing System reanalysis and the Climate Analysis Center sea surface temperature (SST) data, we conduct a diagnostic study of the interannual and decadal scale variability of summer rainfall over South America. Results show three leading modes of rainfall variation identified with interannual, decadal, and long-term trend variability. Together, these modes explain more than half the total variance. The first mode is highly correlated with El Nino/southern oscillation (ENSO), showing severe drought over Northeast Brazil and copious rainfall over the Ecuador coast and the area of Uruguay-Southern Brazil in El Nino years. This pattern is attributed to the large scale zonal shift of the Walker circulation and local Hadley cell anomaly induced by positive (negative) SST anomaly over the eastern (western) equatorial Pacific. In El Nino years, two convective belts indicated by upper tropospheric velocity potential trough and mid-tropospheric rising motion, which are somewhat symmetric about the equator, extend toward the northeast and the southeast into the tropical North and South Atlantic respectively. Sandwiched between the ascent is a region of descending motion over Northeast Brazil. The southern branch of the anomalous Hadley cell is dynamically linked to the increase of rainfall over Uruguay-Southern Brazil. The regional response of anomalous circulation shows a stronger South American summer monsoon and an enhanced (weakened) subtropical high over the South Atlantic (South Pacific) Ocean. The decadal variation displays a meridional shift of the Intertropical Convergence Zone (ITCZ), which is tie to the anomalous cross-equatorial SST gradient over the Atlantic and the eastern Pacific. In conjunction with this mode is a large scale mass swing between the polar regions and midlatitudes in both hemispheres. Over the South Atlantic and the South Pacific, the changes of the strength of the subtropical high and the associated surface wind are dynamically consistent with the distribution of local SST anomalies, suggesting the importance of the atmospheric forcing in the decadal time scale. The decadal mode also presents a weak summer monsoon in its positive phase, which reduces the moisture supply from the equatorial Atlantic and the Amazon Basin and results in negative rainfall anomalies over the central Andes and Gran Chaco. The long-term trend shows decrease of rainfall from the northwest coast to the southeast subtropical region and a southward shift of Atlantic ITCZ that leads to increased rainfall over northern and eastern Brazil. Our result shows a close link of this mode to the observed SST warming trend over the subtropical South Atlantic and a remote connection to the interdecadal SST variation over the extratropical North Atlantic found in previous studies.

Long-term reconstructions of total solar irradiance

NASA Astrophysics Data System (ADS)

Krivova, Natalie; Solanki, Sami K.; Dasi Espuig, Maria

2012-07-01

Solar irradiance is the main external driver of the Earth's climate, although its relative contribution compared to other internal and anthropogenic factors is not yet well determined. Variations of total solar irradiance have being measured for over three decades and are relatively well understood. Reconstructions of the irradiance into the past remain, however, rather uncertain. In particular, the magnitude of the secular change is highly debated. The reason is the lack of direct and well-sampled proxies of solar magnetic activity on time scales longer than a few decades. Reconstructions on time scales of centuries rely on sunspot observations available since 1610. Reconstructions on millennial time scales use concentrations of the cosmogenic isotopes in terrestrial archives. We will review long-term reconstructions of the solar irradiance using the SATIRE set of models, compare them with other recent models and discuss the remaining uncertainties.

The genetic architecture of coronary artery disease: current knowledge and future opportunities

USDA-ARS?s Scientific Manuscript database

Recent Findings Large-scale studies in human populations, coupled with rapid advances in genetic technologies over the last decade, have clearly established the association of common genetic variation with risk of CAD. However, the effect sizes of the susceptibility alleles are for the most part mod...

Decadal predictability of winter windstorm frequency in Eastern Europe

NASA Astrophysics Data System (ADS)

Höschel, Ines; Grieger, Jens; Ulbrich, Uwe

2017-04-01

Winter windstorms are one of the most impact relevant extreme-weather events in Europe. This study is focussed on windstorm frequency in Eastern Europe at multi-year time scale. Individual storms are identified by using 6-hourly 10m-wind-fields. The impact-oriented tracking algorithm is based on the exceedance of the local 98 percentile of wind speed and a minimum duration of 18 hours. Here, storm frequency is the number of 1000km-footprints of identified windstorms touching the location during extended boreal winter from October to March. The temporal development of annual storm frequencies in Eastern Europe shows variations on a six to fifteen years period. Higher than normal windstorm frequency occurred end of the 1950s and in beginning of the seventies, while lower than normal frequency were around 1960 and in the forties, for example. The correlation between bandpass filtered storm frequency and North Atlantic sea surface temperature shows a significant pattern with a positive correlation in the subtropical East Atlantic and significant negative correlations in the Gulfstream region. The relationship between these multi-year variations and predictability on decadal time scales is discussed. The resulting skill of winter wind storms in the German decadal prediction system MiKlip, based on the numerical earth system model MPI-ESM, will be presented.

Trends and Natural Variability of Spring Onset in the Coterminous United States as Evaluated by a New Gridded Dataset of Spring Indices

NASA Astrophysics Data System (ADS)

Ault, T.; Schwartz, M. D.; Zurita-Milla, R.; Weltzin, J. F.; Betancourt, J. L.

2015-12-01

Climate change is expected to modify the timing of seasonal transitions this century, impacting wildlife migrations, ecosystem function, and agricultural activity. Tracking seasonal transitions in a consistent manner across space and through time requires indices that can be used for monitoring and managing biophysical and ecological systems during the coming decades. Here a new gridded dataset of spring indices is described and used to understand interannual, decadal, and secular trends across the coterminous US. This dataset is derived from daily interpolated meteorological data, and results are compared with historical station data to ensure the trends and variations are robust. Regional trends in the first leaf index range from -0.8 to -1.6 days per decade, while first bloom index trends are between -0.4 and -1.2 for most regions. However, these trends are modulated by interannual to multidecadal variations, which are substantial throughout the regions considered here. These findings emphasize the important role large-scale climate modes of variability play in modulating spring onset on interannual to multidecadal timescales. Finally, there is some potential for successful sub-seasonal forecasts of spring onset, as indices from most regions are significantly correlated with antecedent large-scale modes of variability.

Precipitation and temperature changes in the major Chinese river basins during 1957-2013 and links to sea surface temperature

NASA Astrophysics Data System (ADS)

Tian, Qing; Prange, Matthias; Merkel, Ute

2016-05-01

The variation characteristics of precipitation and temperature in the three major Chinese river basins (Yellow River, Yangtze River and Pearl River) in the period of 1957-2013 were analyzed on an annual and seasonal basis, as well as their links to sea surface temperature (SST) variations in the tropical Pacific and Indian Ocean on both interannual and decadal time scales. Annual mean temperature of the three river basins increased significantly overall since 1957, with an average warming rate of about 0.19 °C/10a, but the warming was characterized by a staircase form with steps around 1987 and 1998. The significant increase of annual mean temperature could mostly be attributed to the remarkable warming trend in spring, autumn and winter. Warming rates in the northern basins were generally much higher than in the southern basins. However, both the annual precipitation and seasonal mean precipitation of the three river basins showed little change in the study area average, but distinct interannual variations since 1957 and clear regional differences. An overall warming-wetting tendency was found in the northwestern and southeastern river basins in 1957-2013, while the central regions tended to become warmer and drier. Results from a Maximum Covariance Analysis (MCA) showed that the interannual variations of seasonal mean precipitation and surface air temperature over the three river basins were both associated with the El Niño-Southern Oscillation (ENSO) since 1957. ENSO SST patterns affected precipitation and surface air temperature variability throughout the year, but with very different response patterns in the different seasons. For instance, temperature in most of the river basins was positively correlated with central-eastern equatorial Pacific SST in winter and spring, but negatively correlated in summer and autumn. On the decadal time scale, the seasonal mean precipitation and surface air temperature variations were strongly associated with the Pacific Quasi-Decadal Oscillation.

A 320-year AMM+SOI Index Reconstruction from Historical Atlantic Tropical Cyclone Records

NASA Astrophysics Data System (ADS)

Chenoweth, M.; Divine, D.

2010-12-01

Trends in the frequency of North Atlantic tropical cyclones, including major hurricanes, are dominated by those originating in the deep tropics. In addition, these tropical cyclones are stronger when making landfall and their total power dissipation is higher than storms forming elsewhere in the Atlantic basin. Both the Atlantic Meridional Mode (AMM) and El Nino-Southern Oscillation (ENSO) are the leading modes of coupled air-sea interaction in the Atlantic and Pacific, respectively, and have well-established relationships with Atlantic hurricane variability. Here we use a 320-year record of tropical cyclone activity in the Lesser Antilles region of the North Atlantic from historical manuscript and newspaper records to reconstruct a normalized seasonal (July-October) index combining the Southern Oscillation Index (SOI) and AMM employing both the modern analog technique and back-propagation artificial neural networks. Our results indicate that the AMM+SOI index since 1690 shows no long-term trend but is dominated by both short-term (<10 years) and long-term (quasi-decadal to bi-decadal) variations. The decadal-scale variation is consistent with both instrumental and proxy records elsewhere from the global tropics. Distinct periods of high and low index values, corresponding to high and low tropical cyclone frequency, are regularly-appearing features in the record and provides further evidence that natural decadal -scale variability in Atlantic tropical cyclone frequency must be accounted for when determining trends in records and attribution of climate change.

Variations/Changes in Daily Precipitation Extremes Derived from Satellite-Based Products

NASA Astrophysics Data System (ADS)

Gu, G.; Adler, R. F.

2017-12-01

Interannual/decadal-scale variations/changes in daily precipitation extremes are investigated by means of satellite-based high-spatiotemporal resolution precipitation products, including TRMM-TMPA, PERSIANN-CDR-Daily, GPCP 1DD, etc. Extreme precipitation indices at grids are first defined, including the maximum daily precipitation amount (Rx1day), the simple precipitation intensity index (SDII), the conditional (Rcond) daily precipitation rate (Pr>0 mm day-1), and monthly frequencies of rainy (FOCc) and wet (FOCw) days. Other two precipitation intensity indices, i.e., mean daily precipitation rates for Pr ≥10 mm day-1 (Pr10II) and for Pr ≥ 20 mm day-1 (Pr20II), are also constructed. Consistency analyses of daily extreme indices among these data sets are then performed by comparing corresponding averages over large domains such as tropical (30oN-30oS) land, ocean, land+ocean, for their common period (post-1997). This can provide a preliminary uncertainty analysis of these data sets in describing daily extreme precipitation events. Discrepancies can readily be found among these products regarding the magnitudes of area-averaged extreme indices. However, generally consistent temporal variations can be found among the indices derived from different satellite products. Interannual variability in daily precipitation extremes are then examined and compared at grids by exploring their relations with the El Nino-Southern Oscillation (ENSO). Linear correlation and composite analyses are used to examine the impact of ENSO on these extreme indices at grids and over large domains during the post-1997 period. Decadal-scale variability/change in daily extreme events is further examined by using the PERSIANN-CDR-Daily that can cover the entire post-1983 period, based on its general consistency with other two products during the post-1979 period. We specifically focus on exploring and discriminating the effects of decadal-scale internal variability such as the Pacific Decadal Oscillation (PDO) and anthropogenic forcings including the greenhouse-gases (GHG) related warming. Comparisons are also made over global land with the results from two gridded daily rain-gauge products, GPCC Full-record daily (1988-2013) and NOAA/CPC Unified daily (1979-present).

Interannual Atmospheric Variability Simulated by a Mars GCM: Impacts on the Polar Regions

NASA Technical Reports Server (NTRS)

Bridger, Alison F. C.; Haberle, R. M.; Hollingsworth, J. L.

2003-01-01

It is often assumed that in the absence of year-to-year dust variations, Mars weather and climate are very repeatable, at least on decadal scales. Recent multi-annual simulations of a Mars GCM reveal however that significant interannual variations may occur with constant dust conditions. In particular, interannual variability (IAV) appears to be associated with the spectrum of atmospheric disturbances that arise due to baroclinic instability. One quantity that shows significant IAV is the poleward heat flux associated with these waves. These variations and their impacts on the polar heat balance will be examined here.

Consistency of Estimated Global Water Cycle Variations Over the Satellite Era

NASA Technical Reports Server (NTRS)

Robertson, F. R.; Bosilovich, M. G.; Roberts, J. B.; Reichle, R. H.; Adler, R.; Ricciardulli, L.; Berg, W.; Huffman, G. J.

2013-01-01

Motivated by the question of whether recent indications of decadal climate variability and a possible "climate shift" may have affected the global water balance, we examine evaporation minus precipitation (E-P) variability integrated over the global oceans and global land from three points of view-remotely sensed retrievals / objective analyses over the oceans, reanalysis vertically-integrated moisture convergence (MFC) over land, and land surface models forced with observations-based precipitation, radiation and near-surface meteorology. Because monthly variations in area-averaged atmospheric moisture storage are small and the global integral of moisture convergence must approach zero, area-integrated E-P over ocean should essentially equal precipitation minus evapotranspiration (P-ET) over land (after adjusting for ocean and land areas). Our analysis reveals considerable uncertainty in the decadal variations of ocean evaporation when integrated to global scales. This is due to differences among datasets in 10m wind speed and near-surface atmospheric specific humidity (2m qa) used in bulk aerodynamic retrievals. Precipitation variations, all relying substantially on passive microwave retrievals over ocean, still have uncertainties in decadal variability, but not to the degree present with ocean evaporation estimates. Reanalysis MFC and P-ET over land from several observationally forced diagnostic and land surface models agree best on interannual variations. However, upward MFC (i.e. P-ET) reanalysis trends are likely related in part to observing system changes affecting atmospheric assimilation models. While some evidence for a low-frequency E-P maximum near 2000 is found, consistent with a recent apparent pause in sea-surface temperature (SST) rise, uncertainties in the datasets used here remain significant. Prospects for further reducing uncertainties are discussed. The results are interpreted in the context of recent climate variability (Pacific Decadal Oscillation, Atlantic Meridional Overturning), and efforts to distinguish these modes from longer-term trends.

Variable solar irradiance as a plausible agent for multidecadal variations in the Arctic-wide surface air temperature record of the past 130 years

NASA Astrophysics Data System (ADS)

Soon, Willie W.-H.

2005-08-01

This letter offers new evidence motivating a more serious consideration of the potential Arctic temperature responses as a consequence of the decadal, multidecadal and longer-term persistent forcing by the ever-changing solar irradiance both in terms of total solar irradiance (TSI, i.e., integrated over all wavelengths) and the related UV irradiance. The support for such a solar modulator can be minimally derived from the large (>75%) explained variance for the decadally-smoothed Arctic surface air temperatures (SATs) by TSI and from the time-frequency structures of the TSI and Arctic SAT variability as examined by wavelet analyses. The reconstructed Arctic SAT time series based on the inverse wavelet transform, which includes decadal (5-15 years) and multidecadal (40-80 years) variations and a longer-term trend, contains nonstationary but persistent features that are highly correlated with the Sun's intrinsic magnetic variability especially on multidecadal time scales.

Analysis of the Nonlinear Trends and Non-Stationary Oscillations of Regional Precipitation in Xinjiang, Northwestern China, Using Ensemble Empirical Mode Decomposition

PubMed Central

Guo, Bin; Chen, Zhongsheng; Guo, Jinyun; Liu, Feng; Chen, Chuanfa; Liu, Kangli

2016-01-01

Changes in precipitation could have crucial influences on the regional water resources in arid regions such as Xinjiang. It is necessary to understand the intrinsic multi-scale variations of precipitation in different parts of Xinjiang in the context of climate change. In this study, based on precipitation data from 53 meteorological stations in Xinjiang during 1960–2012, we investigated the intrinsic multi-scale characteristics of precipitation variability using an adaptive method named ensemble empirical mode decomposition (EEMD). Obvious non-linear upward trends in precipitation were found in the north, south, east and the entire Xinjiang. Changes in precipitation in Xinjiang exhibited significant inter-annual scale (quasi-2 and quasi-6 years) and inter-decadal scale (quasi-12 and quasi-23 years). Moreover, the 2–3-year quasi-periodic fluctuation was dominant in regional precipitation and the inter-annual variation had a considerable effect on the regional-scale precipitation variation in Xinjiang. We also found that there were distinctive spatial differences in variation trends and turning points of precipitation in Xinjiang. The results of this study indicated that compared to traditional decomposition methods, the EEMD method, without using any a priori determined basis functions, could effectively extract the reliable multi-scale fluctuations and reveal the intrinsic oscillation properties of climate elements. PMID:27007388

Dynamic Evaluation of Two Decades of WRF-CMAQ Ozone Simulations over the Contiguous United States (2017 CMAS)

EPA Science Inventory

Weather Research and Forecasting (WRF)–Community Multi-scale Air Quality (CMAQ) model over the contiguous United States is conducted to assess how well the changes in observed ozone air quality are simulated by the model. The changes induced by variations in meteorology and...

On the origin of multi-decadal to centennial Greenland temperature anomalies over the past 800 yr

NASA Astrophysics Data System (ADS)

Kobashi, T.; Shindell, D. T.; Kodera, K.; Box, J. E.; Nakaegawa, T.; Kawamura, K.

2012-11-01

The surface temperature of the Greenland ice sheet is among the most important climate variables for assessing how climate change may impact human societies associated with accelerating sea level rise. However, the causes of multi-decadal-to-centennial temperature changes in Greenland are not well understood, largely owing to short observational records. To examine the causes of the Greenland temperature variability, we calculated the Greenland temperature anomalies (GTA(G-NH)) over the past 800 yr by subtracting the standardised NH temperature from the standardised Greenland temperature. It decomposes the Greenland temperature variation into background climate (NH); Polar amplification; and Regional variability (GTA(G-NH)). The Central Greenland polar amplification factor as expressed by the variance ratio = Greenland/NH is 2.6 over the past 161 yr, and 3.3-4.2 over the past 800 yr. The GTA explains 31-35% of the variation of Greenland temperature in the multi-decadal-to-centennial time scale over the past 800 yr. Another orthogonal component of the Greenland and NH temperatures, GTP(G+NH) (Greenland temperature plus = standardized Greenland temperature + standardized NH temperature) exhibited the multi-decadal variations that were likely induced by large volcanic eruptions, increasing greenhouse gasses, and internal variation of climate. We found that the GTA(G-NH) has been influenced by solar-induced changes in atmospheric circulation patterns such as those produced by North Atlantic Oscillation/Arctic Oscillation (NAO/AO). Climate modelling indicates that the anomaly is also likely linked to solar-paced changes in the Atlantic meridional overturning circulation (AMOC) and to associated changes in northward oceanic heat transport.

Variability of sea surface height and circulation in the North Atlantic: Forcing mechanisms and linkages

NASA Astrophysics Data System (ADS)

Wang, Zeliang; Lu, Youyu; Dupont, Frederic; W. Loder, John; Hannah, Charles; G. Wright, Daniel

2015-03-01

Simulations with a coarse-resolution global ocean model during 1958-2004 are analyzed to understand the inter-annual and decadal variability of the North Atlantic. Analyses of Empirical Orthogonal Functions (EOFs) suggest relationships among basin-scale variations of sea surface height (SSH) and depth-integrated circulation, and the winter North Atlantic Oscillation (NAO) or the East Atlantic Pattern (EAP) indices. The linkages between the atmospheric indices and ocean variables are shown to be related to the different roles played by surface momentum and heat fluxes in driving ocean variability. In the subpolar region, variations of the gyre strength, SSH in the central Labrador Sea and the NAO index are highly correlated. Surface heat flux is important in driving variations of SSH and circulation in the upper ocean and decadal variations of the Atlantic Meridional Overturning Circulation (AMOC). Surface momentum flux drives a significant barotropic component of flow and makes a noticeable contribution to the AMOC. In the subtropical region, momentum flux plays a dominant role in driving variations of the gyre circulation and AMOC; there is a strong correlation between gyre strength and SSH at Bermuda.

Solar Changes and Climate Changes. (Invited)

NASA Astrophysics Data System (ADS)

Feynman, J.

2009-12-01

During the early decades of the Space Age there was general agreement in the scientific community on two facts: (1) sunspot cycles continued without interruption; (2) decadal timescale variations in the solar output has no effect on Earth’s climate. Then in 1976 Jack Eddy published a paper called ‘The Maunder Minimum” in Science magazine arguing that neither of these two established facts was true. He reviewed the observations from the 17th century that show the Sun did not appear to cycle for several decades and he related that to the cold winters in Northern Europe at that time. The paper has caused three decades of hot discussions. When Jack Eddy died on June 10th of this year the arguments were sill going on, and there were no sunspots that day. The Sun was in the longest and deepest solar minimum since 1900. In this talk I will describe the changes in the solar output that have taken place over the last few decades and put them in their historical context. I will also review recent work on the influence of decadal and century scale solar variations on the Earth’s climate. It is clear that this long, deep “solar minimum” is an opportunity to make fundamental progress on our understanding of the solar dynamo and to separate climate change due to the Sun from anthropogenic climate change.

Indo-Pacific sea level variability at multidecadal time scales

NASA Astrophysics Data System (ADS)

Merrifield, M. A.; Thompson, P. R.

2016-12-01

Long tide gauge and atmospheric pressure measurements are used to infer multidecadal fluctuations in trade wind forcing and the associated Indo-Pacific sea level response along coastal and equatorial waveguides. The trade wind variations are marked by a weakening beginning with the late 1970s climate shift and a subsequent return to mean conditions since the early 1990s. These fluctuations covary with multidecadal wind changes at mid-latitudes, as measured by the Pacific Decadal Oscillation or the North Pacific indices; however, the mid-latitude multidecadal variations prior to 1970 or noticeably absent in the inferred trade wind record. The different behavior of tropical and mid-latitude winds support the notion that multidecadal climate variations in the Pacific result from a combination of processes and not a single coherent mode spanning the basin. In particular, the two-decade long satellite altimeter record represents a period of apparent connection between the two regions that was not exhibited earlier in the century.

Corrigendum to "Decadal to millennial variations in water column parameters in pelagic marine environments of the Western Tethys (Carpathian realm) during Middle-Late Jurassic - Evidence from the radiolarian record" [Glob. Planet. Chang. 162 (2018) 148-162

NASA Astrophysics Data System (ADS)

Bąk, Marta; Bąk, Krzysztof; Michalik, Mariola

2018-04-01

The authors regret (Abstract. The causal link between changes in Middle-Late Jurassic radiolarian habitat group abundances, microfacies and water column conditions in the Western Tethys was studied based on the examination of siliceous limestones and cherts from the Tatra Mountains, Central Western Carpathians. Deposition occurred on a morphological high with incised pelagic sedimentation within a tropical zone. High-resolution quantitative analyses of millimetre-thick microlaminae show changes in microfacies constituents that most likely record the fluxes of nutrients and biological activity in superficial waters. Variability of radiolarian assemblages that are classified to represent (i) upwelling and (ii) stratified water taxa suggest successive changes in water conditions that fluctuated between periods of upwelling and periods of formation of a thick, stratified, warm superficial layer above a deep thermocline during middle Bajocian-late Oxfordian time. Such variations would be strongly influenced by ocean-atmosphere global circulation patterns, which are caused by pressure gradients and are the result of Walker circulation along the equatorial part of the Tethys and the Panthalassa Ocean, including the duration of El Niño-like and La Niña-like cycles, which affect sea surface temperature trends on decadal scales. The fluctuations in radiolarian assemblages in the sediments indicate that long-term palaeoceanographic changes occurred on multi-decadal to centennial-scales during the Bajocian, but lengthened in duration to millennial-scale during the Bathonian through the Oxfordian.)

Contribution of Phenological and Physiological Variations on Northern Vegetation Productivity Changes over Last Three Decades

NASA Technical Reports Server (NTRS)

Ganguly, Sangram

2015-01-01

Plant phenology and maximum photosynthetic state determine spatiotemporal variability of gross primary productivity (GPP) of vegetation. Recent warming induced impacts accelerate shifts of phenology and physiological status over Northern vegetated land. Thus, understanding and quantifying these changes are very important. Here, we investigate 1) how vegetation phenology and physiological status (maximum photosynthesis) are evolved over last three decades and 2) how such components (phenology and physiological status) contribute on inter-annual variation of the GPP during the last three decades. We utilized both long-term remotely sensed (GIMMS (Global Inventory Modeling and Mapping Studies), NDVI3g (Normalized Difference Vegetation Index 3rd generation) and MODIS (Moderate Resolution Imaging Spectroradiometer)) to extract larger scale phenology metrics (growing season start, end and duration); and productivity (i.e., growing season integrated vegetation index, GSIVI) to answer these questions. For evaluation purpose, we also introduced field-measured phenology and productivity datasets (e.g., FLUXNET) and possible remotely-sensed and modeled metrics at continental and regional scales. From this investigation, we found that onset of the growing season has advanced by 1.61 days per decade and the growing season end has delayed by 0.67 days per decade over the circumpolar region. This asymmetric extension of growing season results in a longer growing-season trend (2.96 days per decade) and widespread increasing vegetation-productivity trend (2.96 GSIVI per decade) over Northern land. However, the regionally-diverged phenology shift and maximum photosynthetic state contribute differently characterized productivity, inter-annual variability and trend. We quantified that about 50 percent, 13 percent and 6.5 percent of Northern land's inter-annual variability are dominantly controlled by the onset of the growing season, the end of the growing season and the maximum photosynthetic state, respectively. Productivity characterization over the other approximately 30 percent region has been driven by these co-dominant drivers. Our study clearly shows that regionally different contribution of phenological and physiological components on characterizing vegetation production over the last three decades.

Uncertainty in detecting trend: a new criterion and its applications to global SST

NASA Astrophysics Data System (ADS)

Lian, Tao

2017-10-01

In most parts of the global ocean, the magnitude of the long-term linear trend in sea surface temperature (SST) is much smaller than the amplitude of multi-scale internal variation. One can thus use a specific period in a much longer record to arbitrarily determine the sign of long-term trend, which is statistically significant, in regional SST. This could lead to a controversial conclusion on how global SST responded to the anthropogenic forcing in the recent history. In this study, the uncertainty in the linear trend due to multi-scale internal variation is theoretically investigated. It is found that the "estimated" trend will not change its sign only when its magnitude is greater than a theoretical threshold that scales the influence from the multi-scale internal variation. Otherwise, the sign of the "estimated" trend may depend on the period used. The new criterion is found to be superior over the existing methods when the de-trended time series is dominated by the oscillatory term. Applying this new criterion to a global SST reconstruction from 1881 to 2013 reveals that the influences from multi-scale internal variation on the sign of "estimated" linear trend cannot be excluded in most parts of the Pacific, the southern Indian Ocean and the northern Atlantic; therefore, the warming or/and cooling trends found in these regions cannot be interpreted as the consequences of anthropogenic forcing. It's also suggested that the recent hiatus can be explained by combined uncertainty from internal variations at the interannual and decadal time scales.

Uncertainty in Detecting Trend: A New Criterion and Its Applications to Global SST

NASA Astrophysics Data System (ADS)

Lian, Tao

2017-04-01

In most parts of the global ocean, the magnitude of the long-term linear trend in sea surface temperature (SST) is much smaller than the amplitude of multi-scale internal variation. One can thus use a specific period in a much longer record to arbitrarily determine the sign of long-term trend, which is statistically significant, in regional SST. This could lead to a controversial conclusion on how global SST responded to the anthropogenic forcing in the recent history. In this study, the uncertainty in the linear trend due to multi-scale internal variation is theoretically investigated. It is found that the "estimated" trend will not change its sign only when its magnitude is greater than a theoretical threshold that scales the influence from the multi-scale internal variation. Otherwise, the sign of the "estimated" trend may depend on the period used. The new criterion is found to be superior over the existing methods when the de-trended time series is dominated by the oscillatory term. Applying this new criterion to a global SST reconstruction from 1881 to 2013 reveals that the influences from multi-scale internal variation on the sign of "estimated" linear trend cannot be excluded in most parts of the Pacific, the southern Indian Ocean and the northern Atlantic; therefore, the warming or/and cooling trends found in these regions cannot be interpreted as the consequences of anthropogenic forcing. It's also suggested that the recent hiatus can be explained by combined uncertainty from internal variations at the interannual and decadal time scales.

About the variations on lightning activity in Brazil from 1960s to 1990s based on thunderstorm days: preliminary results

NASA Astrophysics Data System (ADS)

Pinto, O.; Pinto, I. R.

2009-12-01

Thunder day frequencies (TD) have been collected throughout the world in a systematic way since the beginning of the twenty century, producing the longest lightning-related data set available to investigate possible climatic changes in the global, tropical or, even, regional lightning activity. Such changes may be related to natural climate variations associated with many different large scale phenomena and/or to anthropogenic warming variations. The role of each component may be different at different spatial scales. In Brazil TD data have been recorded in many stations throughout the country. In this report, TD data from 1960s to 1990s in different stations in Brazil are analyzed looking for variations related to volcanic eruptions, El Niño Southern Oscillation (ENSO), tropical Atlantic sea-surface temperature (SST) anomaly, Pacific Decadal Oscillation (POD), solar irradiance and urban effects. The preliminary results are discussed in the context of their implications for future climatic changes in the lightning activity.

Homogeneity of the coefficient of linear thermal expansion of ZERODUR: a review of a decade of evaluations

NASA Astrophysics Data System (ADS)

Jedamzik, Ralf; Westerhoff, Thomas

2017-09-01

The coefficient of thermal expansion (CTE) and its spatial homogeneity from small to large formats is the most important property of ZERODUR. Since more than a decade SCHOTT has documented the excellent CTE homogeneity. It started with reviews of past astronomical telescope projects like the VLT, Keck and GTC mirror blanks and continued with dedicated evaluations of the production. In recent years, extensive CTE measurements on samples cut from randomly selected single ZERODUR parts in meter size and formats of arbitrary shape, large production boules and even 4 m sized blanks have demonstrated the excellent CTE homogeneity in production. The published homogeneity data shows single ppb/K peak to valley CTE variations on medium spatial scale of several cm down to small spatial scale of only a few mm mostly at the limit of the measurement reproducibility. This review paper summarizes the results also in respect to the increased CTE measurement accuracy over the last decade of ZERODUR production.

Variability and change of sea level and its components in the Indo-Pacific region during the altimetry era

NASA Astrophysics Data System (ADS)

Wu, Quran; Zhang, Xuebin; Church, John A.; Hu, Jianyu

2017-03-01

Previous studies have shown that regional sea level exhibits interannual and decadal variations associated with the modes of climate variability. A better understanding of those low-frequency sea level variations benefits the detection and attribution of climate change signals. Nonetheless, the contributions of thermosteric, halosteric, and mass sea level components to sea level variability and trend patterns remain unclear. By focusing on signals associated with dominant climate modes in the Indo-Pacific region, we estimate the interannual and decadal fingerprints and trend of each sea level component utilizing a multivariate linear regression of two adjoint-based ocean reanalyses. Sea level interannual, decadal, and trend patterns primarily come from thermosteric sea level (TSSL). Halosteric sea level (HSSL) is of regional importance in the Pacific Ocean on decadal time scale and dominates sea level trends in the northeast subtropical Pacific. The compensation between TSSL and HSSL is identified in their decadal variability and trends. The interannual and decadal variability of temperature generally peak at subsurface around 100 m but that of salinity tend to be surface-intensified. Decadal temperature and salinity signals extend deeper into the ocean in some regions than their interannual equivalents. Mass sea level (MassSL) is critical for the interannual and decadal variability of sea level over shelf seas. Inconsistencies exist in MassSL trend patterns among various estimates. This study highlights regions where multiple processes work together to control sea level variability and change. Further work is required to better understand the interaction of different processes in those regions.

Vegetation Interaction Enhances Interdecadal Climate Variability in the Sahel

NASA Technical Reports Server (NTRS)

Zeng, Ning; Neelin, J. David; Lau, William K.-M.

1999-01-01

The role of naturally varying vegetation in influencing the climate variability in the Sahel is explored in a coupled atmosphere-land-vegetation model. The Sahel rainfall variability is influenced by sea surface temperature (SST) variations in the oceans. Land-surface feedback is found to increase this variability both on interannual and interdecadal time scales. Interactive vegetation enhances the interdecadal variation significantly, but can reduce year to year variability due to a phase lag introduced by the relatively slow vegetation adjustment time. Variations in vegetation accompany the changes in rainfall, in particular, the multi-decadal drying trend from the 1950s to the 80s.

Decadal atmosphere-ocean variations in the Pacific

NASA Astrophysics Data System (ADS)

Trenberth, Kevin E.; Hurrell, James W.

1994-03-01

Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1988. Observed significant changes in the atmospheric circulation throughout the troposphere revealed a deeper and eastward shifted Aleutian low pressure system in the winter half year which advected warmer and moister air along the west coast of North America and into Alaska and colder air over the north Pacific. Consequently, there were increases in temperatures and sea surface temperatures (SSTs) along the west coast of North America and Alaska but decreases in SSTs over the central north Pacific, as well as changes in coastal rainfall and streamflow, and decreases in sea ice in the Bering Sea. Associated changes occurred in the surface wind stress, and, by inference, in the Sverdrup transport in the north Pacific Ocean. Changes in the monthly mean flow were accompanied by a southward shift in the storm tracks and associated synoptic eddy activity and in the surface ocean sensible and latent heat fluxes. In addition to the changes in the physical environment, the deeper Aleutian low increased the nutrient supply as seen through increases in total chlorophyll in the water column, phytoplankton and zooplankton. These changes, along with the altered ocean currents and temperatures, changed the migration patterns and increased the stock of many fish species. A north Pacific (NP) index is defined to measure the decadal variations, and the temporal variability of the index is explored on daily, annual, interannual and decadal time scales. The dominant atmosphere-ocean relation in the north Pacific is one where atmospheric changes lead SSTs by one to two months. However, strong ties are revealed with events in the tropical Pacific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months. Changes in the storm tracks in the north Pacific help to reinforce and maintain the anomalous circulation in the upper troposphere. A hypothesis is put forward outlining the tropical and extratropical realtionships which stresses the role of tropical forcing but with important feed-backs in the extratropics that serve to emphasize the decadal relative to interannual time scales. The Pacific decadal timescale variations are linked to recent changes in the frequency and intensity of El Niño versus La Nina events but whether climate change associated with “global warming” is a factor is an open question.

Land surface phenological responses to land use and climate variation in a changing Central Asia

NASA Astrophysics Data System (ADS)

Kariyeva, Jahan

During the last few decades Central Asia has experienced widespread changes in land cover and land use following the socio-economic and institutional transformations of the region catalyzed by the USSR collapse in 1991. The decade-long drought events and steadily increasing temperature regimes in the region came on top of these institutional transformations, affecting the long term and landscape scale vegetation responses. This research is based on the need to better understand the potential ecological and policy implications of climate variation and land use practices in the contexts of landscape-scale changes dynamics and variability patterns of land surface phenology responses in Central Asia. The land surface phenology responses -- the spatio-temporal dynamics of terrestrial vegetation derived from the remotely sensed data -- provide measurements linked to the timing of vegetation growth cycles (e.g., start of growing season) and total vegetation productivity over the growing season, which are used as a proxy for the assessment of effects of variations in environmental settings. Local and regional scale assessment of the before and after the USSR collapse vegetation response patterns in the natural and agricultural systems of the Central Asian drylands was conducted to characterize newly emerging links (since 1991) between coupled human and natural systems, e.g., socio-economic and policy drivers of altered land and water use and distribution patterns. Spatio-temporal patterns of bioclimatic responses were examined to determine how phenology is associated with temperature and precipitation in different land use types, including rainfed and irrigated agricultural types. Phenological models were developed to examine relationship between environmental drivers and effect of their altitudinal and latitudinal gradients on the broad-scale vegetation response patterns in non-cropland ecosystems of the desert, steppe, and mountainous regional landscapes of Central Asia. The study results demonstrated that the satellite derived measurements of temporal cycles of vegetation greenness and productivity data was a valuable bioclimatic integrator of climatic and land use variation in Central Asia. The synthesis of broad-scale phenological changes in Central Asia showed that linkages of natural and human systems vary across space and time comprising complex and tightly integrated patterns and processes that are not evident when studied separately.

Changes in US extreme sea levels and the role of large scale climate variations

NASA Astrophysics Data System (ADS)

Wahl, T.; Chambers, D. P.

2015-12-01

We analyze a set of 20 tide gauge records covering the contiguous United States (US) coastline and the period from 1929 to 2013 to identify long-term trends and multi-decadal variations in extreme sea levels (ESLs) relative to changes in mean sea level (MSL). Significant but small long-term trends in ESLs above/below MSL are found at individual sites along most coastline stretches, but are mostly confined to the southeast coast and the winter season when storm surges are primarily driven by extra-tropical cyclones. We identify six regions with broadly coherent and considerable multi-decadal ESL variations unrelated to MSL changes. Using a quasi-non-stationary extreme value analysis approach we show that the latter would have caused variations in design relevant return water levels (RWLs; 50 to 200 year return periods) ranging from ~10 cm to as much as 110 cm across the six regions. To explore the origin of these temporal changes and the role of large-scale climate variability we develop different sets of simple and multiple linear regression models with RWLs as dependent variables and climate indices, or tailored (toward the goal of predicting multi-decadal RWL changes) versions of them, and wind stress curl as independent predictors. The models, after being tested for spatial and temporal stability, explain up to 97% of the observed variability at individual sites and almost 80% on average. Using the model predictions as covariates for the quasi-non-stationary extreme value analysis also significantly reduces the range of change in the 100-year RWLs over time, turning a non-stationary process into a stationary one. This highlights that the models - when used with regional and global climate model output of the predictors - should also be capable of projecting future RWL changes to be used by decision makers for improved flood preparedness and long-term resiliency.

Pulse-to-pulse variations in accreting X-ray pulsars

NASA Astrophysics Data System (ADS)

Kretschmar, Peter; Marcu, Diana; Kühnel, Matthias; Klochkov, Dmitry; Pottschmidt, Katja; Staubert, Rüdiger; Wilson-Hodge, Colleen A.; Jenke, Peter A.; Caballero, Isabel; Fürst, Felix

2014-01-01

In most accreting X-ray pulsars, the periodic signal is very clear and easily shows up as soon as data covering sufficient pulse periods (a few ten) are available. The mean pulse profile is often quite typical for a given source and with minor variations repeated and recognisable across observations done years or even decades apart. At the time scale of individual pulses, significant pulse-to-pulse variations are commonly observed. While at low energies some of these variations might be explained by absorption, in the hard X-rays they will reflect changes in the accretion and subsequent emission. The amount of these variations appears to be quite different between sources and contains information about the surrounding material as well ass possibly interactions at the magnetosphere. We investigate such variations for a sample of well-known sources.

Are the traditional large-scale drought indices suitable for shallow water wetlands? An example in the Everglades.

PubMed

Zhao, Dehua; Wang, Penghe; Zuo, Jie; Zhang, Hui; An, Shuqing; Ramesh, Reddy K

2017-08-01

Numerous drought indices have been developed over the past several decades. However, few studies have focused on the suitability of indices for studies of ephemeral wetlands. The objective is to answer the following question: can the traditional large-scale drought indices characterize drought severity in shallow water wetlands such as the Everglades? The question was approached from two perspectives: the available water quantity and the response of wetland ecosystems to drought. The results showed the unsuitability of traditional large-scale drought indices for characterizing the actual available water quantity based on two findings. (1) Large spatial variations in precipitation (P), potential evapotranspiration (PE), water table depth (WTD) and the monthly water storage change (SC) were observed in the Everglades; notably, the spatial variation in SC, which reflects the monthly water balance, was 1.86 and 1.62 times larger than the temporal variation between seasons and between years, respectively. (2) The large-scale water balance measured based on the water storage variation had an average indicating efficiency (IE) of only 60.01% due to the redistribution of interior water. The spatial distribution of variations in the Normalized Different Vegetation Index (NDVI) in the 2011 dry season showed significantly positive, significantly negative and weak correlations with the minimum WTD in wet prairies, graminoid prairies and sawgrass wetlands, respectively. The significant and opposite correlations imply the unsuitability of the traditional large-scale drought indices in evaluating the effect of drought on shallow water wetlands. Copyright © 2017 Elsevier Ltd. All rights reserved.

A Picea crassifolia Tree-Ring Width-Based Temperature Reconstruction for the Mt. Dongda Region, Northwest China, and Its Relationship to Large-Scale Climate Forcing.

PubMed

Liu, Yu; Sun, Changfeng; Li, Qiang; Cai, Qiufang

2016-01-01

The historical May-October mean temperature since 1831 was reconstructed based on tree-ring width of Qinghai spruce (Picea crassifolia Kom.) collected on Mt. Dongda, North of the Hexi Corridor in Northwest China. The regression model explained 46.6% of the variance of the instrumentally observed temperature. The cold periods in the reconstruction were 1831-1889, 1894-1901, 1908-1934 and 1950-1952, and the warm periods were 1890-1893, 1902-1907, 1935-1949 and 1953-2011. During the instrumental period (1951-2011), an obvious warming trend appeared in the last twenty years. The reconstruction displayed similar patterns to a temperature reconstruction from the east-central Tibetan Plateau at the inter-decadal timescale, indicating that the temperature reconstruction in this study was a reliable proxy for Northwest China. It was also found that the reconstruction series had good consistency with the Northern Hemisphere temperature at a decadal timescale. Multi-taper method spectral analysis detected some low- and high-frequency cycles (2.3-2.4-year, 2.8-year, 3.4-3.6-year, 5.0-year, 9.9-year and 27.0-year). Combining these cycles, the relationship of the low-frequency change with the Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) and Southern Oscillation (SO) suggested that the reconstructed temperature variations may be related to large-scale atmospheric-oceanic variations. Major volcanic eruptions were partly reflected in the reconstructed temperatures after high-pass filtering; these events promoted anomalous cooling in this region. The results of this study not only provide new information for assessing the long-term temperature changes in the Hexi Corridor of Northwest China, but also further demonstrate the effects of large-scale atmospheric-oceanic circulation on climate change in Northwest China.

Asynchrony in the inter-annual recruitment of lake whitefish Coregonus clupeaformis in the Great Lakes region

USGS Publications Warehouse

Zischke, Mitchell T.; Bunnell, David B.; Troy, Cary D.; Berglund, Eric K.; Caroffino, David C.; Ebener, Mark P.; He, Ji X.; Sitar, Shawn P.; Hook, Tomas O.

2017-01-01

Spatially separated fish populations may display synchrony in annual recruitment if the factors that drive recruitment success, particularly abiotic factors such as temperature, are synchronised across broad spatial scales. We examined inter-annual variation in recruitment among lake whitefish (Coregonus clupeaformis) populations in lakes Huron, Michigan and Superior using fishery-dependent and -independent data from 1971 to 2014. Relative year-class strength (RYCS) was calculated from catch-curve residuals for each year class across multiple sampling years. Pairwise comparison of RYCS among datasets revealed no significant associations either within or between lakes, suggesting that recruitment of lake whitefish is spatially asynchronous. There was no consistent correlation between pairwise agreement and the distance between datasets, and models to estimate the spatial scale of recruitment synchrony did not fit well to these data. This suggests that inter-annual recruitment variation of lake whitefish is asynchronous across broad spatial scales in the Great Lakes. While our method primarily evaluated year-to-year recruitment variation, it is plausible that recruitment of lake whitefish varies at coarser temporal scales (e.g. decadal). Nonetheless, our findings differ from research on some other Coregonus species and suggest that local biotic or density-dependent factors may contribute strongly to lake whitefish recruitment rather than inter-annual variability in broad-scale abiotic factors.

Decadal variations of Pacific North Equatorial Current bifurcation from multiple ocean products

NASA Astrophysics Data System (ADS)

Zhai, Fangguo; Wang, Qingye; Wang, Fujun; Hu, Dunxin

2014-02-01

In this study, we examine the decadal variations of the Pacific North Equatorial Current (NEC) bifurcation latitude (NBL) averaged over upper 100 m and underlying dynamics over the past six decades using 11 ocean products, including seven kinds of ocean reanalyzes based on ocean data assimilation systems, two kinds of numerical simulations without assimilating observations and two kinds of objective analyzes based on in situ observations only. During the period of 1954-2007, the multiproduct mean of decadal NBL anomalies shows maxima around 1965/1966, 1980/1981, 1995/1996, and 2003/2004, and minima around 1958, 1971/1972, 1986/1987, and 2000/2001, respectively. The NBL decadal variations are related to the first Empirical Orthogonal Function mode of decadal anomalies of sea surface height (SSH) in the northwestern tropical Pacific Ocean, which shows spatially coherent variation over the whole region and explains most of the total variance. Further regression and composite analyzes indicate that northerly/southerly NBL corresponds to negative/positive SSH anomalies and cyclonic/anticyclonic gyre anomalies in the northwestern tropical Pacific Ocean. These decadal circulation variations and thus the decadal NBL variations are governed mostly by the first two vertical modes and attribute the most to the first baroclinic mode. The NBL decadal variation is highly positively correlated with the tropical Pacific decadal variability (TPDV) around the zero time lag. With a lead of about half the decadal cycle the NBL displays closer but negative relationship to TPDV in four ocean products, possibly manifesting the dynamical role of the circulation in the northwestern tropical Pacific in the phase-shifting of TPDV.

Multi-Decadal Oscillations of the Ocean Active Upper-Layer Heat Content

NASA Astrophysics Data System (ADS)

Byshev, Vladimir I.; Neiman, Victor G.; Anisimov, Mikhail V.; Gusev, Anatoly V.; Serykh, Ilya V.; Sidorova, Alexandra N.; Figurkin, Alexander L.; Anisimov, Ivan M.

2017-07-01

Spatial patterns in multi-decadal variability in upper ocean heat content for the last 60 years are examined using a numerical model developed at the Institute of Numerical Mathematics of Russia (INM Model) and sea water temperature-salinity data from the World Ocean Database (in: Levitus, NOAA Atlas NESDIS 66, U.S. Wash.: Gov. Printing Office, 2009). Both the model and the observational data show that the heat content of the Active Upper Layer (AUL) in particular regions of the Atlantic, Pacific and Southern oceans have experienced prominent simultaneous variations on multi-decadal (25-35 years) time scales. These variations are compared earlier revealed climatic alternations in the Northern Atlantic region during the last century (Byshev et al. in Doklady Earth Sci 438(2):887-892, 2011). We found that from the middle of 1970s to the end of 1990s the AUL heat content decreased in several oceanic regions, while the mean surface temperature increased on Northern Hemisphere continents according to IPCC (in: Stocker et al. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change, Cambridge University Press, Cambridge, 2013). This means that the climate-forcing effect of the ocean-atmosphere interaction in certain energy-active areas determines not only local climatic processes, but also have an influence on global-scale climate phenomena. Here we show that specific regional features of the AUL thermal structure are in a good agreement with climatic conditions on the adjacent continents. Further, the ocean AUL in the five distinctive regions identified in our study have resumed warming in the first decade of this century. By analogy inference from previous climate scenarios, this may signal the onset of more continental climate over mainlands.

Variability of the Tropical Ocean Surface Temperatures at Decadal-Multidecadal Timescales. Part I: The Atlantic Ocean.

NASA Astrophysics Data System (ADS)

Mehta, Vikram M.

1998-09-01

Gridded time series from the Global Ocean Surface Temperature Atlas were analyzed with a variety of techniques to identify spatial structures and oscillation periods of the tropical Atlantic sea surface temperature (SST) variations at decadal timescales, and to develop physical interpretations of statistical patterns of decadal SST variations. Each time series was 110 yr (1882-1991) long. The tropical Atlantic SST variations were compared with decadal variations in a 74-yr-long (1912-85) north Nordeste Brazil rainfall time series and a 106-yr-long (1886-1991) tropical Atlantic cyclone activity index time series. The tropical Atlantic SST variations were also compared with decadal variations in the extratropical Atlantic SST.Multiyear to multidecadal variations in the cross-equatorial dipole pattern identified as a dominant empirical pattern of the tropical Atlantic SST variations in earlier and present studies are shown to be variations in the approximately north-south gradient of SST anomalies. It is also shown that there was no dynamical-thermodynamical, dipole mode of SST variations during the analysis period. There was a distinct decadal timescale (12-13 yr) of SST variations in the tropical South Atlantic, whereas no distinct decadal timescale was found in the tropical North Atlantic SST variations. Approximately 80% of the coherent decadal variance in the cross-equatorial SST gradient was `explained' by coherent decadal oscillations in the tropical South Atlantic SSTs. There were three, possibly physical, modes of decadal variations in the tropical Atlantic SSTs during the analysis period. In the more energetic mode of the North Atlantic decadal SST variations, anomalies traveled into the tropical North Atlantic from the extratropical North Atlantic along the eastern boundary of the basin. The anomalies strengthened and resided in the tropical North Atlantic for several years, then frequently traveled northward into the mid-high-latitude North Atlantic along the western boundary of the basin, and completed a clockwise rotation around the North Atlantic basin. In the less energetic North Atlantic decadal mode, SST anomalies originated in the tropical-subtropical North Atlantic near the African coast, and traveled northwestward and southward. In the South Atlantic decadal SST mode, anomalies either developed in situ or traveled into the tropical South Atlantic from the subtropical South Atlantic along the eastern boundary of the basin. The anomalies strengthened and resided in the tropical South Atlantic for several years, then frequently traveled southward into the subtropical South Atlantic along the western boundary of the basin, and completed a counterclockwise rotation around the South Atlantic basin. These decadal modes were not a permanent feature of the tropical Atlantic SST variations. The tropical North and South Atlantic SST anomalies frequently extended across the equator. Uncorrelated alignments of decadal SST anomalies having opposite signs on two sides of the equator occasionally created the apperance of a dipole.Independent analyses of the north Nordeste Brazil rainfall showed physical consistency and high coherence with the cross-equatorial SST gradient oscillations at 12-13-yr period. The tropical Atlantic cyclone index showed physical consistency but moderate coherence with the tropical North Atlantic decadal SST variations. The quasi-regularity of the 12-13-yr oscillations in the cross-equatorial SST gradient may provide an opportunity for long lead-time, skillful predictions of climate anomalies in the tropical Atlantic sector.

Periodic fluctuation of reference evapotranspiration during the past five decades: Does Evaporation Paradox really exist in China?

PubMed

Xing, Wanqiu; Wang, Weiguang; Shao, Quanxi; Yu, Zhongbo; Yang, Tao; Fu, Jianyu

2016-12-19

Evidence that the pan evaporation or reference evapotranspiration (ET 0 ) as the indicator of atmospheric evaporation capability have decreased along with the continuous increase in temperature over the past decades (coined as "evaporation paradox") has been reported worldwide. Here, we provide a nationwide investigation of spatiotemporal change of ET 0 using meteorological data from 602 stations with the updated data (1961-2011). In addition, we explore the trigger mechanism by quantitative assessment on the contribution of climatic factors to ET 0 change based on a differential equation method. In despite of different shift points regionally, our results suggest that the ET 0 generally present decadal variations rather than monotonic response to climate change reported in previous studies. The significant decrease in net radiation dominate the decrease in ET 0 before early 1990s in southern regions, while observed near-surface wind speed is the primary contributor to the variations of ET 0 for the rest regions during the same periods. The enhancements of atmospheric evaporation capability after early 1990s are driven primarily by recent relative humidity limitation in China. From a continental scale view, as highly correlating with to Pacific Decadal Oscillation, the shift behaviors of ET 0 is likely an episodic phenomenon of the ocean-atmosphere interaction in earth.

Periodic fluctuation of reference evapotranspiration during the past five decades: Does Evaporation Paradox really exist in China?

NASA Astrophysics Data System (ADS)

Xing, Wanqiu; Wang, Weiguang; Shao, Quanxi; Yu, Zhongbo; Yang, Tao; Fu, Jianyu

2016-12-01

Evidence that the pan evaporation or reference evapotranspiration (ET0) as the indicator of atmospheric evaporation capability have decreased along with the continuous increase in temperature over the past decades (coined as “evaporation paradox”) has been reported worldwide. Here, we provide a nationwide investigation of spatiotemporal change of ET0 using meteorological data from 602 stations with the updated data (1961-2011). In addition, we explore the trigger mechanism by quantitative assessment on the contribution of climatic factors to ET0 change based on a differential equation method. In despite of different shift points regionally, our results suggest that the ET0 generally present decadal variations rather than monotonic response to climate change reported in previous studies. The significant decrease in net radiation dominate the decrease in ET0 before early 1990s in southern regions, while observed near-surface wind speed is the primary contributor to the variations of ET0 for the rest regions during the same periods. The enhancements of atmospheric evaporation capability after early 1990s are driven primarily by recent relative humidity limitation in China. From a continental scale view, as highly correlating with to Pacific Decadal Oscillation, the shift behaviors of ET0 is likely an episodic phenomenon of the ocean-atmosphere interaction in earth.

Contrasting spatial structures of Atlantic Multidecadal Oscillation between observations and slab ocean model simulations

NASA Astrophysics Data System (ADS)

Sun, Cheng; Li, Jianping; Kucharski, Fred; Xue, Jiaqing; Li, Xiang

2018-04-01

The spatial structure of Atlantic multidecadal oscillation (AMO) is analyzed and compared between the observations and simulations from slab ocean models (SOMs) and fully coupled models. The observed sea surface temperature (SST) pattern of AMO is characterized by a basin-wide monopole structure, and there is a significantly high degree of spatial coherence of decadal SST variations across the entire North Atlantic basin. The observed SST anomalies share a common decadal-scale signal, corresponding to the basin-wide average (i. e., the AMO). In contrast, the simulated AMO in SOMs (AMOs) exhibits a tripole-like structure, with the mid-latitude North Atlantic SST showing an inverse relationship with other parts of the basin, and the SOMs fail to reproduce the observed strong spatial coherence of decadal SST variations associated with the AMO. The observed spatial coherence of AMO SST anomalies is identified as a key feature that can be used to distinguish the AMO mechanism. The tripole-like SST pattern of AMOs in SOMs can be largely explained by the atmosphere-forced thermodynamics mechanism due to the surface heat flux changes associated with the North Atlantic Oscillation (NAO). The thermodynamic forcing of AMOs by the NAO gives rise to a simultaneous inverse NAO-AMOs relationship at both interannual and decadal timescales and a seasonal phase locking of the AMOs variability to the cold season. However, the NAO-forced thermodynamics mechanism cannot explain the observed NAO-AMO relationship and the seasonal phase locking of observed AMO variability to the warm season. At decadal timescales, a strong lagged relationship between NAO and AMO is observed, with the NAO leading by up to two decades, while the simultaneous correlation of NAO with AMO is weak. This lagged relationship and the spatial coherence of AMO can be well understood from the view point of ocean dynamics. A time-integrated NAO index, which reflects the variations in Atlantic meridional overturning circulation (AMOC) and northward ocean heat transport caused by the accumulated effect of NAO forcing, reasonably well captures the observed multidecadal fluctuations in the AMO. Further analysis using the fully coupled model simulations provides direct modeling evidence that the observed spatial coherence of decadal SST variations across North Atlantic basin can be reproduced only by including the AMOC-related ocean dynamics, and the AMOC acts as a common forcing signal that results in a spatially coherent variation of North Atlantic SST.

Analysis of Sea Level Rise in Singapore Strait

NASA Astrophysics Data System (ADS)

Tkalich, Pavel; Luu, Quang-Hung

2013-04-01

Sea level in Singapore Strait is governed by various scale phenomena, from global to local. Global signals are dominated by the climate change and multi-decadal variability and associated sea level rise; at regional scale seasonal sea level variability is caused by ENSO-modulated monsoons; locally, astronomic tides are the strongest force. Tide gauge records in Singapore Strait are analyzed to derive local sea level trend, and attempts are made to attribute observed sea level variability to phenomena at various scales, from global to local. It is found that at annual scale, sea level anomalies in Singapore Strait are quasi-periodic, of the order of ±15 cm, the highest during northeast monsoon and the lowest during southwest monsoon. Interannual regional sea level falls are associated with El Niño events, while the rises are related to La Niña episodes; both variations are in the range of ±9 cm. At multi-decadal scale, sea level in Singapore Strait has been rising at the rate 1.2-1.9 mm/year for the period 1975-2009, 2.0±0.3 mm/year for 1984-2009, and 1.3-4.7 mm/year for 1993-2009. When compared with the respective global trends of 2.0±0.3, 2.4, and 2.8±0.8 mm/year, Singapore Strait sea level rise trend was weaker at the earlier period and stronger at the recent decade.

Seasonal to Decadal Variations of Water Vapor in the Tropical Lower Stratosphere Observed with Balloon-Borne Cryogenic Frost Point Hygrometers

NASA Technical Reports Server (NTRS)

Fujiwara, M.; Voemel, H.; Hasebe, F.; Shiotani, M.; Ogino, S.-Y.; Iwasaki, S.; Nishi, N.; Shibata, T.; Shimizu, K.; Nishimoto, E.;

The Impact of High-Turbidity Water's Seasonal and Decadal Variations on Offshore Phytoplankton and Nutrients Dynamics around The Changjiang Estuary

NASA Astrophysics Data System (ADS)

Ge, J.; Torres, R.; Chen, C.; Bellerby, R. G. J.

2017-12-01

The Changjiang Estuary is characterized as strong river discharge into the inner shelf of the East China Sea with abundant sediment load, producing significant high-turbidity water coverage from river mouth to deep region. The growth of offshore phytoplankton is dynamically controlled by river flushed low-salinity and high-turbidity water, and salter water from inner shelf of East China Sea. During last decade, the sediment and nutrients from the Changjiang River has significantly changed, which lead to the variation of offshore phytoplankton dynamics. The variations of sediment, nutrients, and their influenced phytoplankton has been simulated through a comprehensive modeling system, which integrated a multi-scale current-wave-sediment FVCOM model and generic marine biogeochemistry and ecosystem ERSEM model through The Framework for Aquatic Biogeochemical Models (FABM). This model system has successfully revealed the seasonal and decadal variations of sediment, nutrients transport around the inner shelf of the East China Sea. The spring and autumn peaks of phytoplankton growth were correctly captured by simulation. The modeling results, as well as MODIS and GOCI remote sensing, shows a strong sediment decreasing from northern to southern region, which creates different patterns of Chlorophyll-a distribution and seasonal variations. These results indicate the high-turbidity water in northern region strongly influenced the light attenuation in the water column and limits the phytoplankton growth in this relatively higher-nutrient area, especially in the wintertime. The relatively low-turbidity southern region has significant productivity of phytoplankton, even during low-temperature winter. The phytoplankton growth increased in the northern region from 2005 to 2010, with the increase of the nutrient load during this period. Then it became a decreasing trend after 2010.

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

Hurrell, J.W.

Greenland ice-core data have revealed large decadal climate variations over the North Atlantic that can be related to a major source of low-frequency variability, the North Atlantic Oscillation. Over the past decade, the Oscillation has remained in one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.more » 27 refs., 4 figs., 1 tab.« less

Modulation of the SSTA decadal variation on ENSO events and relationships of SSTA With LOD,SOI, etc

NASA Astrophysics Data System (ADS)

Liao, D. C.; Zhou, Y. H.; Liao, X. H.

2007-01-01

Interannual and decadal components of the length of day (LOD), Southern Oscillation Index (SOI) and Sea Surface Temperature anomaly (SSTA) in Nino regions are extracted by band-pass filtering, and used for research of the modulation of the SSTA on the ENSO events. Results show that besides the interannual components, the decadal components in SSTA have strong impacts on monitoring and representing of the ENSO events. When the ENSO events are strong, the modulation of the decadal components of the SSTA tends to prolong the life-time of the events and enlarge the extreme anomalies of the SST, while the ENSO events, which are so weak that they can not be detected by the interannual components of the SSTA, can also be detected with the help of the modulation of the SSTA decadal components. The study further draws attention to the relationships of the SSTA interannual and decadal components with those of LOD, SOI, both of the sea level pressure anomalies (SLPA) and the trade wind anomalies (TWA) in tropic Pacific, and also with those of the axial components of the atmospheric angular momentum (AAM) and oceanic angular momentum (OAM). Results of the squared coherence and coherent phases among them reveal close connections with the SSTA and almost all of the parameters mentioned above on the interannual time scales, while on the decadal time scale significant connections are among the SSTA and SOI, SLPA, TWA, ?3w and ?3w+v as well, and slight weaker connections between the SSTA and LOD, ?3pib and ?3bp

Tree-Ring Based May-July Temperature Reconstruction Since AD 1630 on the Western Loess Plateau, China

PubMed Central

Song, Huiming; Liu, Yu; Li, Qiang; Gao, Na; Ma, Yongyong; Zhang, Yanhua

2014-01-01

Tree-ring samples from Chinese Pine (Pinus tabulaeformis Carr.) collected at Mt. Shimen on the western Loess Plateau, China, were used to reconstruct the mean May–July temperature during AD 1630–2011. The regression model explained 48% of the adjusted variance in the instrumentally observed mean May–July temperature. The reconstruction revealed significant temperature variations at interannual to decadal scales. Cool periods observed in the reconstruction coincided with reduced solar activities. The reconstructed temperature matched well with two other tree-ring based temperature reconstructions conducted on the northern slope of the Qinling Mountains (on the southern margin of the Loess Plateau of China) for both annual and decadal scales. In addition, this study agreed well with several series derived from different proxies. This reconstruction improves upon the sparse network of high-resolution paleoclimatic records for the western Loess Plateau, China. PMID:24690885

Continental-Scale Temperature Reconstructions from the PAGES 2k Network

NASA Astrophysics Data System (ADS)

Kaufman, D. S.

2012-12-01

We present a major new synthesis of seven regional temperature reconstructions to elucidate the global pattern of variations and their association with climate-forcing mechanisms over the past two millennia. To coordinate the integration of new and existing data of all proxy types, the Past Global Changes (PAGES) project developed the 2k Network. It comprises nine working groups representing eight continental-scale regions and the oceans. The PAGES 2k Consortium, authoring this paper, presently includes 79 representatives from 25 countries. For this synthesis, each of the PAGES 2k working groups identified the proxy climate records for reconstructing past temperature and associated uncertainty using the data and methodologies that they deemed most appropriate for their region. The datasets are from 973 sites where tree rings, pollen, corals, lake and marine sediment, glacier ice, speleothems, and historical documents record changes in biologically and physically mediated processes that are sensitive to temperature change, among other climatic factors. The proxy records used for this synthesis are available through the NOAA World Data Center for Paleoclimatology. On long time scales, the temperature reconstructions display similarities among regions, and a large part of this common behavior can be explained by known climate forcings. Reconstructed temperatures in all regions show an overall long-term cooling trend until around 1900 C.E., followed by strong warming during the 20th century. On the multi-decadal time scale, we assessed the variability among the temperature reconstructions using principal component (PC) analysis of the standardized decadal mean temperatures over the period of overlap among the reconstructions (1200 to 1980 C.E.). PC1 explains 35% of the total variability and is strongly correlated with temperature reconstructions from the four Northern Hemisphere regions, and with the sum of external forcings including solar, volcanic, and greenhouse gases. PC2 captures 18% of the variability and is correlated most strongly with the Southern Hemisphere regions of Australasia and South America. PC3 captures 15% of the variability in the temperature reconstructions with a predominant loading from Antarctica. The timing of extremely warm and cold decades (10th percentiles) in each region were analyzed and compared with climate forcings. Only 22% of the regionally coldest decades can be ascribed to extreme minima in solar forcing, and 17% to volcanic forcing. The association between extremely warm regional temperatures and solar maxima is weaker than for cold temperatures and their corresponding solar minima. Spatially, volcanic forcing moderately increased the frequency of extremely cold decades in the Northern Hemisphere reconstructions, but had no significant effect in the Southern Hemisphere. Solar and volcanic impacts do not induce globally consistent decadal temperature shifts, but they increase the probability of cooling or warming at the continental scale. The majority of cold and warm decades identified here cannot be explained by changes in the records of volcanic activity or solar forcing. This indicates that at this timescale, prior to the anthropogenic buildup of greenhouse gases, unforced internal variability in the coupled ocean/atmosphere system was the dominant control on temperature variation.

Effects of the Bermuda High and the Great Plains low-level jet upon background and peak ozone concentrations in Texas urban areas

NASA Astrophysics Data System (ADS)

Estes, M. J.; Wang, Y.; Lei, R.; Wang, S. C.; Jia, B.

2017-12-01

Previous studies have established that the westward extent of the Bermuda High is strongly linked to the ozone concentrations in Houston. This study examines the linkages between the Bermuda High, the Great Plains low-level jet, background ozone in the eastern half of Texas, and local contributions to peak ozone in Texas urban areas. Analysis of North American Regional Reanalysis (NARR) wind and pressure fields will be used to establish the presence and strength of synoptic-scale weather features, and this information will be used with ozone data from air quality networks to determine the effects upon the seasonal and interannual variations of ozone. Quantification of the effects of large-scale meteorological factors will improve understanding of the causes of ozone variations, including decadal trends in Texas cities.

Centennial-scale fluctuations and regional complexity characterize Pacific salmon population dynamics over the past five centuries.

PubMed

Rogers, Lauren A; Schindler, Daniel E; Lisi, Peter J; Holtgrieve, Gordon W; Leavitt, Peter R; Bunting, Lynda; Finney, Bruce P; Selbie, Daniel T; Chen, Guangjie; Gregory-Eaves, Irene; Lisac, Mark J; Walsh, Patrick B

2013-01-29

Observational data from the past century have highlighted the importance of interdecadal modes of variability in fish population dynamics, but how these patterns of variation fit into a broader temporal and spatial context remains largely unknown. We analyzed time series of stable nitrogen isotopes from the sediments of 20 sockeye salmon nursery lakes across western Alaska to characterize temporal and spatial patterns in salmon abundance over the past ∼500 y. Although some stocks varied on interdecadal time scales (30- to 80-y cycles), centennial-scale variation, undetectable in modern-day catch records and survey data, has dominated salmon population dynamics over the past 500 y. Before 1900, variation in abundance was clearly not synchronous among stocks, and the only temporal signal common to lake sediment records from this region was the onset of commercial fishing in the late 1800s. Thus, historical changes in climate did not synchronize stock dynamics over centennial time scales, emphasizing that ecosystem complexity can produce a diversity of ecological responses to regional climate forcing. Our results show that marine fish populations may alternate between naturally driven periods of high and low abundance over time scales of decades to centuries and suggest that management models that assume time-invariant productivity or carrying capacity parameters may be poor representations of the biological reality in these systems.

Centennial-scale fluctuations and regional complexity characterize Pacific salmon population dynamics over the past five centuries

PubMed Central

Rogers, Lauren A.; Schindler, Daniel E.; Lisi, Peter J.; Holtgrieve, Gordon W.; Leavitt, Peter R.; Bunting, Lynda; Finney, Bruce P.; Selbie, Daniel T.; Chen, Guangjie; Gregory-Eaves, Irene; Lisac, Mark J.; Walsh, Patrick B.

2013-01-01

Observational data from the past century have highlighted the importance of interdecadal modes of variability in fish population dynamics, but how these patterns of variation fit into a broader temporal and spatial context remains largely unknown. We analyzed time series of stable nitrogen isotopes from the sediments of 20 sockeye salmon nursery lakes across western Alaska to characterize temporal and spatial patterns in salmon abundance over the past ∼500 y. Although some stocks varied on interdecadal time scales (30- to 80-y cycles), centennial-scale variation, undetectable in modern-day catch records and survey data, has dominated salmon population dynamics over the past 500 y. Before 1900, variation in abundance was clearly not synchronous among stocks, and the only temporal signal common to lake sediment records from this region was the onset of commercial fishing in the late 1800s. Thus, historical changes in climate did not synchronize stock dynamics over centennial time scales, emphasizing that ecosystem complexity can produce a diversity of ecological responses to regional climate forcing. Our results show that marine fish populations may alternate between naturally driven periods of high and low abundance over time scales of decades to centuries and suggest that management models that assume time-invariant productivity or carrying capacity parameters may be poor representations of the biological reality in these systems. PMID:23322737

Non-stationarity of extreme weather events in a changing climate - an application to long-term droughts in the US Southwest

NASA Astrophysics Data System (ADS)

Grossmann, I.

2013-12-01

Return periods of many extreme weather events are not stationary over time, given increasing risks due to global warming and multidecadal variability resulting from large scale climate patterns. This is problematic as extreme weather events and long-term climate risks such as droughts are typically conceptualized via measures such as return periods that implicitly assume non-stationarity. I briefly review these problems and present an application to the non-stationarity of droughts in the US Southwest. The US Southwest relies on annual precipitation maxima during winter and the North American Monsoon (NAM), both of which vary with large-scale climate patterns, in particular ENSO, the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). The latter two exhibit variability on longer (multi-decadal) time scales in addition to short-term variations. The region is also part of the subtropical belt projected to become more arid in a warming climate. The possible multidecadal impacts of the PDO on precipitation in the study region are analyzed with a focus on Arizona and New Mexico, using GPCC and CRU data since 1900. The projected impacts of the PDO on annual precipitation during the next three decades with GPCC data are similar in scale to the impacts of global warming on precipitation according to the A1B scenario and the CMIP2 multi-model means, while the combined impact of the PDO and AMO is about 19% larger. The effects according to the CRU dataset are about half as large as the projected global warming impacts. Given the magnitude of the projected impacts from both multidecadal variability and global warming, water management needs to explicitly incorporate both of these trends into long-term planning. Multi-decadal variability could be incorporated into the concept of return periods by presenting return periods as time-varying or as conditional on the respective 'phase' of relevant multidecadal patterns and on global warming. Problems in detecting the PDO signal and potential solutions are also discussed. We find that the long-term effect of the PDO can be more clearly separated from short-term variability by considering return periods of multi-year drought measures rather than return periods of simple drought measures that are more affected by short-term variations.

Precipitation driven decadal scale decline and recovery of wetlands of Lake Pannon during the Tortonian

PubMed Central

Kern, Andrea K.; Harzhauser, Mathias; Soliman, Ali; Piller, Werner E.; Gross, Martin

2012-01-01

High resolution pollen and dinoflagellate analyses were performed on a continuous 98-cm-long core from Tortonian deposits of Lake Pannon in the Styrian Basin in Austria. The sample distance of 1-cm corresponds to a resolution of roughly one decade, allowing insights into environmental and climatic changes over a millennium of Late Miocene time. Shifts in lake level, surface water productivity on a decadal- to centennial-scale can be explained by variations of rainfall during the Tortonian climatic optimum. Related to negative fine scale shifts of mean annual precipitation, shoreline vegetation belts reacted in an immediate replacement of Poaceae by Cyperaceae as dominant grasses in the marshes fringing the lake. In contrast to such near-synchronous ecosystem-responses to precipitation, a delayed lake level rise of 4–6 decades is evident in the hydrological budget of Lake Pannon. This transgression, caused by a precipitation increase up to > 1200 mm/yr, resulted in a complete dieback of marshes. Simultaneously, “open-water” dinoflagellates, such as Impagidinium, took over in the brackish lagoon and fresh water dinoflagellates disappeared. As soon as the rainfall switched back to moderate levels of ~ 1100–1200 mm/yr, the rise of the lake level slowed down, the marsh plants could keep up again and the former vegetation belts became re-established. Thus, mean annual precipitation, more than temperature, was the main driving force for high-frequency fluctuations in the Tortonian wetlands and surface water conditions of Lake Pannon. Such high resolution studies focusing on Tortonian decadal to centennial climate change will be crucial to test climate models which try to compare the Tortonian models with predictions for future climate change. PMID:23576820

Periodic fluctuation of reference evapotranspiration during the past five decades: Does Evaporation Paradox really exist in China?

PubMed Central

Xing, Wanqiu; Wang, Weiguang; Shao, Quanxi; Yu, Zhongbo; Yang, Tao; Fu, Jianyu

2016-01-01

Evidence that the pan evaporation or reference evapotranspiration (ET0) as the indicator of atmospheric evaporation capability have decreased along with the continuous increase in temperature over the past decades (coined as “evaporation paradox”) has been reported worldwide. Here, we provide a nationwide investigation of spatiotemporal change of ET0 using meteorological data from 602 stations with the updated data (1961–2011). In addition, we explore the trigger mechanism by quantitative assessment on the contribution of climatic factors to ET0 change based on a differential equation method. In despite of different shift points regionally, our results suggest that the ET0 generally present decadal variations rather than monotonic response to climate change reported in previous studies. The significant decrease in net radiation dominate the decrease in ET0 before early 1990s in southern regions, while observed near-surface wind speed is the primary contributor to the variations of ET0 for the rest regions during the same periods. The enhancements of atmospheric evaporation capability after early 1990s are driven primarily by recent relative humidity limitation in China. From a continental scale view, as highly correlating with to Pacific Decadal Oscillation, the shift behaviors of ET0 is likely an episodic phenomenon of the ocean-atmosphere interaction in earth. PMID:27991576

Interactions Between the Thermohaline Circulation and Tropical Atlantic SST in a Coupled General Circulation Model

NASA Technical Reports Server (NTRS)

Miller, Ron; Jiang, Xing-Jian; Travis, Larry (Technical Monitor)

2001-01-01

Tropical Atlantic SST shows a (statistically well-defined) decadal time scale in a 104-year simulation of unforced variability by a coupled general circulation model (CGCM). The SST anomalies superficially resemble observed Tropical Atlantic variability (TAV), and are associated with changes in the atmospheric circulation. Brazilian rainfall is modulated with a decadal time scale, along with the strength of the Atlantic trade winds, which are associated with variations in evaporation and the net surface heat flux. However, in contrast to observed tropical Atlantic variability, the trade winds damp the associated anomalies in ocean temperature, indicating a negative feedback. Tropical SST anomalies in the CGCM, though opposed by the surface heat flux, are advected in from the Southern Hemisphere mid-latitudes. These variations modulate the strength of the thermohaline circulation (THC): warm, salty anomalies at the equator sink drawing cold, fresh mid-latitude water. Upon reaching the equator, the latter inhibit vertical overturning and advection from higher latitudes, which allows warm, salty anomalies to reform, returning the cycle to its original state. Thus, the cycle results from advection of density anomalies and the effect of these anomalies upon the rate of vertical overturning and surface advection. This decadal modulation of Tropical Atlantic SST and the thermohaline circulation is correlated with ocean heat transport to the Northern Hemisphere high latitudes and Norwegian Sea SST. Because of the central role of equatorial convection, we question whether this mechanism is present in the current climate, although we speculate that it may have operated in palaeo times, depending upon the stability of the tropical water column.

Modulation of Bjerknes feedback on the decadal variations in ENSO predictability

NASA Astrophysics Data System (ADS)

Zheng, Fei; Fang, Xiang-Hui; Zhu, Jiang; Yu, Jin-Yi; Li, Xi-Chen

2016-12-01

Clear decadal variations exist in the predictability of the El Niño-Southern Oscillation (ENSO), with the most recent decade having the lowest ENSO predictability in the past six decades. The Bjerknes Feedback (BF) intensity, which dominates the development of ENSO, has been proposed to determine ENSO predictability. Here we demonstrate that decadal variations in BF intensity are largely a result of the sensitivity of the zonal winds to the zonal sea level pressure (SLP) gradient in the equatorial Pacific. Furthermore, the results show that during low-ENSO predictability decades, zonal wind anomalies over the equatorial Pacific are more linked to SLP variations in the off-equatorial Pacific, which can then transfer this information into surface temperature and precipitation fields through the BF, suggesting a weakening in the ocean-atmosphere coupling in the tropical Pacific. This result indicates that more attention should be paid to off-equatorial processes in the prediction of ENSO.

Long term hydrographic variability near Bermuda and relation to surface forcing

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

Joyce, T.M.

1997-11-01

This paper provides an extremely brief description of long-term hydrographic observations at Bermuda. The time series of observations near the island goes back to 1922. A secular increase of temperature of approximately 0.5 C per century in the deep water pressure range has been observed; this depth layer is the only one observed at Bermuda to have such a long-term increase. Decadal time scale fluctuations have also been identified, and are correlated to decadal variations in the Labrador Sea. The recent period of decreasing temperature at Bermuda may be a reflection of the increased cooling in the Labrador Sea inmore » recent years. 2 figs.« less

Collaborative Research: Separating Forced and Unforced Decadal Predictability in Models and Observations

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

Tippett, Michael K.

2014-04-09

This report is a progress report of the accomplishments of the research grant “Collaborative Research: Separating Forced and Unforced Decadal Predictability in Models and Observa- tions” during the period 1 May 2011- 31 August 2013. This project is a collaborative one between Columbia University and George Mason University. George Mason University will submit a final technical report at the conclusion of their no-cost extension. The purpose of the proposed research is to identify unforced predictable components on decadal time scales, distinguish these components from forced predictable components, and to assess the reliability of model predictions of these components. Components ofmore » unforced decadal predictability will be isolated by maximizing the Average Predictability Time (APT) in long, multimodel control runs from state-of-the-art climate models. Components with decadal predictability have large APT, so maximizing APT ensures that components with decadal predictability will be detected. Optimal fingerprinting techniques, as used in detection and attribution analysis, will be used to separate variations due to natural and anthropogenic forcing from those due to unforced decadal predictability. This methodology will be applied to the decadal hindcasts generated by the CMIP5 project to assess the reliability of model projections. The question of whether anthropogenic forcing changes decadal predictability, or gives rise to new forms of decadal predictability, also will be investigated.« less

Whether the decadal shift of South Asia High intensity around the late 1970s exists or not

NASA Astrophysics Data System (ADS)

Xue, Xu; Chen, Wen; Nath, Debashis; Zhou, Dingwen

2015-05-01

This study compares the decadal means of the seasonal (June-July-August (JJA)) mean geopotential heights available from the NCEP1 and ERA-40 reanalysis data in the Northern Hemisphere. The interdecadal changes in the South Asia High (SAH) intensity derived from the reanalysis data are also compared with ground-based radiosonde observations and atmospheric model outputs. The JJA mean geopotential heights in the 1980s are distinctly larger than the 1970s in NCEP1 over most of the regions in the Northern Hemisphere, while no obvious difference is observed in ERA-40. The interannual variation of the SAH strength is very close in the two reanalysis data, so that it is appropriate to utilize the reanalysis data to study the interannual variation of SAH strength after removing the interdecadal trend. However, the discrepancy in SAH intensity between NCEP1 and ERA-40 mainly exists on the interdecadal time scale. The SAH intensity in the NCEP1 was close to that in the ERA-40 before the late 1970s but became remarkably stronger after the late 1970s, leading to a much larger decadal strengthening during the period 1970-1990. Based on the six radiosonde observation stations in the area of the SAH, the results indicate that the decadal reinforcing in the SAH strength occurs around the mid-1980s. Thus, NCEP1 may overestimate the decadal shift in the SAH intensity around the late 1970s, while ERA-40 may underestimate it. Much attention needs to be paid when we use the reanalysis data to study the decadal variability of the SAH intensity.

Impacts of variation in planktivorous fish on abundance of daphnids: A simulation model of the Lake Mendota food web: Chapter 20

USGS Publications Warehouse

Luecke, Chris; Lunte, Cynthia C.; Wright, Russell A.; Robertson, Dale M.; McLain, Ann S.; Kitchell, James F.

1992-01-01

Previous chapters in this volume have outlined the goals of the Lake Mendota food web manipulation study (Rudstam et al., Ch. 12) and have reported on variations in phytoplankton and zooplankton abundances during the past 15 years (Lathrop and Carpenter, Ch. 7 and 8). Because of the long time scales inherent in such a lake management manipulation, it became imperative to attempt to predict how the lake would respond to changes in planktivorous fish abundance over time scales of several decades. We know from the past 15 years of study (Lathrop and Carpenter, Ch. 7 and 8; Magnuson and Lathrop, Ch. 11) that substantial variation of planktivorous fish, zooplankton, and phytoplankton abundances can occur the lake. Given the current stocking of piscivores, we have the potential to substantially modify the abundance of planktivorous fish and possibly shift the assemblages of phytoplankton and zooplankton beyond the ranges of those which occurred previously. In this chapter we describe the construction and use of a simulation model designed to examine how variation in plantivore abundance might impact zooplankton biomass and species composition.

Model under-representation of decadal Pacific trade wind trends and its link to tropical Atlantic bias

NASA Astrophysics Data System (ADS)

Kajtar, Jules B.; Santoso, Agus; McGregor, Shayne; England, Matthew H.; Baillie, Zak

2018-02-01

The strengthening of the Pacific trade winds in recent decades has been unmatched in the observational record stretching back to the early twentieth century. This wind strengthening has been connected with numerous climate-related phenomena, including accelerated sea-level rise in the western Pacific, alterations to Indo-Pacific ocean currents, increased ocean heat uptake, and a slow-down in the rate of global-mean surface warming. Here we show that models in the Coupled Model Intercomparison Project phase 5 underestimate the observed range of decadal trends in the Pacific trade winds, despite capturing the range in decadal sea surface temperature (SST) variability. Analysis of observational data suggests that tropical Atlantic SST contributes considerably to the Pacific trade wind trends, whereas the Atlantic feedback in coupled models is muted. Atmosphere-only simulations forced by observed SST are capable of recovering the time-variation and the magnitude of the trade wind trends. Hence, we explore whether it is the biases in the mean or in the anomalous SST patterns that are responsible for the under-representation in fully coupled models. Over interannual time-scales, we find that model biases in the patterns of Atlantic SST anomalies are the strongest source of error in the precipitation and atmospheric circulation response. In contrast, on decadal time-scales, the magnitude of the model biases in Atlantic mean SST are directly linked with the trade wind variability response.

Decadal variations in the strength of ENSO teleconnections with precipitation in the western United States

USGS Publications Warehouse

McCabe, G.J.; Dettinger, M.D.

1999-01-01

Changing patterns of correlations between the historical average June-November Southern Oscillation Index (SOI) and October-March precipitation totals for 84 climate divisions in the western US indicate a large amount of variability in SOI/precipitation relations on decadal time scales. Correlations of western US precipitation with SOI and other indices of tropical El Nino-Southern Oscillation (ENSO) processes were much weaker from 1920 to 1950 than during recent decades. This variability in teleconnections is associated with the character of tropical air-sea interactions as indexed by the number of out-of-phase SOI/tropical sea surface temperature (SST) episodes, and with decadal variability in the North Pacific Ocean as indexed by the Pacific Decadal Oscillation (PDO). ENSO teleconnections with precipitation in the western US are strong when SOI and NINO3 are out-of-phase and PDO is negative. ENSO teleconnections are weak when SOI and NINO3 are weakly correlated and PDO is positive. Decadal modes of tropical and North Pacific Ocean climate variability are important indicators of periods when ENSO indices, like SOI, can be used as reliable predictors of winter precipitation in the US.

Antarctic climate and ice sheet changes and their relationship to global scale climate change over the last 2000 years

NASA Astrophysics Data System (ADS)

Steig, E. J.

2012-12-01

It is well known that the Antarctic ice sheet is changing rapidly and is probably now out of balance; at least in West Antarctica, it is now contributing significantly to sea level rise. Yet Antarctica is often thought of as being immune to the influence of anthropogenic climate trends affecting the rest of the planet. This view is based largely on the record of instrumental observations, which is both very short and largely exclusive of regions in West Antarctica that are undergoing rapid change (1). Data from ice cores (2) and boreholes (3) from across the West Antarctic Ice Sheet and the Antarctic Peninsula (4), coupled with new instrumental reconstructions (5, 6) paint a very different picture. The two newest long records from Antarctica --- at WAIS Divide (2) and at James Ross Island on the Antarctic Peninsula (4) -- show that over the last 2000 years, the temporal pattern of temperature change is similar to that for the Arctic: slow decline attributable to Milankovitch orbital forcing, interrupted by recent warming. The century-scale warming trend began early in the 20th century, coincident with strong warming trends across the Southern Hemisphere, and well before the advent of the ozone hole, to which Antarctic climate trends are frequently attributed (e.g. 7). Decadal temperature variability in Antarctica also follows averaged Southern Hemisphere variations: all the major decadal anomalies in the ~150-year instrumental climate record of the Southern Hemisphere appear in West Antarctica. Similar to the rest of the planet, the warmest period since at least 1850 C.E. in the Antarctic was the most recent two decades (1990s and 2000s), and the most recent warming in West Antarctica (including but not limited to the Peninsula) has been as rapid as anywhere else on Earth. The decadal to century-scale variations in West Antarctic temperature reflect by the strong dynamical link between the tropical Pacific and the southern high latitudes described by the Pacific South America (PSA) pattern, analogous to the better-known PNA of the Northern Hemisphere8. The atmospheric circulation anomalies associated with the PSA account not only for the temperature variability, but also for the recent observed changes in sea ice, and the ocean-driven melting of the margins of the large outlet glaciers that drain West Antarctica. Recent Antarctic ice losses are thus directly connected to global scale climate change, and cannot be attributed simply to local decadal variability or stochastic variations in glacier dynamics. 1. E. J. Steig et al., Nature 457, 459 (2009). 2. E. J. Steig et al., Nat. Geosci. in review, (2012). 3. A. J. Orsi, B. D. Cornuelle, J. P. Severinghaus, Geophys. Res. Lett. 39, L09710 (2012). 4. R. Mulvaney et al., Nature in press, (2012). 5. M. Küttel, E. J. Steig, Q. Ding, D. S. Battisti, A. J. Monaghan, Clim. Dyn. in press, (2012). 6. D. Bromwich, pers. comm., 2012. 7. D. W. J. Thompson et al., Nat. Geosci. 4, 741 (2011). 8. Y. Okumura, D. P. Schneider, C. Deser, R. Wilson. J. Climate in press, (2012).

A Picea crassifolia Tree-Ring Width-Based Temperature Reconstruction for the Mt. Dongda Region, Northwest China, and Its Relationship to Large-Scale Climate Forcing

PubMed Central

Liu, Yu; Sun, Changfeng; Li, Qiang; Cai, Qiufang

2016-01-01

The historical May–October mean temperature since 1831 was reconstructed based on tree-ring width of Qinghai spruce (Picea crassifolia Kom.) collected on Mt. Dongda, North of the Hexi Corridor in Northwest China. The regression model explained 46.6% of the variance of the instrumentally observed temperature. The cold periods in the reconstruction were 1831–1889, 1894–1901, 1908–1934 and 1950–1952, and the warm periods were 1890–1893, 1902–1907, 1935–1949 and 1953–2011. During the instrumental period (1951–2011), an obvious warming trend appeared in the last twenty years. The reconstruction displayed similar patterns to a temperature reconstruction from the east-central Tibetan Plateau at the inter-decadal timescale, indicating that the temperature reconstruction in this study was a reliable proxy for Northwest China. It was also found that the reconstruction series had good consistency with the Northern Hemisphere temperature at a decadal timescale. Multi-taper method spectral analysis detected some low- and high-frequency cycles (2.3–2.4-year, 2.8-year, 3.4–3.6-year, 5.0-year, 9.9-year and 27.0-year). Combining these cycles, the relationship of the low-frequency change with the Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) and Southern Oscillation (SO) suggested that the reconstructed temperature variations may be related to large-scale atmospheric-oceanic variations. Major volcanic eruptions were partly reflected in the reconstructed temperatures after high-pass filtering; these events promoted anomalous cooling in this region. The results of this study not only provide new information for assessing the long-term temperature changes in the Hexi Corridor of Northwest China, but also further demonstrate the effects of large-scale atmospheric-oceanic circulation on climate change in Northwest China. PMID:27509206

Using coral Ba/Ca records to investigate seasonal to decadal scale biogeochemical cycling in the surface and intermediate ocean.

NASA Astrophysics Data System (ADS)

LaVigne, M.; Cobb, K. M.; DeLong, K. L.; Freiberger, M. M.; Grottoli, A. G.; Hill, T. M.; Miller, H. R.; Nurhati, I. S.; Richey, J. N.; Serrato Marks, G.; Sherrell, R. M.

2016-12-01

Dissolved barium (BaSW), a bio-intermediate element, is linked to several biogeochemical processes such as the cycling and export of nutrients, organic carbon (Corg), and barite in surface and intermediate oceans. Dynamic BaSW cycling has been demonstrated in the water column on short timescales (days-weeks) while sedimentary records have documented geologic-scale changes in barite preservation driven by export production. Our understanding of how seasonal-decadal scale climate variability impacts these biogeochemical processes currently lacks robust records. Ba/Ca calibrations in surface and deep sea corals suggest barium is incorporated via cationic substitution in both aragonite and calcite. Here we demonstrate the utility of Ba/Ca for reconstructing biogeochemical variability using examples of surface and deep sea coral records. Century-long deep sea coral records from the California Current System (bamboo corals: 900-1500m) record interannual variations in Ba/Ca, likely reflecting changes in barite formation via bacterial Corg respiration or barite saturation state. A surface Porites coral Ba/Ca record from Christmas Island (central equatorial Pacific: 1978-1995) shows maxima during low productivity El Niño warm periods, suggesting that variations in BaSW are driven by biological removal via direct cellular uptake or indirectly via barite precipitation with the decomposition of large phytoplankton blooms at this location. Similarly, a sixteen-year long Siderastera siderea surface coral record from Dry Tortugas, FL (Gulf of Mexico: 1991-2007) shows seasonal Ba/Ca cycles that align with annual chlorophyll and δ13C. Taken together, these records demonstrate the linkages among Corg, nutrient cycling and BaSW in the surface and intermediate ocean on seasonal to decadal timescales. Multi-proxy paleoceanographic reconstructions including Ba/Ca have the potential to elucidate the mechanisms linking past climate, productivity, nutrients, and BaSW cycling in the past.

A Comprehensive Precipitation Data Set for Global Land Areas (TR-051)

DOE Data Explorer

Eischeid, J. K. [Univ. of Colorado, Boulder, CO (United States) Cooperative Inst. for Research in Environmental Sciences (CIRES); NOAA; Diaz, H. F. [Univ. of Colorado, Boulder, CO (United States). Cooperative Inst. for Research in Environmental Sciences (CIRES); NOAA; Bradley, R. S. [University of Massachusetts, Amherst, MA (USA); Jones, P. D. [University of East Anglia, Norwich, United Kingdom

1994-01-01

An expanded and updated compilation of long-term station precipitation data, together with a new set of gridded monthly mean fields for global land areas, are described. The present data set contains 5328 station records of monthly total precipitation, covering the period from the mid-1800s to the late 1980s. The station data were individually tested and visually inspected for the presence of spurious trends, jumps, and other measurement biases. The quality control procedure which was used to check the station records for nonclimatic discontinuities and other biases is detailed. We also discuss some of the problems which typically contribute to potential inhomogeneities in precipitation records. The station data were interpolated onto a 4° latitude by 5° longitude uniform grid. Comparisons of these data with two other global-scale precipitation climatologies are presented. We find good agreement among the three global-scale climatologies over the common areas in each set. Three different indices of long-term precipitation variations over the global land areas all indicate a general increase of annual precipitation since the 1940s, although a decline is evident over the last decade. There is some indication that the last few decades of the 19th century may have been as wet as the recent ones. An interesting feature of this study is the presence of relatively large differences in seasonal trends, with March-May and September-November becoming wetter in the last few decades. The December-February and June-August seasons exhibit smaller overall trends, although the northern winter season does exhibit large decadal-scale fluctuations.

A Combined Length-of-Day Series Spanning 1832-1997

NASA Technical Reports Server (NTRS)

Gross, Richard S.

1999-01-01

The Earth's rotation is not constant but exhibits minute changes on all observable time scales ranging from subdaily to secular. This rich spectrum of observed Earth rotation changes reflects the rich variety of astronomical and geophysical phenomena that are causing the Earth's rotation to change, including, but not limited to, ocean and solid body tides, atmospheric wind and pressure changes, oceanic current and sea level height changes, post-glacial rebound, and torques acting at the core-mantle boundary. In particular, the decadal-scale variations of the Earth's rotation are thought to be largely caused by interactions between the Earth's outer core and mantle. Comparing the inferred Earth rotation variations caused by the various core-mantle interactions to observed variations requires Earth rotation observations spanning decades, if not centuries. During the past century many different techniques have been used to observe the Earth's rotation. By combining the individual Earth rotation series determined by each of these techniques, a series of the Earth's rotation can be obtained that is based upon independent measurements spanning the greatest possible time interval. In this study, independent observations of the Earth's rotation are combined to generate a length-of-day series spanning 1832-1997. The observations combined include lunar occultation measurements spanning 1832-1955, optical astrometric measurements spanning 1956-1982, lunar laser ranging measurements spanning 1970-1997, and very long baseline interferometric measurements spanning 1978-1998. These series are combined using a Kalman filter developed at JPL for just this purpose. The resulting combined length-of-day series will be presented and compared with other available length-of-day series of similar duration.

Tropical Rainfall Variability on Interannual-to-Interdecadal/Longer-Time Scales Derived from the GPCP Monthly Product

NASA Technical Reports Server (NTRS)

Gu, Guojun; Adler, Robert F.; Huffman, George J.; Curtis, Scott

2006-01-01

Global and large regional rainfall variations and possible long-term changes are examined using the 26-year (1979-2004) GPCP monthly dataset (Adler et al., 2003). Our emphasis is to discriminate among variations due to ENSO, volcanic events, and possible long-term climate changes in the tropics. Although the global linear change of precipitation in the data set is near zero during the time period, an increase in tropical rainfall is noted, with a weaker decrease over northern hemisphere middle latitudes. Focusing on the tropics (25degS-25degN), the data set indicates an upward trend (0.06 mm/day/decade) and a downward trend (-0.02 mm/day/decade) over tropical ocean and land, respectively. This corresponds to an about 4.9% increase (ocean) and 1.6% decrease (land) during the entire 26-year time period. Techniques are applied to isolate and quantify variations due to ENSO and two major volcanic eruptions (El Chichon, March 1982; Pinatubo, June 1991) in order to examine longer time-scale changes. The ENSO events generally do not impact the tropical total rainfall, but, of course, induce significant anomalies with opposite signs over tropical land and ocean. The impact of the two volcanic eruptions is estimated to be about a 5% reduction in tropical rainfall over both land and ocean. A modified data set (with ENSO and volcano effects removed) retains the same approximate linear change slopes, but with reduced variance, thereby increasing the confidence levels associated with the long-term rainfall changes in the tropics 2

Variability of tropical cyclone in high frequent occurrence regions over the western North Pacific

NASA Astrophysics Data System (ADS)

Yang, Yuxing; Huang, Fei; Wang, Faming

2014-06-01

In this study, three high frequent occurrence regions of tropical cyclones (TCs), i.e., the northern South China Sea (the region S), the south Philippine Sea (the region P) and the region east of Taiwan Island (the region E), are defined with frequency of TC's occurrence at each grid for a 45-year period (1965-2009), where the frequency of occurrence (FO) of TCs is triple the mean value of the whole western North Pacific. Over the region S, there are decreasing trends in the FO of TCs, the number of TCs' tracks going though this region and the number of TCs' genesis in this region. Over the region P, the FO and tracks demonstrate decadal variation with periods of 10-12 year, while over the region E, a significant 4-5 years' oscillation appears in both FO and tracks. It is demonstrated that the differences of TCs' variation in these three different regions are mainly caused by the variation of the Western Pacific Subtropical High (WPSH) at different time scales. The westward shift of WPSH is responsible for the northwesterly anomaly over the region S which inhibits westward TC movement into the region S. On the decadal timescale, the WPSH stretches northwestward because of the anomalous anticyclone over the northwestern part of the region P, and steers more TCs reaching the region P in the greater FO years of the region P. The retreating of the WPSH on the interannual time scale is the main reason for the FO's oscillation over the region E.

The role of climate on inter-annual variation in stream nitrate fluxes and concentrations.

PubMed

Gascuel-Odoux, Chantal; Aurousseau, Pierre; Durand, Patrick; Ruiz, Laurent; Molenat, Jérôme

2010-11-01

In recent decades, temporal variations in nitrate fluxes and concentrations in temperate rivers have resulted from the interaction of anthropogenic and climatic factors. The effect of climatic drivers remains unclear, while the relative importance of the drivers seems to be highly site dependent. This paper focuses on 2-6 year variations called meso-scale variations, and analyses the climatic drivers of these variations in a study site characterized by high N inputs from intensive animal farming systems and shallow aquifers with impervious bedrock in a temperate climate. Three approaches are developed: 1) an analysis of long-term records of nitrate fluxes and nitrate concentrations in 30 coastal rivers of Western France, which were well-marked by meso-scale cycles in the fluxes and concentration with a slight hysteresis; 2) a test of the climatic control using a lumped two-box model, which demonstrates that hydrological assumptions are sufficient to explain these meso-scale cycles; and 3) a model of nitrate fluxes and concentrations in two contrasted catchments subjected to recent mitigation measures, which analyses nitrate fluxes and concentrations in relation to N stored in groundwater. In coastal rivers, hydrological drivers (i.e., effective rainfall), and particularly the dynamics of the water table and rather stable nitrate concentration, explain the meso-scale cyclic patterns. In the headwater catchment, agricultural and hydrological drivers can interact according to their settings. The requirements to better distinguish the effect of climate and human changes in integrated water management are addressed: long-term monitoring, coupling the analysis and the modelling of large sets of catchments incorporating different sizes, land uses and environmental factors. Copyright © 2009 Elsevier B.V. All rights reserved.

Solar activity, the QBO, and tropospheric responses

NASA Technical Reports Server (NTRS)

Tinsley, Brian A.; Brown, Geoffrey M.; Scherrer, Philip H.

1989-01-01

The suggestion that galactic cosmic rays (GCR) as modulated by the solar wind are the carriers of the component of solar variability that affects weather and climate has been discussed in the literature for 30 years, and there is now a considerable body of evidence that supports it. Variations of GCR occur with the 11 year solar cycle, matching the time scale of recent results for atmospheric variations, as modulated by the quasibiennial oscillation of equatorial stratospheric winds (the QBO). Variations in GCR occur on the time scale of centuries with a well defined peak in the coldest decade of the little ice age. New evidence is presented on the meteorological responses to GCR variations on the time scale of a few days. These responses include changes in the vertical temperature profile in the troposphere and lower stratosphere in the two days following solar flare related high speed plasma streams and associated GCR decreases, and in decreases in Vorticity Area Index (VAI) following Forbush decreases of GCR. The occurrence of correlations of GCR and meteorological responses on all three time scales strengthens the hypothesis of GCR as carriers of solar variability to the lower atmosphere. Both short and long term tropospheric responses are understandable as changes in the intensity of cyclonic storms initiated by mechanisms involving cloud microphysical and cloud electrification processes, due to changes in local ion production from changes in GCR fluxes and other high energy particles in the MeV to low GeV range. The nature of these mechanisms remains undetermined. Possible stratospheric wind (particularly QBO) effects on the transport of HNO3 and other constituents incorporated in cluster ions and possible condensation and freezing nuclei are considered as relevant to the long term variations.

The frequency response of a coupled ice sheet-ice shelf-ocean system to climate forcing variability

NASA Astrophysics Data System (ADS)

Goldberg, D.; Snow, K.; Jordan, J. R.; Holland, P.; Arthern, R. J.

2017-12-01

Changes at the West Antarctic ice-ocean boundary in recent decades has triggered significant increases in the regions contribution to global sea-level rise, coincident with large scale, and in some cases potentially unstable, grounding line retreat. Much of the induced change is thought to be driven by fluctuations in the oceanic heat available at the ice-ocean boundary, transported on-shelf via warm Circumpolar Deep Water (CDW). However, the processes in which ocean heat drives ice-sheet loss remains poorly understood, with observational studies routinely hindered by the extreme environment notorious to the Antarctic region. In this study we apply a novel synchronous coupled ice-ocean model, developed within the MITgcm, and are thus able to provide detailed insight into the impacts of short time scale (interannual to decadal) climate variability and feedbacks within the ice-ocean system. Feedbacks and response are assessed in an idealised ice-sheet/ocean-cavity configuration in which the far field ocean condition is adjusted to emulate periodic climate variability patterns. We reveal a non-linear response of the ice-sheet to periodic variations in thermocline depth. These non-linearities illustrate the heightened sensitivity of fast flowing ice-shelves to periodic perturbations in heat fluxes occurring at interannual and decadal time scales. The results thus highlight how small perturbations in variable climate forcing, like that of ENSO, may trigger large changes in ice-sheet response.

Climate control of decadal-scale increases in apparent ages of eogenetic karst spring water

NASA Astrophysics Data System (ADS)

Martin, Jonathan B.; Kurz, Marie J.; Khadka, Mitra B.

2016-09-01

Water quantity and quality in karst aquifers may depend on decadal-scale variations in recharge or withdrawal, which we hypothesize could be assessed through time-series measurements of apparent ages of spring water. We tested this hypothesis with analyses of various age tracers (3H/3He, SF6, CFC-11, CFC-12, CFC-113) and selected solute concentrations [dissolved oxygen (DO), NO3, Mg, and SO4] from 6 springs in a single spring complex (Ichetucknee springs) in northern Florida over a 16-yr period. These springs fall into two groups that reflect shallow short (Group 1) and deep long (Group 2) flow paths. Some tracer concentrations are altered, with CFC-12 and CFC-113 concentrations yielding the most robust apparent ages. These tracers show a 10-20-yr monotonic increase in apparent age from 1997 to 2013, including the flood recession that followed Tropical Storm Debby in mid-2012. This increase in age indicates most water discharged during the study period recharged the aquifer within a few years of 1973 for Group 2 springs and 1980 for Group 1 springs. Inverse correlations between apparent age and DO and NO3 concentrations reflect reduced redox state in older water. Positive correlations between apparent age and Mg and SO4 concentrations reflect increased water-rock reactions. Concentrated recharge in the decade around 1975 resulted from nearly 2 m of rain in excess of the monthly average that fell between 1960 and 2014, followed by a nearly 4 m deficit to 2014. This excess rain coincided with two major El Niño events during the maximum cool phase in the Atlantic Multidecadal Oscillation. Although regional water withdrawal increased nearly 5-fold between 1980 and 2005, withdrawals represent only 2-5% of Ichetucknee River flow and are less important than decadal-long variations in precipitation. These results suggest that groundwater management should consider climate cycles as predictive tools for future water resources.

Role of the North Atlantic Ocean in Low Frequency Climate Variability

NASA Astrophysics Data System (ADS)

Danabasoglu, G.; Yeager, S. G.; Kim, W. M.; Castruccio, F. S.

2017-12-01

The Atlantic Ocean is a unique basin with its extensive, North - South overturning circulation, referred to as the Atlantic meridional overturning circulation (AMOC). AMOC is thought to represent the dynamical memory of the climate system, playing an important role in decadal and longer time scale climate variability as well as prediction of the earth's future climate on these time scales via its large heat and salt transports. This oceanic memory is communicated to the atmosphere primarily through the influence of persistent sea surface temperature (SST) variations. Indeed, many modeling studies suggest that ocean circulation, i.e., AMOC, is largely responsible for the creation of coherent SST variability in the North Atlantic, referred to as Atlantic Multidecadal Variability (AMV). AMV has been linked to many (multi)decadal climate variations in, e.g., Sahel and Brazilian rainfall, Atlantic hurricane activity, and Arctic sea-ice extent. In the absence of long, continuous observations, much of the evidence for the ocean's role in (multi)decadal variability comes from model simulations. Although models tend to agree on the role of the North Atlantic Oscillation in creating the density anomalies that proceed the changes in ocean circulation, model fidelity in representing variability characteristics, mechanisms, and air-sea interactions remains a serious concern. In particular, there is increasing evidence that models significantly underestimate low frequency variability in the North Atlantic compared to available observations. Such model deficiencies can amplify the relative influence of external or stochastic atmospheric forcing in generating (multi)decadal variability, i.e., AMV, at the expense of ocean dynamics. Here, a succinct overview of the current understanding of the (North) Atlantic Ocean's role on the regional and global climate, including some outstanding questions, will be presented. In addition, a few examples of the climate impacts of the AMV via atmospheric teleconnections from a set of coupled simulations, also considering the relative roles of its tropical and extratropical components, will be highlighted.

What Causes the North Sea Level to Rise Faster over the Last Decade ?

NASA Astrophysics Data System (ADS)

Karpytchev, Mikhail; Letetrel, Camille

2013-04-01

We combined tide gauge records (PSMSL) and satellite altimetry data (TOPEX/POSEIDON-JASON 1-2) to reconstruct the mean level of the North Sea and the Norwegian Sea Shelf (NS-NSS) over 1950-2012. The reconstructed NS-NSS mean sea level fluctuations reveal a pronounced interannual variability and a strong sea level acceleration since the mid-1990's. In order to understand the causes of this acceleration, the NS-NSS mean sea level was cross-correlated with the North Atlantic Oscillation and Arctic Oscillation indices. While the interannual variability of the mean sea level correlates well with the NAO/AO indices, the observed acceleration in the NS-NSS mean level is not linked linearly to the NAO/AO fluctuations. On the other hand, the Empirical Orthogonal Functions (EOF) analysis of steric sea level variations in the eastern North Atlantic gives a dominant EOF pattern (55% of variance explained) that varies on a decadal scale very closely to the NS-NSS mean level flcutuations. Also, the amplification in the temporal amplitude of the dominant steric sea level EOF corresponds to the acceleration observed in the NS-NSS mean sea level signal. This suggests that decadal variations in the mean level of the North Sea - the Norwegian Sea Shelf reflect changes in the Subpolar Front currents (Rossby, 1996).

Analysis of Decadal Vegetation Dynamics Using Multi-Scale Satellite Images

NASA Astrophysics Data System (ADS)

Chiang, Y.; Chen, K.

2013-12-01

This study aims at quantifying vegetation fractional cover (VFC) by incorporating multi-resolution satellite images, including Formosat-2(RSI), SPOT(HRV/HRG), Landsat (MSS/TM) and Terra/Aqua(MODIS), to investigate long-term and seasonal vegetation dynamics in Taiwan. We used 40-year NDVI records for derivation of VFC, with field campaigns routinely conducted to calibrate the critical NDVI threshold. Given different sensor capabilities in terms of their spatial and spectral properties, translation and infusion of NDVIs was used to assure NDVI coherence and to determine the fraction of vegetation cover at different spatio-temporal scales. Based on the proposed method, a bimodal sequence of intra-annual VFC which corresponds to the dual-cropping agriculture pattern was observed. Compared to seasonal VFC variation (78~90%), decadal VFC reveals moderate oscillations (81~86%), which were strongly linked with landuse changes and several major disturbances. This time-series mapping of VFC can be used to examine vegetation dynamics and its response associated with short-term and long-term anthropogenic/natural events.

Long-term visibility variation in Athens (1931-2013): a proxy for local and regional atmospheric aerosol loads

NASA Astrophysics Data System (ADS)

Founda, Dimitra; Kazadzis, Stelios; Mihalopoulos, Nikolaos; Gerasopoulos, Evangelos; Lianou, Maria; Raptis, Panagiotis I.

2016-09-01

This study explores the interdecadal variability and trends of surface horizontal visibility at the urban area of Athens from 1931 to 2013, using the historical archives of the National Observatory of Athens (NOA). A prominent deterioration of visibility in the city was detected, with the long-term linear trend amounting to -2.8 km decade-1 (p < 0.001), over the entire study period. This was not accompanied by any significant trend in relative humidity or precipitation over the same period. A slight recovery of visibility levels seems to be established in the recent decade (2004-2013). It was found that very good visibility (> 20 km) occurred at a frequency of 34 % before the 1950s, while this percentage drops to just 2 % during the decade 2004-2013. The rapid impairment of the visual air quality in Athens around the 1950s points to the increased levels of air pollution on a local and/or regional scale, related to high urbanization rates and/or increased anthropogenic emissions on a global scale at that period. Visibility was found to be negatively/positively correlated with relative humidity/wind speed, the correlation being statistically valid at certain periods. Wind regime and mainly wind direction and corresponding air mass origin were found to highly control visibility levels in Athens. The comparison of visibility variation in Athens and at a non-urban reference site on Crete island revealed similar negative trends over the common period of observations. This suggests that apart local sources, visibility in Athens is highly determined by aerosol load of regional origin. AVHRR and MODIS satellite-derived aerosol optical depth (AOD) retrievals over Athens and surface measurements of PM10 confirmed the relation of visibility to aerosol load.

Decline in global oceanic oxygen content during the past five decades.

PubMed

Schmidtko, Sunke; Stramma, Lothar; Visbeck, Martin

2017-02-15

Ocean models predict a decline in the dissolved oxygen inventory of the global ocean of one to seven per cent by the year 2100, caused by a combination of a warming-induced decline in oxygen solubility and reduced ventilation of the deep ocean. It is thought that such a decline in the oceanic oxygen content could affect ocean nutrient cycles and the marine habitat, with potentially detrimental consequences for fisheries and coastal economies. Regional observational data indicate a continuous decrease in oceanic dissolved oxygen concentrations in most regions of the global ocean, with an increase reported in a few limited areas, varying by study. Prior work attempting to resolve variations in dissolved oxygen concentrations at the global scale reported a global oxygen loss of 550 ± 130 teramoles (10 12  mol) per decade between 100 and 1,000 metres depth based on a comparison of data from the 1970s and 1990s. Here we provide a quantitative assessment of the entire ocean oxygen inventory by analysing dissolved oxygen and supporting data for the complete oceanic water column over the past 50 years. We find that the global oceanic oxygen content of 227.4 ± 1.1 petamoles (10 15  mol) has decreased by more than two per cent (4.8 ± 2.1 petamoles) since 1960, with large variations in oxygen loss in different ocean basins and at different depths. We suggest that changes in the upper water column are mostly due to a warming-induced decrease in solubility and biological consumption. Changes in the deeper ocean may have their origin in basin-scale multi-decadal variability, oceanic overturning slow-down and a potential increase in biological consumption.

Multi-decadal to centennial scale variations in sea surface temperature off southeast Korea over the last 2000 yr

NASA Astrophysics Data System (ADS)

Lee, K. E.; Park, W.; Bae, S. W.; Nam, S. I.

2016-12-01

We have reconstructed variations in sea surface temperature (SST) for the last 2000 yr by using the alkenone unsaturation index of marine sediments of cores TY2010 PC4 and ARA/ES 03-01 GC01 recovered from the southwestern part of the East Sea. The core site is chracterized by very high sedimentation rate so that a new high-resolution continuous SST record can be reconstructed with an average temporal resolution of 2-7 years. The core top alkenone temperature (20.5°C) is higher than the annual averaged in situ SST (18 °C) and it corresponds to those of summer to autumn. During the last 2000 yr, the alkenone temperatures exhibited fluctuations on multi-decadal to centennial time scales. The temperatures were relatively warm fluctuating between 19.6°C and 21°C on centennial time scale during the period of AD 0- 1200. There were two evident cold periods: AD 1200-1400 and AD 1600-1800. The lowest temperature (approximately 18°C) occurred at AD 1290 and AD 1650. The temperatures increased toward 20 centry, which is consistent with anthropogenic global warming. Results of singular spectrum analysis of the last 2000 yr SST record suggest that there is characteristic periodicity of 100 yr and 160 yr and 50-60 yr, which can be natural variability of climate system. In addition, a comparison of the SST record with global volcanic forcing data shows that volcanic events also can be correlated to the distinct cooling events.

Holocene Multi-Decadal to Millennial-Scale Hydrologic Variability on the South American Altiplano

NASA Astrophysics Data System (ADS)

Fritz, S. C.; Baker, P. A.; Ekdahl, E.; Burns, S.

2006-12-01

On orbital timescales, lacustrine sediment records in the tropical central Andes show massive changes in lake level due to mechanisms related to global-scale drivers, varying at precessional timescales. Here we use stable isotopic and diatom records from two lakes in the Lake Titicaca drainage basin to reconstruct multi- decadal to millennial scale precipitation variability during the last 7000 to 8000 years. The records are tightly coupled at multi-decadal to millennial scales with each other and with lake-level fluctuations in Lake Titicaca, indicating that the lakes are recording a regional climate signal. A quantitative reconstruction of precipitation from stable isotopic data indicates that the central Andes underwent significant wet to dry alternations at multi- centennial frequencies with an amplitude of 30 to 40% of total precipitation. A strong millennial-scale component, similar in duration to periods of increased ice rafted debris flux in the North Atlantic, is observed in both lake records, suggesting that tropical North Atlantic sea-surface temperature (SST) variability may partly control regional precipitation. No clear relationship is evident between these records and the inferred ENSO history from Lago Pallcacocha in the northern tropical Andes. In the instrumental period, regional precipitation variability on inter-annual timescales is clearly influenced by Pacific modes; for example, most El Ninos produce dry and warm conditions in this part of the central Andes. However, on longer timescales, the control of tropical Pacific modes is less clear. Our reconstructions suggest that the cold intervals of the Holocene Bond events are periods of increased precipitation in the central Andes, thus indicating an anti-phasing of precipitation variation in the southern tropics of South America relative to the Northern Hemisphere monsoon region.

Intra- and inter-population variability and evaluation of the physical development of a young generation.

PubMed

Yampolskaya, Yulia A

2005-07-01

This study is concerned with long-term anthropometric examinations of children and adolescents aged 3-17 years in Moscow (over 10,500 persons, longitudinal and cross-sectional). Population variability of physical development was analyzed by means of regional estimation tables, which were developed on the basis of a regression analysis (scale of the regression of body mass to body length within a range from M - 1sigmaR to M + 2 sigmaR) and used for individual and group diagnostics taking into account age and sex. Such an approach allowed for the determination of the dynamics of the variability of Moscow schoolchildren from decade to decade (inter-population variability) and variations due to social differences (intra-population variability).

Variability in rainfall over tropical Australia during summer and relationships with the Bilybara High

NASA Astrophysics Data System (ADS)

Reason, C. J. C.

2018-04-01

Variability in summer rainfall over tropical Australia, defined here as that part of the continent north of 25° S, and its linkages with regional circulation are examined. In particular, relationships with the mid-level anticyclone (termed the Bilybara High) that exists over the northwestern Australia/Timor Sea region between August and April are considered. This High forms to the southwest of the upper-level anticyclone via a balance between the upper-level divergence over the region of tropical precipitation maximum and planetary vorticity advection and moves south and strengthens during the spring and summer. It is shown that variations in the strength and position of the Bilybara High are related to anomalies in precipitation and temperature over large parts of tropical Australia as well as some areas in the south and southeast of the landmass. Some of the interannual variations in the High are related to ENSO, but there are also a number of neutral years with large anomalies in the High and hence in rainfall. On decadal time scales, a strong relationship exists between the leading mode of tropical Australian rainfall and the Bilybara High. On both interannual and decadal scales, the relationships between the High and the regional rainfall involve changes in the monsoonal northwesterlies blowing towards northern Australia, and further south, in the easterly trade winds over the region.

Decadal variation in Earth's oblateness (J2) from satellite laser ranging data

NASA Astrophysics Data System (ADS)

Cheng, Minkang; Ries, John C.

2018-02-01

For four decades, satellite laser ranging has recorded the global nature of the long-wavelength hydrological mass redistribution within the Earth system, which results in significant variations in the Earth's dynamical oblateness, characterized by the second degree zonal geopotential spherical harmonic J2 (or C20). Analysis of the J2 time-series has shown a significant variation related to the strong El Niño-Southern Oscillation events with periods of 2-6 yr. In particular, the variation related to the powerful 2015-2016 El Niño that peaked during 2015 November-December was one of the strongest on record, comparable with the 1982-1983 and 1997-1998 events. In this study, we investigate further the hydrological mass transfer between atmosphere-ocean-land and their signature in the decadal variations of J2 with timescales of ˜10 yr. We found that the ˜6.4-yr variations can be accounted for by the atmosphere and ocean mass variations based on the improved Atmosphere-Ocean De-aliasing data, and the observed decadal variation in J2 correlates well with the decadal tropical variability characterized by the 5-yr running mean of the El Niño-Southern Oscillation Index, although existing physical models, especially the land water storage, are limited for the purpose of further studies of the excitation.

Monitoring and understanding changes in heat waves, cold waves, floods, and droughts in the United States: State of knowledge

USGS Publications Warehouse

Peterson, Thomas C.; Heim, Richard R.; Hirsch, Robert M.; Kaiser, Dale P.; Brooks, Harold; Diffenbaugh, Noah S.; Dole, Randall M.; Giovannettone, Jason P.; Guirguis, Kristen; Karl, Thomas R.; Katz, Richard W.; Kunkel, Kenneth E.; Lettenmaier, Dennis P.; McCabe, Gregory J.; Paciorek, Christopher J.; Ryberg, Karen R.; K Wolter, BS Silva; Schubert, Siegfried; Silva, Viviane B. S.; Stewart, Brooke C.; Vecchia, Aldo V.; Villarini, Gabriele; Vose, Russell S.; Walsh, John; Wehner, Michael; Wolock, David; Wolter, Klaus; Woodhouse, Connie A.; Wuebbles, Donald

2013-01-01

Weather and climate extremes have been varying and changing on many different time scales. In recent decades, heat waves have generally become more frequent across the United States, while cold waves have been decreasing. While this is in keeping with expectations in a warming climate, it turns out that decadal variations in the number of U.S. heat and cold waves do not correlate well with the observed U.S. warming during the last century. Annual peak flow data reveal that river flooding trends on the century scale do not show uniform changes across the country. While flood magnitudes in the Southwest have been decreasing, flood magnitudes in the Northeast and north-central United States have been increasing. Confounding the analysis of trends in river flooding is multiyear and even multidecadal variability likely caused by both large-scale atmospheric circulation changes and basin-scale “memory” in the form of soil moisture. Droughts also have long-term trends as well as multiyear and decadal variability. Instrumental data indicate that the Dust Bowl of the 1930s and the drought in the 1950s were the most significant twentieth-century droughts in the United States, while tree ring data indicate that the megadroughts over the twelfth century exceeded anything in the twentieth century in both spatial extent and duration. The state of knowledge of the factors that cause heat waves, cold waves, floods, and drought to change is fairly good with heat waves being the best understood.

The summer North Atlantic Oscillation (SNAO) variability on decadal to paleoclimate time scales

NASA Astrophysics Data System (ADS)

Linderholm, H. W.; Folland, C. K.; Zhang, P.; Gunnarson, B. E.; Jeong, J. H.; Ren, H.

2017-12-01

The summer North Atlantic Oscillation (SNAO), strongly related to the latitude of the North Atlantic and European summer storm tracks, exerts a considerable influence on European summer climate variability and extremes. Here we extend the period covered by the SNAO from July and August to June, July and August (JJA). As well as marked interannual variability, the JJA SNAO has shown a large inter-decadal change since the 1970s. Decadally averaged, there has been a change from a very positive to a rather negative SNAO phase. This change in SNAO phase is opposite in sign from that expected by a number of climate models under enhanced greenhouse forcing by the late twenty first century. It has led to noticeably wetter summers in North West Europe in the last decade. On interannual to multidecadal timescales, SNAO variability is linked to variations in North Atlantic sea surface temperature (SST): observations and models indicate an association between the Atlantic Multi-decadal Oscillation (AMO) where the cold (warm) phase of the AMO corresponds a positive (negative) phase of the SNAO. Observations also indicate a link with SST in the Gulf Stream region of the North Atlantic where, particularly on decadal time scales, SST warming may favour a more positive phase of the SNAO. Influences of Arctic climate change on North Atlantic and European atmospheric circulation may also exist, particularly reduced sea ice coverage, perhaps favouring the negative phase of the SNAO. A new tree-ring data based JJA SNAO reconstruction extending over the last millennium, as well as climate model output for the same period, enables us to examine the influence of North Atlantic SST and Arctic sea-ice coverage, as well as SNAO impacts on European summer climate, in a long-term, pre-industrial context.

Reply to 'Comments on upscaling geochemical reaction rates usingpore-scale network modeling' by Peter C. Lichtner and Qinjun Kang

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

Li, Li; Peters, Catherine A.; Celia, Michael A.

2006-05-03

Our paper "Upscaling geochemical reaction rates usingpore-scale network modeling" presents a novel application of pore-scalenetwork modeling to upscale mineral dissolution and precipitationreaction rates from the pore scale to the continuum scale, anddemonstrates the methodology by analyzing the scaling behavior ofanorthite and kaolinite reaction kinetics under conditions related to CO2sequestration. We conclude that under highly acidic conditions relevantto CO2 sequestration, the traditional continuum-based methodology may notcapture the spatial variation in concentrations from pore to pore, andscaling tools may be important in correctly modeling reactive transportprocesses in such systems. This work addresses the important butdifficult question of scaling mineral dissolution and precipitationreactionmore » kinetics, which is often ignored in fields such as geochemistry,water resources, and contaminant hydrology. Although scaling of physicalprocesses has been studied for almost three decades, very few studieshave examined the scaling issues related to chemical processes, despitetheir importance in governing the transport and fate of contaminants insubsurface systems.« less

Modes and emergent time scales of embayed beach dynamics

NASA Astrophysics Data System (ADS)

Ratliff, Katherine M.; Murray, A. Brad

2014-10-01

In this study, we use a simple numerical model (the Coastline Evolution Model) to explore alongshore transport-driven shoreline dynamics within generalized embayed beaches (neglecting cross-shore effects). Using principal component analysis (PCA), we identify two primary orthogonal modes of shoreline behavior that describe shoreline variation about its unchanging mean position: the rotation mode, which has been previously identified and describes changes in the mean shoreline orientation, and a newly identified breathing mode, which represents changes in shoreline curvature. Wavelet analysis of the PCA mode time series reveals characteristic time scales of these modes (typically years to decades) that emerge within even a statistically constant white-noise wave climate (without changes in external forcing), suggesting that these time scales can arise from internal system dynamics. The time scales of both modes increase linearly with shoreface depth, suggesting that the embayed beach sediment transport dynamics exhibit a diffusive scaling.

Climate fails to predict wood decomposition at regional scales

NASA Astrophysics Data System (ADS)

Bradford, Mark A.; Warren, Robert J., II; Baldrian, Petr; Crowther, Thomas W.; Maynard, Daniel S.; Oldfield, Emily E.; Wieder, William R.; Wood, Stephen A.; King, Joshua R.

2014-07-01

Decomposition of organic matter strongly influences ecosystem carbon storage. In Earth-system models, climate is a predominant control on the decomposition rates of organic matter. This assumption is based on the mean response of decomposition to climate, yet there is a growing appreciation in other areas of global change science that projections based on mean responses can be irrelevant and misleading. We test whether climate controls on the decomposition rate of dead wood--a carbon stock estimated to represent 73 +/- 6 Pg carbon globally--are sensitive to the spatial scale from which they are inferred. We show that the common assumption that climate is a predominant control on decomposition is supported only when local-scale variation is aggregated into mean values. Disaggregated data instead reveal that local-scale factors explain 73% of the variation in wood decomposition, and climate only 28%. Further, the temperature sensitivity of decomposition estimated from local versus mean analyses is 1.3-times greater. Fundamental issues with mean correlations were highlighted decades ago, yet mean climate-decomposition relationships are used to generate simulations that inform management and adaptation under environmental change. Our results suggest that to predict accurately how decomposition will respond to climate change, models must account for local-scale factors that control regional dynamics.

Changes in intense tropical cyclone activity for the western North Pacific during the last decades derived from a regional climate model simulation

NASA Astrophysics Data System (ADS)

Barcikowska, Monika; Feser, Frauke; Zhang, Wei; Mei, Wei

2017-11-01

An atmospheric regional climate model (CCLM) was employed to dynamically downscale atmospheric reanalyses (NCEP/NCAR 1, ERA 40) over the western North Pacific and South East Asia. This approach is used for the first time to reconstruct a tropical cyclone climatology, which extends beyond the satellite era and serves as an alternative data set for inhomogeneous observation-derived records (Best Track Data sets). The simulated TC climatology skillfully reproduces observations of the recent decades (1978-2010), including spatial patterns, frequency, lifetime, trends, variability on interannual and decadal time scales and their association with the large-scale circulation patterns. These skills, facilitated here with the spectral nudging method, seem to be a prerequisite to understand the factors determining spatio-temporal variability of TC activity over the western North Pacific. Long-term trends (1948-2011 and 1959-2001) in both simulations show a strong increase of intense tropical cyclone activity. This contrasts with pronounced multidecadal variations found in observations. The discrepancy may partly originate from temporal inhomogeneities in atmospheric reanalyses and Best Track Data, which affect both the model-based and observational-based trends. An adjustment, which removes the simulated upward trend, reduces the apparent discrepancy. Ultimately, our observational and modeling analysis suggests an important contribution of multi-decadal fluctuations in the TC activity during the last six decades. Nevertheless, due to the uncertainties associated with the inconsistencies and quality changes of those data sets, we call for special caution when reconstructing long-term TC statistics either from atmospheric reanalyses or Best Track Data.

Decadal Variations in Eastern Canada's Taiga Wood Biomass Production Forced by Ocean-Atmosphere Interactions.

PubMed

Boucher, Etienne; Nicault, Antoine; Arseneault, Dominique; Bégin, Yves; Karami, Mehdi Pasha

2017-05-26

Across Eastern Canada (EC), taiga forests represent an important carbon reservoir, but the extent to which climate variability affects this ecosystem over decades remains uncertain. Here, we analyze an extensive network of black spruce (Picea mariana Mill.) ring width and wood density measurements and provide new evidence that wood biomass production is influenced by large-scale, internal ocean-atmosphere processes. We show that while black spruce wood biomass production is primarily governed by growing season temperatures, the Atlantic ocean conveys heat from the subtropics and influences the decadal persistence in taiga forests productivity. Indeed, we argue that 20-30 years periodicities in Sea Surface Temperatures (SSTs) as part of the the Atlantic Multi-decadal Oscillation (AMO) directly influence heat transfers to adjacent lands. Winter atmospheric conditions associated with the North Atlantic Oscillation (NAO) might also impact EC's taiga forests, albeit indirectly, through its effect on SSTs and sea ice conditions in surrounding seas. Our work emphasizes that taiga forests would benefit from the combined effects of a warmer atmosphere and stronger ocean-to-land heat transfers, whereas a weakening of these transfers could cancel out, for decades or longer, the positive effects of climate change on Eastern Canada's largest ecosystem.

Individualistic sensitivities and exposure to climate change explain variation in species’ distribution and abundance changes

PubMed Central

Palmer, Georgina; Hill, Jane K.; Brereton, Tom M.; Brooks, David R.; Chapman, Jason W.; Fox, Richard; Oliver, Tom H.; Thomas, Chris D.

2015-01-01

The responses of animals and plants to recent climate change vary greatly from species to species, but attempts to understand this variation have met with limited success. This has led to concerns that predictions of responses are inherently uncertain because of the complexity of interacting drivers and biotic interactions. However, we show for an exemplar group of 155 Lepidoptera species that about 60% of the variation among species in their abundance trends over the past four decades can be explained by species-specific exposure and sensitivity to climate change. Distribution changes were less well predicted, but nonetheless, up to 53% of the variation was explained. We found that species vary in their overall sensitivity to climate and respond to different components of the climate despite ostensibly experiencing the same climate changes. Hence, species have undergone different levels of population “forcing” (exposure), driving variation among species in their national-scale abundance and distribution trends. We conclude that variation in species’ responses to recent climate change may be more predictable than previously recognized. PMID:26601276

Analysis of Vegetation Index Variations and the Asian Monsoon Climate

NASA Technical Reports Server (NTRS)

Shen, Sunhung; Leptoukh, Gregory G.; Gerasimov, Irina

2012-01-01

Vegetation growth depends on local climate. Significant anthropogenic land cover and land use change activities over Asia have changed vegetation distribution as well. On the other hand, vegetation is one of the important land surface variables that influence the Asian Monsoon variability through controlling atmospheric energy and water vapor conditions. In this presentation, the mean and variations of vegetation index of last decade at regional scale resolution (5km and higher) from MODIS have been analyzed. Results indicate that the vegetation index has been reduced significantly during last decade over fast urbanization areas in east China, such as Yangtze River Delta, where local surface temperatures were increased significantly in term of urban heat Island. The relationship between vegetation Index and climate (surface temperature, precipitation) over a grassland in northern Asia and over a woody savannas in southeast Asia are studied. In supporting Monsoon Asian Integrated Regional Study (MAIRS) program, the data in this study have been integrated into Giovanni, the online visualization and analysis system at NASA GES DISC. Most images in this presentation are generated from Giovanni system.

Interplay of water and reactive elements in oxidation of alumina-forming alloys.

PubMed

Mortazavi, N; Geers, C; Esmaily, M; Babic, V; Sattari, M; Lindgren, K; Malmberg, P; Jönsson, B; Halvarsson, M; Svensson, J E; Panas, I; Johansson, L G

2018-06-11

High-temperature alloys are crucial to many important technologies that underpin our civilization. All these materials rely on forming an external oxide layer (scale) for corrosion protection. Despite decades of research on oxide scale growth, many open questions remain, including the crucial role of the so-called reactive elements and water. Here, we reveal the hitherto unknown interplay between reactive elements and water during alumina scale growth, causing a metastable 'messy' nano-structured alumina layer to form. We propose that reactive-element-decorated, hydroxylated interfaces between alumina nanograins enable water to access an inner cathode in the bottom of the scale, at odds with the established scale growth scenario. As evidence, hydride-nanodomains and reactive element/hydrogen (deuterium) co-variation are observed in the alumina scale. The defect-rich alumina subsequently recrystallizes to form a protective scale. First-principles modelling is also performed to validate the RE effect. Our findings open up promising avenues in oxidation research and suggest ways to improve alloy properties.

Climate of the Arctic marine environment.

PubMed

Walsh, John E

2008-03-01

The climate of the Arctic marine environment is characterized by strong seasonality in the incoming solar radiation and by tremendous spatial variations arising from a variety of surface types, including open ocean, sea ice, large islands, and proximity to major landmasses. Interannual and decadal-scale variations are prominent features of Arctic climate, complicating the distinction between natural and anthropogenically driven variations. Nevertheless, climate models consistently indicate that the Arctic is the most climatically sensitive region of the Northern Hemisphere, especially near the sea ice margins. The Arctic marine environment has shown changes over the past several decades, and these changes are part of a broader global warming that exceeds the range of natural variability over the past 1000 years. Record minima of sea ice coverage during the past few summers and increased melt from Greenland have important implications for the hydrographic regime of the Arctic marine environment. The recent changes in the atmosphere (temperature, precipitation, pressure), sea ice, and ocean appear to be a coordinated response to systematic variations of the large-scale atmospheric circulation, superimposed on a general warming that is likely associated with increasing greenhouse gases. The changes have been sufficiently large in some sectors (e.g., the Bering/Chukchi Seas) that consequences for marine ecosystems appear to be underway. Global climate models indicate an additional warming of several degrees Celsius in much of the Arctic marine environment by 2050. However, the warming is seasonal (largest in autumn and winter), spatially variable, and closely associated with further retreat of sea ice. Additional changes predicted for 2050 are a general decrease of sea level pressure (largest in the Bering sector) and an increase of precipitation. While predictions of changes in storminess cannot be made with confidence, the predicted reduction of sea ice cover will almost certainly lead to increased oceanic mixing, ocean wave generation, and coastal flooding.

The Baltic Sea natural long-term variability of salinity

NASA Astrophysics Data System (ADS)

Schimanke, Semjon; Markus Meier, H. E.

2015-04-01

The Baltic Sea is one of the largest brackish sea areas of the world. The sensitive state of the Baltic Sea is sustained by a fresh-water surplus by river discharge and precipitation on one hand as well as inflows of highly saline and oxygen-rich water masses from the North Sea on the other. Major inflows which are crucial for the renewal of the deep water occur very intermittent with a mean frequency of approximately one per year. Stagnation periods (periods without major inflows) lead for instance to a reduction of oxygen concentration in the deep Baltic Sea spreading hypoxic conditions. Depending on the amount of salt water inflow and fresh-water supply the deep water salinity of the Baltic Sea varies between 11 to 14 PSU on the decadal scale. The goal of this study is to understand the contribution of different driving factors for the decadal to multi-decadal variability of salinity in the Baltic Sea. Continuous measurement series of salinity exist from the 1950 but are not sufficiently long for the investigation of long-term fluctuations. Therefore, a climate simulation of more than 800 years has been carried out with the Rossby Center Ocean model (RCO). RCO is a biogeochemical regional climate model which covers the entire Baltic Sea. It is driven with atmospheric data dynamical downscaled from a GCM mimicking natural climate variability. The analysis focus on the role of variations in river discharge and precipitation, changes in wind speed and direction, fluctuations in temperature and shifts in large scale pressure patterns (e.g. NAO). Hereby, the length of the simulation will allow to identify mechanisms working on decadal to multi-decadal time scales. Moreover, it will be discussed how likely long stagnation periods are under natural climate variability and if the observed exceptional long stagnation period between 1983-1993 might be related to beginning climate change.

Periodic variation in the geomagnetic activity - A study based on the Ap index

NASA Technical Reports Server (NTRS)

De Gonzalez, Alicia L. C.; Gonzalez, Walter D.; Dutra, Severino L. G.; Tsurutani, Bruce T.

1993-01-01

The monthly and daily samples of the Ap index for the interval from 1932 through 1982 were studied using the power spectrum technique. Results obtained for Bartel's period (about 27 days), the semiannual period, the dual-peak solar cycle distribution of geomagnetic storms, and certain other medium-scale periodicities are examined in detail. In addition, results on the cumulative occurrence number of storms per decade as a function of the Ap and Dst indices for the storm are presented.

Global dimming and brightening: A review

NASA Astrophysics Data System (ADS)

Wild, Martin

2009-05-01

There is increasing evidence that the amount of solar radiation incident at the Earth's surface is not stable over the years but undergoes significant decadal variations. Here I review the evidence for these changes, their magnitude, their possible causes, their representation in climate models, and their potential implications for climate change. The various studies analyzing long-term records of surface radiation measurements suggest a widespread decrease in surface solar radiation between the 1950s and 1980s ("global dimming"), with a partial recovery more recently at many locations ("brightening"). There are also some indications for an "early brightening" in the first part of the 20th century. These variations are in line with independent long-term observations of sunshine duration, diurnal temperature range, pan evaporation, and, more recently, satellite-derived estimates, which add credibility to the existence of these changes and their larger-scale significance. Current climate models, in general, tend to simulate these decadal variations to a much lesser degree. The origins of these variations are internal to the Earth's atmosphere and not externally forced by the Sun. Variations are not only found under cloudy but also under cloud-free atmospheres, indicative of an anthropogenic contribution through changes in aerosol emissions governed by economic developments and air pollution regulations. The relative importance of aerosols, clouds, and aerosol-cloud interactions may differ depending on region and pollution level. Highlighted are further potential implications of dimming and brightening for climate change, which may affect global warming, the components and intensity of the hydrological cycle, the carbon cycle, and the cryosphere among other climate elements.

FISM 2.0: Improved Spectral Range, Resolution, and Accuracy

NASA Technical Reports Server (NTRS)

Chamberlin, Phillip C.

2012-01-01

The Flare Irradiance Spectral Model (FISM) was first released in 2005 to provide accurate estimates of the solar VUV (0.1-190 nm) irradiance to the Space Weather community. This model was based on TIMED SEE as well as UARS and SORCE SOLSTICE measurements, and was the first model to include a 60 second temporal variation to estimate the variations due to solar flares. Along with flares, FISM also estimates the tradition solar cycle and solar rotational variations over months and decades back to 1947. This model has been highly successful in providing driving inputs to study the affect of solar irradiance variations on the Earth's ionosphere and thermosphere, lunar dust charging, as well as the Martian ionosphere. The second version of FISM, FISM2, is currently being updated to be based on the more accurate SDO/EVE data, which will provide much more accurate estimations in the 0.1-105 nm range, as well as extending the 'daily' model variation up to 300 nm based on the SOLSTICE measurements. with the spectral resolution of SDO/EVE along with SOLSTICE and the TIMED and SORCE XPS 'model' products, the entire range from 0.1-300 nm will also be available at 0.1 nm, allowing FISM2 to be improved a similar 0.1nm spectral bins. FISM also will have a TSI component that will estimate the total radiated energy during flares based on the few TSI flares observed to date. Presented here will be initial results of the FISM2 modeling efforts, as well as some challenges that will need to be overcome in order for FISM2 to accurately model the solar variations on time scales of seconds to decades.

Ground-water/surface-water responses to global climate simulations, Santa Clara-Calleguas basin, Ventura County, California, 1950-93

USGS Publications Warehouse

Hanson, Randall T.; Dettinger, Michael D.

2005-01-01

Climate variations can play an important, if not always crucial, role in successful conjunctive management of ground water and surface water resources. This will require accurate accounting of the links between variations in climate, recharge, and withdrawal from the resource systems, accurate projection or predictions of the climate variations, and accurate simulation of the responses of the resource systems. To assess linkages and predictability of climate influences on conjunctive management, global climate model (GCM) simulated precipitation rates were used to estimate inflows and outflows from a regional ground water model (RGWM) of the coastal aquifers of the Santa Clara-Calleguas Basin at Ventura, California, for 1950 to 1993. Interannual to interdecadal time scales of the El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) climate variations are imparted to simulated precipitation variations in the Southern California area and are realistically imparted to the simulated ground water level variations through the climate-driven recharge (and discharge) variations. For example, the simulated average ground water level response at a key observation well in the basin to ENSO variations of tropical Pacific sea surface temperatures is 1.2 m/°C, compared to 0.9 m/°C in observations. This close agreement shows that the GCM-RGWM combination can translate global scale climate variations into realistic local ground water responses. Probability distributions of simulated ground water level excursions above a local water level threshold for potential seawater intrusion compare well to the corresponding distributions from observations and historical RGWM simulations, demonstrating the combination's potential usefulness for water management and planning. Thus the GCM-RGWM combination could be used for planning purposes and — when the GCM forecast skills are adequate — for near term predictions.

Ground water/surface water responses to global climate simulations, Santa Clara-Calleguas Basin, Ventura, California

USGS Publications Warehouse

Hanson, R.T.; Dettinger, M.D.

2005-01-01

Climate variations can play an important, if not always crucial, role in successful conjunctive management of ground water and surface water resources. This will require accurate accounting of the links between variations in climate, recharge, and withdrawal from the resource systems, accurate projection or predictions of the climate variations, and accurate simulation of the responses of the resource systems. To assess linkages and predictability of climate influences on conjunctive management, global climate model (GCM) simulated precipitation rates were used to estimate inflows and outflows from a regional ground water model (RGWM) of the coastal aquifers of the Santa ClaraCalleguas Basin at Ventura, California, for 1950 to 1993. Interannual to interdecadal time scales of the El Nin??o Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) climate variations are imparted to simulated precipitation variations in the Southern California area and are realistically imparted to the simulated ground water level variations through the climate-driven recharge (and discharge) variations. For example, the simulated average ground water level response at a key observation well in the basin to ENSO variations of tropical Pacific sea surface temperatures is 1.2 m/??C, compared to 0.9 m/??C in observations. This close agreement shows that the GCM-RGWM combination can translate global scale climate variations into realistic local ground water responses. Probability distributions of simulated ground water level excursions above a local water level threshold for potential seawater intrusion compare well to the corresponding distributions from observations and historical RGWM simulations, demonstrating the combination's potential usefulness for water management and planning. Thus the GCM-RGWM combination could be used for planning purposes and - when the GCM forecast skills are adequate - for near term predictions.

Ring-widths of the above tree-line shrub Rhododendron reveal the change of minimum winter temperature over the past 211 years in Southwestern China

NASA Astrophysics Data System (ADS)

Bi, Yingfeng; Xu, Jianchu; Yang, Jinchao; Li, Zongshan; Gebrekirstos, Aster; Liang, Eryuan; Zhang, Shibao; Yang, Yang; Yang, Yongping; Yang, Xuefei

2017-06-01

Changes in minimum winter temperature (MWT) and their potential effects on plant growth and development have been gaining increased scientific attention. To better understand these changes across long temporal scales, the present study used dendroclimatological techniques to assess variations in MWT in Southwestern China. Using data from Rhododendron species distributed in areas above the tree-line, a regional composite chronology was generated for a 341-year period. Based on the significant negative correlation between MWT values and ring-width, the most reliable parts of this chronological data were then used to reconstruct MWT values for the past 211 years. This reconstructed MWT series showed decadal to multi-decadal fluctuations. Three distinct cold periods prevailed during 1823-1858, 1882-1891 and 1922-1965, while four warm intervals occurred in 1800-1822, 1858-1881, 1892-1921 and 1966-2011. Our reconstructed MWT reveals a warming trend over the most recent eight decades, which is in agreement with instrumental observations. However, the MWT values and rate of warming over the past seven decades did not exceed those found in the reconstructed temperature data for the past 211 years. Spatial correlations reveal that the MWT in Southwest China is strongly associated with regional temperatures in the Eastern and Central Himalaya, Northern China, and the Indian Peninsula. Larger scale climate oscillations of the Western Pacific and Northern Indian Ocean as well as the North Atlantic Oscillation probably influenced the region's temperature in the past.

Investigation of decadal-scale divergence in tree-ring density chronologies

NASA Astrophysics Data System (ADS)

Vaccaro, A.; Emile-Geay, J.; Anchukaitis, K. J.; Wang, J.

2013-12-01

Tree-ring data from certain forest sites at northern circumpolar latitudes and from some at higher elevation show an anomalous decrease in temperature-sensitivity of tree growth starting in the mid-20th century. This phenomenon, known as the ';divergence problem' (DP), leads to tree-ring reconstructions that underestimate the warming trend exhibited by instrumental measurements over recent decades (e.g. D'Arrigo et al. 2008). In a study conducted in 1998, Briffa et al. discovered a type of divergence wherein latewood density (MXD) chronologies from an early manifestation of the Schweingruber tree-ring dataset showed strong interannual correlation to summer temperature measurements, but increasing divergence between the decadal-scale trends of the tree-rings and temperature records during the second half of the 20th century. This low-frequency divergence suggests that although tree-rings may accurately trace year-to-year changes in temperature, they might not capture longer-term warming trends, making them unsuitable for reconstructions of long-term climate variations. There is reason to believe, however, that the divergence found by Briffa (1998) is at least partly due to detrending or related statistical issues (Esper et al. 2009). Herein, we will investigate the distribution of this decadal-scale ';Briffa-style' divergence to see if it is confined to the earlier chronologies in the Schweingruber dataset or if it is persistent throughout more recent tree-ring data as well. Following the methodology of previous DP investigations (e.g. Briffa et al. 1998), we will draw comparisons between a network of MXD data and instrumental temperature records over an early period (1850-1960) and a recent period (1961-2000) to detect decadal-scale divergence in recent decades. We will apply the Mann et al. 2009 (M09) style of RegEM reconstruction to the M09 dataset, with and without controlling for divergence, and also to a new tree-ring database assembled using strict, objective criteria, including most of the updated Schweingruber network. Other climate field reconstruction (CFR) methods as described by Wang et al. (2013) will be used on our new tree-ring network to check for robustness. The tree-ring data will be independently compared to instrumental temperature series derived from the GHCN-monthly, HadCRUT4, and the M09 infilled HadCRUT3v temperature datasets for cross-validation. Implications for large-scale temperature reconstructions of the Common Era will be discussed. Briffa, K.R., F. H. Schweingruber, P.D. Jones, T.J. Osborn, S.G. Shiyatov, and E.A. Vaganov (1998),Reduced sensitivity of recent tree-growth to temperature at high northern latitudes, Nature, 391, 678-682. D'Arrigo, R., R. Wilson, B. Liepert, and P. Cherubini (2008), On the ';Divergence Problem' in Northern Forests: A review of the tree-ring evidence and possible causes, GAPC, 60, 289-305. Esper, J. and D. Frank (2009), Divergence pitfalls in tree-ring research, Climate Change, 94, 261-266. Mann, M.E., Z. Zhang, M.K. Hughes, R.S. Bradley, S.K. Miller, S. Rutherford, and F. Ni (2009), Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia, PNAS, 105 (36) 13252-13257. Wang, J., J. Emile-Geay, D. Guillot, and J. E. Smerdon (2013), Evaluating climate field reconstruction techniques using improved emulations of real-world conditions. CPD, 9, 3015-3060.

From macro-scale to micro-scale computational anatomy: a perspective on the next 20 years.

PubMed

Mori, Kensaku

2016-10-01

This paper gives our perspective on the next two decades of computational anatomy, which has made great strides in the recognition and understanding of human anatomy from conventional clinical images. The results from this field are now used in a variety of medical applications, including quantitative analysis of organ shapes, interventional assistance, surgical navigation, and population analysis. Several anatomical models have also been used in computational anatomy, and these mainly target millimeter-scale shapes. For example, liver-shape models are almost completely modeled at the millimeter scale, and shape variations are described at such scales. Most clinical 3D scanning devices have had just under 1 or 0.5 mm per voxel resolution for over 25 years, and this resolution has not changed drastically in that time. Although Z-axis (head-to-tail direction) resolution has been drastically improved by the introduction of multi-detector CT scanning devices, in-plane resolutions have not changed very much either. When we look at human anatomy, we can see different anatomical structures at different scales. For example, pulmonary blood vessels and lung lobes can be observed in millimeter-scale images. If we take 10-µm-scale images of a lung specimen, the alveoli and bronchiole regions can be located in them. Most work in millimeter-scale computational anatomy has been done by the medical-image analysis community. In the next two decades, we encourage our community to focus on micro-scale computational anatomy. In this perspective paper, we briefly review the achievements of computational anatomy and its impacts on clinical applications; furthermore, we show several possibilities from the viewpoint of microscopic computational anatomy by discussing experimental results from our recent research activities. Copyright © 2016 Elsevier B.V. All rights reserved.

Climatic controls of the interannual to decadal variability in Saudi Arabian dust activity: Towards the development of a seasonal prediction tool

NASA Astrophysics Data System (ADS)

Yu, Y.; Notaro, M.; Liu, Z.; Alkolibi, F.; Fadda, E.; Bakhrjy, F.

2013-12-01

Atmospheric dust significantly influences the climate system, as well as human life in Saudi Arabia. Skillful seasonal prediction of dust activity with climatic variables will help prevent some negative social impacts of dust storms. Yet, the climatic regulators on Saudi Arabian dust activity remain largely unaddressed. Remote sensing and station observations show consistent seasonal cycles in Saudi Arabian dust activity, which peaks in spring and summer. The climatic controls on springtime and summertime Saudi Arabian dust activity during 1975-2010 are studied using observational and reanalysis data. Empirical Orthogonal Function (EOF) of the observed Saudi Arabian dust storm frequency shows a dominant homogeneous pattern across the country, which has distinct interannual and decadal variations, as revealed by the power spectrum. Regression and correlation analyses reveal that Saudi Arabian dust activity is largely tied to precipitation on the Arabian Peninsula in spring and northwesterly (Shamal) wind in summer. On the seasonal-interannual time scale, warm El Niño-Southern Oscillation (ENSO) phase (El Niño) in winter-to-spring inhibits spring dust activity by increasing the precipitation over the Rub'al Khali Desert, a major dust source region on the southern Arabian Peninsula; warm ENSO and warm Indian Ocean Basin Mode (IOBM) in winter-to-spring favor less summer dust activity by producing anomalously low sea-level pressure over eastern north Africa and Arabian Peninsula, which leads to the reduced Shamal wind speed. The decadal variation in dust activity is likely associated with the Atlantic Multidecadal Oscillation (AMO), which impacts Sahel rainfall and North African dust, and likely dust transport to Saudi Arabia. The Pacific Decadal Oscillation (PDO) and tropical Indian Ocean SST also have influence on the decadal variation in Saudi Arabian dust activity, by altering precipitation over the Arabian Peninsula and summer Shamal wind speed. Using eastern tropical Pacific SST as the high-frequency predictor and antecedent accumulated precipitation over the Arabian Peninsula and North Africa as low-frequency predictors, the predicted seasonal dust activity over Saudi Arabia is well correlated with the original time series (correlation above 0.6).

Analysis of spatial patterns underlying the linkage between solar irradiance and near-surface air temperatures

NASA Astrophysics Data System (ADS)

Balling, Robert C.; Roy, Shouraseni Sen

2005-06-01

Many scientists have noted that global temperature anomalies were highly correlated with solar irradiance values until sometime in the 1970s, but since that time, the pronounced warming in the near-surface temperature record is not explained by variations or trends in solar receipt. In this investigation, spatial dimensions are explored in the relationship between irradiance and near-surface air temperatures. At the scale of individual 5° by 5° grid cells, the solar control on annual temperature variations is not statistically significant. When the temperature data are aggregated by 5° latitudinal bands, the solar - temperature connect is generally significant, and in every band, there is substantial evidence that a non-solar control has become dominant in recent decades. The buildup of greenhouse gases and/or some other global-scale feedback, such as widespread changes in atmospheric water vapor, emerge as potential explanations for the recent residual warming found in all latitudinal bands.

On the Observed Changes in Upper Stratospheric and Mesospheric Temperatures from UARS HALOE

NASA Technical Reports Server (NTRS)

Remsberg, Ellis E.

2006-01-01

Temperature versus pressure or T(p) time series from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) have been extended and re-analyzed for the period of 1991-2005 and for the upper stratosphere and mesosphere in 10-degree wide latitude zones from 60S to 60N. Even though sampling from a solar occultation experiment is somewhat limited, it is shown to be quite adequate for developing both the seasonal and longer-term variations in T(p). Multiple linear regression (MLR) techniques were used in the re-analyses for the seasonal and the significant interannual, solar cycle (SC-like or decadal-scale), and linear trend terms. A simple SC-like term of 11-yr period was fitted to the time series residuals after accounting for the seasonal and interannual terms. Highly significant SC-like responses were found for both the upper mesosphere and the upper stratosphere. The phases of these SC-like terms were checked for their continuity with latitude and pressure-altitude, and in almost all cases they are directly in-phase with that of standard proxies for the solar flux variations. The analyzed, max minus min, responses at low latitudes are of order 1 K, while at middle latitudes they are as large as 3 K in the upper mesosphere. Highly significant, linear cooling trends were found at middle latitudes of the middle to upper mesosphere (about -2 K/decade), at tropical latitudes of the middle mesosphere (about -1 K/decade), and at 2 hPa (or order -1 K/decade).

Dominance of ENSO-Like Variability in Controlling Tropical Ocean Surface Energy Fluxes in the Satellite Era

NASA Technical Reports Server (NTRS)

Robertson, F. R.; Miller, T. L.; Bosilovich, M. G.

2008-01-01

Ocean surface turbulent and radiative 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. Moreover, interannual to decadal climate variability depends crucially on the nature of these exchange processes. For example, addressing the question of the degree to which the global hydrologic cycle is changing depends on our ability to observe and model these fluxes accurately. In this work we investigate the interannual to decadal variation of fluxes over the global tropics, especially the tropical oceans. Recent versions of satellite-derived fresh water flux estimates as well as some reanalyses (e.g. products from Remote Sensing Systems, the Woods Hole Oceanographic Institute, and Global Precipitation Climatology Project) suggest that increases in evaporation and precipitation over the past 20 years exceed those expected on the basis of climate model projected responses to greenhouse gas forcing. At the same time, it is well known that E1 Nino / Southern Oscillation behavior in the Pacific exhibits significant variability at scales longer than interannual. We examine here the degree to which surface fluxes attending these interannual to decadal fluctuations are related to ENSO. We examine consistency between these data sets and explore relationships between SST variations, flux changes and modulation of tropical Walker and Hadley circulations.

Magnetic activity of red secondaries: clues from the outburst cycle variations of dwarf novae

NASA Astrophysics Data System (ADS)

Chinarova, L. L.

Photometric variations of 6 dwarf novae stars are studied based on the photographic observations from the Odessa, Moscow and Sonneberg plate collections and published visual monitoring data from the AFOEV database (Schweitzer E.: 1993, Bull. AFOEV, 64, 14). The moments of maxima are determined by using the "running parabola" fit (Andronov I.L., 1990, Kinematika Fizika Nebesn. Tel., v.6,,N 6, 87) with automatically determined filter half-width (Andronov I.L., 1997, As.Ap. Suppl., in press). All investigated stars exhibit significant changes not only from cycle-to-cycle, but from season-to-season as well. Secondary decade-scale cycles of smooth variations (Bianchini A., 1990, AJ 99, 1941) and abrupt switchings (Andronov I.L., Shakun L.I., 1990, ASS 169, 237) were interpreted by a solar-type activity of the red dwarf secondary in a binary system and may argue for existence of two different subgroups of the dwarf novae.

Indo-Pacific sea level variability during recent decades

NASA Astrophysics Data System (ADS)

Yamanaka, G.; Tsujino, H.; Nakano, H.; Urakawa, S. L.; Sakamoto, K.

2016-12-01

Decadal variability of sea level in the Indo-Pacific region is investigated using a historical OGCM simulation. The OGCM driven by the atmospheric forcing removing long-term trends clearly exhibits decadal sea level variability in the Pacific Ocean, which is associated with eastern tropical Pacific thermal anomalies. During the period of 1977-1987, the sea level anomalies are positive in the eastern equatorial Pacific and show deviations from a north-south symmetric distribution, with strongly negative anomalies in the western tropical South Pacific. During the period of 1996-2006, in contrast, the sea level anomalies are negative in the eastern equatorial Pacific and show a nearly north-south symmetric pattern, with positive anomalies in both hemispheres. Concurrently, sea level anomalies in the south-eastern Indian Ocean vary with those in the western tropical Pacific. These sea level variations are closely related to large-scale wind fields. Indo-Pacific sea level distributions are basically determined by wind anomalies over the equatorial region as well as wind stress curl anomalies over the off-equatorial region.

Characteristic variations of sea surface temperature with multiple time scales in the North Pacific

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

Tanimoto, Youichi; Hanawa, Kimio; Toba, Yoshiaki

1993-06-01

It is unclear whether the recent increases in global temperatures are really due to the increase of greenhouse gases or are a manifestation of natural variability. Temporal evolution and spectral structure of sea surface temperature (SST) anomalies in the North Pacific over the last 37 years are investigated on the three characteristic time scales: shorter than 24 months (HF), 24-60 months (ES), and longer than 60 months (DC). The leading empirical-orthogonal function (EOF) for the DC time scale is characterized by a zonally elongated monopole centered at around 40[degrees]N, 180[degrees]. The leading EOF for the HF time scale is somewhatmore » similar to that for the DC time scale, although there are two centers of action with the same polarity at the mid and western Pacific. The leading EOF for the ES time scale, however, exhibits a different pattern whose center of action at the mid Pacific is located farther southeastward. In the time evolution of the SST anomalies associated with the leading EOF of the DC time scale, several anomaly periods can be identified that last five years or longer. The transition from a persistent period to another with the opposite polarity is generally very brief, except for the one that lasts throughout the late 1960s. The EOF analysis was repeated separately on these persistent anomaly periods and the long transition period. The spatial structure of the leading EOF of the SST variability with the ES time scale is found to be sensitive to the polarity of the decadal anomaly. These results are suggestive of the possible influence of the decadal SST variability upon the spatial structure of the variability with shorter time scales. 31 refs., 8 figs.« less

Time-scale dependent sediment flux in the Tajik Pamir Mountains

NASA Astrophysics Data System (ADS)

Pohl, Eric; Gloaguen, Richard; Andermann, Christoff; Fuchs, Margret C.

2014-05-01

The Pamir Mountains (Pamirs) offer the unique possibility to observe landscape shaping processes in a complex climatic environment. While the Westerlies provide most of the moisture as snow in winter, the Indian summer monsoon can also contribute quite significantly to the water budget in summer. Water from snow and ice melt induced by temperature and rainfall mobilizes sediments from hillslopes, debris fans, and moraine remnants. These sediments are transported, re-deposited, and eventually carried out of the orogene. Different approaches are available to assess and quantify the erosion processes at different time-scales. Recent studies applying cosmogenic nuclide (CN) dating suggest erosion rates of approximately 0.65mm/yr for the last 1000 years. In this contribution we want to present modern erosion rates derived from historical archive suspended sediment yield (SSY) data and very recent in situ sampling data, including high-resolution turbidimeter measurements. 10-day averaged SSY data recorded in the past show less erosion by a factor of 2 to 10 compared to CN-derived erosion rates for different catchments. The 10-day SSY data are based on measurements that have been conducted in the morning and evening, thus not accounting for the entire diurnal variation. We installed a turbidimeter with a measuring interval of 10 minutes to better resolve these diurnal variations. We calibrate turbidity with in situ measurements carried out on a daily basis for 9 months to see whether the differences between CN and SSY measurements are really owed to diurnal variations or if rare high magnitude events. e.g. mudflows, landslides, or avalanches disclose this discrepancy. We present single high magnitude SSY events, uncover periodic diurnal sediment variations that systematically lag diurnal temperature variations and relate the sediment amount of such high magnitude events to the smoothed annual cycle. We use the obtained results to discuss whether past changes in climate could explain the observed difference between millennial scale CN vs decadal scale SSY measurements or if single high magnitude events must play the dominant role.

Synchronous centennial-scale variability in abundance of remote sardine populations in the Pacific

NASA Astrophysics Data System (ADS)

Kuwae, M.; Takashige, S.; Yamamoto, M.; Sagawa, T.; Takeoka, H.

2012-12-01

A number of studies have identified evidence for connections between Pacific climate decadal variability and variations in Pacific marine ecosystems which are typically shown in abundance of remote sardine and anchovy species off Japan, California, Peru, and Chile as well as Alaska salmon species. The variations in climate indices and abundance of sardine and anchovy species most likely have 50-70 year cycles and therefore these natural perturbations in climates and Pacific ecosystems should be considered for developing predictive models of fisheries productions and the managements. Despite the importance of natural perturbations for long-term predictions, one issue, whether synchronous centennial-variations in remote Pacific fisheries productions in response to climate variability exists in the past, has not been questioned, because there has never been long-term reconstructed time series in the western North Pacific. Here we present well preserved, fossil fish scale-based abundance record of Japanese sardine over the last 1100 years reconstructed from a seasonal anoxic basin in the western Seto Inland Sea near their spawning areas in the western North Pacific. A comparison of our record with other previous records clearly showed centennial-scale variations in abundance of sardine species off Japan, California, and Chile, characterized by centennial-scale alternations between low abundance regimes and high abundance regimes in which multidecadal fluctuations with large amplitudes occurred once or several times. High abundance regimes from 1450 to 1650 AD and after 1800 AD and a low abundance regime from 1650 to 1800 AD corresponded to low frequency patterns of PDO index reconstructed from tree-ring records in North America. This indicates that connections between Pacific climate variability and variations in Pacific marine ecosystems exist not only on multidecadal timescales but on centennial timescales. Three to four hundred-yr periodicity of the Pacific climate-ecosystem dynamics suggests possibility of a change into a century-long, low sardine abundance regime in the next 100 years.

Spatial variability of the dose rate from (137)Cs fallout in settlements in Russia and Belarus more than two decades after the Chernobyl accident.

PubMed

Bernhardsson, C; Rääf, C L; Mattsson, S

2015-11-01

Radionuclides from the 1986 Chernobyl accident were released and dispersed during a limited period of time, but under widely varying weather conditions. As a result, there was a high geographical variation in the deposited radioactive fallout per unit area over Europe, depending on the released composition of fission products and the weather during the 10 days of releases. If the plume from Chernobyl coincided with rain, then the radionuclides were unevenly distributed on the ground. However, large variations in the initial fallout also occurred locally or even on a meter scale. Over the ensuing years the initial deposition may have been altered further by different weathering processes or human activities such as agriculture, gardening, and decontamination measures. Using measurements taken more than two decades after the accident, we report on the inhomogeneous distribution of the ground deposition of the fission product (137)Cs and its influence on the dose rate 1 m above ground, on both large and small scales (10ths of km(2) - 1 m(2)), in the Gomel-Bryansk area close to the border between Belarus and Russia. The dose rate from the deposition was observed to vary by one order of magnitude depending on the size of the area considered, whether human processes were applied to the surface or not, and on location specific properties (e.g. radionuclide migration in soil). Copyright © 2015 Elsevier Ltd. All rights reserved.

The impact of multi-decadal sub-surface circulation changes on sea surface chlorophyll patterns in the tropical Pacific

NASA Astrophysics Data System (ADS)

Schollaert Uz, S.; Busalacchi, A. J.; Smith, T. M.; Evans, M. N.; Brown, C.; Hackert, E. C.; Wang, X.

2016-12-01

The tropical Pacific is a region of strong forcing where physical oceanography primarily controls biological variability over the seasonal to interannual time scales observed since dedicated ocean color satellite remote sensing began in 1997. To quantify how multi-decadal, climate-scale changes impact marine biological dynamics, we used the correlation with sea-surface temperature and height to reconstruct a 50-year time series of surface chlorophyll concentrations. The reconstruction demonstrates greatest skill away from the coast and within 10o of the equator where chlorophyll variance is greatest and primarily associated with El Niño Southern Oscillation (ENSO) dynamics and secondarily associated with decadal variability. We observe significant basin-wide differences between east and central Pacific events when the El Niño events are strong: chlorophyll increases with La Niña and decreases with El Niño, with larger declines east of 180o for remotely-forced east Pacific events and west of 180o for locally-forced central Pacific events. Chlorophyll variations also reflect the physical dynamics of Pacific decadal variability with small but significant differences between cool and warm eras: consistent with advection variability west of 180o and likely driven by subsurface changes in the nutricline depth between 110-140oW. Comparisons with output from a fully-coupled biogeochemical model support the hypothesis that this anomalous region is controlled by lower frequency changes in subsurface circulation patterns that transport nutrients to the surface. Basin-wide chlorophyll distributions exhibiting spatial heterogeneity in response to multi-decadal climate forcing imply similar long-term changes in phytoplankton productivity, with implications for the marine food web and the ocean's role as a carbon sink.

A sub-decadal trend in diacids in atmospheric aerosols in eastern Asia

NASA Astrophysics Data System (ADS)

Kundu, S.; Kawamura, K.; Kobayashi, M.; Tachibana, E.; Lee, M.; Fu, P. Q.; Jung, J.

2016-01-01

Change in secondary organic aerosols (SOAs) has been predicted to be highly uncertain in the future atmosphere in Asia. To better quantify the SOA change, we examine the sub-decadal (2001-2008) trend in major surrogate compounds (C2-C10 diacids) of SOA in atmospheric aerosols from Gosan site on Cheju Island, South Korea. The Gosan site is influenced by pollution outflows from eastern Asia. The molecular distributions of diacids were characterized by the predominance of oxalic (C2) acid followed by malonic (C3) and succinic (C4) acids in each year. The seasonal variations in diacids in each year were characterized by the highest concentrations of saturated diacids in spring and unsaturated diacids in winter. The consistent molecular distributions and seasonal variations along with significantly similar air mass transport patterns are indicative of similar pollution sources for diacids in eastern Asia on a sub-decadal scale. However, the intensity of the pollution sources has increased as evidenced by the increases in major diacids at the rate of 3.9-47.4 % per year, particularly in April. The temporal variations in atmospheric tracer compounds (carbon monoxide, levoglucosan, 2-methyltetrols, pinic acid, glyoxylic acid, glyoxal and methylglyoxal) suggest that the increases in diacids are due to enhanced precursor emissions associated with more anthropogenic than biogenic activities followed by the compounds' chemical processing in the atmosphere. The trends in diacids contrast with the reported decreases in sulfate, nitrate and ammonium in recent years in eastern Asia. This study demonstrates that recent pollution control strategies in eastern Asia were not able to decrease organic acidic species in the atmosphere. The increases in water-soluble organic acid fraction could modify the aerosol organic composition and its sensitivity to climate relevant physical properties.

The forcing of southwestern Asia teleconnections by low-frequency sea surface temperature variability during boreal winter

USGS Publications Warehouse

Hoell, Andrew; Funk, Christopher C.; Mathew Barlow,

2015-01-01

Southwestern Asia, defined here as the domain bounded by 20°–40°N and 40°–70°E, which includes the nations of Iraq, Iran, Afghanistan, and Pakistan, is a water-stressed and semiarid region that receives roughly 75% of its annual rainfall during November–April. The November–April climate of southwestern Asia is strongly influenced by tropical Indo-Pacific variability on intraseasonal and interannual time scales, much of which can be attributed to sea surface temperature (SST) variations. The influences of lower-frequency SST variability on southwestern Asia climate during November–April Pacific decadal SST (PDSST) variability and the long-term trend in SST (LTSST) is examined. The U.S. Climate Variability and Predictability Program (CLIVAR) Drought Working Group forced global atmospheric climate models with PDSST and LTSST patterns, identified using empirical orthogonal functions, to show the steady atmospheric response to these modes of decadal to multidecadal SST variability. During November–April, LTSST forces an anticyclone over southwestern Asia, which results in reduced precipitation and increases in surface temperature. The precipitation and tropospheric circulation influences of LTSST are corroborated by independent observed precipitation and circulation datasets during 1901–2004. The decadal variations of southwestern Asia precipitation may be forced by PDSST variability, with two of the three models indicating that the cold phase of PDSST forces an anticyclone and precipitation reductions. However, there are intermodel circulation variations to PDSST that influence subregional precipitation patterns over the Middle East, southwestern Asia, and subtropical Asia. Changes in wintertime temperature and precipitation over southwestern Asia forced by LTSST and PDSST imply important changes to the land surface hydrology during the spring and summer.

Impacts of wind stilling on solar radiation variability in China

PubMed Central

Lin, Changgui; Yang, Kun; Huang, Jianping; Tang, Wenjun; Qin, Jun; Niu, Xiaolei; Chen, Yingying; Chen, Deliang; Lu, Ning; Fu, Rong

2015-01-01

Solar dimming and wind stilling (slowdown) are two outstanding climate changes occurred in China over the last four decades. The wind stilling may have suppressed the dispersion of aerosols and amplified the impact of aerosol emission on solar dimming. However, there is a lack of long-term aerosol monitoring and associated study in China to confirm this hypothesis. Here, long-term meteorological data at weather stations combined with short-term aerosol data were used to assess this hypothesis. It was found that surface solar radiation (SSR) decreased considerably with wind stilling in heavily polluted regions at a daily scale, indicating that wind stilling can considerably amplify the aerosol extinction effect on SSR. A threshold value of 3.5 m/s for wind speed is required to effectively reduce aerosols concentration. From this SSR dependence on wind speed, we further derived proxies to quantify aerosol emission and wind stilling amplification effects on SSR variations at a decadal scale. The results show that aerosol emission accounted for approximately 20% of the typical solar dimming in China, which was amplified by approximately 20% by wind stilling. PMID:26463748

Assessment of international reference materials for isotope-ratio analysis (IUPAC Technical Report)

USGS Publications Warehouse

Brand, Willi A.; Coplen, Tyler B.; Vogl, Jochen; Rosner, Martin; Prohaska, Thomas

2014-01-01

Since the early 1950s, the number of international measurement standards for anchoring stable isotope delta scales has mushroomed from 3 to more than 30, expanding to more than 25 chemical elements. With the development of new instrumentation, along with new and improved measurement procedures for studying naturally occurring isotopic abundance variations in natural and technical samples, the number of internationally distributed, secondary isotopic reference materials with a specified delta value has blossomed in the last six decades to more than 150 materials. More than half of these isotopic reference materials were produced for isotope-delta measurements of seven elements: H, Li, B, C, N, O, and S. The number of isotopic reference materials for other, heavier elements has grown considerably over the last decade. Nevertheless, even primary international measurement standards for isotope-delta measurements are still needed for some elements, including Mg, Fe, Te, Sb, Mo, and Ge. It is recommended that authors publish the delta values of internationally distributed, secondary isotopic reference materials that were used for anchoring their measurement results to the respective primary stable isotope scale.

Towards decadal soil salinity mapping using Landsat time series data

NASA Astrophysics Data System (ADS)

Fan, Xingwang; Weng, Yongling; Tao, Jinmei

2016-10-01

Salinization is one of the major soil problems around the world. However, decadal variation in soil salinization has not yet been extensively reported. This study exploited thirty years (1985-2015) of Landsat sensor data, including Landsat-4/5 TM (Thematic Mapper), Landsat-7 ETM+ (Enhanced Thematic Mapper Plus) and Landsat-8 OLI (Operational Land Imager), for monitoring soil salinity of the Yellow River Delta, China. The data were initially corrected for atmospheric effects, and then matched the spectral bands of EO-1 (Earth Observing One) ALI (Advanced Land Imager). Subsequently, soil salinity maps were derived with a previously developed PLSR (Partial Least Square Regression) model. On intra-annual scale, the retrievals showed that soil salinity increased in February, stabilized in March, and decreased in April. On inter-annual scale, soil salinity decreased within 1985-2000 (-0.74 g kg-1/10a, p < 0.001), and increased within 2000-2015 (0.79 g kg-1/10a, p < 0.001). Our study presents a new perspective for use of multiple Landsat data in soil salinity retrieval, and further the understanding of soil salinization development over the Yellow River Delta.

Glacial Boundary Features Delineated Using Enhanced-resolution Passive-microwave Data to Determine Melt Season Variation of the Vatnajokull Ice Cap, Iceland

NASA Astrophysics Data System (ADS)

Marzillier, D. M.; Ramage, J. M.

2017-12-01

Temperate glaciers such as those seen in Iceland experience high annual mass flux, thereby responding to small scale changes in Earth's climate. Decadal changes in the glacial margins of Iceland's ice caps are observable in the Landsat record, however twice daily AMSR-E Calibrated Enhanced-Resolution Passive Microwave Daily EASE-Grid 2.0 Brightness Temperature (CETB) Earth System Data Record (ESDR) allow for observation on a daily temporal scale and a 3.125 km spatial scale, which can in turn be connected to patterns seen over longer periods of time. Passive microwave data allow for careful observation of melt onset and duration in Iceland's glacial regions by recording changes in emissivity of the ice surface, known as brightness temperature (TB), which is sensitive to fluctuations in the liquid water content of snow and ice seen during melting in glaciated regions. Enhanced resolution of this data set allows for a determination of a threshold that defines the melting season. The XPGR snowmelt algorithm originally presented by Abdalati and Steffen (1995) is used as a comparison with the diurnal amplitude variation (DAV) values on Iceland's Vatnajokull ice cap located at 64.4N, -16.8W. Ground-based air temperature data in this region, digital elevation models (DEMs), and river discharge dominated by glacial runoff are used to confirm the glacial response to changes in global climate. Results show that Iceland glaciers have a bimodal distribution of brightness temperature delineating when the snow/ice is melting and refreezing. Ground based temperatures have increased on a decadal trend. Clear glacial boundaries are visible on the passive microwave delineating strong features, and we are working to understand their variability and contribution to glacier evolution. The passive microwave data set allows connections to be made between observations seen on a daily scale and the long term glacier changes observed by the Landsat satellite record that integrates the overall glacier changes.

Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge

NASA Astrophysics Data System (ADS)

Bakker, Pepijn; Clark, Peter U.; Golledge, Nicholas R.; Schmittner, Andreas; Weber, Michael E.

2017-01-01

Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean-atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations.

Time and length scales within a fire and implications for numerical simulation

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

TIESZEN,SHELDON R.

2000-02-02

A partial non-dimensionalization of the Navier-Stokes equations is used to obtain order of magnitude estimates of the rate-controlling transport processes in the reacting portion of a fire plume as a function of length scale. Over continuum length scales, buoyant times scales vary as the square root of the length scale; advection time scales vary as the length scale, and diffusion time scales vary as the square of the length scale. Due to the variation with length scale, each process is dominant over a given range. The relationship of buoyancy and baroclinc vorticity generation is highlighted. For numerical simulation, first principlesmore » solution for fire problems is not possible with foreseeable computational hardware in the near future. Filtered transport equations with subgrid modeling will be required as two to three decades of length scale are captured by solution of discretized conservation equations. By whatever filtering process one employs, one must have humble expectations for the accuracy obtainable by numerical simulation for practical fire problems that contain important multi-physics/multi-length-scale coupling with up to 10 orders of magnitude in length scale.« less

Centennial- to decadal-scale monsoon precipitation variations in the upper Hanjiang River region, China over the past 6650 years

NASA Astrophysics Data System (ADS)

Tan, Liangcheng; Cai, Yanjun; Cheng, Hai; Edwards, Lawrence R.; Gao, Yongli; Xu, Hai; Zhang, Haiwei; An, Zhisheng

2018-01-01

The upper Hanjiang River region is the recharge area of the middle route of South-to-North Water Transfer Project. The region is under construction of the Hanjiang-Weihe River Water Transfer Project in China. Monsoon precipitation variations in this region are critical to water resource and security of China. In this study, high-resolution monsoon precipitation variations were reconstructed in the upper Hanjiang River region over the past 6650 years from δ18O and δ13C records of four stalagmites in Xianglong cave. The long term increasing trend of stalagmite δ18O record since the middle Holocene is consistent with other speleothem records from monsoonal China. This trend follows the gradually decreasing Northern Hemisphere summer insolation, which indicates that solar insolation may control the orbital-scale East Asian summer monsoon (EASM) variations. Despite the declined EASM intensity since the middle Holocene, local precipitation may not have decreased remarkably, as revealed by the δ13C records. A series of centennial- to decadal-scale cyclicity was observed, with quasi-millennium-, quasi-century-, 57-, 36- and 22-year cycles by removing the long-term trend of stalagmite δ18O record. Increased monsoon precipitation during periods of 4390-3800 a BP, 3590-2960 a BP, 2050-1670 a BP and 1110-790 a BP had caused four super-floods in the upper reach of Hanjiang River. Dramatically dry climate existed in this region during the 5.0 ka and 2.8 ka events, coinciding with notable droughts in other regions of monsoonal China. Remarkably intensified and southward Westerly jet, together with weakened summer monsoon, may delay the onset of rainy seasons, resulting in synchronous decreasing of monsoon precipitation in China during the two events. During the 4.2 ka event and the Little Ice Age, the upper Hanjiang River region was wet, which was similar to the climate conditions in central and southern China, but was the opposite of drought observed in northern China. We propose that weakened summer monsoon and less strengthened or normal Westerly jet may cause rain belt stay longer in the southward region, which reduced rainfall in northern China but enhanced it in central and southern China.

Variability and prediction of freshwater and nitrate fluxes for the Louisiana-Texas shelf: Mississippi and Atchafalaya River source functions

USGS Publications Warehouse

Bratkovich, A.; Dinnel, S.P.; Goolsby, D.A.

1994-01-01

Time histories of riverine water discharge, nitrate concentration, and nitrate, flux have been analyzed for the Mississippi and Atchafalaya rivers. Results indicate that water discharge variability is dominated by the annual cycle and shorter-time-scale episodic events presumably associated with snowmelt runoff and spring or summer rains. Interannual variability in water discharge is relatively small compared to the above. In contrast, nitrate concentration exhibits strongest variability at decadal time scales. The interannual variability is not monotonic but more complicated in structure. Weak covariability between water discharge and nitrate concentration leads to a relatively “noisy” nitrate flux signal. Nitrate flux variations exhibit a low-amplitude, long-term modulation of a dominant annual cycle. Predictor-hindcastor analyses indicate that skilled forecasts of nitrate concentration and nitrate flux fields are feasible. Water discharge was the most reliably hindcast (on seasonal to interannual time scales) due to the fundamental strength of the annual hydrologic cycle. However, the forecasting effort for this variable was less successful than the hindcasting effort, mostly due to a phase shift in the annual cycle during our relatively short test period (18 mo). Nitrate concentration was more skillfully predicted (seasonal to interannual time scales) due to the relative dominance of the decadal-scale portion of the signal. Nitrate flux was also skillfully forecast even though historical analyses seemed to indicate that it should be more difficult to predict than either water discharge or nitrate concentration.

Synchronous multi-decadal climate variability of the whole Pacific areas revealed in tree rings since 1567

NASA Astrophysics Data System (ADS)

Fang, Keyan; Cook, Edward; Guo, Zhengtang; Chen, Deliang; Ou, Tinghai; Zhao, Yan

2018-02-01

Oceanic and atmospheric patterns play a crucial role in modulating climate variability from interannual to multi-decadal timescales by causing large-scale co-varying climate changes. The brevity of the existing instrumental records hinders the ability to recognize climate patterns before the industrial era, which can be alleviated using proxies. Unfortunately, proxy based reconstructions of oceanic and atmospheric modes of the past millennia often have modest agreements with each other before the instrumental period, raising questions about the robustness of the reconstructions. To ensure the stability of climate signals in proxy data through time, we first identified tree-ring datasets from distant regions containing coherent variations in Asia and North America, and then interpreted their climate information. We found that the multi-decadal covarying climate patterns of the middle and high latitudinal regions around the northern Pacific Ocean agreed quite well with the climate reconstructions of the tropical and southern Pacific areas. This indicates a synchronous variability at the multi-decadal timescale of the past 430 years for the entire Pacific Ocean. This pattern is closely linked to the dominant mode of the Pacific sea surface temperature (SST) after removing the warming trend. This Pacific multi-decadal SST variability resembles the Interdecadal Pacific Oscillation.

Predictability of the Indian Ocean Dipole in the coupled models

NASA Astrophysics Data System (ADS)

Liu, Huafeng; Tang, Youmin; Chen, Dake; Lian, Tao

2017-03-01

In this study, the Indian Ocean Dipole (IOD) predictability, measured by the Indian Dipole Mode Index (DMI), is comprehensively examined at the seasonal time scale, including its actual prediction skill and potential predictability, using the ENSEMBLES multiple model ensembles and the recently developed information-based theoretical framework of predictability. It was found that all model predictions have useful skill, which is normally defined by the anomaly correlation coefficient larger than 0.5, only at around 2-3 month leads. This is mainly because there are more false alarms in predictions as leading time increases. The DMI predictability has significant seasonal variation, and the predictions whose target seasons are boreal summer (JJA) and autumn (SON) are more reliable than that for other seasons. All of models fail to predict the IOD onset before May and suffer from the winter (DJF) predictability barrier. The potential predictability study indicates that, with the model development and initialization improvement, the prediction of IOD onset is likely to be improved but the winter barrier cannot be overcome. The IOD predictability also has decadal variation, with a high skill during the 1960s and the early 1990s, and a low skill during the early 1970s and early 1980s, which is very consistent with the potential predictability. The main factors controlling the IOD predictability, including its seasonal and decadal variations, are also analyzed in this study.

On hydrostatic flows in isentropic coordinates

NASA Astrophysics Data System (ADS)

Bokhove, Onno

2000-01-01

The hydrostatic primitive equations of motion which have been used in large-scale weather prediction and climate modelling over the last few decades are analysed with variational methods in an isentropic Eulerian framework. The use of material isentropic coordinates for the Eulerian hydrostatic equations is known to have distinct conceptual advantages since fluid motion is, under inviscid and statically stable circumstances, confined to take place on quasi-horizontal isentropic surfaces. First, an Eulerian isentropic Hamilton's principle, expressed in terms of fluid parcel variables, is therefore derived by transformation of a Lagrangian Hamilton's principle to an Eulerian one. This Eulerian principle explicitly describes the boundary dynamics of the time-dependent domain in terms of advection of boundary isentropes sB; these are the values the isentropes have at their intersection with the (lower) boundary. A partial Legendre transform for only the interior variables yields an Eulerian ‘action’ principle. Secondly, Noether's theorem is used to derive energy and potential vorticity conservation from the Eulerian Hamilton's principle. Thirdly, these conservation laws are used to derive a wave-activity invariant which is second-order in terms of small-amplitude disturbances relative to a resting or moving basic state. Linear stability criteria are derived but only for resting basic states. In mid-latitudes a time- scale separation between gravity and vortical modes occurs. Finally, this time-scale separation suggests that conservative geostrophic and ageostrophic approximations can be made to the Eulerian action principle for hydrostatic flows. Approximations to Eulerian variational principles may be more advantageous than approximations to Lagrangian ones because non-dimensionalization and scaling tend to be based on Eulerian estimates of the characteristic scales involved. These approximations to the stratified hydrostatic formulation extend previous approximations to the shallow- water equations. An explicit variational derivation is given of an isentropic version of Hoskins & Bretherton's model for atmospheric fronts.

Modeling thermospheric neutral density

NASA Astrophysics Data System (ADS)

Qian, Liying

Satellite drag prediction requires determination of thermospheric neutral density. The NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) and the global-mean Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIMEGCM) were used to quantify thermospheric neutral density and its variations, focusing on annual/semiannual variation, the effect of using measured solar irradiance on model calculations of solar-cycle variation, and global change in the thermosphere. Satellite drag data and the MSIS00 empirical model were utilized to compare to the TIEGCM simulations. The TIEGCM simulations indicated that eddy diffusion and its annual/semiannual variation is a mechanism for annual/semiannual density variation in the thermosphere. It was found that eddy diffusion near the turbopause can effectively influence thermospheric neutral density. Eddy diffusion, together with annual insolation variation and large-scale circulation, generated global annual/semiannual density variation observed by satellite drag. Using measured solar irradiance as solar input for the TIEGCM improved the solar-cycle dependency of the density calculation shown in F10.7 -based thermospheric empirical models. It has been found that the empirical models overestimate density at low solar activity. The TIEGCM simulations did not show such solar-cycle dependency. Using historic measurements of CO2 and F 10.7, simulations of the global-mean TIMEGCM showed that thermospheric neutral density at 400 km had an average long-term decrease of 1.7% per decade from 1970 to 2000. A forecast of density decrease for solar cycle 24 suggested that thermospheric density will decrease at 400 km from present to the end of solar cycle 24 at a rate of 2.7% per decade. Reduction in thermospheric density causes less atmospheric drag on earth-orbiting space objects. The implication of this long-term decrease of thermospheric neutral density is that it will increase the lifetime of satellites, but also it will increase the amount of space junk.

A Century Trend of Precipitation in Forest Watersheds from the Lower Mississippi River Basin

NASA Astrophysics Data System (ADS)

Feng, G.; Ouyang, Y.; Leininger, T.; Han, Y.

2017-12-01

Estimates of hydrological processes in forest watersheds are essential to water supply planning, water quality protection, water resources management, and ecological restoration; whereas the century precipitation variation due to climate change could exacerbate forest watershed hydrological processes and add uncertainties to the processes. In this study, the multivariate statisitcal analysis technique was employed to identify a century temporal trend of precipitation in forest watersheds from the Lower Mississippi River Basin (LMRB). Seveal surface water monitoring stations in the LMRB, located in forest watersheds with very little land use disturbance and a century record, were selected to obtain precipitation data. Using frequency distribution analysis with HYDSTRA model, we found that the mean annual precipitation in a decadal scale increased as time elapsed over a 100-year period. Our study further revealed that the precipitation intensity for one-hour duration increased sigificantly in every 10 years for a 100-year period. During this period, the annual mean dry day frequency decreased in a decadal scale, whereas the annual mean wet day frequency increased for the same scale. Results indicated the precipitation pattern has been altered in the LMRB and the selected forest watersheds in this basin seems to become wetter during the past 100 years as a result of climate change.

Long-term Observations of Intense Precipitation Small-scale Spatial Variability in a Semi-arid Catchment

NASA Astrophysics Data System (ADS)

Cropp, E. L.; Hazenberg, P.; Castro, C. L.; Demaria, E. M.

2017-12-01

In the southwestern US, the summertime North American Monsoon (NAM) provides about 60% of the region's annual precipitation. Recent research using high-resolution atmospheric model simulations and retrospective predictions has shown that since the 1950's, and more specifically in the last few decades, the mean daily precipitation in the southwestern U.S. during the NAM has followed a decreasing trend. Furthermore, days with more extreme precipitation have intensified. The current work focuses the impact of these long-term changes on the observed small-scale spatial variability of intense precipitation. Since limited long-term high-resolution observational data exist to support such climatological-induced spatial changes in precipitation frequency and intensity, the current work utilizes observations from the USDA-ARS Walnut Gulch Experimental Watershed (WGEW) in southeastern Arizona. Within this 150 km^2 catchment over 90 rain gauges have been installed since the 1950s, measuring at sub-hourly resolution. We have applied geospatial analyses and the kriging interpolation technique to identify long-term changes in the spatial and temporal correlation and anisotropy of intense precipitation. The observed results will be compared with the previously model simulated results, as well as related to large-scale variations in climate patterns, such as the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO).

Lightning and Climate

NASA Astrophysics Data System (ADS)

Williams, E.

2012-12-01

Lightning is of interest in the domain of climate change for several reasons: (1) thunderstorms are extreme forms of moist convection, and lightning flash rate is a sensitive measure of that extremity, (2) thunderstorms are deep conduits for delivering water substance from the boundary layer to the upper troposphere and stratosphere, and (3) global lightning can be monitored continuously and inexpensively within a natural framework (the Earth-ionosphere waveguide and Schumann resonances). Lightning and temperature, and lightning and upper tropospheric water vapor, are positively correlated on weather-related time scales (diurnal, semiannual, and annual) with a lightning temperature sensitivity of order 10% per oC. Lightning also follows temperature variations on the ENSO time scale, both locally and globally. The response of lightning in some of its extreme forms (exceptional flash rates and the prevalence of sprite-producing mesoscale lightning, for example) to temperature variations will be addressed. Consistently obtained records of lightning activity on longer time scales are scarce as stable detection networks are uncommon. As a consequence, thunder day data have been used to extend the lightning record for climate studies, with evidence for increases over decades in urban areas. Global records of lightning following Schumann resonance intensity and from space-based optical sensors (OTD and LIS) are consistent with the record of ionospheric potential representing the global electrical circuit in showing flat behavior over the few decades. This flatness is not well understood, though the majority of all lightning flashes are found in the tropics, the most closely regulated portion of the atmosphere. Other analysis of frequency variations of Schumann resonances in recent decades shows increased lightning in the northern hemisphere, where the global warming is most pronounced. The quantity more fundamental than temperature for lightning control is cloud buoyancy as this forces the updraft in thunderstorm convection and strongly influences the ice phase microphysics on which the charge separation and lightning depends. The vertical integration of cloud buoyancy is Convective Available Potential Energy (CAPE), a rather delicate quantity. Though many GCM results show evidence for an extended tail in distributions of CAPE in a warmer world, its real variation over the last century is not well established. The CCN component of aerosol is now recognized to influence the cloud water content and thereby the profile of cloud buoyancy, and so the response of lightning to climate is not entirely a thermodynamic one. Key evidence here is the recent finding of a weekend effect in lightning activity. A number of contrasting phenomena between land and ocean (and between urban and rural environments), including the dramatic continental dominance of lightning (and the urban dominance of lightning), and in upper level cirrus cloud and in warm rain production, have explanations in both thermodynamics and in aerosol-modulated microphysics. Sorting out these contributions has proven to be a challenging task. The prevailing view is that lightning responds to climate change. Another perspective is that cloud electrification and lightning can cause changes in climate, either by influencing chemistry or large scale dynamics. These issues will also be addressed.

Modeling Study of the Effect of Anthropogenic Aerosols on Late Spring Drought in South China

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

Hu, Ning; Liu, Xiaohong

2013-10-01

In this study, the mechanisms underlying the decadal variability of late spring precipitation in south China are investigated using the latest version 1 of Community Earth System Model (CESM1). We aim to unravel the effects of different climate forcing agents, such as aerosols and greenhouse gases (GHGs), on the decadal variation of precipitation with transient experiments from pre-industry (for year 1850) to present-day (for year 2000). Our results reveal that: (1) CESM1 can reproduce the climatological features of atmospheric circulation and precipitation for the late spring in south China; (2) Only simulations including the forcing of anthropogenic aerosols can reproducemore » the observed decreasing trend of late spring precipitation from 1950-2000 in south China; (3) Aerosols affect the decadal change of precipitation mainly by altering the large scale atmospheric circulation, and to a less extent by increasing the lower-tropospheric stability to inhibit the convective precipitation; and (4) In comparison, other climate forcing agents, such as GHGs, have much smaller effects on the decadal change of spring precipitation in south China. Key words: precipitation, aerosols, climate change, south China, Community Earth System Model« less

Basin-Wide Oceanographic Array Bridges the South Atlantic

NASA Astrophysics Data System (ADS)

Ansorge, I. J.; Baringer, M. O.; Campos, E. J. D.; Dong, S.; Fine, R. A.; Garzoli, S. L.; Goni, G.; Meinen, C. S.; Perez, R. C.; Piola, A. R.; Roberts, M. J.; Speich, S.; Sprintall, J.; Terre, T.; Van den Berg, M. A.

2014-02-01

The meridional overturning circulation (MOC) is a global system of surface, intermediate, and deep ocean currents. The MOC connects the surface layer of the ocean and the atmosphere with the huge reservoir of the deep sea and is the primary mechanism for transporting heat, freshwater, and carbon between ocean basins. Climate models show that past changes in the strength of the MOC were linked to historical climate variations. Further research suggests that the MOC will continue to modulate climate change scenarios on time scales ranging from decades to centuries [Latif et al., 2006].

Cis-regulatory Elements and Human Evolution

PubMed Central

Siepel, Adam

2014-01-01

Modification of gene regulation has long been considered an important force in human evolution, particularly through changes to cis-regulatory elements (CREs) that function in transcriptional regulation. For decades, however, the study of cis-regulatory evolution was severely limited by the available data. New data sets describing the locations of CREs and genetic variation within and between species have now made it possible to study CRE evolution much more directly on a genome-wide scale. Here, we review recent research on the evolution of CREs in humans based on large-scale genomic data sets. We consider inferences based on primate divergence, human polymorphism, and combinations of divergence and polymorphism. We then consider “new frontiers” in this field stemming from recent research on transcriptional regulation. PMID:25218861

Decadal Variation of Precipitation in Saudi Arabia induced by Agricultural Irrigation

NASA Astrophysics Data System (ADS)

Lo, M. H.; Wey, H. W.; Wada, Y.; IM, E. S.; Chien, R. Y.; Wu, R. J.

2017-12-01

Decadal variation of wet-season precipitation has been found in the arid region of central Saudi Arabia. 1980s has been a rather wet decade compared with the decades before. Previous studies have mentioned that the irrigation moisture may contribute to the precipitation anomalies in Saudi Arabia. In the current study, we show from observational data that the contribution of the variation comes mostly from February to May. As the irrigation is a localized forcing, we therefore use the Weather Research and Forecasting (WRF) Model to simulate the response of the land-atmosphere interaction to the wet soil moisture resulted from additional irrigation moisture supply. Preliminary result shows in the irrigated simulation that precipitation in central Saudi Arabia is enhanced, indicating the possible link between irrigation expansion in the 1980s and the decadal precipitation variation over central Saudi Arabia. We propose it is the anomalous convergence induced by irrigation as well as additional moisture that contribute to the enhanced precipitation over heavily irrigation region in the central Saudi Arabian. In addition, analysis on the daily precipitation from the WRF outputs indicates that positive rainfall anomalies tend to happen when there is rainfall originally; that is, irrigation enhances rainfall but not creates rainfall.

Coral Records of 20th Century Central Tropical Pacific SST and Salinity: Signatures of Natural and Anthropogenic Climate Change

NASA Astrophysics Data System (ADS)

Nurhati, I. S.; Cobb, K.; Di Lorenzo, E.

2011-12-01

Accurate forecasts of regional climate changes in many regions of the world largely depend on quantifying anthropogenic trends in tropical Pacific climate against its rich background of interannual to decadal-scale climate variability. However, the strong natural climate variability combined with limited instrumental climate datasets have obscured potential anthropogenic climate signals in the region. Here, we present coral-based sea-surface temperature (SST) and salinity proxy records over the 20th century (1898-1998) from the central tropical Pacific - a region sensitive to El Niño-Southern Oscillation (ENSO) whose variability strongly impacts the global climate. The SST and salinity proxy records are reconstructed via coral Sr/Ca and the oxygen isotopic composition of seawater (δ18Osw), respectively. On interannual (2-7yr) timescales, the SST proxy record tracks both eastern- and central-Pacific flavors of ENSO variability (R=0.65 and R=0.67, respectively). Interannual-scale salinity variability in our coral record highlights profound differences in precipitation and ocean advections during the two flavors of ENSO. On decadal (8yr-lowpassed) timescales, the central tropical Pacific SST and salinity proxy records are controlled by different sets of dynamics linked to the leading climate modes of North Pacific climate variability. Decadal-scale central tropical Pacific SST is highly correlated to the recently discovered North Pacific Gyre Oscillation (NPGO; R=-0.85), reflecting strong dynamical links between the central Pacific warming mode and extratropical decadal climate variability. Whereas decadal-scale salinity variations in the central tropical Pacific are significantly correlated with the Pacific Decadal Oscillation (PDO; R=0.54), providing a better understanding on low-frequency salinity variability in the region. Having characterized natural climate variability in this region, the coral record shows a +0.5°C warming trend throughout the last century. However, the most prominent feature of the new coral records is an unprecedented freshening trend since the mid-20th century, in line with global climate models (GCMs) projections of enhanced hydrological patterns (wet areas are getting wetter and vice versa) under greenhouse forcing. Taken together, the coral records provide key constraints on tropical Pacific climate trends that may improve regional climate projections in areas affected by tropical Pacific climate variability.
Central Tropical Pacific SST and Salinity Proxy Records

Reconstructed storm tracks reveal three centuries of changing moisture delivery to North America

PubMed Central

Wise, Erika K.; Dannenberg, Matthew P.

2017-01-01

Moisture delivery to western North America is closely linked to variability in the westerly storm tracks of midlatitude cyclones, which are, in turn, modified by larger-scale features such as the El Niño–Southern Oscillation system. Instrumental and modeling data suggest that extratropical storm tracks may be intensifying and shifting poleward due to anthropogenic climate change, but it is difficult to separate recent trends from natural variability because of the large amount of decadal and longer variation in storm tracks and their limited instrumental record. We reconstruct cool-season, midlatitude Pacific storm-track position and intensity from 1693 to 1995 CE using existing tree-ring chronologies along with a network of newly developed chronologies from the U.S. Pacific Northwest, where small variations in storm-track position can have a major influence on hydroclimate patterns. Our results show high interannual-to-multidecadal variability in storm-track position and intensity over the past 303 years, with spectral signatures characteristic of tropical and northern Pacific influences. Comparison with reconstructions of precipitation and tropical sea surface temperature confirms the relationship between shifting drought patterns in the Pacific Northwest and storm-track variability through time and demonstrates the long-term influence of El Niño. These results allow us to place recent storm-track changes in the context of decadal and multidecadal fluctuations across the long-term record, showing that recent changes in storm-track intensity likely represent a warming-related increase amplified by natural decadal variability. PMID:28630900

Reconstructed storm tracks reveal three centuries of changing moisture delivery to North America.

PubMed

Wise, Erika K; Dannenberg, Matthew P

2017-06-01

Moisture delivery to western North America is closely linked to variability in the westerly storm tracks of midlatitude cyclones, which are, in turn, modified by larger-scale features such as the El Niño-Southern Oscillation system. Instrumental and modeling data suggest that extratropical storm tracks may be intensifying and shifting poleward due to anthropogenic climate change, but it is difficult to separate recent trends from natural variability because of the large amount of decadal and longer variation in storm tracks and their limited instrumental record. We reconstruct cool-season, midlatitude Pacific storm-track position and intensity from 1693 to 1995 CE using existing tree-ring chronologies along with a network of newly developed chronologies from the U.S. Pacific Northwest, where small variations in storm-track position can have a major influence on hydroclimate patterns. Our results show high interannual-to-multidecadal variability in storm-track position and intensity over the past 303 years, with spectral signatures characteristic of tropical and northern Pacific influences. Comparison with reconstructions of precipitation and tropical sea surface temperature confirms the relationship between shifting drought patterns in the Pacific Northwest and storm-track variability through time and demonstrates the long-term influence of El Niño. These results allow us to place recent storm-track changes in the context of decadal and multidecadal fluctuations across the long-term record, showing that recent changes in storm-track intensity likely represent a warming-related increase amplified by natural decadal variability.

Persistent millennial-scale shifts in moisture regimes in western Canada during the past six millennia

PubMed Central

Cumming, Brian F.; Laird, Kathleen R.; Bennett, Joseph R.; Smol, John P.; Salomon, Anne K.

2002-01-01

Inferences of past climatic conditions from a sedimentary record from Big Lake, British Columbia, Canada, over the past 5,500 years show strong millennial-scale patterns, which oscillate between periods of wet and drier climatic conditions. Higher frequency decadal- to centennial-scale fluctuations also occur within the dominant millennial-scale patterns. These changes in climatic conditions are based on estimates of changes in lake depth and salinity inferred from diatom assemblages in a well dated sediment core. After periods of relative stability, abrupt shifts in diatom assemblages and inferred climatic conditions occur approximately every 1,220 years. The correspondence of these shifts to millennial-scale variations in records of glacial expansion/recession and ice-rafting events in the Atlantic suggest that abrupt millennial-scale shifts are important to understanding climatic variability in North America during the mid- to late Holocene. Unfortunately, the spatial patterns and mechanisms behind these large and abrupt swings are poorly understood. Similar abrupt and prolonged changes in climatic conditions today could pose major societal challenges for many regions. PMID:12461174

Persistent millennial-scale shifts in moisture regimes in western Canada during the past six millennia.

PubMed

Cumming, Brian F; Laird, Kathleen R; Bennett, Joseph R; Smol, John P; Salomon, Anne K

2002-12-10

Inferences of past climatic conditions from a sedimentary record from Big Lake, British Columbia, Canada, over the past 5,500 years show strong millennial-scale patterns, which oscillate between periods of wet and drier climatic conditions. Higher frequency decadal- to centennial-scale fluctuations also occur within the dominant millennial-scale patterns. These changes in climatic conditions are based on estimates of changes in lake depth and salinity inferred from diatom assemblages in a well dated sediment core. After periods of relative stability, abrupt shifts in diatom assemblages and inferred climatic conditions occur approximately every 1,220 years. The correspondence of these shifts to millennial-scale variations in records of glacial expansionrecession and ice-rafting events in the Atlantic suggest that abrupt millennial-scale shifts are important to understanding climatic variability in North America during the mid- to late Holocene. Unfortunately, the spatial patterns and mechanisms behind these large and abrupt swings are poorly understood. Similar abrupt and prolonged changes in climatic conditions today could pose major societal challenges for many regions.

Temperature Responses to Spectral Solar Variability on Decadal Time Scales

NASA Technical Reports Server (NTRS)

Cahalan, Robert F.; Wen, Guoyong; Harder, Jerald W.; Pilewskie, Peter

2010-01-01

Two scenarios of spectral solar forcing, namely Spectral Irradiance Monitor (SIM)-based out-of-phase variations and conventional in-phase variations, are input to a time-dependent radiative-convective model (RCM), and to the GISS modelE. Both scenarios and models give maximum temperature responses in the upper stratosphere, decreasing to the surface. Upper stratospheric peak-to-peak responses to out-of-phase forcing are approx.0.6 K and approx.0.9 K in RCM and modelE, approx.5 times larger than responses to in-phase forcing. Stratospheric responses are in-phase with TSI and UV variations, and resemble HALOE observed 11-year temperature variations. For in-phase forcing, ocean mixed layer response lags surface air response by approx.2 years, and is approx.0.06 K compared to approx.0.14 K for atmosphere. For out-of-phase forcing, lags are similar, but surface responses are significantly smaller. For both scenarios, modelE surface responses are less than 0.1 K in the tropics, and display similar patterns over oceanic regions, but complex responses over land.

Density Anomalies in the Mantle and the Gravitational Core-Mantle Interaction

NASA Technical Reports Server (NTRS)

Kuang, Weijia; Liu, Lanbo

2003-01-01

Seismic studies suggest that the bulk of the mantle is heterogeneous, with density variations in depth as well as in horizontal directions (latitude and longitude). This density variation produces a three- dimensional gravity field throughout the Earth. On the other hand, the core density also varies in both time and space, due to convective core flow. Consequently, the fluid outer core and the solid mantle interact gravitationally due to the mass anomalies in both regions. This gravitational core-mantle interaction could play a significant role in exchange of angular momentum between the core and the mantle, and thus the change in Earth's rotation on time scales of decades and longer. Aiming at estimating the significance of the gravitational core-mantle interaction on Earth's rotation variation, we introduce in our MoSST core dynamics model a heterogeneous mantle, with a density distribution derived from seismic results. In this model, the core convection is driven by the buoyancy forces. And the density variation is determined dynamically with the convection. Numerical simulation is carried out with different parameter values, intending to extrapolate numerical results for geophysical implications.

Real-time evolution of a large-scale relativistic jet

NASA Astrophysics Data System (ADS)

Martí, Josep; Luque-Escamilla, Pedro L.; Romero, Gustavo E.; Sánchez-Sutil, Juan R.; Muñoz-Arjonilla, Álvaro J.

2015-06-01

Context. Astrophysical jets are ubiquitous in the Universe on all scales, but their large-scale dynamics and evolution in time are hard to observe since they usually develop at a very slow pace. Aims: We aim to obtain the first observational proof of the expected large-scale evolution and interaction with the environment in an astrophysical jet. Only jets from microquasars offer a chance to witness the real-time, full-jet evolution within a human lifetime, since they combine a "short", few parsec length with relativistic velocities. Methods: The methodology of this work is based on a systematic recalibraton of interferometric radio observations of microquasars available in public archives. In particular, radio observations of the microquasar GRS 1758-258 over less than two decades have provided the most striking results. Results: Significant morphological variations in the extended jet structure of GRS 1758-258 are reported here that were previously missed. Its northern radio lobe underwent a major morphological variation that rendered the hotspot undetectable in 2001 and reappeared again in the following years. The reported changes confirm the Galactic nature of the source. We tentatively interpret them in terms of the growth of instabilities in the jet flow. There is also evidence of surrounding cocoon. These results can provide a testbed for models accounting for the evolution of jets and their interaction with the environment.

Selection on an extreme weapon in the frog-legged leaf beetle (Sagra femorata).

PubMed

O'Brien, Devin M; Katsuki, Masako; Emlen, Douglas J

2017-11-01

Biologists have been fascinated with the extreme products of sexual selection for decades. However, relatively few studies have characterized patterns of selection acting on ornaments and weapons in the wild. Here, we measure selection on a wild population of weapon-bearing beetles (frog-legged leaf beetles: Sagra femorata) for two consecutive breeding seasons. We consider variation in both weapon size (hind leg length) and in relative weapon size (deviations from the population average scaling relationship between hind leg length and body size), and provide evidence for directional selection on weapon size per se and stabilizing selection on a particular scaling relationship in this population. We suggest that whenever growth in body size is sensitive to external circumstance such as nutrition, then considering deviations from population-level scaling relationships will better reflect patterns of selection relevant to evolution of the ornament or weapon than will variation in trait size per se. This is because trait-size versus body-size scaling relationships approximate underlying developmental reaction norms relating trait growth with body condition in these species. Heightened condition-sensitive expression is a hallmark of the exaggerated ornaments and weapons favored by sexual selection, yet this plasticity is rarely reflected in the way we think about-and measure-selection acting on these structures in the wild. © 2017 The Author(s). Evolution © 2017 The Society for the Study of Evolution.

Carbon recycling in deltaic sediments: variations at different timescales in the Rhone River delta

NASA Astrophysics Data System (ADS)

Rabouille, C.; Rassmann, J.; Toussaint, F.; Cathalot, C.; Tisnerat-Laborde, N.; Lansard, B.

2016-02-01

Terrestrial aquatic environments and the land-sea connection are a major contributors to the Earth carbon cycle, as these act as a source to the atmosphere of about 1 Gt/yr for rivers and up to 0.4 Gt/yr for estuarine/detaic systems. These estimates are largely uncertain because of the large temporal variability of these systems. In estuarine and deltaic sediments, variability combines hydrological variation from the river (floods and drought) and the hydrology of the coastal seas (storms, current surge, wind induced circulation, upwelling) wich are both influencial on biogeochemistry. This hydrological variability interacts with the seasonal variation of in situ production and with thermal activation of bacterial recycling due to seasonal warming of shallow waters. The combination of these processes gives rise to a range of timescales: typically hours to days for resuspension during storms to interannual variations for particulate discharge modulations. Using in situ oxygen microprofiling devices, we have collected a new dataset on organic matter recycling in the Rhone delta and shelf sediments (Northwestern Mediterranean Sea) which covers a wide range of timescales: from hours to a decade. The hourly variation is collected using a new benthic station deployed on the sediments and specially adapted to monitor short-term variations of sediment oxygen micro-profiles during flood or storms. The seasonal to decadal timescale is constituted by a set of oxygen micro-profiles measured on an array of stations in the Rhône prodelta and shelf by an in situ microprofiler during seasonal cruises over 10 year. The results show that Diffusive Oxygen Fluxes which are related to organic matter recycling vary at all timescales, driven mostly by deposition of river material during floods. Resuspension during storms plays a role over short time scales, and its long-term effect could raise the overall oxygen demand of the sediment by 20-30%.

Refined genetic maps reveal sexual dimorphism in human meiotic recombination at multiple scales

NASA Astrophysics Data System (ADS)

Bhérer, Claude; Campbell, Christopher L.; Auton, Adam

2017-04-01

In humans, males have lower recombination rates than females over the majority of the genome, but the opposite is usually true near the telomeres. These broad-scale differences have been known for decades, yet little is known about differences at the fine scale. By combining data sets, we have collected recombination events from over 100,000 meioses and have constructed sex-specific genetic maps at a previously unachievable resolution. Here we show that, although a substantial fraction of the genome shows some degree of sexually dimorphic recombination, the vast majority of hotspots are shared between the sexes, with only a small number of putative sex-specific hotspots. Wavelet analysis indicates that most of the differences can be attributed to the fine scale, and that variation in rate between the sexes can mostly be explained by differences in hotspot magnitude, rather than location. Nonetheless, known recombination-associated genomic features, such as THE1B repeat elements, show systematic differences between the sexes.

Reconstruction of regional climate and climate change in past decades

NASA Astrophysics Data System (ADS)

von Storch, H.; Feser, F.; Weisse, R.; Zahn, M.

2009-12-01

Regional climate models, which are constrained by large scale information (spectral nudging) provided by re-analyses, allow for the construction of a mostly homogeneous description of regional weather statistics since about 1950. The potential of this approach has been demonstrated for Northern Europe. That data set, named CoastDat, does not only contain hourly data on atmospheric variables, in particular wind, but also on marine weather, i.e., short term water level, current and sea state variations. Another example is the multi-decadal variability of Polar Lows in the subarctic waters. The utility of such data sets is broad, from risk assessments related to coastal wind and wave conditions, assessment of determining the causes for regional climate change, a-posteriori analysis of the efficiency of environmental legislation (example: lead). In the paper, the methodology is outlined, examples are provided and the utility of the product discussed.

Idiocultural Design as a Tool of Cultural Psychology.

PubMed

Cole, Michael

2017-09-01

The study of small group idiocultures offers a productive way to study the role of culture in human cognitive and social development. My evidence is drawn from a multi-decade long study of groups of mixed-aged participants engaged in deliberately designed forms of joint activity taking place several times a week over periods extending over decades in a variety of institutional settings. In each such system, participants ranging from middle childhood to adulthood participate in an after-school program composed of a wide variety of games brought together in a fantasy world watched over by a Wizard. Insights offered by this approach include comparative analysis of skill development in different idiocultural systems, intergenerational changes in the local cultural systems themselves, and intra-cultural variations in the behavioral changes of individual children occurring over different time scales. Implications of this comparative approach for psychology science are discussed.

Enceladus Plumes: Causes of Decadal Variability

NASA Astrophysics Data System (ADS)

Ingersoll, Andrew P.; Ewald, Shawn P.

2016-10-01

The Enceladus plumes have decreased over the decade that Cassini has been observing them. This long-term variation is superposed on the much shorter-term variation tied to the position of Enceladus in its orbit around Saturn. The observations are ISS and VIMS images, which reveal the particles in the plumes but not the gas. The decadal variability largely consists of a 2-fold decline in the mass of plume material, but there is a hint of a recent turnaround. Here we offer three hypotheses, each with its strengths and weaknesses, to explain the long-term variability. The first is seasonal change, from summer to fall in the southern hemisphere. The loss of sunlight could increase the build-up of ice around the tiger stripes. The weakness is that the sunlight is likely to have a small effect, e.g., decreasing the sublimation rate of the ice by only ~1 cm/year. The second hypothesis is a statistical fluctuation in the number of active plumes, which tend to turn themselves off due to build-up of ice at the throat of the vent. The weakness is that the plumes are likely to fluctuate independently, and if there are ~100 plumes, their sum will only fluctuate by 10%. The third hypothesis is that the variation is part of a well-known decadal cycle of orbital eccentricity, which varies by ±2.5% around a mean of 0.0047. The peak eccentricity occurred in 2009-2010, and the minimum occurred in 2015. Since eccentricity controls the short-term orbital cycle variations, it could also control the longer-term decadal variations. The weakness is that the eccentricity variation is small, from 0.0046 to 0.0048. It is not certain that such a small variation could cause a 2-fold variation in the strength of the plumes. An independent study, still in its infancy, is the possibility that liquid water reaches the surface during part of the orbital cycle.

Spatially Extensive Standardized Surveys Reveal Widespread, Multi-Decadal Increase in East Antarctic Adélie Penguin Populations.

PubMed

Southwell, Colin; Emmerson, Louise; McKinlay, John; Newbery, Kym; Takahashi, Akinori; Kato, Akiko; Barbraud, Christophe; DeLord, Karine; Weimerskirch, Henri

2015-01-01

Seabirds are considered to be useful and practical indicators of the state of marine ecosystems because they integrate across changes in the lower trophic levels and the physical environment. Signals from this key group of species can indicate broad scale impacts or response to environmental change. Recent studies of penguin populations, the most commonly abundant Antarctic seabirds in the west Antarctic Peninsula and western Ross Sea, have demonstrated that physical changes in Antarctic marine environments have profound effects on biota at high trophic levels. Large populations of the circumpolar-breeding Adélie penguin occur in East Antarctica, but direct, standardized population data across much of this vast coastline have been more limited than in other Antarctic regions. We combine extensive new population survey data, new population estimation methods, and re-interpreted historical survey data to assess decadal-scale change in East Antarctic Adélie penguin breeding populations. We show that, in contrast to the west Antarctic Peninsula and western Ross Sea where breeding populations have decreased or shown variable trends over the last 30 years, East Antarctic regional populations have almost doubled in abundance since the 1980's and have been increasing since the earliest counts in the 1960's. The population changes are associated with five-year lagged changes in the physical environment, suggesting that the changing environment impacts primarily on the pre-breeding age classes. East Antarctic marine ecosystems have been subject to a number of changes over the last 50 years which may have influenced Adélie penguin population growth, including decadal-scale climate variation, an inferred mid-20th century sea-ice contraction, and early-to-mid 20th century exploitation of fish and whale populations.

Spatially Extensive Standardized Surveys Reveal Widespread, Multi-Decadal Increase in East Antarctic Adélie Penguin Populations

PubMed Central

Southwell, Colin; Emmerson, Louise; McKinlay, John; Newbery, Kym; Takahashi, Akinori; Kato, Akiko; Barbraud, Christophe; DeLord, Karine; Weimerskirch, Henri

2015-01-01

Seabirds are considered to be useful and practical indicators of the state of marine ecosystems because they integrate across changes in the lower trophic levels and the physical environment. Signals from this key group of species can indicate broad scale impacts or response to environmental change. Recent studies of penguin populations, the most commonly abundant Antarctic seabirds in the west Antarctic Peninsula and western Ross Sea, have demonstrated that physical changes in Antarctic marine environments have profound effects on biota at high trophic levels. Large populations of the circumpolar-breeding Adélie penguin occur in East Antarctica, but direct, standardized population data across much of this vast coastline have been more limited than in other Antarctic regions. We combine extensive new population survey data, new population estimation methods, and re-interpreted historical survey data to assess decadal-scale change in East Antarctic Adélie penguin breeding populations. We show that, in contrast to the west Antarctic Peninsula and western Ross Sea where breeding populations have decreased or shown variable trends over the last 30 years, East Antarctic regional populations have almost doubled in abundance since the 1980’s and have been increasing since the earliest counts in the 1960’s. The population changes are associated with five-year lagged changes in the physical environment, suggesting that the changing environment impacts primarily on the pre-breeding age classes. East Antarctic marine ecosystems have been subject to a number of changes over the last 50 years which may have influenced Adélie penguin population growth, including decadal-scale climate variation, an inferred mid-20th century sea-ice contraction, and early-to-mid 20th century exploitation of fish and whale populations. PMID:26488299

Reviews and syntheses: Four decades of modeling methane cycling in terrestrial ecosystems

NASA Astrophysics Data System (ADS)

Xu, Xiaofeng; Yuan, Fengming; Hanson, Paul J.; Wullschleger, Stan D.; Thornton, Peter E.; Riley, William J.; Song, Xia; Graham, David E.; Song, Changchun; Tian, Hanqin

2016-06-01

Over the past 4 decades, a number of numerical models have been developed to quantify the magnitude, investigate the spatial and temporal variations, and understand the underlying mechanisms and environmental controls of methane (CH4) fluxes within terrestrial ecosystems. These CH4 models are also used for integrating multi-scale CH4 data, such as laboratory-based incubation and molecular analysis, field observational experiments, remote sensing, and aircraft-based measurements across a variety of terrestrial ecosystems. Here we summarize 40 terrestrial CH4 models to characterize their strengths and weaknesses and to suggest a roadmap for future model improvement and application. Our key findings are that (1) the focus of CH4 models has shifted from theoretical to site- and regional-level applications over the past 4 decades, (2) large discrepancies exist among models in terms of representing CH4 processes and their environmental controls, and (3) significant data-model and model-model mismatches are partially attributed to different representations of landscape characterization and inundation dynamics. Three areas for future improvements and applications of terrestrial CH4 models are that (1) CH4 models should more explicitly represent the mechanisms underlying land-atmosphere CH4 exchange, with an emphasis on improving and validating individual CH4 processes over depth and horizontal space, (2) models should be developed that are capable of simulating CH4 emissions across highly heterogeneous spatial and temporal scales, particularly hot moments and hotspots, and (3) efforts should be invested to develop model benchmarking frameworks that can easily be used for model improvement, evaluation, and integration with data from molecular to global scales. These improvements in CH4 models would be beneficial for the Earth system models and further simulation of climate-carbon cycle feedbacks.

Quantifying climatic variability in monsoonal northern China over the last 2200 years and its role in driving Chinese dynastic changes

NASA Astrophysics Data System (ADS)

Li, Jianyong; Dodson, John; Yan, Hong; Zhang, David D.; Zhang, Xiaojian; Xu, Qinghai; Lee, Harry F.; Pei, Qing; Cheng, Bo; Li, Chunhai; Ni, Jian; Sun, Aizhi; Lu, Fengyan; Zong, Yongqiang

2017-03-01

Our understanding on the spatial-temporal patterns of climatic variability over the last few millennia in the East Asian monsoon-dominated northern China (NC), and its role at a macro-scale in affecting the prosperity and depression of Chinese dynasties is limited. Quantitative high-resolution, regionally-synthesized palaeoclimatic reconstructions as well as simulations, and numerical analyses of their relationships with various fine-scale, numerical agro-ecological, social-economic, and geo-political historical records during the period of China's history, are presented here for NC. We utilize pollen data together with climate modeling to reconstruct and simulate decadal- to centennial-scale variations in precipitation or temperature for NC during the last 2200 years (-200-2000 AD). We find an overall cyclic-pattern (wet/warm or dry/cold) in the precipitation and temperature anomalies on centennial- to millennial-scale that can be likely considered as a representative for the entire NC by comparison with other related climatic records. We suggest that solar activity may play a key role in driving the climatic fluctuations in NC during the last 22 centuries, with its quasi ∼100, 50, 23, or 22-year periodicity clearly identified in our climatic reconstructions. We employ variation partitioning and redundancy analysis to quantify the independent effects of climatic factors on accounting for the total variation of 17 fine-grained numerical Chinese historical records. We quantitatively illustrate that precipitation (67.4%) may have been more important than temperature (32.5%) in causing the overall agro-ecological and macro-geopolitical shifts in imperial China with NC as the central ruling region and an agricultural heartland over the last 2200 years.

Localized Hotspots Drive Continental Geography of Abnormal Amphibians on U.S. Wildlife Refuges

PubMed Central

Reeves, Mari K.; Medley, Kimberly A.; Pinkney, Alfred E.; Holyoak, Marcel; Johnson, Pieter T. J.; Lannoo, Michael J.

2013-01-01

Amphibians with missing, misshapen, and extra limbs have garnered public and scientific attention for two decades, yet the extent of the phenomenon remains poorly understood. Despite progress in identifying the causes of abnormalities in some regions, a lack of knowledge about their broader spatial distribution and temporal dynamics has hindered efforts to understand their implications for amphibian population declines and environmental quality. To address this data gap, we conducted a nationwide, 10-year assessment of 62,947 amphibians on U.S. National Wildlife Refuges. Analysis of a core dataset of 48,081 individuals revealed that consistent with expected background frequencies, an average of 2% were abnormal, but abnormalities exhibited marked spatial variation with a maximum prevalence of 40%. Variance partitioning analysis demonstrated that factors associated with space (rather than species or year sampled) captured 97% of the variation in abnormalities, and the amount of partitioned variance decreased with increasing spatial scale (from site to refuge to region). Consistent with this, abnormalities occurred in local to regional hotspots, clustering at scales of tens to hundreds of kilometers. We detected such hotspot clusters of high-abnormality sites in the Mississippi River Valley, California, and Alaska. Abnormality frequency was more variable within than outside of hotspot clusters. This is consistent with dynamic phenomena such as disturbance or natural enemies (pathogens or predators), whereas similarity of abnormality frequencies at scales of tens to hundreds of kilometers suggests involvement of factors that are spatially consistent at a regional scale. Our characterization of the spatial and temporal variation inherent in continent-wide amphibian abnormalities demonstrates the disproportionate contribution of local factors in predicting hotspots, and the episodic nature of their occurrence. PMID:24260103

In the Shadow of Coal: How Large-Scale Industries Contributed to Present-Day Regional Differences in Personality and Well-Being.

PubMed

Obschonka, Martin; Stuetzer, Michael; Rentfrow, Peter J; Shaw-Taylor, Leigh; Satchell, Max; Silbereisen, Rainer K; Potter, Jeff; Gosling, Samuel D

2017-11-20

Recent research has identified regional variation of personality traits within countries but we know little about the underlying drivers of this variation. We propose that the Industrial Revolution, as a key era in the history of industrialized nations, has led to a persistent clustering of well-being outcomes and personality traits associated with psychological adversity via processes of selective migration and socialization. Analyzing data from England and Wales, we examine relationships between the historical employment share in large-scale coal-based industries (coal mining and steam-powered manufacturing industries that used this coal as fuel for their steam engines) and today's regional variation in personality and well-being. Even after controlling for possible historical confounds (historical energy supply, education, wealth, geology, climate, population density), we find that the historical local dominance of large-scale coal-based industries predicts today's markers of psychological adversity (lower Conscientiousness [and order facet scores], higher Neuroticism [and anxiety and depression facet scores], lower activity [an Extraversion facet], and lower life satisfaction and life expectancy). An instrumental variable analysis, using the historical location of coalfields, supports the causal assumption behind these effects (with the exception of life satisfaction). Further analyses focusing on mechanisms hint at the roles of selective migration and persisting economic hardship. Finally, a robustness check in the U.S. replicates the effect of the historical concentration of large-scale industries on today's levels of psychological adversity. Taken together, the results show how today's regional patterns of personality and well-being (which shape the future trajectories of these regions) may have their roots in major societal changes underway decades or centuries earlier. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

Evaluation of semiarid grassland degradation in North China from multiple perspectives

NASA Astrophysics Data System (ADS)

Han, D.; Wang, G.; Xue, B. L.; Xu, X.

2017-12-01

There has been increasing interest in grassland ecosystem degradation resulting from intensive human activity and climate change, especially in arid and semiarid regions. Species composition, grassland desertification, and aboveground biomass (AGB) are used as indicators of grassland degradation in this study. We comprehensively analyzed variations in these three indicators in semiarid grassland in North China, on multiple time scales, based on MODIS products and field sampling datasets. Since 1984, species composition has become simpler and species indicative of grassland degradation, such as Potentilla acaulis and Artemisia frigida, have become dominant. These changes indicate that serious grassland degradation has occurred since 1984. Grassland degradation was also analyzed on shorter time scales. Analyses of interannual variations during 2005-2015 showed that desertification decreased and average AGB in the growth season increased over the study area, indicating that grassland was recovering. Analyses of spatial variations showed that the position of slightly desertified grassland shifted and formed a band in the west, where the lowest AGB in the growth season was recorded but tendency ratio of AGB increased from 2005 to 2015. Climatic factors had critical effects on grassland degradation, as identified by the three indicators on different time scales. The simpler species composition resulted from the increase in average temperature and decrease in average precipitation over the past 30 years. For nearly a decade, an increase in precipitation and decreases in temperature and potential evapotranspiration reduced desertification and increased AGB in the growth season overall. Consequently, there has distinct difference in grassland degradation between analysis results on above two time scales, indicating multiple perspectives should be considered to accurately assess the state and characteristics of grassland degradation.

Variation in the macrofaunal community over large temporal and spatial scales in the southern Yellow Sea

NASA Astrophysics Data System (ADS)

Xu, Yong; Sui, Jixing; Yang, Mei; Sun, Yue; Li, Xinzheng; Wang, Hongfa; Zhang, Baolin

2017-09-01

To detect large, temporal- and spatial-scale variations in the macrofaunal community in the southern Yellow Sea, data collected along the western, middle and eastern regions of the southern Yellow Sea from 1958 to 2014 were organized and analyzed. Statistical methods such as cluster analysis, non-metric multidimensional scaling ordination (nMDS), permutational multivariate analysis of variance (PERMANOVA), redundancy analysis (RDA) and canonical correspondence analysis (CCA) were applied. The abundance of polychaetes increased in the western region but decreased in the eastern region from 1958 to 2014, whereas the abundance of echinoderms showed an opposite trend. For the entire macrofaunal community, Margalef's richness (d), the Shannon-Wiener index (H‧) and Pielou's evenness (J‧) were significantly lower in the eastern region when compared with the other two regions. No significant temporal differences were found for d and H‧, but there were significantly lower values of J‧ in 2014. Considerable variation in the macrofaunal community structure over the past several decades and among the geographical regions at the species, genus and family levels were observed. The species, genera and families that contributed to the temporal variation in each region were also identified. The most conspicuous pattern was the increase in the species Ophiura sarsii vadicola in the eastern region. In the western region, five polychaetes (Ninoe palmata, Notomastus latericeus, Paralacydonia paradoxa, Paraprionospio pinnata and Sternaspis scutata) increased consistently from 1958 to 2014. The dominance curves showed that both the species diversity and the dominance patterns were relatively stable in the western and middle regions. Environmental parameters such as depth, temperature and salinity could only partially explain the observed biological variation in the southern Yellow Sea. Anthropogenic activities such as demersal fishing and other unmeasured environmental variables may be more responsible for the long-term changes in the macrofaunal community.

Estimating variations in global surface water storage

NASA Astrophysics Data System (ADS)

Lettenmaier, D. P.

2016-12-01

Arguably, the most dramatic advances attributable to remote sensing in the hydrologic sciences have involved the extension of knowledge about processes and state variables from the scale of field experiments to regions, continents, and the entire Earth. However, despite the availability of information about total terrestrial water storage over large areas provided by the Gravity Recovery and Climate Experiment (GRACE) mission, we still have remarkably little knowledge of the magnitude of freshwater stored at and near the land surface, and its temporal scales of variation. This is especially true with respect to freshwater storage in natural lakes and manmade reservoirs. Estimates of the amount of water that could be stored in artificial reservoirs are in the neighborhood of 15% of the mean annual runoff from the continents or around 7-8000 km3. However, while global reservoir storage was increasing through about 1980 due to filling of new reservoirs constructed in the second half of the 20th century, it is not even known whether aggregate usable reservoir storage is increasing or decreasing, due to sedimentation effects. With the advent of satellite altimeters (mostly intended to measure ocean surface topography and or the surface elevation of glaciers and ice sheets), along with improved methods for estimating space-time variations in the extent of surface waters, new opportunities have arisen to piece together estimates of storage variations of fractions approaching one-half of the global surface water storage, for periods approaching two decades in some cases. Although this ability is nascent, it offers encouragement that, with the launch of the planned Surface Water and Ocean Topography (SWOT) satellite mission in 2020, which has as a specific objective the measurement of surface water variations, climate-scale understanding of this source of variability in Earth's surface water balance may be at hand. I discuss specific examples of the technology and resulting data sets, including successes and failures.

Role of the North Atlantic Oscillation in decadal temperature trends

NASA Astrophysics Data System (ADS)

Iles, Carley; Hegerl, Gabriele

2017-11-01

Global temperatures have undergone periods of enhanced warming and pauses over the last century, with greater variations at local scales due to internal variability of the climate system. Here we investigate the role of the North Atlantic Oscillation (NAO) in decadal temperature trends in the Northern Hemisphere for periods with large decadal NAO trends. Using a regression based technique we find a best estimate that trends in the NAO more than halved (reduced by 57%, 5%-95%: 47%-63%) the winter warming over the Northern Hemisphere extratropics (NH; 30N-90N) from 1920-1971 and account for 45% (±14%) of the warming there from 1963-1995, with larger impacts on regional scales. Over the period leading into the so-called warming hiatus, 1989-2013, the NAO reduced NH winter warming to around one quarter (24%; 19%-31%) of what it would have been, and caused large negative regional trends, for example, in Northern Eurasia. Warming is more spatially uniform across the Northern Hemisphere after removing the NAO influence in winter, and agreement with multi-model mean simulated trends improves. The impact of the summer NAO is much weaker, but still discernible over Europe, North America and Greenland, with the downward trend in the summer NAO from 1988-2012 reducing warming by about a third in Northern Europe and a half in North America. A composite analysis using CMIP5 control runs suggests that the ocean response to prolonged NAO trends may increase the influence of decadal NAO trends compared to estimates based on interannual regressions, particularly in the Arctic. Results imply that the long-term NAO trends over the 20th century alternately masked or enhanced anthropogenic warming, and will continue to temporarily offset or enhance its effects in the future.

A century of Amazon burning driven by Atlantic climate

NASA Astrophysics Data System (ADS)

Makou, M.; Thompson, L. G.; Davis, M. E.; Eglinton, T. I.

2011-12-01

Very little is known about annual burning trends in the Amazon Basin prior to remote sensing of fires beginning in the late 1970's. Fires reduce Amazon forest biomass and species richness, release pollutant aerosols, and impact the carbon cycle, compelling further investigation of fire-climate dynamics. We measured organic compounds derived from vegetation burning in ice core samples from the Quelccaya Ice Cap in Peru at better than annual resolution to reconstruct wet and dry season burning throughout the Twentieth Century. Variations in the abundance of methyl hexadecanoate, which is produced by thermal alteration of vascular plant alkanoic acids, were used as a proxy for past fire activity. Concentrations of this compound in Quelccaya ice varied strongly on seasonal, interannual, and decadal time scales over the last 100 years, with high-amplitude dry season variability and muted, decadal-scale changes in wet season fire activity. Decade-long periods of repeatedly enhanced burning occurred during the 1930's and 1960's when dry season precipitation was perpetually reduced, as evidenced by low stages of the Rio Negro. These decadal trends suggest that changes in dry season precipitation drive fire activity in the western Amazon and highlight the potential of Amazon forests to undergo repeated strong burning. Fires occurred during years when sea surface temperatures (SSTs) in the north tropical Atlantic were elevated and the north-south tropical Atlantic SST gradient was enhanced; this SST pattern likely displaced the intertropical convergence zone northward, driving subsidence and drought in the western and southern Amazon basin. Thus, our novel ice core record suggests that Amazon forest fire activity during the Twentieth Century was driven primarily by Atlantic climate processes, and future forest health will depend heavily on the evolution of tropical climate.

Variability modes of precipitation along a Central Mediterranean area and their relations with ENSO, NAO, and other climatic patterns

NASA Astrophysics Data System (ADS)

Kalimeris, Anastasios; Ranieri, Ezio; Founda, Dimitra; Norrant, Caroline

2017-12-01

This study analyses a century-long set of precipitation time series in the Central Mediterranean (encompassing the Greek Ionian and the Italian Puglia regions) and investigates the statistically significant modes of the interannual precipitation variability using efficient methods of spectral decomposition. The statistical relations and the possible physical couplings between the detected modes and the global or hemispheric patterns of climatic variability (the El Niño Southern Oscillation or ENSO, the North Atlantic Oscillation or NAO, the East Atlantic or EA, the Scandinavian or SCAND, and others) were examined in the time-frequency domain and low-order synchronization events were sought. Significant modes of precipitation variability were detected in the Taranto Gulf and the southern part of the Greek Ionian region at the sub-decadal scales (mostly driven by the SCAND pattern) and particularly at the decadal and quasi-decadal scales, where strong relations found with the ENSO activity (under complex implications of EA and NAO) prior to the 1930s or after the early-1970s. The precipitation variations in the Adriatic stations of Puglia are dominated by significant bi-decadal modes which found to be coherent with the ENSO activity and also weakly related with the Atlantic Ocean sea surface temperature intrinsic variability. Additionally, important discontinuities characterize the evolution of precipitation in certain stations of the Taranto Gulf and the Greek Ionian region during the early-1960s and particularly during the early-1970s, followed by significant reductions in the mean annual precipitation. These discontinuities seem to be associated with regional effects of NAO and SCAND, probably combined with the impact of the 1970s climatic shift in the Pacific and the ENSO variability.

The autism sequencing consortium: large-scale, high-throughput sequencing in autism spectrum disorders.

PubMed

Buxbaum, Joseph D; Daly, Mark J; Devlin, Bernie; Lehner, Thomas; Roeder, Kathryn; State, Matthew W

2012-12-20

Research during the past decade has seen significant progress in the understanding of the genetic architecture of autism spectrum disorders (ASDs), with gene discovery accelerating as the characterization of genomic variation has become increasingly comprehensive. At the same time, this research has highlighted ongoing challenges. Here we address the enormous impact of high-throughput sequencing (HTS) on ASD gene discovery, outline a consensus view for leveraging this technology, and describe a large multisite collaboration developed to accomplish these goals. Similar approaches could prove effective for severe neurodevelopmental disorders more broadly. Copyright © 2012 Elsevier Inc. All rights reserved.

Why are earthquakes nudging the pole towards 140°E?

NASA Astrophysics Data System (ADS)

Spada, Giorgio

Earthquakes have collectively the tendency to displace the pole of rotation of the earth towards a preferred direction (∼140°E). This trend, which is still unexplained on quantitative grounds, has been revealed by computations of earthquake-induced inertia variations on both a secular and a decade time-scale. Purpose of this letter is to show that the above trend results from the combined effects of the geographical distribution of hypocenters and of the prevailing dip-slip nature of large earthquakes in this century. Our findings are based on the static dislocation theory and on simple geometrical arguments.

Role of climate anomalies on decadal variation in the occurrence of wintertime haze in the Yangtze River Delta, China.

PubMed

Xu, Jianming; Chang, Luyu; Yan, Fengxia; He, JinHai

2017-12-01

The wintertime haze day (HD) in the Yangtze River Delta (YRD) region of China shows a significant upward trend during the past decades due to the rapid industrialization and urbanization. Besides the enhanced anthropogenic emission, climate change also plays the important role in the long term HD variations. In this study, the significant decadal variation of wintertime HD during the period 1960-2012 in YRD is examined by the empirical orthogonal function (EOF) analysis, featured as less HD occurrence before 1980 and more occurrence after 2000. The numerical simulations by the global transport and chemical model (Model for Ozone and Related chemical Tracers, MOZART) with the same emission inventory suggest 8.4% enhancement of wintertime PM 2.5 (particulate matter with the equivalent diameter of air dynamics less than or equal to 2.5μm) mass concentration in YRD during 2001-2009 compared with that during 1971-1979 attributed to meteorological changes, indicating the significant effect of climate anomaly on the decadal variations of wintertime HD. Through the composite analysis on the atmospheric dynamical and thermal conditions based on the reanalysis data, the faster warming in the lower and middle troposphere over the continent in the recent decade is suggested to be important for the out-of-phase decadal HD variation in YRD. The thermal anomaly not only reverses the zonal thermal difference of land-sea to stimulate the anomalous southerlies over YRD leading to reduced prevailing north wind in winter, but also develops the deep inversion below the mid-troposphere to enhance the atmospheric stability. As a result, more frequent and persistent air stagnations in recent decade are expected for the reduction of atmospheric horizontal dispersion and vertical diffusion capacity leading to more occurrence of wintertime HD in YRD. Copyright © 2017 Elsevier B.V. All rights reserved.

Recent changes of sediment flux to the western Pacific Ocean from major rivers in East and Southeast Asia

NASA Astrophysics Data System (ADS)

Wang, Houjie; Saito, Yoshiki; Zhang, Yong; Bi, Naishuang; Sun, Xiaoxiao; Yang, Zuosheng

2011-09-01

The five largest rivers in East and Southeast Asia (Yellow, Yangtze, Pearl, Red and Mekong) are important contributors of terrigenous sediment to the western Pacific Ocean. Although they have annually delivered ~ 2000 × 10 9 kg of sediment to the ocean since 1000 yr BP, they presently contribute only ~ 600 × 10 9 kg/yr, which is reverting to a level typical of the relatively undisturbed watersheds before the rise in human activities in East and Southeast Asia at 2000 yr BP. During the most recent decades flow regulation by dams and sediment entrapment by reservoirs, as well as human-influenced soil erosion in the river basins, have sharply reduced the sediment delivered from the large river basins to the ocean. We constructed a time series of data on annual water discharges and sediment fluxes from these large rivers to the western Pacific Ocean covering the period 1950-2008. These data indicate that the short-term (interannual scale) variation of sediment flux is dominated by natural climatic oscillations such as the El Niño/La Niña cycle and that anthropogenic causes involving dams and land use control the long-term (decadal scale) decrease in sediment flux to the ocean. In contrast to the relatively slow historical increase in sediment flux during the period 2000-1000 yr BP, the recent sediment flux has been decreased at an accelerating rate over centennial scales. The alterations of these large river systems by both natural and anthropogenic forcing present severe environmental challenges in the coastal ocean, including the sinking of deltas and declines in coastal wetland areas due to the decreasing sediment supply. Our work thus provides a regional perspective on the large river-derived sediment flux to the ocean over millennial and decadal scales, which will be important for understanding and managing the present and future trends of delivery of terrigenous sediment to the ocean in the context of global change.

Beach-ridge sedimentology as an archive of terrestrial climate change: Insights from a geochemical and stratigraphic study of the Tijucas Strandplain, southern Brazil

NASA Astrophysics Data System (ADS)

Krask, J. L.; Hein, C. J.; Galy, V.; FitzGerald, D.; Henrique de Fontoura Klein, A.

2017-12-01

Whereas millennial-scale variations in climate forcing drives changes in terrestrial processes, which are in turn directly linked to fluvial sediment loads (e.g., weathering and erosion), the impact of decadal- to centennial- scale climate fluctuations on downstream coastal sedimentation patterns and landscape evolution remains unclear. Specifically, the connection between long-term (decades or more) precipitation seasonality and sediment export from river systems has not been established. This study examines the manner in which sub-millennial-scale fluctuations in precipitation over river catchments may be recorded in coastal progradational sedimentary archives. The 5-km wide Tijucas Strandplain (southern Brazil) formed over the last 5800 years through the rapid reworking of sediment discharged from the Tijucas River in a regime of falling sea level. In an overall regime shift from sand- to mud- dominance (linked to a long-term reduction in wave energy caused by bay shoaling) are nearly 70 distinct transitions between shore-parallel sand- and mud- dominated facies. Bulk organic carbon and terrestrial plant-wax fatty acid stable hydrogen (δD) and carbon (δ13C) isotopic measurements from sediments from select sandy and muddy ridges across the plain reveal that these two sedimentological regimes are geochemically distinct. Specifically, waxes from sediments deposited during periods of sandy progradation had δD values, on average, >10 ‰ higher than those from mud-dominated periods, indicating that these sedimentary units reflect different hydroclimatic conditions within the river drainage basin at the time of deposition. Comparison of plant wax isotopic signatures of river, bay, and beach sediments during the current period of mud-dominated progradation reveals a close correlation with earlier periods of mud deposition within the Tijucas Strandplain. Thus, decadal- to centennial- scale sedimentologic transitions within the plain are interpreted to reflect climate-driven changes in mud export rates, as product of modifications in river basin vegetation and soil formation and erosional processes.

The Spatiotemporal Structure of 20th Century Climate Variations in Observations and Reanalyses. Part 1; Long-term Trend

NASA Technical Reports Server (NTRS)

Chen, Junye; DelGenio, Anthony D.; Carlson, Barbara e.; Bosilovich, Michael G.

2007-01-01

The dominant interannual El Nino-Southern Oscillation phenomenon (ENSO) and the short length of climate observation records make it difficult to study long-term climate variations in the spatiotemporal domain. Based on the fact that the ENS0 signal spreads to remote regions and induces delayed climate variation through atmospheric teleconnections, we develop an ENSO-removal method through which the ENS0 signal can be approximately removed at the grid box level from the spatiotemporal field of a climate parameter. After this signal is removed, long-term climate variations, namely, the global warming trend (GW) and the Pacific pan-decadal variability (PDV), are isolated at middle and low latitudes in the climate parameter fields from observed and reanalyses datasets. Except for known GW characteristics, the warming that occurs in the Pacific basin (approximately 0.4K in the 2oth century) is much weaker than in surrounding regions and the other two ocean basins (approximately 0.8K). The modest warming in the Pacific basin is likely due to its dynamic nature on the interannual and decadal time scales and/or the leakage of upper ocean water through the Indonesian Throughflow. Based on NCEP/NCAR and ERA-40 reanalyses, a comprehensive atmospheric structure associated with GW is given. Significant discrepancies exist between the two datasets, especially in the tightly coupled dynamic and water vapor fields. The dynamic field based on NCEP/NCAR reanalysis, which shows a change in the Walker Circulation, is consistent with the GW change in the surface temperature field. However, intensification in the Hadley Circulation is associated with GW trend in the ERA-40 reanalysis.

A decadal observation of vegetation dynamics using multi-resolution satellite images

NASA Astrophysics Data System (ADS)

Chiang, Yang-Sheng; Chen, Kun-Shan; Chu, Chang-Jen

2012-10-01

Vegetation cover not just affects the habitability of the earth, but also provides potential terrestrial mechanism for mitigation of greenhouse gases. This study aims at quantifying such green resources by incorporating multi-resolution satellite images from different platforms, including Formosat-2(RSI), SPOT(HRV/HRG), and Terra(MODIS), to investigate vegetation fractional cover (VFC) and its inter-/intra-annual variation in Taiwan. Given different sensor capabilities in terms of their spatial coverage and resolution, infusion of NDVIs at different scales was used to determine fraction of vegetation cover based on NDVI. Field campaign has been constantly conducted on a monthly basis for 6 years to calibrate the critical NDVI threshold for the presence of vegetation cover, with test sites covering IPCC-defined land cover types of Taiwan. Based on the proposed method, we analyzed spatio- temporal changes of VFC for the entire Taiwan Island. A bimodal sequence of VFC was observed for intra-annual variation based on MODIS data, with level around 5% and two peaks in spring and autumn marking the principal dual-cropping agriculture pattern in southwestern Taiwan. Compared to anthropogenic-prone variation, the inter-annual VFC (Aug.-Oct.) derived from HRV/HRG/RSI reveals that the moderate variations (3%) and the oscillations were strongly linked with regional climate pattern and major disturbances resulting from extreme weather events. Two distinct cycles (2002-2005 and 2005-2009) were identified in the decadal observations, with VFC peaks at 87.60% and 88.12% in 2003 and 2006, respectively. This time-series mapping of VFC can be used to examine vegetation dynamics and its response associated with short-term and long-term anthropogenic/natural events.

Decadal variability of extreme wave height representing storm severity in the northeast Atlantic and North Sea since the foundation of the Royal Society.

PubMed

Santo, H; Taylor, P H; Gibson, R

2016-09-01

Long-term estimation of extreme wave height remains a key challenge because of the short duration of available wave data, and also because of the possible impact of climate variability on ocean waves. Here, we analyse storm-based statistics to obtain estimates of extreme wave height at locations in the northeast Atlantic and North Sea using the NORA10 wave hindcast (1958-2011), and use a 5 year sliding window to examine temporal variability. The decadal variability is correlated to the North Atlantic oscillation and other atmospheric modes, using a six-term predictor model incorporating the climate indices and their Hilbert transforms. This allows reconstruction of the historic extreme climate back to 1661, using a combination of known and proxy climate indices. Significant decadal variability primarily driven by the North Atlantic oscillation is observed, and this should be considered for the long-term survivability of offshore structures and marine renewable energy devices. The analysis on wave climate reconstruction reveals that the variation of the mean, 99th percentile and extreme wave climates over decadal time scales for locations close to the dominant storm tracks in the open North Atlantic are comparable, whereas the wave climates for the rest of the locations including the North Sea are rather different.

Decadal variability of extreme wave height representing storm severity in the northeast Atlantic and North Sea since the foundation of the Royal Society

NASA Astrophysics Data System (ADS)

Santo, H.; Taylor, P. H.; Gibson, R.

2016-09-01

Long-term estimation of extreme wave height remains a key challenge because of the short duration of available wave data, and also because of the possible impact of climate variability on ocean waves. Here, we analyse storm-based statistics to obtain estimates of extreme wave height at locations in the northeast Atlantic and North Sea using the NORA10 wave hindcast (1958-2011), and use a 5 year sliding window to examine temporal variability. The decadal variability is correlated to the North Atlantic oscillation and other atmospheric modes, using a six-term predictor model incorporating the climate indices and their Hilbert transforms. This allows reconstruction of the historic extreme climate back to 1661, using a combination of known and proxy climate indices. Significant decadal variability primarily driven by the North Atlantic oscillation is observed, and this should be considered for the long-term survivability of offshore structures and marine renewable energy devices. The analysis on wave climate reconstruction reveals that the variation of the mean, 99th percentile and extreme wave climates over decadal time scales for locations close to the dominant storm tracks in the open North Atlantic are comparable, whereas the wave climates for the rest of the locations including the North Sea are rather different.

Inner core rotation from event-pair analysis

NASA Astrophysics Data System (ADS)

Song, Xiaodong; Poupinet, Georges

2007-09-01

The last decade has witnessed an animated debate on whether the inner core rotation is a fact or an artifact. Here we examine the temporal change of inner core waves using a technique that compares differential travel times at the same station but between two events. The method does not require precise knowledge of earthquake locations and earth models. The pairing of the events creates a large data set for the application of statistical tools. Using measurements from 87 events in the South Sandwich Islands recorded at College, Alaska station, we conclude the temporal change is robust. The estimates of the temporal change range from about 0.07 to 0.10 s/decade over the past 50 yr. If we used only pairs with small inter-event distances, which reduce the influence of mantle heterogeneity, the rates range from 0.084 to 0.098 s/decade, nearly identical to the rate inferred by Zhang et al. [Zhang, J., Song, X.D., Li, Y.C., Richards, P.G., Sun, X.L., Waldhauser, F., Inner core differential motion confirmed by earthquake waveform doublets, Science 309 (5739) (2005) 1357-1360.] from waveform doublets. The rate of the DF change seems to change with time, which may be explained by lateral variation of the inner core structure or the change in rotation rate on decadal time scale.

Snowpack Variation and Hydrologic Impacts across the Middle East and North Africa

NASA Astrophysics Data System (ADS)

Robinson, D. A.; Ward, M. N.

2017-12-01

The Middle East is a region historically sensitive to climate variability and change, and contains snowpacks that have been shown to be important inputs to key regional water resources, including the Tigris-Euphrates river system. Focusing on the Middle East (and the smaller snowpacks of northwestern Africa), this presentation aims to (i) quantify each year's snowpack development and recession over recent decades, highlighting interannual to decadal variability, and (ii) advance understanding on the connection between the snowpack variations and aspects of regional hydrology. The presentation draws on satellite-based products, station data, and model reanalyses. Variation is summarized using space-time statistical techniques, as well as simpler regional indices: Northwestern Iran / Southern Caucasus (NWIC, includes Zagros Mountains); Eastern Turkey (ETKY, includes Taurus Mountains); and smaller scale indices for Lebanon and the Atlas Mountains. The Interactive Multisensor Snow and Ice Mapping System archives daily snow cover extent at 24 km resolution for 1999-present (primarily from visible satellite imagery). These data show that for both NWIC and ETKY, the mean snow extent peaks in late January with substantial coverage ( 300,000 km2 in each region), contracting to near zero by late June. A very large mid-winter interannual variance is also shown, implying substantial variation in hydrologic impacts during spring melt. Variability and decadal trends are compared with station snow depth reports (Global Historical Climatology Network - Daily). Strong agreement gives confidence in data quality, as well as, indicating high covariation of depth and extent. The connection with hydrologic impacts is investigated using reanalysis products, including the Global Land Data Assimilation System V2, which for the Middle East, shows broad agreement with observed maximum snow extent and spring retreat. The connections internal to the reanalysis between snow cover, melt and runoff are quantified, delivering insights into the mechanisms of variability and change in the regional water resources and their dependence on snowpack. Specific case study melt seasons highlight the ways in which snowpack and seasonal climate combine to produce changes in magnitude and timing of runoff during late winter and spring.

Rising Water Storage in the Niger River basin: Clues and Cause

NASA Astrophysics Data System (ADS)

Werth, S.

2016-12-01

Heavily populated west African regions along the Niger River are affected by climate and land cover changes, altering the distribution of water resources. To maintain a reliable water supply in the region, water management authorities require knowledge of hydrological changes at various spatial and temporal scales. Local and regional studies reported rising water tables over the last decades as a consequence of complex responses on land use change in the Sahel zone. The spatial extend of this responses is not well understood, as of yet. Thus, this study provides an in-depth investigation of long-term changes in the water storages of Niger River basin and its sub-regions by analyzing more than a decade of satellite based gravity data from the Gravity Recovery And Climate Change (GRACE) satellites. Soil moisture data from four global hydrological models serve to separate freshwater resources (WR) from GRACE-based terrestrial water storage variations. Surface water variations from a global water storage model and trends from altimetry data were applied to separate the groundwater component from WR trends. Errors of all datasets are taken into account. Trends in WR are positive, except for the tropical Upper Niger with negative trends. For the Niger basin, a rise in GW stocks was detected. On the subbasin scale, GW changes are positive for the Sahelian Middle Niger and the Benue. The findings confirm previous observations of water tables in the Sahel and tropical zones, indicating that reported effects of land use change are relevant on large, i.e. basin and subbasin, scales. Our results have implications for Niger water management strategies. While areas with rising water storage are stocking a comfortable backup to mitigate possible future droughts and to deliver water to remote areas with no access to rivers or reservoirs. Increasing groundwater recharges may be accompanied by a reduction in water quality. This study helps to inform authority's decision to address risks for affected communities.

Sunshine duration reconstruction in the southeastern Tibetan Plateau based on tree-ring width and its relationship to volcanic eruptions.

PubMed

Sun, Changfeng; Liu, Yu; Song, Huiming; Cai, Qiufang; Li, Qiang; Wang, Lu; Mei, Ruochen; Fang, Congxi

2018-07-01

Sunshine is as essential as temperature and precipitation for tree growth, but sunshine duration reconstructions based on tree rings have not yet been conducted in China. In this study, we presented a 497-year sunshine duration reconstruction for the southeastern Tibetan Plateau using a width chronology of Abies forrestii from the central Hengduan Mountains. The reconstruction accounted for 53.5% of the variance in the observed sunshine during the period of 1961-2013 based on a stable and reliable linear regression. This reconstructed sunshine duration contained six sunny periods (1630-1656, 1665-1697, 1731-1781, 1793-1836, 1862-1895 and 1910-1992) and seven cloudy periods (1522-1629, 1657-1664, 1698-1730, 1782-1792, 1837-1861, 1896-1909 and 1993-2008) at a low-frequency scale. There was an increasing trend from the 16th century to the late 18th and early 19th centuries and a decreasing trend from the mid-19th to the early 21st centuries. Sunshine displayed inverse patterns to the local Palmer drought severity index on a multidecadal scale, indicating that this region likely experienced droughts under more sunshine conditions. The decrease in sunshine particularly in recent decades was mainly due to increasing atmospheric anthropogenic aerosols. In terms of the interannual variations in sunshine, weak sunshine years matched well with years of major volcanic eruptions. The significant cycles of the 2- to 7-year, 20.0-year and 35.2-year durations as well as the 60.2-year and 78.7-year durations related to the El-Niño Southern Oscillation, the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation suggested that the variation in sunshine duration in the southeastern Tibetan Plateau was possibly affected by large-scale ocean-atmosphere circulations. Copyright © 2018 Elsevier B.V. All rights reserved.

Turbulence scaling study in an MHD wind tunnel on the Swarthmore Spheromak Experiment

NASA Astrophysics Data System (ADS)

Schaffner, D. A.; Brown, M. R.; Wan, A.

2013-12-01

The turbulence of colliding plasmas is explored in an MHD wind tunnel on the SSX in an effort to understand solar wind physics in a laboratory setting. Fully ionized hydrogen plasma is produced by two plasma guns on opposite sides of a 1m by 15cm copper cylinder creating plasma with L/ρi ~ 75-150, β ~ 0.1-0.2 and Lundquist number ~ 1000. Modification of B-field, Ti and β are made through stuffing flux variation of the plasma guns. Presented here are turbulent f-/k-spectra and correlation times and lengths of B-field fluctuations as measured by a 16 channel B-dot radial probe array at the chamber midplane using both FFT and wavelet analysis techniques. Power-law behavior is observed spanning about two decades of frequencies [100kHz-10MHz] and about one decade of wavelength [10cm-1cm]. Power-law fits to spectra show scaling in these regions to be robust to changes in stuffing flux; fits are on the order of f-4 and k-2 for all flux variations. Low frequency fluctuations [<100kHz] can vary significantly suggesting a range of energy injection at large scales. Evidence for dissipation range modification of the spectra is also observed; divergence from power-law behavior is seen in f-spectra for frequencies around f=fci while changes in k-spectra slopes appear around 1/k ~ 5ρi. Dissipation range fits are made with an exponentially modified power-law model [Terry et al, PoP 2012]. Fluctuation measurements in axial velocity are made using a Mach probe with edge flows reaching M ~ 0.4. Both B-field and velocity fluctuations persist on the same timescale in these experiments, though Mach velocity f-spectra show power-laws slightly shallower than those for B-field. Comparison of spectra from MHD and Hall MHD simulations of SSX performed within the HiFi modeling framework are made to the experimental results.

Multidecadal variations in the early Holocene outflow of Red Sea Water into the Arabian Sea

NASA Astrophysics Data System (ADS)

Jung, S. J. A.; Ganssen, G. M.; Davies, G. R.

2001-12-01

We present Holocene stable oxygen isotope data from the deep Arabian Sea off Somalia at a decadal time resolution as a proxy for the history of intermediate/upper deep water. These data show an overall δ18O reduction by 0.5‰ between 10 and ˜6.5 kyr B.P. superimposed upon short-term δ18O variations at a decadal-centennial timescale. The amplitude of the decadal variations is 0.3‰ prior, and up to 0.6‰ subsequent, to ˜8.1 kyr B.P. We conclude from modeling experiments that the short-term δ18O variations between 10 and ˜6.5 kyr B.P. most likely document changes in the evaporation-precipitation balance in the central Red Sea. Changes in water temperature and salinity cause the outflowing Red Sea Water to settle roughly 800 m deeper than today.

Influence of prolonged Anomalies in North Atlantic Sea Surface Temperature on Winter Windstorms

NASA Astrophysics Data System (ADS)

Höschel, Ines; Schuster, Mareike; Grieger, Jens; Ulbrich, Uwe

2016-04-01

The focus of this presentation is on decadal scale variations in the frequency and in the intensity of mid-latitude winter windstorms. Projections for the end of the next century are often beyond the time horizon of business, thus there is an increasing interest on decadal prediction, especially for infrastructural planning and in the insurance industry. One source of decadal predictability is the Atlantic multidecadal variability (AMV), a change in the sea surface temperature of the North Atlantic, strongly linked to the meridional overturning circulation. Correlation patterns between annual AMV-indices and annual mean of geopotential height at 500 hPa in reanalysis data show an anti-correlation in the North Atlantic. That is, during AMV warm phases the North Atlantic Oscillation (NAO) is more negative. Consequently, AMV should influence the characteristics of winter windstorms at multi-year scales. For the presented investigations a 10-member ensemble of 38-year-long idealized simulations with the atmosphere model ECHAM6 with lower boundary conditions, representing warm and cool phases of the AMV, is used. In the idealized simulations, the anti-correlation between AMV and NAO is well represented. For the identification of winter windstorms an objective wind tracking algorithm based on the exceedance of the local 98th percentile of 10m wind speed is applied. Storms under AMV-warm and AMV-cool conditions will be compared in terms of storm track density and probability distribution of storm characteristics.

The many faces of fear: a synthesis of the methodological variation in characterizing predation risk.

PubMed

Moll, Remington J; Redilla, Kyle M; Mudumba, Tutilo; Muneza, Arthur B; Gray, Steven M; Abade, Leandro; Hayward, Matt W; Millspaugh, Joshua J; Montgomery, Robert A

2017-07-01

Predators affect prey by killing them directly (lethal effects) and by inducing costly antipredator behaviours in living prey (risk effects). Risk effects can strongly influence prey populations and cascade through trophic systems. A prerequisite for assessing risk effects is characterizing the spatiotemporal variation in predation risk. Risk effects research has experienced rapid growth in the last several decades. However, preliminary assessments of the resultant literature suggest that researchers characterize predation risk using a variety of techniques. The implications of this methodological variation for inference and comparability among studies have not been well recognized or formally synthesized. We couple a literature survey with a hierarchical framework, developed from established theory, to quantify the methodological variation in characterizing risk using carnivore-ungulate systems as a case study. Via this process, we documented 244 metrics of risk from 141 studies falling into at least 13 distinct subcategories within three broader categories. Both empirical and theoretical work suggest risk and its effects on prey constitute a complex, multi-dimensional process with expressions varying by spatiotemporal scale. Our survey suggests this multi-scale complexity is reflected in the literature as a whole but often underappreciated in any given study, which complicates comparability among studies and leads to an overemphasis on documenting the presence of risk effects rather than their mechanisms or scale of influence. We suggest risk metrics be placed in a more concrete conceptual framework to clarify inference surrounding risk effects and their cascading effects throughout ecosystems. We recommend studies (i) take a multi-scale approach to characterizing risk; (ii) explicitly consider 'true' predation risk (probability of predation per unit time); and (iii) use risk metrics that facilitate comparison among studies and the evaluation of multiple competing hypotheses. Addressing the pressing questions in risk effects research, including how, to what extent and on what scale they occur, requires leveraging the advantages of the many methods available to characterize risk while minimizing the confusion caused by variability in their application. © 2017 The Authors. Journal of Animal Ecology © 2017 British Ecological Society.

Drought and Heat Waves: The Role of SST and Land Surface Feedbacks

NASA Technical Reports Server (NTRS)

Schubert, Siegfried

2011-01-01

Drought occurs on a wide range of time scales, and within a variety of different types of regional climates. At the shortest time scales it is often associated with heat waves that last only several weeks to a few months but nevertheless can have profound detrimental impacts on society (e.g., heat-related impacts on human health, desiccation of croplands, increased fire hazard), while at the longest time scales it can extend over decades and can lead to long term structural changes in many aspects of society (e.g., agriculture, water resources, wetlands, tourism, population shifts). There is now considerable evidence that sea surface temperatures (SSTs) play a leading role in the development of drought world-wide, especially at seasonal and longer time scales, though land-atmosphere feedbacks can also play an important role. At shorter (subseasonal) time scales, SSTs are less important, but land feedbacks can play a critical role in maintaining and amplifying the atmospheric conditions associated with heat waves and short-term droughts. This talk reviews our current understanding of the physical mechanisms that drive precipitation and temperature variations on subseasonal to centennial time scales. This includes an assessment of predictability, prediction skill, and user needs at all time scales.

Long-term Variation of Ventilation System in the East Sea (Japan Sea) Revealed by Heat Content Change and Water Mass Analysis

NASA Astrophysics Data System (ADS)

Yoon, S.; Chang, K. I.; Kim, K. R.; Lobanov, V. B.

2016-02-01

The semi-enclosed East Sea (ES) is called a miniature ocean with its own thermohaline circulation characterized by the formation of deep and intermediate water masses in the Japan Basin, southward discharge of those subsurface water masses towards the Ulleung and Yamato basins, and northward heat transport by the Tsushima Warm Current in the upper layer. Reports have been given of rapid changes of physical and biogeochemical properties associated with its ventilation system. We present results on upper ocean heat content variations and changes in water mass structure and properties from the analysis of historical and most recent hydrographic data. The analysis of non-seasonal heat content (HCA) variations in the upper 500 m from 1976 to 2007 highlights the 2-year lagged in-phase decadal-scale HCA variations in the eastern and western ES until 1995 followed by uncorrelated variations between two regions thereafter with pronounced interannual variations. Long-term trend of HCA in the entire ES shows an increasing trend, but with a large increase in the eastern part and relatively weaker but statistically significant decrease in the western part. The thickness variation of water warmer than 10°C mainly contributes to the HCA variation. Analyses of upper circulation in conjunction with climate indices suggest the importance of the wind-stress curl pattern represented by the Western Pacific index in the western ES and the influence of the Siberian High in the eastern ES. The thickness and temperature variation of 1-5°C representing the East Sea Intermediate Water (ESIW) is relatively minor contributor to the HCA variation in the upper 500 m. However, the thickness (temperature) of the ESIW has been increased (decreased) in the entire ES since 1992, which implies that the formation of the ESIW has been activated in recent decades. To investigate water mass changes in deeper than 500 m, we use full-depth CTD data obtained from CREAMS expeditions from 1993 to 2015. Temperature deeper than 1000 m has been increased about 0.03°C during 20 years and the depth of deep salinity minimum depth which is the lower (upper) limit of the East Sea Central Water (Deep Water) has been deepened. Other characteristics of water mass structure and property changes will be presented.

Inter-annual and Long-term Temperature Variations in the Mesopause Region at High Latitudes Generated by the Stratospheric QBO

NASA Technical Reports Server (NTRS)

Mayr, Hans G.; Mengel, John G.; Huang, Frank T.

2007-01-01

The Numerical Spectral Model (NSM) simulates the Quasi-biennial Oscillation (QBO) that dominates the zonal circulation of the lower stratosphere at low latitudes. In the model, the QBO is generated with parameterized small-scale gravity waves (GW), which are partially augmented in 3D with planetary waves owing to baroclinic instability. Due to GW filtering, the QBO extends into the upper mesosphere, evident in UARS zonal wind and TIMED temperature measurements. While the QBO zonal winds are confined to equatorial latitudes, even in simulations with latitude-independent wave source, the associated temperature variations extend to high latitudes. The meridional circulation redistributes some of the QBO energy to focus it partially onto the Polar Regions. The resulting QBO temperature variations away from the equator tend to increase at higher altitudes to produce inter-annual variations that can exceed 5 K in the polar mesopause region -- and our 3D model simulations show that the effect is variable from year to year and can produce large differences between the two hemispheres, presumably due to interactions involving the seasonal variations. Modeling studies with the NSM have shown that long-term variations can also be generated by the QBO interacting with the seasonal cycles through OW node-filtering. A 30-month QBO, optimally synchronized by the 6-month Semi-Annual Oscillation (SAO), thus produces a 5-year or semi-decadal (SD) oscillation -- and observational evidence for that has been provided by a recent analysis of stratospheric NCEP data. In a simulation with the 2D version of the NSM, this SD oscillation extends into the upper mesosphere, and we present results to show that the related temperature variations could contribute significantly to the long-term variations of the polar mesopause region. Quasi-decadal variations could furthermore arise from the modeled solar cycle modulations of the QBO and 12-month annual oscillation. Our numerical results are discussed in the context of the observed low summer temperatures reproduced by the model, to demonstrate that the above interannual and long-term variations could contribute significantly to the climatology of Polar Mesospheric Clouds (PMC) investigated by the Aeronomy of Ice in the Mesosphere (AIM) mission.

Long-term variabilities of meridional geostrophic volumn transport in North Pacific Ocean

NASA Astrophysics Data System (ADS)

Zhou, H.; Yuan, D.; Dewar, W. K.

2016-02-01

The meridional geostrophic volumn transport (MGVT) by the ocean plays a very important role in the climatic water mass and heat balance because of its large heat capacity which enables the oceans to store the large amount of radiation received in the summer and to release it in winter. Better understanding of the role of the oceans in climate variability is essential to assess the likely range of future climate fluctuations. In the last century the North Pacific Ocean experienced considerable climate variability, especially on decadal time scale. Some studies have shown that the North Pacific Ocean is the origin of North Pacific multidecadal variability (Latif and Barnett, 1994; Barnett et al., 1999). These fluctuations were associated with large anomalies in sea level, temperature, storminess and rainfall, the heat transport and other extremes are changing as well. If the MGVT of the ocean is well-determined, it can be used as a test of the validity of numerical, global climate models. In this paper, we investigate the long-term variability of the MGVT in North Pacific ocean based on 55 years long global ocean heat and salt content data (Levitus et al., 2012). Very clear inter-decadal variations can be seen in tropical , subtropical and subpolar regions of North Pacific Ocean. There are very consistent variations between the MGVT anomalies and the inter-decadal pacific oscillation (IPO) index in the tropical gyre with cold phase of IPO corresponding to negative MGVT anomalies and warm phase corresponding to positive MGVT anomalies. The subtropical gyre shows more complex variations, and the subpolar gyre shows a negative MGVT anomaly before late 1970's and a positive anomaly after that time. The geostrophic velocities of North Pacific Ocean show significantly different anomalies during the two IPO cold phases of 1955-1976 and 1999 to present, which suggests a different mechanism of the two cold phases. The long term variations of Sverdrup transport compares well with that of the MGVT in the basin of 8-10N and north of 35N, but the two compares poorly or even reversed in the middle part of the basin. A reduced gravity model is used to investigate the mechanisms of the above variations.

Increase in winter haze over eastern China in recent decades: Roles of variations in meteorological parameters and anthropogenic emissions: INCREASE IN WINTER HAZE IN EASTERN CHINA

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

Yang, Yang; Liao, Hong; Lou, Sijia

The increase in winter haze over eastern China in recent decades due to variations in meteorological parameters and anthropogenic emissions was quantified using observed atmospheric visibility from the National Climatic Data Center Global Summary of Day database for 1980–2014 and simulated PM2.5 concentrations for 1985–2005 from the Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem). Observed winter haze days averaged over eastern China (105–122.5°E, 20–45°N) increased from 21 d in 1980 to 42 d in 2014, and from 22 to 30 d between 1985 and 2005. The GEOS-Chem model captured the increasing trend of winter PM2.5 concentrations for 1985–2005,more » with concentrations averaged over eastern China increasing from 16.1 μg m -3 in 1985 to 38.4 μg m -3 in 2005. Considering variations in both anthropogenic emissions and meteorological parameters, the model simulated an increase in winter surface-layer PM2.5 concentrations of 10.5 (±6.2) μg m -3 decade -1 over eastern China. The increasing trend was only 1.8 (±1.5) μg m -3 decade -1 when variations in meteorological parameters alone were considered. Among the meteorological parameters, the weakening of winds by -0.09 m s -1 decade -1 over 1985–2005 was found to be the dominant factor leading to the decadal increase in winter aerosol concentrations and haze days over eastern China during recent decades.« less

Recent advances in radar remote sensing of forest

NASA Technical Reports Server (NTRS)

Letoan, Thuy

1993-01-01

On a global scale, forests represent most of the terrestrial standing biomass (80 to 90 percent). Thus, natural and anthropogenic change in forest covers can have major impacts not only on local ecosystems but also on global hydrologic, climatic, and biogeochemical cycles that involve exchange of energy, water, carbon, and other elements between the earth and atmosphere. Quantitative information on the state and dynamics of forest ecosystems and their interactions with the global cycles appear necessary to understand how the earth works as a natural system. The information required includes the lateral and vertical distribution of forest cover, the estimates of standing biomass (woody and foliar volume), the phenological and environmental variations and disturbances (clearcutting, fires, flood), and the longer term variations following deforestation (regeneration, successional stages). To this end, seasonal, annual, and decadal information is necessary in order to separate the long term effects in the global ecosystem from short term seasonal and interannual variations. Optical remote sensing has been used until now to study the forest cover at local, regional, and global scales. Radar remote sensing, which provides recent SAR data from space on a regular basis, represents an unique means of consistently monitoring different time scales, at all latitudes and in any atmospheric conditions. Also, SAR data have shown the potential to detect several forest parameters that cannot be inferred from optical data. The differences--and complementarity--lie in the penetration capabilities of SAR data and their sensitivity to dielectric and geometric properties of the canopy volume, whereas optical data are sensitive to the chemical composition of the external foliar layer of the vegetation canopy.

Variability and predictability of decadal mean temperature and precipitation over China in the CCSM4 last millennium simulation

NASA Astrophysics Data System (ADS)

Ying, Kairan; Frederiksen, Carsten S.; Zheng, Xiaogu; Lou, Jiale; Zhao, Tianbao

2018-02-01

The modes of variability that arise from the slow-decadal (potentially predictable) and intra-decadal (unpredictable) components of decadal mean temperature and precipitation over China are examined, in a 1000 year (850-1850 AD) experiment using the CCSM4 model. Solar variations, volcanic aerosols, orbital forcing, land use, and greenhouse gas concentrations provide the main forcing and boundary conditions. The analysis is done using a decadal variance decomposition method that identifies sources of potential decadal predictability and uncertainty. The average potential decadal predictabilities (ratio of slow-to-total decadal variance) are 0.62 and 0.37 for the temperature and rainfall over China, respectively, indicating that the (multi-)decadal variations of temperature are dominated by slow-decadal variability, while precipitation is dominated by unpredictable decadal noise. Possible sources of decadal predictability for the two leading predictable modes of temperature are the external radiative forcing, and the combined effects of slow-decadal variability of the Arctic oscillation (AO) and the Pacific decadal oscillation (PDO), respectively. Combined AO and PDO slow-decadal variability is associated also with the leading predictable mode of precipitation. External radiative forcing as well as the slow-decadal variability of PDO are associated with the second predictable rainfall mode; the slow-decadal variability of Atlantic multi-decadal oscillation (AMO) is associated with the third predictable precipitation mode. The dominant unpredictable decadal modes are associated with intra-decadal/inter-annual phenomena. In particular, the El Niño-Southern Oscillation and the intra-decadal variability of the AMO, PDO and AO are the most important sources of prediction uncertainty.

Decadal Transition of Moisture Sources and Transport in Northwestern China During Summer From 1982 to 2010

NASA Astrophysics Data System (ADS)

Hua, Lijuan; Zhong, Linhao; Ma, Zhuguo

2017-12-01

The northwestern corner of China (NWCC) experienced a decadal transition in summer precipitation during 1982-2010, with a significant upward trend in 1982-2000 (P1) but a downward one in 2001-2010 (P2). A spatially unbounded dynamic recycling model is developed to estimate the moisture sources and moisture transport variations based on ERA-Interim data. The results suggest that more than 88% of NWCC precipitation has external moisture origins in the southwest and northwest terrestrial areas. The increasing precipitation trend during P1 can be explained by the increasing moisture contribution from the southwest and decreasing contribution from the northwest. However, the opposite trends cause the decreasing precipitation trend during P2. In general, the decadal precipitation transition is mainly determined by the variation of short-distance moisture transport from central Asia, although opposite moisture transport variations exist in the Ural Mountains and Northeast Europe. The variation of the precipitation trend is closely associated with a well-organized wave train propagation from the North Atlantic to central Asia. During P1, the wave train structure consists of a titled positive phase North Atlantic Oscillation (NAO), an anticyclonic circulation over Europe, and a cyclonic anomaly over central Asia, which promotes the southwest moisture flux to NWCC. But the opposite circulation pattern dominates P2. The energy dispersion due to the breakdown of the NAO determines the phase and strength of the downstream wave anomalies over Eurasia. This suggests that the summer NAO might influence the decadal variation of NWCC precipitation through the decadal modulation of the Eurasia wave train.

Characterization of the time-dependent strain field at seismogenic depths using first-motion focal mechanisms: Observations of large-scale decadal variations in stress along the San Andrea fault system

USGS Publications Warehouse

Sipkin, S.A.; Silver, P.G.

2003-01-01

We present a method for summing moment tensors derived from first-motion focal mechanisms to study temporal dependence in features of the subsurface regional strain field. Time-dependent processes are inferred by comparing mechanisms summed over differing time periods. We apply this methodology to seismogenic zones in central and southern California using focal mechanisms produced by the Northern and Southern California Seismograph Networks for events during 1980-1999. We find a consistent pattern in both the style of deformation (strike-slip versus compressional) and seismicity rate across the entire region. If these temporal variations are causally related, it suggests a temporal change in the regional-scale stress field. One change consistent with the observations is a rotation in the regional maximum horizontal compressive stress direction, followed by a reversal to the original direction. Depending upon the dominant style of deformation locally, this change in orientation of the regional stress will tend to either enhance or hinder deformation. The mode of enhanced deformation can range from increased microseismicity and creep to major earthquakes. We hypothesize that these temporal changes in the regional stress field are the result of subtle changes in apparent relative plate motion between the Pacific and North American plates, perhaps due to long-range postseismic stress diffusion. Others have hypothesized that small changes in plate motion over thousands of years, and/or over decades, are responsible for changes in the style of deformation in southern California. We propose that such changes, over the course of just a few years, also affect the style of deformation.

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.

Small-scale shifting mosaics of two dominant grassland species: the possible role of soil-borne pathogens.

PubMed

Olff, H; Hoorens, B; de Goede, R G M; van der Putten, W H; Gleichman, J M

2000-10-01

We analyzed the dynamics of dominant plant species in a grazed grassland over 17 years, and investigated whether local shifts in these dominant species, leading to vegetation mosaics, could be attributed to interactions between plants and soil-borne pathogens. We found that Festuca rubra and Carex arenaria locally alternated in abundance, with different sites close together behaving out of phase, resulting in a shifting mosaic. The net effect of killing all soil biota on the growth of these two species was investigated in a greenhouse experiment using gamma radiation, controlling for possible effects of sterilization on soil chemistry. Both plant species showed a strong net positive response to soil sterilization, indicating that pathogens (e.g., nematodes, pathogenic fungi) outweighed the effect of mutualists (e.g., mycorrhizae). This positive growth response towards soil sterilization appeared not be due to effects of sterilization on soil chemistry. Growth of Carex was strongly reduced by soil-borne pathogens (86% reduction relative to its growth on sterilized soil) on soil from a site where this species decreased during the last decade (and Festuca increased), while it was reduced much less (50%) on soil from a nearby site where it increased in abundance during the last decade. Similarly, Festuca was reduced more (67%) on soil from the site where it decreased (and Carex increased) than on soil from the site where it increased (55%, the site where Carex decreased). Plant-feeding nematodes showed high small-scale variation in densities, and we related this variation to the observed growth reductions in both plant species. Carex growth on unsterilized soil was significantly more reduced at higher densities of plant-feeding nematodes, while the growth reduction in Festuca was independent of plant-feeding nematode densities. At high plant-feeding nematode densities, growth of Carex was reduced more than Festuca, while at low nematode densities the opposite was found. Each plant species thus seems to be affected by different (groups of) soil-borne pathogens. The resulting interaction web of plants and soil-borne pathogens is discussed. We hypothesize that soil disturbances by digging ants and rabbits may explain the small-scale variation in nematode densities, by locally providing "fresh" sand. We conclude that soil-borne pathogens may contribute to plant diversity and spatial mosaics of plants in grasslands.

Genetics of Resistant Hypertension: the Missing Heritability and Opportunities.

PubMed

Teixeira, Samantha K; Pereira, Alexandre C; Krieger, Jose E

2018-05-19

Blood pressure regulation in humans has long been known to be a genetically determined trait. The identification of causal genetic modulators for this trait has been unfulfilling at the least. Despite the recent advances of genome-wide genetic studies, loci associated with hypertension or blood pressure still explain a very low percentage of the overall variation of blood pressure in the general population. This has precluded the translation of discoveries in the genetics of human hypertension to clinical use. Here, we propose the combined use of resistant hypertension as a trait for mapping genetic determinants in humans and the integration of new large-scale technologies to approach in model systems the multidimensional nature of the problem. New large-scale efforts in the genetic and genomic arenas are paving the way for an increased and granular understanding of genetic determinants of hypertension. New technologies for whole genome sequence and large-scale forward genetic screens can help prioritize gene and gene-pathways for downstream characterization and large-scale population studies, and guided pharmacological design can be used to drive discoveries to the translational application through better risk stratification and new therapeutic approaches. Although significant challenges remain in the mapping and identification of genetic determinants of hypertension, new large-scale technological approaches have been proposed to surpass some of the shortcomings that have limited progress in the area for the last three decades. The incorporation of these technologies to hypertension research may significantly help in the understanding of inter-individual blood pressure variation and the deployment of new phenotyping and treatment approaches for the condition.

A lacustrine carbonate record of Holocene seasonality and climate

USGS Publications Warehouse

Wittkop, Chad A.; Teranes, Jane L.; Dean, Walter E.; Guilderson, Thomas P.

2009-01-01

Annually laminated (varved) Holocene sediments from Derby Lake, Michigan, display variations in endogenic calcite abundance reflecting a long-(millennial-scale) decrease in burial punctuated with frequent short- (decadal-scale) oscillations due to carbonate dissolution. Since 6000 cal yr B.P., sediment carbonate abundance has followed a decreasing trend while organic-carbon abundance has increased. The correlation between organic-carbon abundance and the sum of March-April-October-November insolation has an r2 value of 0.58. We interpret these trends to represent a precession-driven lengthening of the Holocene growing season that has reduced calcite burial by enhancing net annual organic-matter production and associated calcite dissolution. Correlations with regional paleoclimate records suggest that changes in temperature and moisture balance have impacted the distribution of short- oscillations in carbonate and organic-matter abundance superimposed on the precession-driven trends.

The Walker circulation, diabatic heating, and outgoing longwave radiation

NASA Astrophysics Data System (ADS)

Stechmann, S. N.; Ogrosky, H. R.

2014-12-01

For the tropical atmosphere on planetary scales, it is common to model the circulation using strong damping. Here, with new data analysis techniques, evidence suggests that damping can actually be neglected. Specifically, near the equator, the east--west overturning circulation is in agreement with the undamped wave response to atmospheric heating. To estimate the heating, satellite observations of outgoing longwave radiation (OLR) are used. Frequently OLR is used as a heuristic indicator of cloudiness. Here, the results further suggest that OLR variations are actually proportional to total diabatic heating variations, with a proportionality constant of 18 W m-2 (K/day)-1. While the agreement holds best over long time averages of years or decades, it also holds over shorter periods of one season or one month. Consequently, it is suggested that the strength of the Walker circulation -- and its evolution in time -- could be estimated using satellite data.

Multi-decadal trend and space-time variability of sea level over the Indian Ocean since the 1950s: impact of decadal climate modes

NASA Astrophysics Data System (ADS)

Han, W.; Stammer, D.; Meehl, G. A.; Hu, A.; Sienz, F.

2016-12-01

Sea level varies on decadal and multi-decadal timescales over the Indian Ocean. The variations are not spatially uniform, and can deviate considerably from the global mean sea level rise (SLR) due to various geophysical processes. One of these processes is the change of ocean circulation, which can be partly attributed to natural internal modes of climate variability. Over the Indian Ocean, the most influential climate modes on decadal and multi-decadal timescales are the Interdecadal Pacific Oscillation (IPO) and decadal variability of the Indian Ocean dipole (IOD). Here, we first analyze observational datasets to investigate the impacts of IPO and IOD on spatial patterns of decadal and interdecadal (hereafter decal) sea level variability & multi-decadal trend over the Indian Ocean since the 1950s, using a new statistical approach of Bayesian Dynamical Linear regression Model (DLM). The Bayesian DLM overcomes the limitation of "time-constant (static)" regression coefficients in conventional multiple linear regression model, by allowing the coefficients to vary with time and therefore measuring "time-evolving (dynamical)" relationship between climate modes and sea level. For the multi-decadal sea level trend since the 1950s, our results show that climate modes and non-climate modes (the part that cannot be explained by climate modes) have comparable contributions in magnitudes but with different spatial patterns, with each dominating different regions of the Indian Ocean. For decadal variability, climate modes are the major contributors for sea level variations over most region of the tropical Indian Ocean. The relative importance of IPO and decadal variability of IOD, however, varies spatially. For example, while IOD decadal variability dominates IPO in the eastern equatorial basin (85E-100E, 5S-5N), IPO dominates IOD in causing sea level variations in the tropical southwest Indian Ocean (45E-65E, 12S-2S). To help decipher the possible contribution of external forcing to the multi-decadal sea level trend and decadal variability, we also analyze the model outputs from NCAR's Community Earth System Model (CESM) Large Ensemble Experiments, and compare the results with our observational analyses.

Lake transparency: a window into decadal variations in dissolved organic carbon concentrations in Lakes of Acadia National Park, Maine

USGS Publications Warehouse

Roesler, Collin S.; Culbertson, Charles W.

2016-01-01

A forty year time series of Secchi depth observations from approximately 25 lakes in Acadia National Park, Maine, USA, evidences large variations in transparency between lakes but relatively little seasonal cycle within lakes. However, there are coherent patterns over the time series, suggesting large scale processes are responsible. It has been suggested that variations in colored dissolved organic matter (CDOM) are primarily responsible for the variations in transparency, both between lakes and over time and further that CDOM is a robust optical proxy for dissolved organic carbon (DOC). Here we present a forward model of Secchi depth as a function of DOC based upon first principles and bio-optical relationships. Inverting the model to estimate DOC concentration from Secchi depth observations compared well with the measured DOC concentrations collected since 1995 (RMS error < 1.3 mg C l-1). This inverse model allows the time series of DOC to be extended back to the mid 1970s when only Secchi depth observations were collected, and thus provides a means for investigating lake response to climate forcing, changing atmospheric chemistry and watershed characteristics, including land cover and land use.

Runoff and sediment variation in the areas with high and coarse sediment yield of the middle Yellow River

NASA Astrophysics Data System (ADS)

Zhang, Pan; Yao, Wenyi; Xiao, Peiqing; Sun, Weiying

2018-02-01

Massive water and soil conservation works (WSCW) have been conducted in the areas with high and coarse sediment yield of the middle Yellow River since 1982. With the impending effects of climate change, it is necessary to reconsider the effects of WSCW on runoff and sediment variation at decadal and regional scales. Using long-term official and synthesized data, the WSCW impacts on reducing water and soil loss were studied in Sanchuanhe River watershed. Results showed that the sediment and runoff generated from this area showed a decreasing trend in the past 50 years. A great progress has been achieved in erosion control since the 1970s. After the 4 soil and water conservation harnessing stages during the period from 1970 to 2006, the sediment and runoff yield showed decreases with the extension of harnessing. The results revealed that human activities exerted the largest effects on the sediment reduction and explained 66.6% of the variation in the specific sediment yield. The contribution of rainfall variation to runoff reduction was as large as human activities. A great benefit have been obtained in water and soil loss control in this area.

North Atlantic sea-level variability during the last millennium

NASA Astrophysics Data System (ADS)

Gehrels, Roland; Long, Antony; Saher, Margot; Barlow, Natasha; Blaauw, Maarten; Haigh, Ivan; Woodworth, Philip

2014-05-01

Climate modelling studies have demonstrated that spatial and temporal sea-level variability observed in North Atlantic tide-gauge records is controlled by a complex array of processes, including ice-ocean mass exchange, freshwater forcing, steric changes, changes in wind fields, and variations in the speed of the Gulf Stream. Longer records of sea-level change, also covering the pre-industrial period, are important as a 'natural' and long-term baseline against which to test model performance and to place recent and future sea-level changes and ice-sheet change into a long-term context. Such records can only be reliably and continuously reconstructed from proxy methods. Salt marshes are capable of recording decimetre-scale sea-level variations with high precision and accuracy. In this paper we present four new high-resolution proxy records of (sub-) decadal sea-level variability reconstructed from salt-marsh sediments in Iceland, Nova Scotia, Maine and Connecticut that span the past 400 to 900 years. Our records, based on more than 100 new radiocarbon analyses, Pb-210 and Cs-137 measurements as well as other biological and geochemical age markers, together with hundreds of new microfossil observations from contemporary and fossil salt marshes, capture not only the rapid 20th century sea-level rise, but also small-scale (decimetre, multi-decadal) sea-level fluctuations during preceding centuries. We show that in Iceland three periods of rapid sea-level rise are synchronous with the three largest positive shifts of the reconstructed North Atlantic Oscillation (NAO) index. Along the North American east coast we compare our data with salt-marsh records from New Jersey, North Carolina and Florida and observe a trend of increased pre-industrial sea-level variability from south to north (Florida to Nova Scotia). Mass changes and freshwater forcing cannot explain this pattern. Based on comparisons with instrumental sea-level data and modelling studies we hypothesise that multi-decadal to centennial changes in wind and air pressure are more important than mass flux from land-based ice as drivers of North Atlantic sea-level variability during the last millennium.

Southern Ocean Convection and tropical telleconnections

NASA Astrophysics Data System (ADS)

Marinov, I.; Cabre, A.; Gnanadesikan, A.

2014-12-01

We show that Southern Ocean (SO) temperatures in the latest generation of Earth System Models exhibit two major modes of variation, one driven by deep convection, the other by tropical variability. We perform a CMIP5 model intercomparison to understand why different climate models represent SO variability so differently in long, control simulations. We show that multiyear variability in Southern Ocean sea surface temperatures (SSTs) can in turn influence oceanic and atmospheric conditions in the tropics on short (atmospheric) time-scales. We argue that the strength and pattern of SO-tropical teleconnections depends on the intensity of SO deep convection. Periodic convection in the SO is a feature of most CMIP5 models under preindustrial forcing (deLavergne et al., 2014). Models show a wide distribution in the spatial extent, periodicity and intensity of their SO convection, with some models convecting most of the time, and some showing very little convection. In a highly convective coupled model, we find that multidecadal variability in SO and global SSTs, as well as SO heat storage are driven by Weddell Sea convective variability, with convective decades relatively warm due to the heat released from the deep southern ocean and non-convective decades cold due to the subsurface storage of heat. Furthermore, pulses of SO convection drive SST and sea ice variations, influencing absorbed shortwave and emitted longwave radiation, wind, cloud and precipitation patterns, with climatic implications for the low latitudes via fast atmospheric teleconnections. We suggest that these high-low latitude teleconnection mechanisms are relevant for understanding hiatus decades. Additionally, Southern Ocean deep convection varied significantly during past, natural climate changes such as during the last deglaciation. Weddell Sea open convection was recently weakened, likely as a consequence of anthropogenic forcing and the resulting surface freshening. Our study opens up the tantalizing possibility that such large-scale changes in SO deep convection might have tropical and indeed global implications via atmospheric teleconnections. We advocate the collection of both paleo and modern proxies that can verify these model-derived mechanisms and global teleconnections.

A mechanism of midlatitude noontime foE long-term variations inferred from European observations

NASA Astrophysics Data System (ADS)

Mikhailov, A. V.; Perrone, L.; Nusinov, A. A.

2017-04-01

Manually scaled June noontime monthly median foE values at three European stations Rome, Juliusruh, and Slough/Chilton were used to understand the mechanism of foE long-term variations. The 11 year running mean smoothed foE manifests long-term (for some solar cycles) variations with the rising phase at the end of 1960-1985 and the falling phase after 1985. A close relationship (even in details) between (foEave)11y and (R12)11y variations with the correlation coefficient of 0.996 (absolutely significant according to Fisher F criterion) suggests that the Sun is the source of these (foEave)11y long-term variations. After removing solar activity long-term variations the residual (foEave)11y trend is very small ( 0.029% per decade) being absolutely insignificant. This means that all (foEave)11y variations are removed with one solar activity index, (R12)11y, i.e., this means that long-term variations are fully controlled by solar activity. Theory of midlatitude daytime E region tells us that long-term variations of solar EUV in two lines λ = 977 Å (CIII) and λ = 1025.7 Å (HLyβ) and X-ray radiation with λ < 100 Å (both manifesting the same long-term variations with the rising phase at the end of 1960-1985 and the falling phase after 1985) are responsible for the observed (foEave)11y variations. Therefore, the observed daytime midlatitude foE long-term variations have a natural (not anthropogenic) origin related to long-term variations of solar activity. No peculiarities in relation with the last deep solar minimum in 2008-2009 have been revealed.

Mediterranean sea water budget long-term trend inferred from salinity observations

NASA Astrophysics Data System (ADS)

Skliris, N.; Zika, J. D.; Herold, L.; Josey, S. A.; Marsh, R.

2018-01-01

Changes in the Mediterranean water cycle since 1950 are investigated using salinity and reanalysis based air-sea freshwater flux datasets. Salinity observations indicate a strong basin-scale multi-decadal salinification, particularly in the intermediate and deep layers. Evaporation, precipitation and river runoff variations are all shown to contribute to a very strong increase in net evaporation of order 20-30%. While large temporal uncertainties and discrepancies are found between E-P multi-decadal trend patterns in the reanalysis datasets, a more robust and spatially coherent structure of multi-decadal change is obtained for the salinity field. Salinity change implies an increase in net evaporation of 8 to 12% over 1950-2010, which is considerably lower than that suggested by air-sea freshwater flux products, but still largely exceeding estimates of global water cycle amplification. A new method based on water mass transformation theory is used to link changes in net evaporation over the Mediterranean Sea with changes in the volumetric distribution of salinity. The water mass transformation distribution in salinity coordinates suggests that the Mediterranean basin salinification is driven by changes in the regional water cycle rather than changes in salt transports at the straits.

Separating decadal global water cycle variability from sea level rise.

PubMed

Hamlington, B D; Reager, J T; Lo, M-H; Karnauskas, K B; Leben, R R

2017-04-20

Under a warming climate, amplification of the water cycle and changes in precipitation patterns over land are expected to occur, subsequently impacting the terrestrial water balance. On global scales, such changes in terrestrial water storage (TWS) will be reflected in the water contained in the ocean and can manifest as global sea level variations. Naturally occurring climate-driven TWS variability can temporarily obscure the long-term trend in sea level rise, in addition to modulating the impacts of sea level rise through natural periodic undulation in regional and global sea level. The internal variability of the global water cycle, therefore, confounds both the detection and attribution of sea level rise. Here, we use a suite of observations to quantify and map the contribution of TWS variability to sea level variability on decadal timescales. In particular, we find that decadal sea level variability centered in the Pacific Ocean is closely tied to low frequency variability of TWS in key areas across the globe. The unambiguous identification and clean separation of this component of variability is the missing step in uncovering the anthropogenic trend in sea level and understanding the potential for low-frequency modulation of future TWS impacts including flooding and drought.

The relative contribution of climate to changes in lesser prairie-chicken abundance

USGS Publications Warehouse

Ross, Beth E.; Haukos, David A.; Hagen, Christian A.; Pitman, James

2016-01-01

Managing for species using current weather patterns fails to incorporate the uncertainty associated with future climatic conditions; without incorporating potential changes in climate into conservation strategies, management and conservation efforts may fall short or waste valuable resources. Understanding the effects of climate change on species in the Great Plains of North America is especially important, as this region is projected to experience an increased magnitude of climate change. Of particular ecological and conservation interest is the lesser prairie-chicken (Tympanuchus pallidicinctus), which was listed as “threatened” under the U.S. Endangered Species Act in May 2014. We used Bayesian hierarchical models to quantify the effects of extreme climatic events (extreme values of the Palmer Drought Severity Index [PDSI]) relative to intermediate (changes in El Niño Southern Oscillation) and long-term climate variability (changes in the Pacific Decadal Oscillation) on trends in lesser prairie-chicken abundance from 1981 to 2014. Our results indicate that lesser prairie-chicken abundance on leks responded to environmental conditions of the year previous by positively responding to wet springs (high PDSI) and negatively to years with hot, dry summers (low PDSI), but had little response to variation in the El Niño Southern Oscillation and the Pacific Decadal Oscillation. Additionally, greater variation in abundance on leks was explained by variation in site relative to broad-scale climatic indices. Consequently, lesser prairie-chicken abundance on leks in Kansas is more strongly influenced by extreme drought events during summer than other climatic conditions, which may have negative consequences for the population as drought conditions intensify throughout the Great Plains.

Temporal variation of the wind environment and its possible causes in the Mu Us Dunefield of Northern China, 1960-2014

NASA Astrophysics Data System (ADS)

Cui, Xujia; Sun, Hu; Dong, Zhibao; Liu, Zhengyao; Li, Chao; Zhang, Zhengcai; Li, Xiaolan; Li, Lulu

2018-02-01

Research on the wind environment variation improves our understanding of the process of climate change. This study examines temporal variation of the near-surface wind environment and investigates its possible causes in the Mu Us Dunefield of Northern China from 1960 to 2014, through analyzing the meteorological data from seven stations and the land use and land cover (LUCC) change data with 100 m resolution. The wind speed had a widespread significant decrease with an average trend of - 0.111 m s-1 decade-1, although the rate of decrease differed seasonally. This negative trend was also found in the winds that were above a 5 m s-1 threshold, as well as the percentage of their days, which influenced the wind speed change more strongly. Overall, 88.69% of the annual decrease resulted from decreases in the maximum wind speed, and the percentage even reached 100% in autumn and winter. We further found that the drift potential decreased at decadal time scales, mainly focusing on three prevailing wind groups: the northerly, westerly, and southerly winds. This revealed the weakened East Asian monsoon and westerly circulation in the lower atmosphere. Against the context of climate warming, the decline of wind speeds in spring was closely related to the greenhouse gas, while the winter decline was closely associated with the aerosol or atmospheric dust. Moreover, the LUCC change showed the decreased areas of sand land and the increased areas of vegetation-covered land, which increased the ground surface roughness and was another reason for the weakened wind environment.

Recent changes of the Earth's core derived from satellite observations of magnetic and gravity fields.

PubMed

Mandea, Mioara; Panet, Isabelle; Lesur, Vincent; de Viron, Olivier; Diament, Michel; Le Mouël, Jean-Louis

2012-11-20

To understand the dynamics of the Earth's fluid, iron-rich outer core, only indirect observations are available. The Earth's magnetic field, originating mainly within the core, and its temporal variations can be used to infer the fluid motion at the top of the core, on a decadal and subdecadal time-scale. Gravity variations resulting from changes in the mass distribution within the Earth may also occur on the same time-scales. Such variations include the signature of the flow inside the core, though they are largely dominated by the water cycle contributions. Our study is based on 8 y of high-resolution, high-accuracy magnetic and gravity satellite data, provided by the CHAMP and GRACE missions. From the newly derived geomagnetic models we have computed the core magnetic field, its temporal variations, and the core flow evolution. From the GRACE CNES/GRGS series of time variable geoid models, we have obtained interannual gravity models by using specifically designed postprocessing techniques. A correlation analysis between the magnetic and gravity series has demonstrated that the interannual changes in the second time derivative of the core magnetic field under a region from the Atlantic to Indian Ocean coincide in phase with changes in the gravity field. The order of magnitude of these changes and proposed correlation are plausible, compatible with a core origin; however, a complete theoretical model remains to be built. Our new results and their broad geophysical significance could be considered when planning new Earth observation space missions and devising more sophisticated Earth's interior models.

Measurement of Great Salt Lake Loading by the BARGEN Continuous GPS Network

NASA Astrophysics Data System (ADS)

Elósegui, P.; Davis, J. L.; Mitrovica, J. X.; Wernicke, B. P.; Bennett, R. A.

2002-12-01

The northernmost segment of the Basin and Range Geodetic network (BARGEN) forms an east-west transect from western Utah to eastern California between the latitudes of N~40° and N~41°. Two of our GPS sites, COON and CEDA, are located within 20~km south of the Great Salt Lake (GSL), which extends NNW for a length of ~100~km. Lake level records for GSL during the period of the operation of BARGEN (mid-1996 to present) indicate seasonal elevation variations of ~0.5~m amplitude superimposed on a roughly ``decadal'' feature of amplitude ~1~m. Using an elastic Green's function based on PREM and a simplified load geometry for GSL, we calculate that these elevation variations translate into vertical crustal loading signals of +/-0.5~mm (seasonal) and +/- 1~mm (decadal). The calculated maximum horizontal loading signals are roughly a factor of two smaller. Despite the small size of the expected loading signals, we conclude that we can observe them using time series for the three-dimensional coordinates of COON and CEDA. For CEDA, the variations in the time series are in phase with, and the same magnitude as, both the predicted seasonal and decadal variations. For COON, we obtain a similar match for the decadal variations, but the observed seasonal variations, although in-phase with the predicted variations, are a factor of 3--4 larger. We speculate that this difference may be caused by some combination of local precipitation-induced site motion, unmodeled loading from other nearby sources, errors in the GSL load geometry, and atmospheric errors. We will present these results, and also discuss the loading effect as an error source for estimates of long-term site velocity.

Projected Changes in Mean and Interannual Variability of Surface Water over Continental China

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

Leng, Guoyong; Tang, Qiuhong; Huang, Maoyi

Five General Circulation Model (GCM) climate projections under the RCP8.5 emission scenario were used to drive the Variable Infiltration Capacity (VIC) hydrologic model to investigate the impacts of climate change on hydrologic cycle over continental China in the 21st century. The bias-corrected climatic variables were generated for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) by the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP). Results showed much larger fractional changes of annual mean Evaportranspiration (ET) per unit warming than the corresponding fractional changes of Precipitation (P) per unit warming across the country especially for South China,more » which led to notable decrease of surface water variability (P-E). Specifically, negative trends for annual mean runoff up to -0.33%/decade and soil moisture trends varying between -0.02 to -0.13%/decade were found for most river basins across China. Coincidentally, interannual variability for both runoff and soil moisture exhibited significant positive trends for almost all river basins across China, implying an increase in extremes relative to the mean conditions. Noticeably, the largest positive trends for runoff variability and soil moisture variability, which were up to 38 0.41%/decade and 0.90%/decade, both occurred in Southwest China. In addition to the regional contrast, intra-seasonal variation was also large for the runoff mean and runoff variability changes, but small for the soil moisture mean and variability changes. Our results suggest that future climate change could further exacerbate existing water-related risks (e.g. floods and droughts) across China as indicated by the marked decrease of surface water amounts combined with steady increase of interannual variability throughout the 21st century. This study highlights the regional contrast and intra-seasonal variations for the projected hydrologic changes and could provide muti-scale guidance for assessing effective adaptation strategies for the country on a river basin, regional, or as whole.« less

Rapid climate fluctuations over the past millennium: evidence from a lacustrine record of Basomtso Lake, southeastern Tibetan Plateau

PubMed Central

Li, Kai; Liu, Xingqi; Herzschuh, Ulrike; Wang, Yongbo

2016-01-01

Abrupt climate changes and fluctuations over short time scales are superimposed on long-term climate changes. Understanding rapid climate fluctuations at the decadal time scale over the past millennium will enhance our understanding of patterns of climate variability and aid in forecasting climate changes in the future. In this study, climate changes on the southeastern Tibetan Plateau over the past millennium were determined from a 4.82-m-long sediment core from Basomtso Lake. At the centennial time scale, the Medieval Climate Anomaly (MCA), Little Ice Age (LIA) and Current Warm Period (CWP) are distinct in the Basomtso region. Rapid climate fluctuations inferred from five episodes with higher sediment input and likely warmer conditions, as well as seven episodes with lower sediment input and likely colder conditions, were well preserved in our record. These episodes with higher and lower sediment input are characterized by abrupt climate changes and short time durations. Spectral analysis indicates that the climate variations at the centennial scale on the southeastern Tibetan Plateau are influenced by solar activity during the past millennium. PMID:27091591

Characterizing Air Temperature Changes in the Tarim Basin over 1960–2012

PubMed Central

Peng, Dongmei; Wang, Xiujun; Zhao, Chenyi; Wu, Xingren; Jiang, Fengqing; Chen, Pengxiang

2014-01-01

There has been evidence of warming rate varying largely over space and between seasons. However, little has been done to evaluate the spatial and temporal variability of air temperature in the Tarim Basin, northwest China. In this study, we collected daily air temperature from 19 meteorological stations for the period of 1960–2012, and analyzed annual mean temperature (AMT), the annual minimum (Tmin) and maximum temperature (Tmax), and mean temperatures of all twelve months and four seasons and their anomalies. Trend analyses, standard deviation of the detrended anomaly (SDDA) and correlations were carried out to characterize the spatial and temporal variability of various mean air temperatures. Our data showed that increasing trend was much greater in the Tmin (0.55°C/10a) than in the AMT (0.25°C/10a) and Tmax (0.12°C/10a), and the fluctuation followed the same order. There were large spatial variations in the increasing trends of both AMT (from −0.09 to 0.43 °C/10a) and Tmin (from 0.15 to 1.12°C/10a). Correlation analyses indicated that AMT had a significantly linear relationship with Tmin and the mean temperatures of four seasons. There were also pronounced changes in the monthly air temperature from November to March at decadal time scale. The seasonality (i.e., summer and winter difference) of air temperature was stronger during the period of 1960–1979 than over the recent three decades. Our preliminary analyses indicated that local environmental conditions (such as elevation) might be partly responsible for the spatial variability, and large scale climate phenomena might have influences on the temporal variability of air temperature in the Tarim Basin. In particular, there was a significant correlation between index of El Niño-Southern Oscillation (ENSO) and air temperature of May (P = 0.004), and between the index of Pacific Decadal Oscillation (PDO) and air temperature of July (P = 0.026) over the interannual to decadal time scales. PMID:25375648

Prediction Activities at NASA's Global Modeling and Assimilation Office

NASA Technical Reports Server (NTRS)

Schubert, Siegfried

2010-01-01

The Global Modeling and Assimilation Office (GMAO) is a core NASA resource for the development and use of satellite observations through the integrating tools of models and assimilation systems. Global ocean, atmosphere and land surface models are developed as components of assimilation and forecast systems that are used for addressing the weather and climate research questions identified in NASA's science mission. In fact, the GMAO is actively engaged in addressing one of NASA's science mission s key questions concerning how well transient climate variations can be understood and predicted. At weather time scales the GMAO is developing ultra-high resolution global climate models capable of resolving high impact weather systems such as hurricanes. The ability to resolve the detailed characteristics of weather systems within a global framework greatly facilitates addressing fundamental questions concerning the link between weather and climate variability. At sub-seasonal time scales, the GMAO is engaged in research and development to improve the use of land information (especially soil moisture), and in the improved representation and initialization of various sub-seasonal atmospheric variability (such as the MJO) that evolves on time scales longer than weather and involves exchanges with both the land and ocean The GMAO has a long history of development for advancing the seasonal-to-interannual (S-I) prediction problem using an older version of the coupled atmosphere-ocean general circulation model (AOGCM). This includes the development of an Ensemble Kalman Filter (EnKF) to facilitate the multivariate assimilation of ocean surface altimetry, and an EnKF developed for the highly inhomogeneous nature of the errors in land surface models, as well as the multivariate assimilation needed to take advantage of surface soil moisture and snow observations. The importance of decadal variability, especially that associated with long-term droughts is well recognized by the climate community. An improved understanding of the nature of decadal variability and its predictability has important implications for efforts to assess the impacts of global change in the coming decades. In fact, the GMAO has taken on the challenge of carrying out experimental decadal predictions in support of the IPCC AR5 effort.

Global sea level linked to global temperature

PubMed Central

Vermeer, Martin; Rahmstorf, Stefan

2009-01-01

We propose a simple relationship linking global sea-level variations on time scales of decades to centuries to global mean temperature. This relationship is tested on synthetic data from a global climate model for the past millennium and the next century. When applied to observed data of sea level and temperature for 1880–2000, and taking into account known anthropogenic hydrologic contributions to sea level, the correlation is >0.99, explaining 98% of the variance. For future global temperature scenarios of the Intergovernmental Panel on Climate Change's Fourth Assessment Report, the relationship projects a sea-level rise ranging from 75 to 190 cm for the period 1990–2100. PMID:19995972

A monthly global paleo-reanalysis of the atmosphere from 1600 to 2005 for studying past climatic variations

PubMed Central

Franke, Jörg; Brönnimann, Stefan; Bhend, Jonas; Brugnara, Yuri

2017-01-01

Climatic variations at decadal scales such as phases of accelerated warming or weak monsoons have profound effects on society and economy. Studying these variations requires insights from the past. However, most current reconstructions provide either time series or fields of regional surface climate, which limit our understanding of the underlying dynamics. Here, we present the first monthly paleo-reanalysis covering the period 1600 to 2005. Over land, instrumental temperature and surface pressure observations, temperature indices derived from historical documents and climate sensitive tree-ring measurements were assimilated into an atmospheric general circulation model ensemble using a Kalman filtering technique. This data set combines the advantage of traditional reconstruction methods of being as close as possible to observations with the advantage of climate models of being physically consistent and having 3-dimensional information about the state of the atmosphere for various variables and at all points in time. In contrast to most statistical reconstructions, centennial variability stems from the climate model and its forcings, no stationarity assumptions are made and error estimates are provided. PMID:28585926

Measuring the benefit of orthophosphate treatment on lead in drinking water.

PubMed

Cardew, P T

2009-03-01

Many water companies are adding low concentrations of orthophosphate to the water supply in order to reduce lead concentrations in drinking water produced from corrosion of lead service pipes. Despite the erratic nature of lead concentrations measured at customer properties it has been possible to quantify the impact of treatment on lead concentrations and thereby quantify the effectiveness of treatment at both a regional and zonal level. This showed that the treatment policy has delivered more than 90 per cent reduction in lead concentrations, and was largely in accordance with theory. Across the region, lead performance and the reduction in lead performance show significant variation. A large part of this variation can be accounted for by variations in the proportion of leaded properties supplied through lead service pipes. Analysis showed that the proportion of particulate lead has also reduced significantly over the last decade. This is attributed to improved mechanical robustness of the corrosion layer caused by changes in its physical structure. This appears to be a very slow process with a natural time-scale of years.

Large short-term deviations from dipolar field during the Levantine Iron Age Geomagnetic Anomaly ca. 1050-700 BCE

NASA Astrophysics Data System (ADS)

Shaar, R.; Tauxe, L.; Ebert, Y.

2017-12-01

Continuous decadal-resolution paleomagnetic data from archaeological and sedimentary sources in the Levant revealed the existence a local high-field anomaly, which spanned the first 350 years of the first millennium BCE. This so-called "the Levantine Iron Age geomagnetic Anomaly" (LIAA) was characterized by a high averaged geomagnetic field (virtual axial dipole moments, VADM > 140 Z Am2, nearly twice of today's field), short decadal-scale geomagnetic spikes (VADM of 160-185 Z Am2), fast directional and intensity variations, and substantial deviation (20°-25°) from dipole field direction. Similar high field values in the time frame of LIAA have been observed north, and northeast to the Levant: Eastern Anatolia, Turkmenistan, and Georgia. West of the Levant, in the Balkans, field values in the same time are moderate to low. The overall data suggest that the LIAA is a manifestation of a local positive geomagnetic field anomaly similar in magnitude and scale to the presently active negative South Atlantic Anomaly. In this presentation we review the overall archaeomagnetic and sedimentary evidences supporting the local anomaly hypothesis, and compare these observations with today's IGRF field. We analyze the global data during the first two millennia BCE, which suggest some unexpected large deviations from a simple dipolar geomagnetic structure.

Decadal variability of extreme wave height representing storm severity in the northeast Atlantic and North Sea since the foundation of the Royal Society

PubMed Central

Taylor, P. H.; Gibson, R.

2016-01-01

Long-term estimation of extreme wave height remains a key challenge because of the short duration of available wave data, and also because of the possible impact of climate variability on ocean waves. Here, we analyse storm-based statistics to obtain estimates of extreme wave height at locations in the northeast Atlantic and North Sea using the NORA10 wave hindcast (1958–2011), and use a 5 year sliding window to examine temporal variability. The decadal variability is correlated to the North Atlantic oscillation and other atmospheric modes, using a six-term predictor model incorporating the climate indices and their Hilbert transforms. This allows reconstruction of the historic extreme climate back to 1661, using a combination of known and proxy climate indices. Significant decadal variability primarily driven by the North Atlantic oscillation is observed, and this should be considered for the long-term survivability of offshore structures and marine renewable energy devices. The analysis on wave climate reconstruction reveals that the variation of the mean, 99th percentile and extreme wave climates over decadal time scales for locations close to the dominant storm tracks in the open North Atlantic are comparable, whereas the wave climates for the rest of the locations including the North Sea are rather different. PMID:27713662

A Census of Atmospheric Variability From Seconds to Decades

NASA Astrophysics Data System (ADS)

Williams, Paul D.; Alexander, M. Joan; Barnes, Elizabeth A.; Butler, Amy H.; Davies, Huw C.; Garfinkel, Chaim I.; Kushnir, Yochanan; Lane, Todd P.; Lundquist, Julie K.; Martius, Olivia; Maue, Ryan N.; Peltier, W. Richard; Sato, Kaoru; Scaife, Adam A.; Zhang, Chidong

2017-11-01

This paper synthesizes and summarizes atmospheric variability on time scales from seconds to decades through a phenomenological census. We focus mainly on unforced variability in the troposphere, stratosphere, and mesosphere. In addition to atmosphere-only modes, our scope also includes coupled modes, in which the atmosphere interacts with the other components of the Earth system, such as the ocean, hydrosphere, and cryosphere. The topics covered include turbulence on time scales of seconds and minutes, gravity waves on time scales of hours, weather systems on time scales of days, atmospheric blocking on time scales of weeks, the Madden-Julian Oscillation on time scales of months, the Quasi-Biennial Oscillation and El Niño-Southern Oscillation on time scales of years, and the North Atlantic, Arctic, Antarctic, Pacific Decadal, and Atlantic Multidecadal Oscillations on time scales of decades. The paper serves as an introduction to a special collection of Geophysical Research Letters on atmospheric variability. We hope that both this paper and the collection will serve as a useful resource for the atmospheric science community and will act as inspiration for setting future research directions.

A Zonal Mode in the Indian Ocean over the Past Millennium? Isotopic Evidence from Continental Climate Archives and Model Simulations

NASA Astrophysics Data System (ADS)

Konecky, B.; Russell, J. M.; Vuille, M.; Rodysill, J. R.; Cohen, L. R.; Chuman, A. F.; Huang, Y.

2011-12-01

We present new evidence for multi-decadal to millennial scale hydro-climatic change in the continental Indian Ocean region over the past two millennia. We assess regional hydrological variability using new records of the δD of terrestrial plant waxes from the sediments of several lakes in tropical East Africa and Indonesia. We compare these new data to previous δ18O and δD records from the region and interpret these results in light of an isotope-enabled climate model simulation of the past 130 years. Long-term trends in our data support a southward migration of the Intertropical Convergence Zone (ITCZ)'s mean position over the past millennium, bringing progressively wetter conditions and D-depleted waxes to our southernmost site (~8°S) starting around 950 C.E. while maintaining overall wet conditions at our northernmost site (~0°N) until the end of the 19th century. Superimposed on this long-term trend are a series of pronounced, multi-decadal to centennial scale isotopic excursions that are of the same timing but in opposite directions on the two sides of the Indian Ocean. These zonally asymmetric isotopic fluctuations become progressively more pronounced beginning around 1400 C.E., with the onset of Little Ice Age cool conditions recorded in sea surface temperature reconstructions from the Northern Hemisphere and the Indo-Pacific Warm Pool (IPWP). Previous work in the IPWP region suggests cooler SST, reduced boreal summer Asian monsoon intensity, and less ENSO-like activity during the Little Ice Age [Oppo et al., 2009, Nature 460:1113, and references therein], although recent paleolimnological reconstructions from Java indicate punctuated droughts during this time [Rodysill et al., 2010, Eos Trans. AGU, 91(52), Fall Meet. Suppl., Abstract PP51B-04]. Our records suggest that multi-decadal to centennial precipitation variability was in fact enhanced during this time period in parts of equatorial East Africa and western Indonesia. The direction of isotopic excursions in our records resembles the variations associated with the negative mode of the Indian Ocean Zonal Mode (IOZM) observed in modern seasonal data. To investigate the potential for an IOZM-like mode to explain multi-decadal phenomena over the past millennium, we compare the variations in our records and in other previously published δ18O and δD records from the region to a model simulation of the past 130 years by the Stable Water Isotope INtercomparison Group (SWING). We find significant multi-decadal isotopic variability associated with the IOZM in the SWING experiment. We analyze the isotopic signature associated with both the IOZM and ENSO and use these findings to help interpret the multi-decadal variability evident in continental paleoclimate archives over the past millennium in the Indian Ocean region.

Coupling large scale hydrologic-reservoir-hydraulic models for impact studies in data sparse regions

NASA Astrophysics Data System (ADS)

O'Loughlin, Fiachra; Neal, Jeff; Wagener, Thorsten; Bates, Paul; Freer, Jim; Woods, Ross; Pianosi, Francesca; Sheffied, Justin

2017-04-01

As hydraulic modelling moves to increasingly large spatial domains it has become essential to take reservoirs and their operations into account. Large-scale hydrological models have been including reservoirs for at least the past two decades, yet they cannot explicitly model the variations in spatial extent of reservoirs, and many reservoirs operations in hydrological models are not undertaken during the run-time operation. This requires a hydraulic model, yet to-date no continental scale hydraulic model has directly simulated reservoirs and their operations. In addition to the need to include reservoirs and their operations in hydraulic models as they move to global coverage, there is also a need to link such models to large scale hydrology models or land surface schemes. This is especially true for Africa where the number of river gauges has consistently declined since the middle of the twentieth century. In this study we address these two major issues by developing: 1) a coupling methodology for the VIC large-scale hydrological model and the LISFLOOD-FP hydraulic model, and 2) a reservoir module for the LISFLOOD-FP model, which currently includes four sets of reservoir operating rules taken from the major large-scale hydrological models. The Volta Basin, West Africa, was chosen to demonstrate the capability of the modelling framework as it is a large river basin ( 400,000 km2) and contains the largest man-made lake in terms of area (8,482 km2), Lake Volta, created by the Akosombo dam. Lake Volta also experiences a seasonal variation in water levels of between two and six metres that creates a dynamic shoreline. In this study, we first run our coupled VIC and LISFLOOD-FP model without explicitly modelling Lake Volta and then compare these results with those from model runs where the dam operations and Lake Volta are included. The results show that we are able to obtain variation in the Lake Volta water levels and that including the dam operations and Lake Volta has significant impacts on the water levels across the domain.

Antarctic warming driven by internal Southern Ocean deep convection oscillations

NASA Astrophysics Data System (ADS)

Martin, Torge; Pedro, Joel B.; Steig, Eric J.; Jochum, Markus; Park, Wonsun; Rasmussen, Sune O.

2016-04-01

Simulations with the free-running, complex coupled Kiel Climate Model (KCM) show that heat release associated with recurring Southern Ocean deep convection can drive centennial-scale Antarctic temperature variations of 0.5-2.0 °C. We propose a mechanism connecting the intrinsic ocean variability with Antarctic warming that involves the following three steps: Preconditioning: heat supplied by the lower branch of the Atlantic Meridional Overturning Circulation (AMOC) accumulates at depth in the Southern Ocean, trapped by the Weddell Gyre circulation; Convection onset: wind and/or sea-ice changes tip the preconditioned, thermally unstable system into the convective state; Antarctic warming: fast sea-ice-albedo feedbacks (on annual to decadal timescales) and slower Southern Ocean frontal and sea-surface temperature adjustments to the convective heat release (on multi-decadal to centennial timescales), drive an increase in atmospheric heat and moisture transport towards Antarctica resulting in warming over the continent. Further, we discuss the potential role of this mechanism to explain climate variability observed in Antarctic ice-core records.

Spatial climate patterns explain negligible variation in strength of compensatory density feedbacks in birds and mammals.

PubMed

Herrando-Pérez, Salvador; Delean, Steven; Brook, Barry W; Cassey, Phillip; Bradshaw, Corey J A

2014-01-01

The use of long-term population data to separate the demographic role of climate from density-modified demographic processes has become a major topic of ecological investigation over the last two decades. Although the ecological and evolutionary mechanisms that determine the strength of density feedbacks are now well understood, the degree to which climate gradients shape those processes across taxa and broad spatial scales remains unclear. Intuitively, harsh or highly variable environmental conditions should weaken compensatory density feedbacks because populations are hypothetically unable to achieve or maintain densities at which social and trophic interactions (e.g., competition, parasitism, predation, disease) might systematically reduce population growth. Here we investigate variation in the strength of compensatory density feedback, from long-term time series of abundance over 146 species of birds and mammals, in response to spatial gradients of broad-scale temperature precipitation variables covering 97 localities in 28 countries. We use information-theoretic metrics to rank phylogenetic generalized least-squares regression models that control for sample size (time-series length) and phylogenetic non-independence. Climatic factors explained < 1% of the remaining variation in density-feedback strength across species, with the highest non-control, model-averaged effect sizes related to extreme precipitation variables. We could not link our results directly to other published studies, because ecologists use contrasting responses, predictors and statistical approaches to correlate density feedback and climate--at the expense of comparability in a macroecological context. Censuses of multiple populations within a given species, and a priori knowledge of the spatial scales at which density feedbacks interact with climate, seem to be necessary to determine cross-taxa variation in this phenomenon. Despite the availability of robust modelling tools, the appropriate data have not yet been gathered for most species, meaning that we cannot yet make any robust generalisations about how demographic feedbacks interact with climate.

Spatial Climate Patterns Explain Negligible Variation in Strength of Compensatory Density Feedbacks in Birds and Mammals

PubMed Central

Herrando-Pérez, Salvador; Delean, Steven; Brook, Barry W.; Cassey, Phillip; Bradshaw, Corey J. A.

2014-01-01

The use of long-term population data to separate the demographic role of climate from density-modified demographic processes has become a major topic of ecological investigation over the last two decades. Although the ecological and evolutionary mechanisms that determine the strength of density feedbacks are now well understood, the degree to which climate gradients shape those processes across taxa and broad spatial scales remains unclear. Intuitively, harsh or highly variable environmental conditions should weaken compensatory density feedbacks because populations are hypothetically unable to achieve or maintain densities at which social and trophic interactions (e.g., competition, parasitism, predation, disease) might systematically reduce population growth. Here we investigate variation in the strength of compensatory density feedback, from long-term time series of abundance over 146 species of birds and mammals, in response to spatial gradients of broad-scale temperature precipitation variables covering 97 localities in 28 countries. We use information-theoretic metrics to rank phylogenetic generalized least-squares regression models that control for sample size (time-series length) and phylogenetic non-independence. Climatic factors explained < 1% of the remaining variation in density-feedback strength across species, with the highest non-control, model-averaged effect sizes related to extreme precipitation variables. We could not link our results directly to other published studies, because ecologists use contrasting responses, predictors and statistical approaches to correlate density feedback and climate – at the expense of comparability in a macroecological context. Censuses of multiple populations within a given species, and a priori knowledge of the spatial scales at which density feedbacks interact with climate, seem to be necessary to determine cross-taxa variation in this phenomenon. Despite the availability of robust modelling tools, the appropriate data have not yet been gathered for most species, meaning that we cannot yet make any robust generalisations about how demographic feedbacks interact with climate. PMID:24618822

Caribbean coral growth influenced by anthropogenic aerosol emissions

NASA Astrophysics Data System (ADS)

Kwiatkowski, Lester; Cox, Peter M.; Economou, Theo; Halloran, Paul R.; Mumby, Peter J.; Booth, Ben B. B.; Carilli, Jessica; Guzman, Hector M.

2013-05-01

Coral growth rates are highly dependent on environmental variables such as sea surface temperature and solar irradiance. Multi-decadal variability in coral growth rates has been documented throughout the Caribbean over the past 150-200 years, and linked to variations in Atlantic sea surface temperatures. Multi-decadal variability in sea surface temperatures in the North Atlantic, in turn, has been linked to volcanic and anthropogenic aerosol forcing. Here, we examine the drivers of changes in coral growth rates in the western Caribbean between 1880 and 2000, using previously published coral growth chronologies from two sites in the region, and a numerical model. Changes in coral growth rates over this period coincided with variations in sea surface temperature and incoming short-wave radiation. Our model simulations show that variations in the concentration of anthropogenic aerosols caused variations in sea surface temperature and incoming radiation in the second half of the twentieth century. Before this, variations in volcanic aerosols may have played a more important role. With the exception of extreme mass bleaching events, we suggest that neither climate change from greenhouse-gas emissions nor ocean acidification is necessarily the driver of multi-decadal variations in growth rates at some Caribbean locations. Rather, the cause may be regional climate change due to volcanic and anthropogenic aerosol emissions.

Geometric and thermal controls on normal fault seismicity from rate-and-state friction models

NASA Astrophysics Data System (ADS)

Mark, H. F.; Behn, M. D.; Olive, J. A. L.; Liu, Y.

2017-12-01

Seismic and geodetic observations from the last two decades have led to a growing realization that a significant amount of fault slip at plate boundaries occurs aseismically, and that the amount of aseismic displacement varies across settings. Here we investigate controls on the seismogenic behavior of crustal-scale normal faults that accommodate extensional strain at mid-ocean ridges and continental rifts. Seismic moment release rates measured along the fast-spreading East Pacific Rise suggest that the majority of fault growth occurs aseismically with almost no seismic slip. In contrast, at the slow-spreading Mid-Atlantic Ridge seismic slip may represent up to 60% of the total fault displacement. Potential explanations for these variations include heterogeneous distributions of frictional properties on fault surfaces, effects of variable magma supply associated with seafloor spreading, and/or differences in fault geometry and thermal structure. In this study, we use rate-and-state friction models to study the seismic coupling coefficient (the fraction of total fault slip that occurs seismically) for normal faults at divergent plate boundaries, and investigate controls on fault behavior that might produce the variations in the coupling coefficient observed in natural systems. We find that the seismic coupling coefficient scales with W/h*, where W is the downdip width of the seismogenic area of the fault and h* is the critical earthquake nucleation size. At mid-ocean ridges, W is expected to increase with decreasing spreading rate. Thus, the observed relationship between seismic coupling and W/h* explains to first order variations in seismic coupling coefficient as a function of spreading rate. Finally, we use catalog data from the Gulf of Corinth to show that this scaling relationship can be extended into the thicker lithosphere of continental rift systems.

An Assessment of the SST Simulation Using the Climate Forecast System Coupled to the SSiB Surface Model

NASA Astrophysics Data System (ADS)

Wang, Y.; Xue, Y.; Huang, B.; Lee, J.; De Sales, F.

2016-12-01

A long term simulation has been conducted using the Climate Forecast System (CFSv2) coupled to the SSiB-2 land model, which consists of the Global Forecast System atmospheric model (GFS) and the Modular Ocean model - version 4 (MOM4) as the ocean component. This study evaluates the model's performance in simulating sea surface temperature (SST) mean state, trend, and inter-annual and decadal variabilities. The model is able to produce the reasonable spatial distribution of the SST climatology; however, it has prominent large scale biases. In the middle latitude of the Northern Hemisphere, major cold biases is close to the warm side of the large SST gradients, which may be associated with the weaker Kuroshio and Gulf Stream extensions that diffuse the SST gradient. IN addition, warm biases extend along the west coast of the North America continent to the high latitude, which may be related with excessive Ekman down-welling and solar radiation fluxes reaching to the surface due to the lack of cloud there. Warm biases also exist over the tropical cold tough areas in the Pacific and Atlantic. The global SST trend and interannual variations are well captured except for that in the south Hemisphere after year 2000, which is mainly contributed by the bias from the southern Pacific Ocean. Although the model fails to accurately produce ENSO events in proper years, it does reproduce the ENSO frequency well; they are skewed toward more warm events after 1990. The model also shows ability in SST decadal variation, such as the so-called inter-decadal Pacific oscillation (IPO); however, its phases seem to go reversely compared with the observation.

Development of A Dust Climate Indicator for the US National Climate Assessment

NASA Astrophysics Data System (ADS)

Tong, D.; Wang, J. X. L.; Gill, T. E.; Van Pelt, S.; Kim, D.

2016-12-01

Dust activity is a relatively simple but practical indicator to document the response of dryland ecosystems to climate change, making it an integral part of the National Climate Assessment (NCA). We present here a multi-agency collaboration that aims at developing a suite of dust climate indicators to document and monitor the long-term variability and trend of dust storm activity in the western United States. Recent dust observations have revealed rapid intensification of dust storm activity in the western United States. This trend is also closely correlated with a rapid increase in dust deposition in rainwater and "valley fever" hospitalization in southwestern states. It remains unclear, however, if such a trend, when enhanced by predicted warming and rainfall oscillation in the Southwest, will result in irreversible environmental development such as desertification or even another "Dust Bowl". Based on continuous ground aerosol monitoring, we have reconstructed a long-term dust storm climatology in the western United States. We report here direct evidence of rapid intensification of dust storm activity over US deserts in the past decades (1990 to 2013), in contrast to the decreasing trends in Asia and Africa. The US trend is spatially and temporally correlated with incidences of valley fever, an infectious disease caused by soil-dwelling fungus that has increased eight-fold in the past decade. We further investigate the linkage between dust variations and possible climate drivers and find that the regional dust trends are likely driven by large-scale variations of sea surface temperature in the Pacific Ocean, with the strongest correlation with the Pacific Decadal Oscillation (PDO). Future study will explore the link between the temporal and spatial trends of increase in dustiness and vegetation change in southwestern semi-arid and arid ecosystems.

A propagating freshwater mode in the Arctic Ocean with multidecadal time scale

NASA Astrophysics Data System (ADS)

Schmith, Torben; Malskær Olsen, Steffen; Margrethe Ringgaard, Ida

2017-04-01

We apply Principal Oscillatory Pattern analysis to the Arctic Ocean fresh water content as simulated in a 500 year long control run with constant preindustrial forcing with the EC-Earth global climate model. Two modes emerge from this analysis. One mode is a standing mode with decadal time scale describing accumulation and release of fresh water in the Beaufort Gyre, known in the literature as the Beaufort Gyre flywheel. In addition, we identify a propagating mode with a time scale around 80 years, propagating along the rim of the Canadian Basin. This mode has maximum variability of the fresh water content in the Transpolar Drift and represents the bulk of the total variability of the fresh water content in the Arctic Ocean and also projects on the fresh water through the Fram Strait. Therefore, potentially, it can introduce a multidecadal variability to the Atlantic meridional overturning circulation. We will discuss the physical origin of this propagating mode. This include planetary-scale internal Rossby waves with multidecadal time scale, due to the slow variation of the Coriolis parameter at these high latitudes, as well as topographic steering of these Rossby waves.

Evidence for Interannual to Decadal Variations in Hadley and Walker Circulations and Links to Water and Energy Fluxes

NASA Technical Reports Server (NTRS)

Robertson, Franklin; Bosilovich, Michael; Miller, Timothy

2007-01-01

Mass and energy transports associated with the Hadley and Walker circulations are important components of the earth s climate system and are strongly linked to hydrologic processes. Interannual to decadal variation in these flows likely signify a combination of natural climate noise as well as a response to anthropgenic forcing. There remains considerable uncertainty in quantifying variations in these flows. Evidence in the surface pressure record supports a weakening of the Walker circulation over the Pacific in recent decades. Conversely the NCEP / NCAR and ERA 40 reanalyses indicate that the Hadley circulation has increased in strength over the last two decades, though these analyses depict significantly different mass circulation changes. Interestingly, the NCEP - II / DOE reanalysis contains essentially no Hadley circulation changes. Most climate model integrations anticipate a weakening of both tropical circulations associated with stronger static stability. Clearly there is much uncertainty not only with the mass transports, but also how they are linked to water and energy balance of the planet through variations in turbulent heat and radiative fluxes and horizontal exports / imports of energy. Here we examine heat and water budget variations from a number of reanalysis products and focus on the linear and nonlinear response of ENSO warm and cold events as opportunities to study budget variations over the past 15-20 years. Our analysis addresses such questions as To what extent do Hadley and Walker Cell variations compensate each other on mass and energy transport? Do static stability adjustments appear to constrain fractional precipitation response vs. fractional water vapor response? We appeal to constraints offered by GPCP precipitation, SSWI ocean evaporation estimates, and ISCCP-FD radiative fluxes, and other satellite data sets to interpret and confirm reanalysis-based diagnostics. Using our findings we also attempt to place in context the recent findings that tropical ocean evaporation increased by order 5% or more during the 1990s, reconciling this with GPCP precipitation variations.

Hiatus-like decades in the absence of equatorial Pacific cooling and accelerated global ocean heat uptake

NASA Astrophysics Data System (ADS)

von Känel, Lukas; Frölicher, Thomas L.; Gruber, Nicolas

2017-08-01

A surface cooling pattern in the equatorial Pacific associated with a negative phase of the Interdecadal Pacific Oscillation is the leading hypothesis to explain the smaller rate of global warming during 1998-2012, with these cooler than normal conditions thought to have accelerated the oceanic heat uptake. Here using a 30-member ensemble simulation of a global Earth system model, we show that in 10% of all simulated decades with a global cooling trend, the eastern equatorial Pacific actually warms. This implies that there is a 1 in 10 chance that decadal hiatus periods may occur without the equatorial Pacific being the dominant pacemaker. In addition, the global ocean heat uptake tends to slow down during hiatus decades implying a fundamentally different global climate feedback factor on decadal time scales than on centennial time scales and calling for caution inferring climate sensitivity from decadal-scale variability.

Decadal-scale variations of sedimentary dinoflagellate cyst records from the Yellow Sea over the last 400 years

NASA Astrophysics Data System (ADS)

Kim, So-Young; Roh, Youn Ho; Shin, Hyeon Ho; Huh, Sik; Kang, Sung-Ho; Lim, Dhongil

2018-01-01

In recent decades, the Yellow Sea has experienced severe environmental deterioration due to increasing input of anthropogenic pollutants and consequently accelerated eutrophication. Whilst there have been significant advances in documenting historical records of metal pollution in the Yellow Sea region, changes in phytoplankton community structures affected by eutrophication remain understudied. Here, we present a new record of dinoflagellate cyst-based signals in age-dated sediment cores from the Yellow Sea mud deposits to provide better insight into eutrophication history and identification of associated responses of the regional phytoplankton community. It is worthy of note that there were significant variations in abundances and community structures of dinoflagellate cysts in three historical stages in association with increasing anthropogenic activity over the last 400 years. Pervasive effects of human interference altering the Yellow Sea environments are recognized by: 1) an abrupt increase of organic matter, including the diatom-produced biogenic opal concentrations (∼1850); 2) a distinct shift in phytoplankton composition towards dinoflagellate dominance (∼1940), and 3) recent acceleration of dinoflagellate cyst accumulation (∼1990). Particularly in the central Yellow Sea shelf, the anomalously high deposition of dinoflagellate cysts (especially Alexandrium species) is suggested to be a potentially important source of inoculum cells serving as a seed population for localized and recurrent blooms in coastal areas around the Yellow Sea.

Ice core and climate reanalysis analogs to predict Antarctic and Southern Hemisphere climate changes

NASA Astrophysics Data System (ADS)

Mayewski, P. A.; Carleton, A. M.; Birkel, S. D.; Dixon, D.; Kurbatov, A. V.; Korotkikh, E.; McConnell, J.; Curran, M.; Cole-Dai, J.; Jiang, S.; Plummer, C.; Vance, T.; Maasch, K. A.; Sneed, S. B.; Handley, M.

2017-01-01

A primary goal of the SCAR (Scientific Committee for Antarctic Research) initiated AntClim21 (Antarctic Climate in the 21st Century) Scientific Research Programme is to develop analogs for understanding past, present and future climates for the Antarctic and Southern Hemisphere. In this contribution to AntClim21 we provide a framework for achieving this goal that includes: a description of basic climate parameters; comparison of existing climate reanalyses; and ice core sodium records as proxies for the frequencies of marine air mass intrusion spanning the past ∼2000 years. The resulting analog examples include: natural variability, a continuation of the current trend in Antarctic and Southern Ocean climate characterized by some regions of warming and some cooling at the surface of the Southern Ocean, Antarctic ozone healing, a generally warming climate and separate increases in the meridional and zonal winds. We emphasize changes in atmospheric circulation because the atmosphere rapidly transports heat, moisture, momentum, and pollutants, throughout the middle to high latitudes. In addition, atmospheric circulation interacts with temporal variations (synoptic to monthly scales, inter-annual, decadal, etc.) of sea ice extent and concentration. We also investigate associations between Antarctic atmospheric circulation features, notably the Amundsen Sea Low (ASL), and primary climate teleconnections including the SAM (Southern Annular Mode), ENSO (El Nîno Southern Oscillation), the Pacific Decadal Oscillation (PDO), the AMO (Atlantic Multidecadal Oscillation), and solar irradiance variations.

Allergenic pollen season variations in the past two decades under changing climate in the United States

PubMed Central

Zhang, Yong; Bielory, Leonard; Mi, Zhongyuan; Cai, Ting; Robock, Alan; Georgopoulos, Panos

2014-01-01

Many diseases are linked with climate trends and variations. In particular, climate change is expected to alter the spatiotemporal dynamics of allergenic airborne pollen and potentially increase occurrence of allergic airway disease. Understanding the spatiotemporal patterns of changes in pollen season timing and levels is thus important in assessing climate impacts on aerobiology and allergy caused by allergenic airborne pollen. Here we describe the spatiotemporal patterns of changes in the seasonal timing and levels of allergenic airborne pollen for multiple taxa in different climate regions at a continental scale. The allergenic pollen seasons of representative trees, weeds and grass during the past decade (2001–2010) across the contiguous United States have been observed to start 3.0 (95% Confidence Interval (CI), 1.1–4.9) days earlier on average than in the 1990s (1994–2000). The average peak value and annual total of daily counted airborne pollen have increased by 42.4% (95% CI, 21.9%–62.9%) and 46.0% (95% CI, 21.5%–70.5%), respectively. Changes of pollen season timing and airborne levels depend on latitude, and are associated with changes of growing degree days, frost free days, and precipitation. These changes are likely due to recent climate change and particularly the enhanced warming and precipitation at higher latitudes in the contiguous United States. PMID:25266307

Dramatic change of the recurrence time and outburst parameters of the intermediate polar GK Persei

NASA Astrophysics Data System (ADS)

Šimon, V.

2002-02-01

This analysis has shown that the intermediate polar GK Per experienced a very striking evolution. Its outbursts became wider and brighter in the last five decades. These changes were accompanied by striking variations of the recurrence time T_C, from 385 days within the years 1948-1967 to 890 days in 1970. Nowadays, T_C displays a strong trend of linear increase. Decrease of irradiation of the disk by the WD, combined with the decrease of viscosity, offers a plausible explanation. It is argued that variations of the mass transfer rate are unlikely to play a major role. The morphology of the outburst light curves in the optical and the X-ray region is also studied. The decay branch in the optical remains remarkably similar for all the events while the largest changes of the light curve occur in the rising branch. This can be explained if the thermal instability may start at different distances from the disk center. The quiescent level of brightness does not display any secular trend in recent decades but a wave on the time scale of about 30 years with the full amplitude of 0.3 m_v, probably due to activity of the cool star, is detected. This research has made use of the AFOEV database, operated at CDS, France, and the observations provided by the ASM/RXTE team.

Five centuries of Southern Moravian drought variations revealed from living and historic tree rings

NASA Astrophysics Data System (ADS)

Büntgen, Ulf; Brázdil, Rudolf; Dobrovolný, Petr; Trnka, Mirek; Kyncl, Tomáš

2011-08-01

Past, present, and projected fluctuations of the hydrological cycle, associated to anthropogenic climate change, describe a pending challenge for natural ecosystems and human civilizations. Here, we compile and analyze long meteorological records from Brno, Czech Republic and nearby tree-ring measurements of living and historic firs from Southern Moravia. This unique paleoclimatic compilation together with innovative reconstruction methods and error estimates allows regional-scale May-June drought variability to be estimated back to ad 1500. Driest and wettest conditions occurred in 1653 and 1713, respectively. The ten wettest decades are evenly distributed throughout time, whereas the driest episodes occurred in the seventeenth century and from the 1840s onward. Discussion emphasizes agreement between the new reconstruction and documentary evidence, and stresses possible sources of reconstruction uncertainty including station inhomogeneity, limited frequency preservation, reduced climate sensitivity, and large-scale constraints.

The Response of Ice Sheets to Climate Variability

NASA Astrophysics Data System (ADS)

Snow, K.; Goldberg, D. N.; Holland, P. R.; Jordan, J. R.; Arthern, R. J.; Jenkins, A.

2017-12-01

West Antarctic Ice Sheet loss is a significant contributor to sea level rise. While the ice loss is thought to be triggered by fluctuations in oceanic heat at the ice shelf bases, ice sheet response to ocean variability remains poorly understood. Using a synchronously coupled ice-ocean model permitting grounding line migration, this study evaluates the response of an ice sheet to periodic variations in ocean forcing. Resulting oscillations in grounded ice volume amplitude is shown to grow as a nonlinear function of ocean forcing period. This implies that slower oscillations in climatic forcing are disproportionately important to ice sheets. The ice shelf residence time offers a critical time scale, above which the ice response amplitude is a linear function of ocean forcing period and below which it is quadratic. These results highlight the sensitivity of West Antarctic ice streams to perturbations in heat fluxes occurring at decadal time scales.

Decadal Prediction Skill in the GEOS-5 Forecast System

NASA Technical Reports Server (NTRS)

Ham, Yoo-Geun; Rienecker, Michael M.; Suarez, M.; Vikhliaev, Yury V.; Zhao, Bin; Marshak, Jelena; Vernieres, Guillaume; Schubert, Siegfried D.

2012-01-01

A suite of decadal predictions has been conducted with the NASA Global Modeling and Assimilation Office?s GEOS-5 Atmosphere-Ocean General Circulation Model (AOGCM). The hindcasts are initialized every December from 1959 to 2010 following the CMIP5 experimental protocol for decadal predictions. The initial conditions are from a multi-variate ensemble optimal interpolation ocean and sea-ice reanalysis, and from the atmospheric reanalysis (MERRA, the Modern-Era Retrospective Analysis for Research and Applications) generated using the GEOS-5 atmospheric model. The forecast skill of a three-member-ensemble mean is compared to that of an experiment without initialization but forced with observed CO2. The results show that initialization acts to increase the forecast skill of Northern Atlantic SST compared to the uninitialized runs, with the increase in skill maintained for almost a decade over the subtropical and mid-latitude Atlantic. The annual-mean Atlantic Meridional Overturning Circulation (AMOC) index is predictable up to a 5-year lead time, consistent with the predictable signal in upper ocean heat content over the Northern Atlantic. While the skill measured by Mean Squared Skill Score (MSSS) shows 50% improvement up to 10-year lead forecast over the subtropical and mid-latitude Atlantic, however, prediction skill is relatively low in the subpolar gyre, due in part to the fact that the spatial pattern of the dominant simulated decadal mode in upper ocean heat content over this region appears to be unrealistic. An analysis of the large-scale temperature budget shows that this is the result of a model bias, implying that realistic simulation of the climatological fields is crucial for skillful decadal forecasts.

VO-ESD: a virtual observatory approach to describe the geomagnetic field temporal variations with application to Swarm data

NASA Astrophysics Data System (ADS)

Saturnino, Diana; Langlais, Benoit; Amit, Hagay; Mandea, Mioara; Civet, François; Beucler, Éric

2017-04-01

A complete description of the main geomagnetic field temporal variation is crucial to understand dynamics in the core. This variation, termed secular variation (SV), is known with high accuracy at ground magnetic observatory locations. However the description of its spatial variability is hampered by the globally uneven distribution of the observatories. For the past two decades a global coverage of the field changes has been allowed by satellites. Their surveys of the geomagnetic field have been used to derive and improve global spherical harmonic (SH) models through some strict data selection schemes to minimise external field contributions. But discrepancies remain between ground measurements and field predictions by these models. Indeed, the global models do not reproduce small spatial scales of the field temporal variations. To overcome this problem we propose a modified Virtual Observatory (VO) approach by defining a globally homogeneous mesh of VOs at satellite altitude. With this approach we directly extract time series of the field and its temporal variation from satellite measurements as it is done at observatory locations. As satellite measurements are acquired at different altitudes a correction for the altitude is needed. Therefore, we apply an Equivalent Source Dipole (ESD) technique for each VO and each given time interval to reduce all measurements to a unique location, leading to time series similar to those available at ground magnetic observatories. Synthetic data is first used to validate the new VO-ESD approach. Then, we apply our scheme to measurements from the Swarm mission. For the first time, a 2.5 degrees resolution global mesh of VO times series is built. The VO-ESD derived time series are locally compared to ground observations as well as to satellite-based model predictions. The approach is able to describe detailed temporal variations of the field at local scales. The VO-ESD time series are also used to derive global SH models. Without regularization these models describe well the secular trend of the magnetic field. The derivation of longer VO-ESD time series, as more data will be made available, will allow the study of field temporal variations features such as geomagnetic jerks.

Tropical rainforests dominate multi-decadal variability of the global carbon cycle

NASA Astrophysics Data System (ADS)

Zhang, X.; Wang, Y. P.; Peng, S.; Rayner, P. J.; Silver, J.; Ciais, P.; Piao, S.; Zhu, Z.; Lu, X.; Zheng, X.

2017-12-01

Recent studies find that inter-annual variability of global atmosphere-to-land CO2 uptake (NBP) is dominated by semi-arid ecosystems. However, the NBP variations at decadal to multi-decadal timescales are still not known. By developing a basic theory for the role of net primary production (NPP) and heterotrophic respiration (Rh) on NBP and applying it to 100-year simulations of terrestrial ecosystem models forced by observational climate, we find that tropical rainforests dominate the multi-decadal variability of global NBP (48%) rather than the semi-arid lands (35%). The NBP variation at inter-annual timescales is almost 90% contributed by NPP, but across longer timescales is progressively controlled by Rh that constitutes the response from the NPP-derived soil carbon input (40%) and the response of soil carbon turnover rates to climate variability (60%). The NBP variations of tropical rainforests is modulated by the ENSO and the PDO through their significant influences on temperature and precipitation at timescales of 2.5-7 and 25-50 years, respectively. This study highlights the importance of tropical rainforests on the multi-decadal variability of global carbon cycle, suggesting that we need to carefully differentiate the effect of NBP long-term fluctuations associated with ocean-related climate modes on the long-term trend in land sink.

Long-term variability of T Tauri stars using WASP

NASA Astrophysics Data System (ADS)

Rigon, Laura; Scholz, Alexander; Anderson, David; West, Richard

2017-03-01

We present a reference study of the long-term optical variability of young stars using data from the WASP project. Our primary sample is a group of well-studied classical T Tauri stars (CTTSs), mostly in Taurus-Auriga. WASP light curves cover time-scales of up to 7 yr and typically contain 10 000-30 000 data points. We quantify the variability as a function of time-scale using the time-dependent standard deviation 'pooled sigma'. We find that the overwhelming majority of CTTSs have a low-level variability with σ < 0.3 mag dominated by time-scales of a few weeks, consistent with rotational modulation. Thus, for most young stars, monitoring over a month is sufficient to constrain the total amount of variability over time-scales of up to a decade. The fraction of stars with a strong optical variability (σ > 0.3 mag) is 21 per cent in our sample and 21 per cent in an unbiased control sample. An even smaller fraction (13 per cent in our sample, 6 per cent in the control) show evidence for an increase in variability amplitude as a function of time-scale from weeks to months or years. The presence of long-term variability correlates with the spectral slope at 3-5 μm, which is an indicator of inner disc geometry, and with the U-B band slope, which is an accretion diagnostics. This shows that the long-term variations in CTTSs are predominantly driven by processes in the inner disc and in the accretion zone. Four of the stars with long-term variations show periods of 20-60 d, significantly longer than the rotation periods and stable over months to years. One possible explanation is cyclic changes in the interaction between the disc and the stellar magnetic field.

Reviews and syntheses: Four decades of modeling methane cycling in terrestrial ecosystems

DOE PAGES

Xu, Xiaofeng; Yuan, Fengming; Hanson, Paul J.; ...

2016-01-28

A number of numerical models have been developed to quantify the magnitude, over the past 4 decades, such that we have investigated the spatial and temporal variations, and understand the underlying mechanisms and environmental controls of methane (CH 4) fluxes within terrestrial ecosystems. These CH 4 models are also used for integrating multi-scale CH 4 data, such as laboratory-based incubation and molecular analysis, field observational experiments, remote sensing, and aircraft-based measurements across a variety of terrestrial ecosystems. Here we summarize 40 terrestrial CH 4 models to characterize their strengths and weaknesses and to suggest a roadmap for future model improvementmore » and application. Our key findings are that (1) the focus of CH 4 models has shifted from theoretical to site- and regional-level applications over the past 4 decades, (2) large discrepancies exist among models in terms of representing CH 4 processes and their environmental controls, and (3) significant data–model and model–model mismatches are partially attributed to different representations of landscape characterization and inundation dynamics. Furthermore three areas for future improvements and applications of terrestrial CH 4 models are that (1) CH 4 models should more explicitly represent the mechanisms underlying land–atmosphere CH 4 exchange, with an emphasis on improving and validating individual CH 4 processes over depth and horizontal space, (2) models should be developed that are capable of simulating CH 4 emissions across highly heterogeneous spatial and temporal scales, particularly hot moments and hotspots, and (3) efforts should be invested to develop model benchmarking frameworks that can easily be used for model improvement, evaluation, and integration with data from molecular to global scales. Finally, these improvements in CH 4 models would be beneficial for the Earth system models and further simulation of climate–carbon cycle feedbacks.« less

El Niño, Climate and Societies

NASA Astrophysics Data System (ADS)

Haug, G. H.; Peterson, L. C.; Yancheva, G.

2010-03-01

One tropical climate archive with an appropriate memory for the societal most relevant sub-centennial to sub-decadal scale climate swings is the anoxic Cariaco Basin off northern Venezuela. Millimeter to micrometer-scale geochemical data in the laminated sediments of the Cariaco Basin have been interpreted to reflect variations in the hydrological cycle and the mean annual position of the Intertropical Convergence Zone (ITCZ) over tropical South America during the past millennia. These data with decadal to (sub)annual resolution show that the Terminal Collapse of the Classic Maya civilization occurred during an extended dry period. In detail, the Cariaco record reveals evidence for three separate droughts during the period of Maya downfall, each lasting a decade or less. These data suggest that climate change was potentially one immediate cause of the demise of Mayan civilization, with a century-scale decline in rainfall putting a general strain on resources and several multi-year events of more intense drought pushing Mayan society over the edge. An archive of comparable quality and resolution are sediments of lake Huguang Maar in coastal southeast China. The titanium content and redox-sensitive magnetic properties record the strength of winter monsoon winds at subdecadal resolution over the last 16 thousand years. The record indicates a stronger winter monsoon prior to the Bølling Allerød warming, during the Younger Dryas, and during the middle and late Holocene, when cave stalagmite oxygen isotope data indicate a weaker summer monsoon. The anti-correlation between winter and summer monsoon strength is best explained by migrations in the ITCZ that occurred simultaneously in central America and Africa. Drought associated with southward ITCZ migration may have played a role in the termination of several Chinese dynasties. A remarkable similarity of ITCZ migration in east Asia and the Americas from 700 to 900 AD raises the possibility that the coincident declines of the important Tang Dynasty in China and the Classic Maya in Central America were catalyzed by the same ITCZ migrations.

ACRIM3 and the Total Solar Irradiance database

NASA Astrophysics Data System (ADS)

Willson, Richard C.

2014-08-01

The effects of scattering and diffraction on the observations of the ACRIMSAT/ACRIM3 satellite TSI monitoring mission have been characterized by the preflight calibration approach for satellite total solar irradiance (TSI) sensors implemented at the LASP/TRF (Laboratory for Atmospheric and Space Physics/Total Solar Irradiance Radiometer Facility). The TRF also calibrates the SI (International System of units) traceability to the NIST (National Institute of Standards and Technology) cryo-radiometric scale. ACRIM3's self-calibration agrees with NIST to within the uncertainty of the test procedure (˜500 ppm). A correction of ˜5000 ppm was found for scattering and diffraction that has significantly reduced the scale difference between the results of the ACRIMSAT/ACRIM3 and SORCE/TIM satellite experiments. Algorithm updates reflecting more than 10 years of mission experience have been made that further improve the ACRIM3 results by eliminating some thermally driven signal and increasing the signal to noise ratio. The result of these changes is a more precise and detailed picture of TSI variability. Comparison of the results from the ACRIM3, SORCE/TIM and SOHO/VIRGO satellite experiments demonstrate the near identical detection of TSI variability on all sub-annual temporal and amplitude scales during the TIM mission. The largest occurs at the rotational period of the primary solar activity longitudes. On the decadal timescale, while ACRIM3 and VIRGO results exhibit close agreement throughout, TIM exhibits a consistent 500 ppm upward trend relative to ACRIM3 and VIRGO. A solar magnetic activity area proxy for TSI has been used to demonstrate that the ACRIM TSI composite and its +0.037 %/decade TSI trend during solar cycles 21-23 is the most likely correct representation of the extant satellite TSI database. The occurrence of this trend during the last decades of the 20th century supports a more robust contribution of TSI variation to detected global temperature increase during this period than predicted by current climate models.

Long-Term ENSO Variation Over the Last 20,000 Years From the Peru Continental Margin

NASA Astrophysics Data System (ADS)

Skilbeck, G.; Fink, D.; Gagan, M.; Rein, B.

2006-12-01

Three ODP Leg 201 cores from the Peru continental margin comprise highly laminated diatomaceous ooze spanning Last Glacial Maximum to present. Geochemical proxy data, layer counting and spectral analysis of red color variation suggest the layers represent interannual accumulation under the influence tropical ENSO conditions, with darker layers representing El Niño events. AMS 14-C dating (Skilbeck &Fink, 2006) of bulk sediment from Sites 201-1228 and -1229 (~11°S) and comparison with Rein et al. (2005) Core SO147-106KL (~12°S) show that where the shelf is narrow south of ~10.5°S, regionally consistent rates of sediment accumulation have occurred over the late Deglaciation and Holocene, with high rates characterising the late (0-2.0 kyrBP, ~100 cm/ka) and the early (8.5-10 kyrBP, ~80 cm/ka) Holocene. Over these intervals laminae are of interannual resolution. Further north where the shelf is broader, Holocene-Late Deglaciation sediments are thin or absent, but the Early Deglaciation is well represented. In a core from ODP Site 201-1227 (~9°S, 427m water depth), the period 15.5-17.5 kyrBP is characterised by sediment accumulation rates in excess of 300 cm/ka, and interannual laminations are again present. Spectral analysis of the instrumental record of ENSO, the SOI, shows a relative stable mode of variation with an average frequency of about 5.5 yr for the past 130 years. Analysis of our ODP cores shows that the ENSO mode appears to be relatively stable for periods of 300-500 years throughout the Holocene with frequencies varying mostly between 5 and 8 years and relatively sudden mode switches, suggesting inter alia that the instrumental record is not long enough to test predictive models of ENSO variation. Throughout the Holocene, this pattern of variation transcends the sedimentation-rate zones identified above, with the inference that changes in the rate of sedimentation have not influenced the temporal pattern. The later part of the deglaciation period (10-14 kyrBP) appears to be a relatively long period of stable ENSO with a repeat frequency between 5 and 6 years. Layer variation over the interval between 14 to 15.5 yrBP loses interannual variability and is characterised by a dominant frequency of ~11-12 yr, but this may simply reflect the low sedimentation rate during this interval. During Early Deglaciation interannual- to decadal-scale layer variability is present, with over 600 discernable laminae recognisable across the ~1600 year interval represented in Core 210-1227B. ENSO during this time has multiple interannual frequency modes ranging between 4 and 10 yr, particularly over the interval 17.2- 16.2 kyrBP, with mode switches slightly more frequent than during the Holocene at between 200 and 300 years. In addition to the interannual laminations and the centennial-scale pattern of frequency mode variation described above, there is a regular oscillatory pattern in the contrast between dark and light laminations which can be traced to parasequence-like packets of laminations on a centimetre scale, and representing variability in the decadal to centennial range. References Rein, B., A. Luckge, et al. (2005). Paleoceanography 20(PA4003): 17p. Skilbeck, C.G. &D. Fink (2005). ODP Scientific Results 201.

Introduction to the Special Issue on Advancing Methods for Analyzing Dialect Variation.

PubMed

Clopper, Cynthia G

2017-07-01

Documenting and analyzing dialect variation is traditionally the domain of dialectology and sociolinguistics. However, modern approaches to acoustic analysis of dialect variation have their roots in Peterson and Barney's [(1952). J. Acoust. Soc. Am. 24, 175-184] foundational work on the acoustic analysis of vowels that was published in the Journal of the Acoustical Society of America (JASA) over 6 decades ago. Although Peterson and Barney (1952) were not primarily concerned with dialect variation, their methods laid the groundwork for the acoustic methods that are still used by scholars today to analyze vowel variation within and across languages. In more recent decades, a number of methodological advances in the study of vowel variation have been published in JASA, including work on acoustic vowel overlap and vowel normalization. The goal of this special issue was to honor that tradition by bringing together a set of papers describing the application of emerging acoustic, articulatory, and computational methods to the analysis of dialect variation in vowels and beyond.

Forecasting seasonal hydrologic response in major river basins

NASA Astrophysics Data System (ADS)

Bhuiyan, A. M.

2014-05-01

Seasonal precipitation variation due to natural climate variation influences stream flow and the apparent frequency and severity of extreme hydrological conditions such as flood and drought. To study hydrologic response and understand the occurrence of extreme hydrological events, the relevant forcing variables must be identified. This study attempts to assess and quantify the historical occurrence and context of extreme hydrologic flow events and quantify the relation between relevant climate variables. Once identified, the flow data and climate variables are evaluated to identify the primary relationship indicators of hydrologic extreme event occurrence. Existing studies focus on developing basin-scale forecasting techniques based on climate anomalies in El Nino/La Nina episodes linked to global climate. Building on earlier work, the goal of this research is to quantify variations in historical river flows at seasonal temporal-scale, and regional to continental spatial-scale. The work identifies and quantifies runoff variability of major river basins and correlates flow with environmental forcing variables such as El Nino, La Nina, sunspot cycle. These variables are expected to be the primary external natural indicators of inter-annual and inter-seasonal patterns of regional precipitation and river flow. Relations between continental-scale hydrologic flows and external climate variables are evaluated through direct correlations in a seasonal context with environmental phenomenon such as sun spot numbers (SSN), Southern Oscillation Index (SOI), and Pacific Decadal Oscillation (PDO). Methods including stochastic time series analysis and artificial neural networks are developed to represent the seasonal variability evident in the historical records of river flows. River flows are categorized into low, average and high flow levels to evaluate and simulate flow variations under associated climate variable variations. Results demonstrated not any particular method is suited to represent scenarios leading to extreme flow conditions. For selected flow scenarios, the persistence model performance may be comparable to more complex multivariate approaches, and complex methods did not always improve flow estimation. Overall model performance indicates inclusion of river flows and forcing variables on average improve model extreme event forecasting skills. As a means to further refine the flow estimation, an ensemble forecast method is implemented to provide a likelihood-based indication of expected river flow magnitude and variability. Results indicate seasonal flow variations are well-captured in the ensemble range, therefore the ensemble approach can often prove efficient in estimating extreme river flow conditions. The discriminant prediction approach, a probabilistic measure to forecast streamflow, is also adopted to derive model performance. Results show the efficiency of the method in terms of representing uncertainties in the forecasts.

Towards the 1 mm/y stability of the radial orbit error at regional scales

NASA Astrophysics Data System (ADS)

Couhert, Alexandre; Cerri, Luca; Legeais, Jean-François; Ablain, Michael; Zelensky, Nikita P.; Haines, Bruce J.; Lemoine, Frank G.; Bertiger, William I.; Desai, Shailen D.; Otten, Michiel

2015-01-01

An estimated orbit error budget for the Jason-1 and Jason-2 GDR-D solutions is constructed, using several measures of orbit error. The focus is on the long-term stability of the orbit time series for mean sea level applications on a regional scale. We discuss various issues related to the assessment of radial orbit error trends; in particular this study reviews orbit errors dependent on the tracking technique, with an aim to monitoring the long-term stability of all available tracking systems operating on Jason-1 and Jason-2 (GPS, DORIS, SLR). The reference frame accuracy and its effect on Jason orbit is assessed. We also examine the impact of analysis method on the inference of Geographically Correlated Errors as well as the significance of estimated radial orbit error trends versus the time span of the analysis. Thus a long-term error budget of the 10-year Jason-1 and Envisat GDR-D orbit time series is provided for two time scales: interannual and decadal. As the temporal variations of the geopotential remain one of the primary limitations in the Precision Orbit Determination modeling, the overall accuracy of the Jason-1 and Jason-2 GDR-D solutions is evaluated through comparison with external orbits based on different time-variable gravity models. This contribution is limited to an East-West “order-1” pattern at the 2 mm/y level (secular) and 4 mm level (seasonal), over the Jason-2 lifetime. The possibility of achieving sub-mm/y radial orbit stability over interannual and decadal periods at regional scales and the challenge of evaluating such an improvement using in situ independent data is discussed.

Towards the 1 mm/y Stability of the Radial Orbit Error at Regional Scales

NASA Technical Reports Server (NTRS)

Couhert, Alexandre; Cerri, Luca; Legeais, Jean-Francois; Ablain, Michael; Zelensky, Nikita P.; Haines, Bruce J.; Lemoine, Frank G.; Bertiger, William I.; Desai, Shailen D.; Otten, Michiel

2015-01-01

An estimated orbit error budget for the Jason-1 and Jason-2 GDR-D solutions is constructed, using several measures of orbit error. The focus is on the long-term stability of the orbit time series for mean sea level applications on a regional scale. We discuss various issues related to the assessment of radial orbit error trends; in particular this study reviews orbit errors dependent on the tracking technique, with an aim to monitoring the long-term stability of all available tracking systems operating on Jason-1 and Jason-2 (GPS, DORIS, SLR). The reference frame accuracy and its effect on Jason orbit is assessed. We also examine the impact of analysis method on the inference of Geographically Correlated Errors as well as the significance of estimated radial orbit error trends versus the time span of the analysis. Thus a long-term error budget of the 10-year Jason-1 and Envisat GDR-D orbit time series is provided for two time scales: interannual and decadal. As the temporal variations of the geopotential remain one of the primary limitations in the Precision Orbit Determination modeling, the overall accuracy of the Jason-1 and Jason-2 GDR-D solutions is evaluated through comparison with external orbits based on different time-variable gravity models. This contribution is limited to an East-West "order-1" pattern at the 2 mm/y level (secular) and 4 mm level (seasonal), over the Jason-2 lifetime. The possibility of achieving sub-mm/y radial orbit stability over interannual and decadal periods at regional scales and the challenge of evaluating such an improvement using in situ independent data is discussed.

Towards the 1 mm/y Stability of the Radial Orbit Error at Regional Scales

NASA Technical Reports Server (NTRS)

Couhert, Alexandre; Cerri, Luca; Legeais, Jean-Francois; Ablain, Michael; Zelensky, Nikita P.; Haines, Bruce J.; Lemoine, Frank G.; Bertiger, William I.; Desai, Shailen D.; Otten, Michiel

2014-01-01

An estimated orbit error budget for the Jason-1 and Jason-2 GDR-D solutions is constructed, using several measures of orbit error. The focus is on the long-term stability of the orbit time series for mean sea level applications on a regional scale. We discuss various issues related to the assessment of radial orbit error trends; in particular this study reviews orbit errors dependent on the tracking technique, with an aim to monitoring the long-term stability of all available tracking systems operating on Jason-1 and Jason-2 (GPS, DORIS,SLR). The reference frame accuracy and its effect on Jason orbit is assessed. We also examine the impact of analysis method on the inference of Geographically Correlated Errors as well as the significance of estimated radial orbit error trends versus the time span of the analysis. Thus a long-term error budget of the 10-year Jason-1 and Envisat GDR-D orbit time series is provided for two time scales: interannual and decadal. As the temporal variations of the geopotential remain one of the primary limitations in the Precision Orbit Determination modeling, the overall accuracy of the Jason-1 and Jason-2 GDR-D solutions is evaluated through comparison with external orbits based on different time-variable gravity models. This contribution is limited to an East-West "order-1" pattern at the 2 mm/y level (secular) and 4 mm level (seasonal), over the Jason-2 lifetime. The possibility of achieving sub-mm/y radial orbit stability over interannual and decadal periods at regional scales and the challenge of evaluating such an improvement using in situ independent data is discussed.

The Footprint of the Inter-decadal Pacific Oscillation in Indian Ocean Sea Surface Temperatures

NASA Astrophysics Data System (ADS)

Dong, Lu; Zhou, Tianjun; Dai, Aiguo; Song, Fengfei; Wu, Bo; Chen, Xiaolong

2016-02-01

Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871-2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcings account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO’s cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. The decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.

The Footprint of the Inter-decadal Pacific Oscillation in Indian Ocean Sea Surface Temperatures.

PubMed

Dong, Lu; Zhou, Tianjun; Dai, Aiguo; Song, Fengfei; Wu, Bo; Chen, Xiaolong

2016-02-17

Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871-2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcings account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO's cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. The decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.

Is long-term ecological functioning stable: The case of the marine benthos?

NASA Astrophysics Data System (ADS)

Frid, C. L. J.; Caswell, B. A.

2015-04-01

It is widely acknowledged that human activities are contributing to substantial biodiversity loss and that this threatens ecological processes underpinning human exploitation of 'ecosystem services' (defined by the Millennium Ecosystem Assessment as 'the benefits people obtain from ecosystems'). In the present study we consider three 'intermediate ecosystem services' in both contemporary and ancient marine systems and although 'ecosystem services' per se did not exist in the Jurassic our study seeks to consider the future provision of these services and so the term is retained. We consider the temporal patterns in benthic marine ecosystems: (1) spanning four decades at two offshore stations in the North Sea, UK and (2) over millennial scales in Late Jurassic UK palaeocommunities. Biological traits analysis is used to link changes in taxonomic composition to variations in ecological functioning and the potential supply of three 'intermediate' ecosystem services: the ability to provide food to fish and other predators, benthic nutrient regeneration and carbon cycling. We examine whether changes in taxonomic composition drive temporal variation in functioning, whether this variation increases over time and the extent to which species turnover is comparable in contemporary and ancient systems. Taxonomic variability was of a similar magnitude in all three systems and there was evidence for changes in functioning linked to changes in several (key or rivet) taxa. During other periods resilience maintained functioning in the face of taxonomic change. These results suggest that in these benthic systems the Biodiversity-Ecosystem Functioning relationship is idiosyncratic, but a degree of temporal stability in functioning is maintained such that the ecosystem services they underpin would also be stable during decadal and longer-term changes.

Temperature variations in Greenland from 10 to 110 kyr b2k derived from the NGRIP ice core

NASA Astrophysics Data System (ADS)

Kindler, Philippe; Leuenberger, Markus; Landais, Amaelle; Guillevic, Myriam

2013-04-01

During the last ice age dramatic temperature variations of up to 16 °C took place in Greenland which are now known as Dansgaard-Oeschger-events (DO-events). They most probably originate from the North Atlantic oceanic and atmospheric circulation system and are characterised by an abrupt warming within decades followed by a gradual cooling over hundreds to thousands of years. We have determined local temperature variations for DO-event 1 to 25 in Greenland based on δ15N measurements from the NorthGRIP ice core, corresponding to the period from 10 to 110 kyr b2k. The record is a composite of measurements from two laboratories, Laboratoire des Sciences du Climat et de l'Environnement, Paris (DO 18 to 25) and the Climate and Environmental Physics Division of the Physics Institute of the University of Bern (DO 1 to 17) with new measurements from the beginning of the Holocene to DO 8. Temperature variations were reconstructed by reproducing the measured 15N/14N ratio of air enclosed in ice bubbles by the firn densification and heat diffusion model from Schwander. The reconstruction show temperature amplitudes for the DO-events ranging from 5 to 16 °C, thereby the corresponding rates of change can exceed 0.5 °C/decade. In order get an agreement between measured δ15N, Δdepth and Δage values with their modelled analogues, a lower accumulation rate than the one associated with the used ss09sea06bm1 time scale had to be assumed. We had to reduce the accumulation rate time dependently by 0 to nearly 40% with a mean reduction over the whole time period of 16%. With these adjustments both the Δdepth and the Δage values agree between model and measurements.

Similar Processes but Different Environmental Filters for Soil Bacterial and Fungal Community Composition Turnover on a Broad Spatial Scale

PubMed Central

Chemidlin Prévost-Bouré, Nicolas; Dequiedt, Samuel; Thioulouse, Jean; Lelièvre, Mélanie; Saby, Nicolas P. A.; Jolivet, Claudy; Arrouays, Dominique; Plassart, Pierre; Lemanceau, Philippe; Ranjard, Lionel

2014-01-01

Spatial scaling of microorganisms has been demonstrated over the last decade. However, the processes and environmental filters shaping soil microbial community structure on a broad spatial scale still need to be refined and ranked. Here, we compared bacterial and fungal community composition turnovers through a biogeographical approach on the same soil sampling design at a broad spatial scale (area range: 13300 to 31000 km2): i) to examine their spatial structuring; ii) to investigate the relative importance of environmental selection and spatial autocorrelation in determining their community composition turnover; and iii) to identify and rank the relevant environmental filters and scales involved in their spatial variations. Molecular fingerprinting of soil bacterial and fungal communities was performed on 413 soils from four French regions of contrasting environmental heterogeneity (Landes

Similar processes but different environmental filters for soil bacterial and fungal community composition turnover on a broad spatial scale.

PubMed

Chemidlin Prévost-Bouré, Nicolas; Dequiedt, Samuel; Thioulouse, Jean; Lelièvre, Mélanie; Saby, Nicolas P A; Jolivet, Claudy; Arrouays, Dominique; Plassart, Pierre; Lemanceau, Philippe; Ranjard, Lionel

2014-01-01

Spatial scaling of microorganisms has been demonstrated over the last decade. However, the processes and environmental filters shaping soil microbial community structure on a broad spatial scale still need to be refined and ranked. Here, we compared bacterial and fungal community composition turnovers through a biogeographical approach on the same soil sampling design at a broad spatial scale (area range: 13300 to 31000 km2): i) to examine their spatial structuring; ii) to investigate the relative importance of environmental selection and spatial autocorrelation in determining their community composition turnover; and iii) to identify and rank the relevant environmental filters and scales involved in their spatial variations. Molecular fingerprinting of soil bacterial and fungal communities was performed on 413 soils from four French regions of contrasting environmental heterogeneity (Landes

Understanding variation in human fertility: what can we learn from evolutionary demography?

PubMed

Sear, Rebecca; Lawson, David W; Kaplan, Hillard; Shenk, Mary K

2016-04-19

Decades of research on human fertility has presented a clear picture of how fertility varies, including its dramatic decline over the last two centuries in most parts of the world. Why fertility varies, both between and within populations, is not nearly so well understood. Fertility is a complex phenomenon, partly physiologically and partly behaviourally determined, thus an interdisciplinary approach is required to understand it. Evolutionary demographers have focused on human fertility since the 1980s. The first wave of evolutionary demographic research made major theoretical and empirical advances, investigating variation in fertility primarily in terms of fitness maximization. Research focused particularly on variation within high-fertility populations and small-scale subsistence societies and also yielded a number of hypotheses for why fitness maximization seems to break down as fertility declines during the demographic transition. A second wave of evolutionary demography research on fertility is now underway, paying much more attention to the cultural and psychological mechanisms underpinning fertility. It is also engaging with the complex, multi-causal nature of fertility variation, and with understanding fertility in complex modern and transitioning societies. Here, we summarize the history of evolutionary demographic work on human fertility, describe the current state of the field, and suggest future directions. © 2016 The Author(s).

Understanding variation in human fertility: what can we learn from evolutionary demography?

PubMed Central

Sear, Rebecca; Lawson, David W.; Kaplan, Hillard

2016-01-01

Decades of research on human fertility has presented a clear picture of how fertility varies, including its dramatic decline over the last two centuries in most parts of the world. Why fertility varies, both between and within populations, is not nearly so well understood. Fertility is a complex phenomenon, partly physiologically and partly behaviourally determined, thus an interdisciplinary approach is required to understand it. Evolutionary demographers have focused on human fertility since the 1980s. The first wave of evolutionary demographic research made major theoretical and empirical advances, investigating variation in fertility primarily in terms of fitness maximization. Research focused particularly on variation within high-fertility populations and small-scale subsistence societies and also yielded a number of hypotheses for why fitness maximization seems to break down as fertility declines during the demographic transition. A second wave of evolutionary demography research on fertility is now underway, paying much more attention to the cultural and psychological mechanisms underpinning fertility. It is also engaging with the complex, multi-causal nature of fertility variation, and with understanding fertility in complex modern and transitioning societies. Here, we summarize the history of evolutionary demographic work on human fertility, describe the current state of the field, and suggest future directions. PMID:27022071

Stable isotope series from elephant ivory reveal lifetime histories of a true dietary generalist

PubMed Central

Codron, Jacqueline; Codron, Daryl; Sponheimer, Matt; Kirkman, Kevin; Duffy, Kevin J.; Raubenheimer, Erich J.; Mélice, Jean-Luc; Grant, Rina; Clauss, Marcus; Lee-Thorp, Julia A.

2012-01-01

Longitudinal studies have revealed how variation in resource use within consumer populations can impact their dynamics and functional significance in communities. Here, we investigate multi-decadal diet variations within individuals of a keystone megaherbivore species, the African elephant (Loxodonta africana), using serial stable isotope analysis of tusks from the Kruger National Park, South Africa. These records, representing the longest continuous diet histories documented for any extant species, reveal extensive seasonal and annual variations in isotopic—and hence dietary—niches of individuals, but little variation between them. Lack of niche distinction across individuals contrasts several recent studies, which found relatively high levels of individual niche specialization in various taxa. Our result is consistent with theory that individual mammal herbivores are nutritionally constrained to maintain broad diet niches. Individual diet specialization would also be a costly strategy for large-bodied taxa foraging over wide areas in spatio-temporally heterogeneous environments. High levels of within-individual diet variability occurred within and across seasons, and persisted despite an overall increase in inferred C4 grass consumption through the twentieth century. We suggest that switching between C3 browsing and C4 grazing over extended time scales facilitates elephant survival through environmental change, and could even allow recovery of overused resources. PMID:22337695

Stable isotope series from elephant ivory reveal lifetime histories of a true dietary generalist.

PubMed

Codron, Jacqueline; Codron, Daryl; Sponheimer, Matt; Kirkman, Kevin; Duffy, Kevin J; Raubenheimer, Erich J; Mélice, Jean-Luc; Grant, Rina; Clauss, Marcus; Lee-Thorp, Julia A

2012-06-22

Longitudinal studies have revealed how variation in resource use within consumer populations can impact their dynamics and functional significance in communities. Here, we investigate multi-decadal diet variations within individuals of a keystone megaherbivore species, the African elephant (Loxodonta africana), using serial stable isotope analysis of tusks from the Kruger National Park, South Africa. These records, representing the longest continuous diet histories documented for any extant species, reveal extensive seasonal and annual variations in isotopic--and hence dietary--niches of individuals, but little variation between them. Lack of niche distinction across individuals contrasts several recent studies, which found relatively high levels of individual niche specialization in various taxa. Our result is consistent with theory that individual mammal herbivores are nutritionally constrained to maintain broad diet niches. Individual diet specialization would also be a costly strategy for large-bodied taxa foraging over wide areas in spatio-temporally heterogeneous environments. High levels of within-individual diet variability occurred within and across seasons, and persisted despite an overall increase in inferred C(4) grass consumption through the twentieth century. We suggest that switching between C(3) browsing and C(4) grazing over extended time scales facilitates elephant survival through environmental change, and could even allow recovery of overused resources.

Decadal fluctuations in the western Pacific recorded by long precipitation records in Taiwan

NASA Astrophysics Data System (ADS)

Huang, Wan-Ru; Wang, S.-Y. Simon; Guan, Biing T.

2018-03-01

A 110-year precipitation record in Taiwan, located at the western edge of the subtropical North Pacific, depicts a pronounced quasi-decadal oscillation (QDO). The QDO in Taiwan exhibits a fluctuating relationship with the similar decadal variations of sea surface temperature (SST) anomalies in the central equatorial Pacific, known as the Pacific QDO. A regime change was observed around 1960, such that the decadal variation of Taiwan's precipitation became more synchronized with the Pacific QDO's coupled evolutions of SST and atmospheric circulation than before, while the underlying pattern of the Pacific QOD did not change. Using long-term reanalysis data and CMIP5 single-forcing experiments, the presented analysis suggests that increased SST in the subtropical western Pacific and the strengthened western extension of the North Pacific subtropical anticyclone may have collectively enhanced the relationship between the Taiwan precipitation and the Pacific QDO. This finding provides possible clues to similar regime changes in quasi-decadal variability observed around the western Pacific rim.

Regional hydro-climatic impacts of contemporary Amazonian deforestation

NASA Astrophysics Data System (ADS)

Khanna, Jaya

More than 17% of the Amazon rainforest has been cleared in the past three decades triggering important climatological and societal impacts. This thesis is devoted to identifying and explaining the regional hydroclimatic impacts of this change employing multidecadal satellite observations and numerical simulations providing an integrated perspective on this topic. The climatological nature of this study motivated the implementation and application of a cloud detection technique to a new geostationary satellite dataset. The resulting sub daily, high spatial resolution, multidecadal time series facilitated the detection of trends and variability in deforestation triggered cloud cover changes. The analysis was complemented by satellite precipitation, reanalysis and ground based datasets and attribution with the variable resolution Ocean-Land-Atmosphere-Model. Contemporary Amazonian deforestation affects spatial scales of hundreds of kilometers. But, unlike the well-studied impacts of a few kilometers scale deforestation, the climatic response to contemporary, large scale deforestation is neither well observed nor well understood. Employing satellite datasets, this thesis shows a transition in the regional hydroclimate accompanying increasing scales of deforestation, with downwind deforested regions receiving 25% more and upwind deforested regions receiving 25% less precipitation from the deforested area mean. Simulations robustly reproduce these shifts when forced with increasing deforestation alone, suggesting a negligible role of large-scale decadal climate variability in causing the shifts. Furthermore, deforestation-induced surface roughness variations are found necessary to reproduce the observed spatial patterns in recent times illustrating the strong scale-sensitivity of the climatic response to Amazonian deforestation. This phenomenon, inconsequential during the wet season, is found to substantially affect the regional hydroclimate in the local dry and parts of transition seasons, hence occurring in atmospheric conditions otherwise less conducive to thermal convection. Evidence of this phenomenon is found at two large scale deforested areas considered in this thesis. Hence, the 'dynamical' mechanism, which affects the seasons most important for regional ecology, emerges as an impactful convective triggering mechanism. The phenomenon studied in this thesis provides context for thinking about the climate of a future, more patchily forested Amazonia, by articulating relationships between climate and spatial scales of deforestation.

Sea surface temperature variability in the Gulf of Mexico from 1734-2008 CE: A reconstruction using cross-dated Sr/Ca records from the coral Siderastrea siderea

NASA Astrophysics Data System (ADS)

DeLong, K. L.; Flannery, J. A.; Quinn, T. M.; Maupin, C. R.; Lin, K.; Shen, C.

2013-12-01

Sea surface temperature (SST) variability in the Gulf of Mexico impacts climate in Central and North America because the Gulf is a major source of moisture and is a source region for the Gulf Stream, which transports ocean heat northward. Here we use skeletal variations in coral Sr/Ca from three Siderastrea siderea coral colonies within the Dry Tortugas National Park in the southeastern Gulf of Mexico (24°42'N, 82°48'W) to develop 274 years of monthly-resolved SST variations. The cross-dated chronology, determined by counting annual density bands and correlating Sr/Ca variations, is verified by four replicated high precision 230Th dates (×1.7-37 years, 2σ). Calibration and verification of our replicated coral Sr/Ca-SST reconstruction with Dry Tortugas SST (r = 0.98 and 0.55 for monthly and 36-month smoothed, respectively; 1992-2008 CE) and Key West, Florida surface air temperature (1895-2008 CE) measurements reveals similar covariance (r = 0.96 and 0.56 for monthly and 36-month smoothed, respectively). The absolute coral SST reconstruction is consistent with SST recorded at the Dry Tortugas lighthouse from 1879-1907 CE indicating that this coral Sr/Ca-SST relationship is stable on centennial time scales. The Sr/Ca-SST reconstruction reveals ~2.0°C interannual variability, ~1.5°C decadal fluctuations, and a 0.7°C warming trend for the past 274 years. Secular variability in our reconstruction is similar to approximately decadally resolved planktic foraminifer Mg/Ca records from the northern Gulf of Mexico. The coral Sr/Ca-SST reconstruction reveals colder decades (~1.5°C) suggesting a reduction in moisture and ocean heat flux from the Gulf of Mexico. We find winter extremes are more variable than summer extremes (×2.2°C vs. ×1.6°C, 2σ) with a stronger warming trend (1°C) in the summers suggesting continued warming may increase coral bleaching.

Occurrence of major ozone episodes and their time-series trends over the past decade in New England

NASA Astrophysics Data System (ADS)

Lai, Tzu-Ling

The purpose of this dissertation was to examine the influence of meteorology on ozone (O3) magnitudes and variations over the past decade in the New England area. The major results are summarized as follows. First, the highest O3 episodes were driven by multi-scale processes, and the regional/local scale processes controlled the magnitude and timing of the local pollution episodes. For instance, the highest episode on 14 August 2002 at Thompson Farm (TF) was under a stagnant synoptic high-pressure which resulted in accumulation of pollutants in the boundary layer. Ozone mixing ratios in the 2002 episode showed continual high values (>100 ppbv) at the beginning of the episode, and reached 151 ppbv on August 14. At the same time, the mesoscale low-level-jet (LLJ) played an important role in transporting air masses from the polluted Mid-Atlantic areas to the Northeast. Local land-sea-breeze circulations also added to the impact on this episode. Another highest O 3 event on 22 July 2004 at Castle Springs (CS) was driven by two mechanisms, stratospheric intrusion and the Appalachian lee trough (APLT), which was not found during other O3 episodes at the site in the decade long data record. Second, decadal O3 trends revealed that daytime O 3 mixing ratios increased by ˜0.9 ppbv per year in spring and by ˜0.8 ppbv per year in winter, while it decreased by ˜0.2 ppbv per year in summer. The increasing O3 values in spring and winter coincided with warmer temperatures which increased +2.8 (°F/decade) in spring and +0.6 (°F/decade) in winter in New Hampshire (NH). Furthermore, trends in low-, medium-, and the daily maximum of O3 were increasing in both spring and winter with rates between 0.3 to 1.1 ppb per year. Summertime O3 trends either decreased or did not have significant changes. The decreasing summer O3 trends coincided with a weakening of the Bermuda High. Overall, average O3 exhibited higher O3 mixing ratios in spring than in other seasons. However, the highest episodes occurred in summer. Average diurnal patterns indicated that O3 was reduced to its lowest mixing ratios in summer during nighttime, with the strongest O 3 depletion in September.

Asynchronous emergence by loggerhead turtle (Caretta caretta) hatchlings

NASA Astrophysics Data System (ADS)

Houghton, J. D. R.; Hays, G. C.

2001-03-01

For many decades it has been accepted that marine turtle hatchlings from the same nest generally emerge from the sand together. However, for loggerhead turtles (Caretta caretta) nesting on the Greek Island of Kefalonia, a more asynchronous pattern of emergence has been documented. By placing temperature loggers at the top and bottom of nests laid on Kefalonia during 1998, we examined whether this asynchronous emergence was related to the thermal conditions within nests. Pronounced thermal variation existed not only between, but also within, individual nests. These within-nest temperature differences were related to the patterns of hatchling emergence, with hatchlings from nests displaying large thermal ranges emerging over a longer time-scale than those characterised by more uniform temperatures.

Stratospheric ozone as viewed from the Chappuis band. [long term pollution monitoring

NASA Technical Reports Server (NTRS)

Angione, R. J.; Medeiros, E. J.; Roosen, R. G.

1976-01-01

Total stratospheric ozone values above high-altitude stations in southern California from 1912 to 1950 and northern Chile from 1918 to 1948 are determined using data obtained by the Smithsonian Astrophysical Observatory, including transmission measurements made in the Chappuis band (0.5 to 0.7 micron). The results show that at both sites, total ozone amounts commonly exhibit variations of as much as 20% to 30% on time scales ranging from months to decades. Consideration of the amount of incident solar energy absorbed by the Chappuis band suggests that ozone acts as a shutter on the incoming solar radiation and provides a trigger mechanism between solar activity and climatic change.

Multidecadal Variability in Surface Albedo Feedback Across CMIP5 Models

NASA Astrophysics Data System (ADS)

Schneider, Adam; Flanner, Mark; Perket, Justin

2018-02-01

Previous studies quantify surface albedo feedback (SAF) in climate change, but few assess its variability on decadal time scales. Using the Coupled Model Intercomparison Project Version 5 (CMIP5) multimodel ensemble data set, we calculate time evolving SAF in multiple decades from surface albedo and temperature linear regressions. Results are meaningful when temperature change exceeds 0.5 K. Decadal-scale SAF is strongly correlated with century-scale SAF during the 21st century. Throughout the 21st century, multimodel ensemble mean SAF increases from 0.37 to 0.42 W m-2 K-1. These results suggest that models' mean decadal-scale SAFs are good estimates of their century-scale SAFs if there is at least 0.5 K temperature change. Persistent SAF into the late 21st century indicates ongoing capacity for Arctic albedo decline despite there being less sea ice. If the CMIP5 multimodel ensemble results are representative of the Earth, we cannot expect decreasing Arctic sea ice extent to suppress SAF in the 21st century.

Characteristics of variations of climate change and atmospheric CO2 concentration at different time scales over the past 500 Ma

NASA Astrophysics Data System (ADS)

LIU, Z.; Huang, S. S. X. E. C.; Tang, X.

2015-12-01

It is generally believed that current global warming is due to the persistent rise of atmospheric greenhouse gas CO2. The consensus is based mostly on the observational data of past decades and the polar ice core records. To understand the relationship between climate change and atmospheric CO2, their behaviors over a longer interval at different time scales need to be appreciated. Here, we collect and analyze past 500 Ma records of atmospheric CO2 and temperature in six time periods, namely Phanerozoic, Cenozoic, middle Pleistocene, last deglaciation, past millennium, and recent decades. According to the carriers and time spans, we divide these records into three categories: 1.The millionaire and longer records from model calculation and paleosols/paleobotany proxies. Although the trends of both variables are generally consistent on this time scale, it is difficult to establish a clear causal relationship because of great uncertainties and low resolutions of both sets of data. 2.The orbital scale mainly from the polar ice core. High precise CO2 and temperature reconstructions allow for an examination of the possible role of atmospheric CO2 in the glacial-interglacial transformation. 3.The records at centennial and shorter time scales over the past millennium from ice, snow, and instrumental data. The past millennium records are most abundant and accurate, especially CO2 has been measured directly in recent decades. However, due to the difficulties in distinguishing the effect of CO2 from other factors, there are great uncertainties in the interpretation of climate change versus CO2. Overall, we come to the following conclusions:1.Paleoclimatic reconstructions show that both temperature and atmospheric CO2 have generally decreased over the past 500 Ma. However, there are no consistent sequential orders in the changes between these two variables. 2.The Earth's atmospheric CO2 has a drastic oscillation history. There were many high CO2 periods when the values were higher than 5000 ppm, and there are several low CO2 periods when the values dropped to less than 100 ppm. 3.According to global observational data, atmospheric CO2 has recently exceeded 400 ppm. Although there is no conclusive evidence that shows this value has a special significance, it is the highest since the last 800 ka, and rare over the Quaternary.

Orogen-scale uplift in the central Italian Apennines drives episodic behaviour of earthquake faults

PubMed Central

Cowie, P. A.; Phillips, R. J.; Roberts, G. P.; McCaffrey, K.; Zijerveld, L. J. J.; Gregory, L. C.; Faure Walker, J.; Wedmore, L. N. J.; Dunai, T. J.; Binnie, S. A.; Freeman, S. P. H. T.; Wilcken, K.; Shanks, R. P.; Huismans, R. S.; Papanikolaou, I.; Michetti, A. M.; Wilkinson, M.

2017-01-01

Many areas of the Earth’s crust deform by distributed extensional faulting and complex fault interactions are often observed. Geodetic data generally indicate a simpler picture of continuum deformation over decades but relating this behaviour to earthquake occurrence over centuries, given numerous potentially active faults, remains a global problem in hazard assessment. We address this challenge for an array of seismogenic faults in the central Italian Apennines, where crustal extension and devastating earthquakes occur in response to regional surface uplift. We constrain fault slip-rates since ~18 ka using variations in cosmogenic 36Cl measured on bedrock scarps, mapped using LiDAR and ground penetrating radar, and compare these rates to those inferred from geodesy. The 36Cl data reveal that individual faults typically accumulate meters of displacement relatively rapidly over several thousand years, separated by similar length time intervals when slip-rates are much lower, and activity shifts between faults across strike. Our rates agree with continuum deformation rates when averaged over long spatial or temporal scales (104 yr; 102 km) but over shorter timescales most of the deformation may be accommodated by <30% of the across-strike fault array. We attribute the shifts in activity to temporal variations in the mechanical work of faulting. PMID:28322311

Orogen-scale uplift in the central Italian Apennines drives episodic behaviour of earthquake faults.

PubMed

Cowie, P A; Phillips, R J; Roberts, G P; McCaffrey, K; Zijerveld, L J J; Gregory, L C; Faure Walker, J; Wedmore, L N J; Dunai, T J; Binnie, S A; Freeman, S P H T; Wilcken, K; Shanks, R P; Huismans, R S; Papanikolaou, I; Michetti, A M; Wilkinson, M

2017-03-21

Many areas of the Earth's crust deform by distributed extensional faulting and complex fault interactions are often observed. Geodetic data generally indicate a simpler picture of continuum deformation over decades but relating this behaviour to earthquake occurrence over centuries, given numerous potentially active faults, remains a global problem in hazard assessment. We address this challenge for an array of seismogenic faults in the central Italian Apennines, where crustal extension and devastating earthquakes occur in response to regional surface uplift. We constrain fault slip-rates since ~18 ka using variations in cosmogenic 36 Cl measured on bedrock scarps, mapped using LiDAR and ground penetrating radar, and compare these rates to those inferred from geodesy. The 36 Cl data reveal that individual faults typically accumulate meters of displacement relatively rapidly over several thousand years, separated by similar length time intervals when slip-rates are much lower, and activity shifts between faults across strike. Our rates agree with continuum deformation rates when averaged over long spatial or temporal scales (10 4  yr; 10 2  km) but over shorter timescales most of the deformation may be accommodated by <30% of the across-strike fault array. We attribute the shifts in activity to temporal variations in the mechanical work of faulting.

Variations in the Relationship Between Precipitation and Tree Growth in the North-Central Rocky Mountains Identified Using a Tree-Ring Network

NASA Astrophysics Data System (ADS)

Wise, E.

2007-12-01

Much of the western United States is in the midst of a multi-year drought that has placed a renewed sense of urgency on water availability issues. The characterization of variability over relevant space and time scales has emerged as one of the top needs concerning the hydrological cycle, but understanding hydroclimatic variability at decadal and longer time scales has been limited by instrumental data that are both spatially and temporally inadequate. The reconstruction of moisture variables from tree-rings has been recognized as an important source of information on long-term water supply variability. Moisture variables of interest may include annual precipitation, snowpack, summer precipitation, and streamflow. Trees in closely co-located sites can vary widely in the signal they reflect, particularly in a region with the complex topography and hydroclimatic variability that is seen in the north-central Rocky Mountains. In this study, climatic and geospatial information was combined with tree-ring chronologies in order to better-understand factors determining variations in the response of tree growth to a particular precipitation signal. Resulting spatial variability in moisture seasonality and growth response provide insight into the region's moisture patterns and better characterization of the region's hydroclimatic variability.

A century of variation in the dependence of Greenland iceberg calving on ice sheet surface mass balance and regional climate change.

PubMed

Bigg, G R; Wei, H L; Wilton, D J; Zhao, Y; Billings, S A; Hanna, E; Kadirkamanathan, V

2014-06-08

Iceberg calving is a major component of the total mass balance of the Greenland ice sheet (GrIS). A century-long record of Greenland icebergs comes from the International Ice Patrol's record of icebergs (I48N) passing latitude 48° N, off Newfoundland. I48N exhibits strong interannual variability, with a significant increase in amplitude over recent decades. In this study, we show, through a combination of nonlinear system identification and coupled ocean-iceberg modelling, that I48N's variability is predominantly caused by fluctuation in GrIS calving discharge rather than open ocean iceberg melting. We also demonstrate that the episodic variation in iceberg discharge is strongly linked to a nonlinear combination of recent changes in the surface mass balance (SMB) of the GrIS and regional atmospheric and oceanic climate variability, on the scale of the previous 1-3 years, with the dominant causal mechanism shifting between glaciological (SMB) and climatic (ocean temperature) over time. We suggest that this is a change in whether glacial run-off or under-ice melting is dominant, respectively. We also suggest that GrIS calving discharge is episodic on at least a regional scale and has recently been increasing significantly, largely as a result of west Greenland sources.

Classification of Hot Stars by Disk Variability using Hα Line Emission Characteristics

NASA Astrophysics Data System (ADS)

Hoyt Hannah, Christian; Glennon Fagan, W.; Tycner, Christopher

2018-06-01

The variability associated with circumstellar disks around hot and massive stars has been observed on time scales ranging from less than a day to decades. Variations detected in line emission from circumstellar disks on long time scales are typically attributed to disk-growth and disk-loss events. However, in order to fully describe and model such phenomena, adequate spectroscopic observations over long time scales are needed. In this project, we conduct a comprehensive study that is based on spectra recorded over a 14-year period (2005 to 2018) of roughly 100 B-type stars. Using results from a representative sample of over 20 targets, we illustrate how the Hα emission line, one of the most prominent emission features from circumstellar disks, can be used to monitor the variability associated with these systems. Using high-resolution spectra, we utilize line emission characteristics such as equivalent width, peak strength(s), and line-width to setup a classification scheme that describes different types of variabilities. This in turn can be used to divide the systems in disk-growth, disk-loss, variable and stable categories. With additional numerical disk modeling, the recorded variations based on emission line characteristics can also be used to describe changes in disk temperature and density structure. The aim is to develop a tool to help further our understanding of the processes behind the production and eventual dissipation of the circumstellar disks found in hot stars. This work has been supported by NSF grant AST-1614983.

Quantifying predictability in a model with statistical features of the atmosphere

PubMed Central

Kleeman, Richard; Majda, Andrew J.; Timofeyev, Ilya

2002-01-01

The Galerkin truncated inviscid Burgers equation has recently been shown by the authors to be a simple model with many degrees of freedom, with many statistical properties similar to those occurring in dynamical systems relevant to the atmosphere. These properties include long time-correlated, large-scale modes of low frequency variability and short time-correlated “weather modes” at smaller scales. The correlation scaling in the model extends over several decades and may be explained by a simple theory. Here a thorough analysis of the nature of predictability in the idealized system is developed by using a theoretical framework developed by R.K. This analysis is based on a relative entropy functional that has been shown elsewhere by one of the authors to measure the utility of statistical predictions precisely. The analysis is facilitated by the fact that most relevant probability distributions are approximately Gaussian if the initial conditions are assumed to be so. Rather surprisingly this holds for both the equilibrium (climatological) and nonequilibrium (prediction) distributions. We find that in most cases the absolute difference in the first moments of these two distributions (the “signal” component) is the main determinant of predictive utility variations. Contrary to conventional belief in the ensemble prediction area, the dispersion of prediction ensembles is generally of secondary importance in accounting for variations in utility associated with different initial conditions. This conclusion has potentially important implications for practical weather prediction, where traditionally most attention has focused on dispersion and its variability. PMID:12429863

Studying Basin Water Balance Variations at Inter- and Intra-annual Time Scales Based On the Budyko Hypothesis and GRACE Gravimetry Satellite Observations

NASA Astrophysics Data System (ADS)

Shen, H.

2017-12-01

Increasing intensity in global warming and anthropogenic activities has triggered significant changes over regional climates and landscapes, which, in turn, drive the basin water cycle and hydrological balance into a complex and unstable state. Budyko hypothesis is a powerful tool to characterize basin water balance and hydrological variations at long-term average scale. However, due to the absence of basin water storage change, applications of Budyko theory to the inter-annual and intra-annual time scales has been prohibited. The launch of GRACE gavimetry satellites provides a great opportunity to quantify terrestrial water storage change, which can be further introduced into the Budyko hypothesis to reveal the inter- and intra-annual response of basin water components under impacts of climate variability and/or human activities. This research targeted Hai River Basin (in China) and Murray-Darling Basin (in Australia), which have been identified with a continuous groundwater depletion trend as well as impacts by extreme climates in the past decade. This can help us to explore how annual or seasonal precipitation were redistributed to evapotranspiration and runoff via changing basin water storage. Moreover, the impacts of vegetation on annual basin water balance will be re-examined. Our results are expected to provide deep insights about the water cycle and hydrological behaviors for the targeted basins, as well as a proof for a consideration of basin water storage change into the Budyko model at inter- or intra-annual time steps.

Temporal geochemical variations in lavas from Kīlauea's Pu`u `Ō`ō eruption (1983-2010): Cyclic variations from melting of source heterogeneities

NASA Astrophysics Data System (ADS)

Greene, Andrew R.; Garcia, Michael O.; Pietruszka, Aaron J.; Weis, Dominique; Marske, Jared P.; Vollinger, Michael J.; Eiler, John

2013-11-01

Geochemical time series analysis of lavas from Kīlauea's ongoing Pu`u `Ō`ō eruption chronicle mantle and crustal processes during a single, prolonged (1983 to present) magmatic event, which has shown nearly two-fold variation in lava effusion rates. Here we present an update of our ongoing monitoring of the geochemical variations of Pu`u `Ō`ō lavas for the entire eruption through 2010. Oxygen isotope measurements on Pu`u `Ō`ō lavas show a remarkable range (δ18O values of 4.6-5.6‰), which are interpreted to reflect moderate levels of oxygen isotope exchange with or crustal contamination by hydrothermally altered Kīlauea lavas, probably in the shallow reservoir under the Pu`u `Ō`ō vent. This process has not measurably affected ratios of radiogenic isotope or incompatible trace elements, which are thought to vary due to mantle-derived changes in the composition of the parental magma delivered to the volcano. High-precision Pb and Sr isotopic measurements were performed on lavas erupted at ˜6 month intervals since 1983 to provide insights about melting dynamics and the compositional structure of the Hawaiian plume. The new results show systematic variations of Pb and Sr isotope ratios that continued the long-term compositional trend for Kīlauea until ˜1990. Afterward, Pb isotope ratios show two cycles with ˜10 year periods, whereas the Sr isotope ratios continued to increase until ˜2003 and then shifted toward slightly less radiogenic values. The short-term periodicity of Pb isotope ratios may reflect melt extraction from mantle with a fine-scale pattern of repeating source heterogeneities or strands, which are about 1-3 km in diameter. Over the last 30 years, Pu`u `Ō`ō lavas show 15% and 25% of the known isotopic variation for Kīlauea and Mauna Kea, respectively. This observation illustrates that the dominant time scale of mantle-derived compositional variation for Hawaiian lavas is years to decades.

The impact of climate change on ozone-related mortality in Sydney.

PubMed

Physick, William; Cope, Martin; Lee, Sunhee

2014-01-13

Coupled global, regional and chemical transport models are now being used with relative-risk functions to determine the impact of climate change on human health. Studies have been carried out for global and regional scales, and in our paper we examine the impact of climate change on ozone-related mortality at the local scale across an urban metropolis (Sydney, Australia). Using three coupled models, with a grid spacing of 3 km for the chemical transport model (CTM), and a mortality relative risk function of 1.0006 per 1 ppb increase in daily maximum 1-hour ozone concentration, we evaluated the change in ozone concentrations and mortality between decades 1996-2005 and 2051-2060. The global model was run with the A2 emissions scenario. As there is currently uncertainty regarding a threshold concentration below which ozone does not impact on mortality, we calculated mortality estimates for the three daily maximum 1-hr ozone concentration thresholds of 0, 25 and 40 ppb. The mortality increase for 2051-2060 ranges from 2.3% for a 0 ppb threshold to 27.3% for a 40 ppb threshold, although the numerical increases differ little. Our modeling approach is able to identify the variation in ozone-related mortality changes at a suburban scale, estimating that climate change could lead to an additional 55 to 65 deaths across Sydney in the decade 2051-2060. Interestingly, the largest increases do not correspond spatially to the largest ozone increases or the densest population centres. The distribution pattern of changes does not seem to vary with threshold value, while the magnitude only varies slightly.

Tree Rings Show Recent High Summer-Autumn Precipitation in Northwest Australia Is Unprecedented within the Last Two Centuries

PubMed Central

O'Donnell, Alison J.; Cook, Edward R.; Palmer, Jonathan G.; Turney, Chris S. M.; Page, Gerald F. M.; Grierson, Pauline F.

2015-01-01

An understanding of past hydroclimatic variability is critical to resolving the significance of recent recorded trends in Australian precipitation and informing climate models. Our aim was to reconstruct past hydroclimatic variability in semi-arid northwest Australia to provide a longer context within which to examine a recent period of unusually high summer-autumn precipitation. We developed a 210-year ring-width chronology from Callitris columellaris, which was highly correlated with summer-autumn (Dec–May) precipitation (r = 0.81; 1910–2011; p < 0.0001) and autumn (Mar–May) self-calibrating Palmer drought severity index (scPDSI, r = 0.73; 1910–2011; p < 0.0001) across semi-arid northwest Australia. A linear regression model was used to reconstruct precipitation and explained 66% of the variance in observed summer-autumn precipitation. Our reconstruction reveals inter-annual to multi-decadal scale variation in hydroclimate of the region during the last 210 years, typically showing periods of below average precipitation extending from one to three decades and periods of above average precipitation, which were often less than a decade. Our results demonstrate that the last two decades (1995–2012) have been unusually wet (average summer-autumn precipitation of 310 mm) compared to the previous two centuries (average summer-autumn precipitation of 229 mm), coinciding with both an anomalously high frequency and intensity of tropical cyclones in northwest Australia and the dominance of the positive phase of the Southern Annular Mode. PMID:26039148

Tree Rings Show Recent High Summer-Autumn Precipitation in Northwest Australia Is Unprecedented within the Last Two Centuries.

PubMed

O'Donnell, Alison J; Cook, Edward R; Palmer, Jonathan G; Turney, Chris S M; Page, Gerald F M; Grierson, Pauline F

2015-01-01

An understanding of past hydroclimatic variability is critical to resolving the significance of recent recorded trends in Australian precipitation and informing climate models. Our aim was to reconstruct past hydroclimatic variability in semi-arid northwest Australia to provide a longer context within which to examine a recent period of unusually high summer-autumn precipitation. We developed a 210-year ring-width chronology from Callitris columellaris, which was highly correlated with summer-autumn (Dec-May) precipitation (r = 0.81; 1910-2011; p < 0.0001) and autumn (Mar-May) self-calibrating Palmer drought severity index (scPDSI, r = 0.73; 1910-2011; p < 0.0001) across semi-arid northwest Australia. A linear regression model was used to reconstruct precipitation and explained 66% of the variance in observed summer-autumn precipitation. Our reconstruction reveals inter-annual to multi-decadal scale variation in hydroclimate of the region during the last 210 years, typically showing periods of below average precipitation extending from one to three decades and periods of above average precipitation, which were often less than a decade. Our results demonstrate that the last two decades (1995-2012) have been unusually wet (average summer-autumn precipitation of 310 mm) compared to the previous two centuries (average summer-autumn precipitation of 229 mm), coinciding with both an anomalously high frequency and intensity of tropical cyclones in northwest Australia and the dominance of the positive phase of the Southern Annular Mode.

Decoupling of unpolluted temperate forests from rock nutrient sources revealed by natural (87)Sr/(86)Sr and (84)Sr tracer addition.

PubMed

Kennedy, Martin J; Hedin, Lars O; Derry, Louis A

2002-07-23

An experimental tracer addition of (84)Sr to an unpolluted temperate forest site in southern Chile, as well as the natural variation of (87)Sr/(86)Sr within plants and soils, indicates that mechanisms in shallow soil organic horizons are of key importance for retaining and recycling atmospheric cation inputs at scales of decades or less. The dominant tree species Nothofagus nitida feeds nearly exclusively (>90%) on cations of atmospheric origin, despite strong variations in tree size and location in the forest landscape. Our results illustrate that (i) unpolluted temperate forests can become nutritionally decoupled from deeper weathering processes, virtually functioning as atmospherically fed ecosystems, and (ii) base cation turnover times are considerably more rapid than previously recognized in the plant available pool of soil. These results challenge the prevalent paradigm that plants largely feed on rock-derived cations and have important implications for understanding sensitivity of forests to air pollution.

Impact of Ice Ages on the genetic structure of trees and shrubs.

PubMed Central

Lascoux, Martin; Palmé, Anna E; Cheddadi, Rachid; Latta, Robert G

2004-01-01

Data on the genetic structure of tree and shrub populations on the continental scale have accumulated dramatically over the past decade. However, our ability to make inferences on the impact of the last ice age still depends crucially on the availability of informative palaeoecological data. This is well illustrated by the results from a recent project, during which new pollen fossil maps were established and the variation in chloroplast DNA was studied in 22 European species of trees and shrubs. Species exhibit very different levels of genetic variation between and within populations, and obviously went through very different histories after Ice Ages. However, when palaeoecological data are non-informative, inferences on past history are difficult to draw from entirely genetic data. On the other hand, as illustrated by a study in ponderosa pine, when we can infer the species' history with some certainty, coalescent simulations can be used and new hypotheses can be tested. PMID:15101576

Middle atmosphere dynamical sources of the semiannual oscillation in the thermosphere and ionosphere

NASA Astrophysics Data System (ADS)

Jones, M.; Emmert, J. T.; Drob, D. P.; Siskind, D. E.

2017-01-01

The strong global semiannual oscillation (SAO) in thermospheric density has been observed for five decades, but definitive knowledge of its source has been elusive. We use the National Center of Atmospheric Research thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) to study how middle atmospheric dynamics generate the SAO in the thermosphere-ionosphere (T-I). The "standard" TIME-GCM simulates, from first principles, SAOs in thermospheric mass density and ionospheric total electron content that agree well with observed climatological variations. Diagnosis of the globally averaged continuity equation for atomic oxygen ([O]) shows that the T-I SAO originates in the upper mesosphere, where an SAO in [O] is forced by nonlinear, resolved-scale variations in the advective, net tidal, and diffusive transport of O. Contrary to earlier hypotheses, TIME-GCM simulations demonstrate that intra-annually varying eddy diffusion by breaking gravity waves may not be the primary driver of the T-I SAO: A pronounced SAO is produced without parameterized gravity waves.

Solar Cycle Fine Structure and Surface Rotation from Ca II K-Line Time Series Data

NASA Technical Reports Server (NTRS)

Scargle, Jeff; Keil, Steve; Worden, Pete

2011-01-01

Analysis of three and a half decades of data from the NSO/AFRL/Sac Peak K-line monitoring program yields evidence for four components to the variation: (a) the solar cycle, with considerable fine structure and a quasi-periodicity of 122.4 days; (b) a stochastic process, faster than (a) and largely independent of it, (c) a quasi-periodic signal due to rotational modulation, and of course (d) observational errors (shown to be quite small). Correlation and power spectrum analyses elucidate periodic and aperiodic variation of these chromospheric parameters. Time-frequency analysis is especially useful for extracting information about differential rotation, and in particular elucidates the connection between its behavior and fine structure of the solar cycle on approximately one-year time scales. These results further suggest that similar analyses will be useful at detecting and characterizing differential rotation in stars from stellar light-curves such as those being produced at NASA's Kepler observatory.

A photometric study of the nova-like variable TT Arietis with the MOST satellite

NASA Astrophysics Data System (ADS)

Vogt, N.; Chené, A.-N.; Moffat, A. F. J.; Matthews, J. M.; Kuschnig, R.; Guenther, D. B.; Rowe, J. F.; Rucinski, S. M.; Sasselov, D.; Weiss, W. W.

2013-12-01

Variability on all time scales between seconds and decades is typical for cataclysmic variables (CVs). One of the brightest and best studied CVs is TT Ari, a nova-like variable which belongs to the VY Scl subclass, characterized by occasional low states in their light curves. It is also known as a permanent superhumper at high state, revealing ``positive'' (PS> P0) as well as ``negative'' (PS< P0) superhumps, where PS is the period of the superhump and P0 the orbital period. TT Ari was observed by the Canadian space telescope MOST for about 230 hours nearly continuously in 2007, with a time resolution of 48 seconds. Here we analyze these data, obtaining a dominant ``negative'' superhump signal with a period PS = 0.1331 days and a mean amplitude of 0.09 mag. Strong flickering with amplitudes up to 0.2 mag and peak-to-peak time scales of 15-20 minutes is superimposed on the periodic variations. We found no indications for significant quasi-periodic oscillations with periods around 15 minutes, reported by other authors. We discuss the known superhump behaviour of TT Ari during the last five decades and conclude that our period value is at the upper limit of all hitherto determined ``negative'' superhump periods of TT Ari, before and after the MOST run.

The decreasing range between dry- and wet- season precipitation over land and its effect on vegetation primary productivity.

PubMed

Murray-Tortarolo, Guillermo; Jaramillo, Víctor J; Maass, Manuel; Friedlingstein, Pierre; Sitch, Stephen

2017-01-01

One consequence of climate change is the alteration of global water fluxes, both in amount and seasonality. As a result, the seasonal difference between dry- (p < 100 mm/month) and wet-season (p > 100 mm/month) precipitation (p) has increased over land during recent decades (1980-2005). However, our analysis expanding to a 60-year period (1950-2009) showed the opposite trend. This is, dry-season precipitation increased steadily, while wet-season precipitation remained constant, leading to reduced seasonality at a global scale. The decrease in seasonality was not due to a change in dry-season length, but in precipitation rate; thus, the dry season is on average becoming wetter without changes in length. Regionally, wet- and dry-season precipitations are of opposite sign, causing a decrease in the seasonal variation of the precipitation over 62% of the terrestrial ecosystems. Furthermore, we found a high correlation (r = 0.62) between the change in dry-season precipitation and the trend in modelled net primary productivity (NPP), which is explained based on different ecological mechanisms. This trend is not found with wet-season precipitation (r = 0.04), These results build on the argument that seasonal water availability has changed over the course of the last six decades and that the dry-season precipitation is a key driver of vegetation productivity at the global scale.

The decreasing range between dry- and wet- season precipitation over land and its effect on vegetation primary productivity

PubMed Central

2017-01-01

One consequence of climate change is the alteration of global water fluxes, both in amount and seasonality. As a result, the seasonal difference between dry- (p < 100 mm/month) and wet-season (p > 100 mm/month) precipitation (p) has increased over land during recent decades (1980–2005). However, our analysis expanding to a 60-year period (1950–2009) showed the opposite trend. This is, dry-season precipitation increased steadily, while wet-season precipitation remained constant, leading to reduced seasonality at a global scale. The decrease in seasonality was not due to a change in dry-season length, but in precipitation rate; thus, the dry season is on average becoming wetter without changes in length. Regionally, wet- and dry-season precipitations are of opposite sign, causing a decrease in the seasonal variation of the precipitation over 62% of the terrestrial ecosystems. Furthermore, we found a high correlation (r = 0.62) between the change in dry-season precipitation and the trend in modelled net primary productivity (NPP), which is explained based on different ecological mechanisms. This trend is not found with wet-season precipitation (r = 0.04), These results build on the argument that seasonal water availability has changed over the course of the last six decades and that the dry-season precipitation is a key driver of vegetation productivity at the global scale. PMID:29284050

More Intense Mega Heat Waves in the Warmer World

NASA Astrophysics Data System (ADS)

Choi, G.; Robinson, D. A.

2017-12-01

In this study, changes in the occurrences of heat waves on the globe since the mid- 20th century and the synoptic characteristics of mega heat waves at regional scales in the warmer climate are examined. The NCEP-NCAR reanalysis surface data show that there have been no obvious linear changes in the heat wave frequencies at the continental scales since the mid-20th century, but amplified interdecadal variations led to unprecedented intense heat waves in the recent decades at the regional scales. Such mega heat waves have been more frequently observed in the poleward subtropical climate belts as well as in the interior region of continents. According to the analyses of upper tropospheric data, the occurrences of more intense mega heat waves since the late 20th century may be associated with the expansion of subtropical high pressures. These results suggest that populous cities near the subtropical climate zones should provide proactive mega heat wave warning systems for residents due to their vulnerability to the sudden attack of human lives harvest by mega heat waves in the warmer 21st century.

An Experimental Study on Burning Characteristics of n-Heptane/Ethanol Mixture Pool Fires in a Reduced Scaled Tunnel

NASA Astrophysics Data System (ADS)

Yozgatligil, Ahmet; Shafee, Sina

2016-11-01

Fire accidents in recent decades have drawn attention to safety issues associated with the design, construction and maintenance of tunnels. A reduced scale tunnel model constructed based on Froude scaling technique is used in the current work. Mixtures of n-heptane and ethanol are burned with ethanol volumetric fraction up to 30 percent and the longitudinal ventilation velocity varying from 0.5 to 2.5 m/s. The burning rates of the pool fires are measured using a precision load cell. The heat release rates of the fires are calculated according to oxygen calorimetry method and the temperature distributions inside the tunnel are also measured. Results of the experiments show that the ventilation velocity variation has a significant effect on the pool fire burning rate, smoke temperature and the critical ventilation velocity. With increased oxygen depletion in case of increased ethanol content of blended pool fires, the quasi-steady heat release rate values tend to increase as well as the ceiling temperatures while the combustion duration decreases.

Sun, Ocean, Nuclear Bombs, and Fossil Fuels: Radiocarbon Variations and Implications for High-Resolution Dating

NASA Astrophysics Data System (ADS)

Dutta, Koushik

2016-06-01

Radiocarbon, or 14C, is a radiometric dating method ideally suited for providing a chronological framework in archaeology and geosciences for timescales spanning the last 50,000 years. 14C is easily detectable in most common natural organic materials and has a half-life (5,730±40 years) relevant to these timescales. 14C produced from large-scale detonations of nuclear bombs between the 1950s and the early 1960s can be used for dating modern organic materials formed after the 1950s. Often these studies demand high-resolution chronology to resolve ages within a few decades to less than a few years. Despite developments in modern, high-precision 14C analytical methods, the applicability of 14C in high-resolution chronology is limited by short-term variations in atmospheric 14C in the past. This article reviews the roles of the principal natural drivers (e.g., solar magnetic activity and ocean circulation) and the anthropogenic perturbations (e.g., fossil fuel CO2 and 14C from nuclear and thermonuclear bombs) that are responsible for short-term 14C variations in the environment. Methods and challenges of high-resolution 14C dating are discussed.

Cosmogenic isotope beryllium-7 in the atmosphere: Production versus transport

NASA Astrophysics Data System (ADS)

Pacini, Alessandra; Usoskin, Ilya; Evangelista, Heitor; Echer, Ezequiel; Mursula, Kalevi; Leppanen, Ari-Pekka

Cosmogenic isotope 7 Be measured near the ground can provide information about its produc-tion (that occurs in the atmosphere due to the interaction of cosmic rays and atmospheric constituents) and its deposition processes (that involves air mass dynamics, stratosphere-troposphere coupling and local climatic conditions). We present the results of an investigation of the atmospheric 7 Be temporal variations at different geographic locations (Finland and Brazil). This study was based on an analysis of three time series of 7 Be concentration measured in near-surface air samples from Rovaniemi and Loviisa (Finland) and Rio de Janeiro (Brazil) for the last decades. We made use of the wavelet spectral method to identify the frequency-temporal features of the 7 Be temporal variations that allowed us to determine the relative importance of production and deposition process for the observed data. By comparing these time series with climatic indices and the values of 7 Be concentration expected from the model for the same period, we found that the climate system is the main driver of the surface isotopic modulation, while the imprints of the production variations are geographically dependent. Thus,7 Be can be considered a good tool to monitor the large-scale air mass dynamics.

Large-scale disturbance legacies and the climate sensitivity of primary Picea abies forests.

PubMed

Schurman, Jonathan S; Trotsiuk, Volodymyr; Bače, Radek; Čada, Vojtěch; Fraver, Shawn; Janda, Pavel; Kulakowski, Dominik; Labusova, Jana; Mikoláš, Martin; Nagel, Thomas A; Seidl, Rupert; Synek, Michal; Svobodová, Kristýna; Chaskovskyy, Oleh; Teodosiu, Marius; Svoboda, Miroslav

2018-05-01

Determining the drivers of shifting forest disturbance rates remains a pressing global change issue. Large-scale forest dynamics are commonly assumed to be climate driven, but appropriately scaled disturbance histories are rarely available to assess how disturbance legacies alter subsequent disturbance rates and the climate sensitivity of disturbance. We compiled multiple tree ring-based disturbance histories from primary Picea abies forest fragments distributed throughout five European landscapes spanning the Bohemian Forest and the Carpathian Mountains. The regional chronology includes 11,595 tree cores, with ring dates spanning the years 1750-2000, collected from 560 inventory plots in 37 stands distributed across a 1,000 km geographic gradient, amounting to the largest disturbance chronology yet constructed in Europe. Decadal disturbance rates varied significantly through time and declined after 1920, resulting in widespread increases in canopy tree age. Approximately 75% of current canopy area recruited prior to 1900. Long-term disturbance patterns were compared to an historical drought reconstruction, and further linked to spatial variation in stand structure and contemporary disturbance patterns derived from LANDSAT imagery. Historically, decadal Palmer drought severity index minima corresponded to higher rates of canopy removal. The severity of contemporary disturbances increased with each stand's estimated time since last major disturbance, increased with mean diameter, and declined with increasing within-stand structural variability. Reconstructed spatial patterns suggest that high small-scale structural variability has historically acted to reduce large-scale susceptibility and climate sensitivity of disturbance. Reduced disturbance rates since 1920, a potential legacy of high 19th century disturbance rates, have contributed to a recent region-wide increase in disturbance susceptibility. Increasingly common high-severity disturbances throughout primary Picea forests of Central Europe should be reinterpreted in light of both legacy effects (resulting in increased susceptibility) and climate change (resulting in increased exposure to extreme events). © 2018 John Wiley & Sons Ltd.

Population-level consequences of herbivory, changing climate, and source-sink dynamics on a long-lived invasive shrub.

PubMed

van Klinken, R D; Pichancourt, J B

2015-12-01

Long-lived plant species are highly valued environmentally, economically, and socially, but can also cause substantial harm as invaders. Realistic demographic predictions can guide management decisions, and are particularly valuable for long-lived species where population response times can be long. Long-lived species are also challenging, given population dynamics can be affected by factors as diverse as herbivory, climate, and dispersal. We developed a matrix model to evaluate the effects of herbivory by a leaf-feeding biological control agent released in Australia against a long-lived invasive shrub (mesquite, Leguminoseae: Prosopis spp.). The stage-structured, density-dependent model used an annual time step and 10 climatically diverse years of field data. Mesquite population demography is sensitive to source-sink dynamics as most seeds are consumed and redistributed spatially by livestock. In addition, individual mesquite plants, because they are long lived, experience natural climate variation that cycles over decadal scales, as well as anthropogenic climate change. The model therefore explicitly considered the effects of both net dispersal and climate variation. Herbivory strongly regulated mesquite populations through reduced growth and fertility, but additional mortality of older plants will be required to reach management goals within a reasonable time frame. Growth and survival of seeds and seedlings were correlated with daily soil moisture. As a result, population dynamics were sensitive to rainfall scenario, but population response times were typically slow (20-800 years to reach equilibrium or extinction) due to adult longevity. Equilibrium population densities were expected to remain 5% higher, and be more dynamic, if historical multi-decadal climate patterns persist, the effect being dampened by herbivory suppressing seed production irrespective of preceding rainfall. Dense infestations were unlikely to form under a drier climate, and required net dispersal under the current climate. Seed input wasn't required to form dense infestations under a wetter climate. Each factor we considered (ongoing herbivory, changing climate, and source-sink dynamics) has a strong bearing on how this invasive species should be managed, highlighting the need for considering both ecological context (in this case, source-sink dynamics) and the effect of climate variability at relevant temporal scales (daily, multi-decadal, and anthropogenic) when deriving management recommendations for long-lived species.

The footprint of the inter-decadal Pacific oscillation in Indian Ocean sea surface temperatures

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

Dong, Lu; Zhou, Tianjun; Dai, Aiguo

Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871–2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcingsmore » account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO’s cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. As a result, the decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.« less

The footprint of the inter-decadal Pacific oscillation in Indian Ocean sea surface temperatures

DOE PAGES

Dong, Lu; Zhou, Tianjun; Dai, Aiguo; ...

2016-02-17

Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871–2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcingsmore » account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO’s cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. As a result, the decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.« less

Decadal shifts of East Asian summer monsoon in a climate model free of explicit GHGs and aerosols

NASA Astrophysics Data System (ADS)

Lin, Renping; Zhu, Jiang; Zheng, Fei

2016-12-01

The East Asian summer monsoon (EASM) experienced decadal transitions over the past few decades, and the associated "wetter-South-drier-North" shifts in rainfall patterns in China significantly affected the social and economic development in China. Two viewpoints stand out to explain these decadal shifts, regarding the shifts either a result of internal variability of climate system or that of external forcings (e.g. greenhouse gases (GHGs) and anthropogenic aerosols). However, most climate models, for example, the Atmospheric Model Intercomparison Project (AMIP)-type simulations and the Coupled Model Intercomparison Project (CMIP)-type simulations, fail to simulate the variation patterns, leaving the mechanisms responsible for these shifts still open to dispute. In this study, we conducted a successful simulation of these decadal transitions in a coupled model where we applied ocean data assimilation in the model free of explicit aerosols and GHGs forcing. The associated decadal shifts of the three-dimensional spatial structure in the 1990s, including the eastward retreat, the northward shift of the western Pacific subtropical high (WPSH), and the south-cool-north-warm pattern of the upper-level tropospheric temperature, were all well captured. Our simulation supports the argument that the variations of the oceanic fields are the dominant factor responsible for the EASM decadal transitions.

Decadal shifts of East Asian summer monsoon in a climate model free of explicit GHGs and aerosols

PubMed Central

Lin, Renping; Zhu, Jiang; Zheng, Fei

2016-01-01

The East Asian summer monsoon (EASM) experienced decadal transitions over the past few decades, and the associated "wetter-South-drier-North" shifts in rainfall patterns in China significantly affected the social and economic development in China. Two viewpoints stand out to explain these decadal shifts, regarding the shifts either a result of internal variability of climate system or that of external forcings (e.g. greenhouse gases (GHGs) and anthropogenic aerosols). However, most climate models, for example, the Atmospheric Model Intercomparison Project (AMIP)-type simulations and the Coupled Model Intercomparison Project (CMIP)-type simulations, fail to simulate the variation patterns, leaving the mechanisms responsible for these shifts still open to dispute. In this study, we conducted a successful simulation of these decadal transitions in a coupled model where we applied ocean data assimilation in the model free of explicit aerosols and GHGs forcing. The associated decadal shifts of the three-dimensional spatial structure in the 1990s, including the eastward retreat, the northward shift of the western Pacific subtropical high (WPSH), and the south-cool-north-warm pattern of the upper-level tropospheric temperature, were all well captured. Our simulation supports the argument that the variations of the oceanic fields are the dominant factor responsible for the EASM decadal transitions. PMID:27934933

Generating Vegetation Leaf Area Index Earth System Data Record from Multiple Sensors. Part 1; Theory

NASA Technical Reports Server (NTRS)

Ganguly, Sangram; Schull, Mitchell A.; Samanta, Arindam; Shabanov, Nikolay V.; Milesi, Cristina; Nemani, Ramakrishna R.; Knyazikhin, Yuri; Myneni, Ranga B.

2008-01-01

The generation of multi-decade long Earth System Data Records (ESDRs) of Leaf Area Index (LAI) and Fraction of Photosynthetically Active Radiation absorbed by vegetation (FPAR) from remote sensing measurements of multiple sensors is key to monitoring long-term changes in vegetation due to natural and anthropogenic influences. Challenges in developing such ESDRs include problems in remote sensing science (modeling of variability in global vegetation, scaling, atmospheric correction) and sensor hardware (differences in spatial resolution, spectral bands, calibration, and information content). In this paper, we develop a physically based approach for deriving LAI and FPAR products from the Advanced Very High Resolution Radiometer (AVHRR) data that are of comparable quality to the Moderate resolution Imaging Spectroradiometer (MODIS) LAI and FPAR products, thus realizing the objective of producing a long (multi-decadal) time series of these products. The approach is based on the radiative transfer theory of canopy spectral invariants which facilitates parameterization of the canopy spectral bidirectional reflectance factor (BRF). The methodology permits decoupling of the structural and radiometric components and obeys the energy conservation law. The approach is applicable to any optical sensor, however, it requires selection of sensor-specific values of configurable parameters, namely, the single scattering albedo and data uncertainty. According to the theory of spectral invariants, the single scattering albedo is a function of the spatial scale, and thus, accounts for the variation in BRF with sensor spatial resolution. Likewise, the single scattering albedo accounts for the variation in spectral BRF with sensor bandwidths. The second adjustable parameter is data uncertainty, which accounts for varying information content of the remote sensing measurements, i.e., Normalized Difference Vegetation Index (NDVI, low information content), vs. spectral BRF (higher information content). Implementation of this approach indicates good consistency in LAI values retrieved from NDVI (AVHRRmode) and spectral BRF (MODIS-mode). Specific details of the implementation and evaluation of the derived products are detailed in the second part of this two-paper series.

A 500-year seasonally resolved δ18O and δ13C, layer thickness and calcite aspect record from a speleothem deposited in the Han-sur-Lesse cave, Belgium

NASA Astrophysics Data System (ADS)

Van Rampelbergh, M.; Verheyden, S.; Allan, M.; Quinif, Y.; Cheng, H.; Edwards, L. R.; Keppens, E.; Claeys, P.

2015-06-01

Speleothem δ18O and δ13C signals enable climate reconstructions at high resolution. However, scarce decadal and seasonally resolved speleothem records are often difficult to interpret in terms of climate due to the multitude of factors that affect the proxy signals. In this paper, a fast-growing (up to 2 mm yr-1) seasonally laminated speleothem from the Han-sur-Lesse cave (Belgium) is analyzed for its δ18O and δ13C values, layer thickness and changes in calcite aspect. The studied record covers the period between AD 2001 and 1479 as indicated by layer counting and confirmed by 20 U / Th ages. The Proserpine proxies are seasonally biased and document drier (and colder) winters on multidecadal scales. Higher δ13C signals reflect increased prior calcite precipitation (PCP) and lower soil activity during drier (and colder) winters. Thinner layers and darker calcite relate to slower growth and exist during drier (and colder) winter periods. Exceptionally dry (and cold) winter periods occur from 1565 to 1610, at 1730, from 1770 to 1800, from 1810 to 1860, and from 1880 to 1895 and correspond to exceptionally cold periods in historical and instrumental records as well as European winter temperature reconstructions. More relative climate variations, during which the four measured proxies vary independently and display lower amplitude variations, occur between 1479 and 1565, between 1610 and 1730, and between 1730 and 1770. The winters during the first and last periods are interpreted as relatively wetter (and warmer) and correspond to warmer periods in historical data and in winter temperature reconstructions in Europe. The winters in the period between 1610 and 1730 are interpreted as relatively drier (and cooler) and correspond to generally colder conditions in Europe. Interpretation of the seasonal variations in δ18O and δ13C signals differs from that on a decadal and multidecadal scale. Seasonal δ18O variations reflect cave air temperature variations and suggest a 2.5 °C seasonality in cave air temperature during the two relatively wetter (and warmer) winter periods (1479-1565 and 1730-1770), which corresponds to the cave air temperature seasonality observed today. Between 1610 and 1730, the δ18O values suggest a 1.5 °C seasonality in cave air temperature, indicating colder summer temperatures during this drier (and cooler) interval. The δ13C seasonality is driven by PCP and suggests generally lower PCP seasonal effects between 1479 and 1810 compared to today. A short interval of increased PCP seasonality occurs between 1600 and 1660, and reflects increased PCP in summer due to decreased winter recharge.

Spatiotemporal patterns of drought at various time scales in Shandong Province of Eastern China

NASA Astrophysics Data System (ADS)

Zuo, Depeng; Cai, Siyang; Xu, Zongxue; Li, Fulin; Sun, Wenchao; Yang, Xiaojing; Kan, Guangyuan; Liu, Pin

2018-01-01

The temporal variations and spatial patterns of drought in Shandong Province of Eastern China were investigated by calculating the standardized precipitation evapotranspiration index (SPEI) at 1-, 3-, 6-, 12-, and 24-month time scales. Monthly precipitation and air temperature time series during the period 1960-2012 were collected at 23 meteorological stations uniformly distributed over the region. The non-parametric Mann-Kendall test was used to explore the temporal trends of precipitation, air temperature, and the SPEI drought index. S-mode principal component analysis (PCA) was applied to identify the spatial patterns of drought. The results showed that an insignificant decreasing trend in annual total precipitation was detected at most stations, a significant increase of annual average air temperature occurred at all the 23 stations, and a significant decreasing trend in the SPEI was mainly detected at the coastal stations for all the time scales. The frequency of occurrence of extreme and severe drought at different time scales generally increased with decades; higher frequency and larger affected area of extreme and severe droughts occurred as the time scale increased, especially for the northwest of Shandong Province and Jiaodong peninsular. The spatial pattern of drought for SPEI-1 contains three regions: eastern Jiaodong Peninsular and northwestern and southern Shandong. As the time scale increased to 3, 6, and 12 months, the order of the three regions was transformed into another as northwestern Shandong, eastern Jiaodong Peninsular, and southern Shandong. For SPEI-24, the location identified by REOF1 was slightly shifted from northwestern Shandong to western Shandong, and REOF2 and REOF3 identified another two weak patterns in the south edge and north edge of Jiaodong Peninsular, respectively. The potential causes of drought and the impact of drought on agriculture in the study area have also been discussed. The temporal variations and spatial patterns of drought obtained in this study provide valuable information for water resources planning and drought disaster prevention and mitigation in Eastern China.

On the use of satellite VEGETATION time series for monitoring post fire vegetation recovery

NASA Astrophysics Data System (ADS)

de Santis, F.; Didonna, I.

2009-04-01

Fire is one of the most critical factors of disturbance in worldwide ecosystems. The effects of fires on soil, plants, landscape and ecosystems depend on many factors, among them fire frequency, fire severity and plant resistance. The characterization of vegetation post-fire behaviour is a fundamental issue to model and evaluate the fire resilience, which the ability of vegetation to recover after fire. Recent changes in fire regime, due to abandonment of local land use practice and climate change, can induce significant variations in vegetation fire resilience. In the Mediterranean-type communities, post fire vegetation trends have been analysed in a wide range of habitats, although pre- and post-fire investigation has been widely performed at stand level. But, factors controlling regeneration at the landscape scale are less well known. In this study, a time series of normalized difference vegetation index (NDVI) data derived from SPOT-VEGETATION was used to examine the recovery characteristics of fire affected vegetation in some test areas of the Mediterranean ecosystems of Southern Italy. The vegetation indices operate by contrasting intense chlorophyll pigment absorption in the red against the high reflectance of leaf mesophyll in the near infrared. SPOT-VEGETATION Normalized Difference Vegetation Index (NDVI) data from 1998 to 2005 were analyzed in order to evaluate the resilient effects in a some significant test sites of southern Italy. In particular, we considered: (i) one stable area site, one site affected by one fire during the investigated time window, (iii) one site affected by two consecutive fires during the investigated time window. In order to eliminate the phenological fluctuations, for each decadal composition of each pixel, we focused on the departure NDVId = [NDVI - ]/, where is the decadal mean and  is the decadal standard deviation. The decadal mean and the standard deviation were calculated for each decade, e.g. 1st decade of January, by averaging over all years in the record. We analyzed both: 1) Time variation of NDVI from 1998 to 2005 of pixels for the fire affected and fire unaffected areas. 2) Post-fire NDVI spatial patterns on each image date were compared to the pre-fire pattern to determine the extent to which the pre-fire pattern was re-established, and the rate of this recovery. Results show the ability of vegetation to recovery after a single fire. Nevertheless, such ability can be strongly reduced by successive fires. The recursive fire occurrence can significantly diminish the green biomass especially when disturbances occur at short intervals of time.

Variations in Developmental Patterns across Pragmatic Features

ERIC Educational Resources Information Center

Li, Qiong

2016-01-01

Drawing on the findings of longitudinal studies in uninstructed contexts over the last two decades, this synthesis explores variations in developmental patterns across second language (L2) pragmatic features. Two synthesis questions were addressed: (a) What are the variations in developmental patterns across pragmatic features?, and (b) What are…

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

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

Han, Weiqing; Meehl, Gerald A.; Stammer, Detlef

Sea level rise (SLR) can exert significant stress on highly populated coastal societies and low-lying island countries around the world. Because of this, there is huge societal demand for improved decadal predictions and future projections of SLR, particularly on a local scale along coastlines. Regionally, sea level variations can deviate considerably from the global mean due to various geophysical processes. These include changes of ocean circulations, which partially can be attributed to natural, internal modes of variability in the complex Earth’s climate system. Anthropogenic influence may also contribute to regional sea level variations. Separating the effects of natural climate modesmore » and anthropogenic forcing, however, remains a challenge and requires identification of the imprint of specific climate modes in observed sea level change patterns. In this article, we review our current state of knowledge about spatial patterns of sea level variability associated with natural climate modes on interannual-to-multidecadal timescales, with particular focus on decadal-to-multidecadal variability. Relevant climate modes and our current state of understanding their associated sea level patterns and driving mechanisms are elaborated separately for the Pacific, the Indian, the Atlantic, and the Arctic and Southern Oceans. We also discuss the issues, challenges and future outlooks for understanding the regional sea level patterns associated with climate modes. Effects of these internal modes have to be taken into account in order to achieve more reliable near-term predictions and future projections of regional SLR.« less

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

DOE PAGES

Han, Weiqing; Meehl, Gerald A.; Stammer, Detlef; ...

2016-10-04

Sea level rise (SLR) can exert significant stress on highly populated coastal societies and low-lying island countries around the world. Because of this, there is huge societal demand for improved decadal predictions and future projections of SLR, particularly on a local scale along coastlines. Regionally, sea level variations can deviate considerably from the global mean due to various geophysical processes. These include changes of ocean circulations, which partially can be attributed to natural, internal modes of variability in the complex Earth’s climate system. Anthropogenic influence may also contribute to regional sea level variations. Separating the effects of natural climate modesmore » and anthropogenic forcing, however, remains a challenge and requires identification of the imprint of specific climate modes in observed sea level change patterns. In this article, we review our current state of knowledge about spatial patterns of sea level variability associated with natural climate modes on interannual-to-multidecadal timescales, with particular focus on decadal-to-multidecadal variability. Relevant climate modes and our current state of understanding their associated sea level patterns and driving mechanisms are elaborated separately for the Pacific, the Indian, the Atlantic, and the Arctic and Southern Oceans. We also discuss the issues, challenges and future outlooks for understanding the regional sea level patterns associated with climate modes. Effects of these internal modes have to be taken into account in order to achieve more reliable near-term predictions and future projections of regional SLR.« less

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

NASA Astrophysics Data System (ADS)

Han, Weiqing; Meehl, Gerald A.; Stammer, Detlef; Hu, Aixue; Hamlington, Benjamin; Kenigson, Jessica; Palanisamy, Hindumathi; Thompson, Philip

2017-01-01

Sea level rise (SLR) can exert significant stress on highly populated coastal societies and low-lying island countries around the world. Because of this, there is huge societal demand for improved decadal predictions and future projections of SLR, particularly on a local scale along coastlines. Regionally, sea level variations can deviate considerably from the global mean due to various geophysical processes. These include changes of ocean circulations, which partially can be attributed to natural, internal modes of variability in the complex Earth's climate system. Anthropogenic influence may also contribute to regional sea level variations. Separating the effects of natural climate modes and anthropogenic forcing, however, remains a challenge and requires identification of the imprint of specific climate modes in observed sea level change patterns. In this paper, we review our current state of knowledge about spatial patterns of sea level variability associated with natural climate modes on interannual-to-multidecadal timescales, with particular focus on decadal-to-multidecadal variability. Relevant climate modes and our current state of understanding their associated sea level patterns and driving mechanisms are elaborated separately for the Pacific, the Indian, the Atlantic, and the Arctic and Southern Oceans. We also discuss the issues, challenges and future outlooks for understanding the regional sea level patterns associated with climate modes. Effects of these internal modes have to be taken into account in order to achieve more reliable near-term predictions and future projections of regional SLR.

Growing season temperatures in Europe and climate forcings over the past 1400 years.

PubMed

Guiot, Joel; Corona, Christophe

2010-04-01

The lack of instrumental data before the mid-19th-century limits our understanding of present warming trends. In the absence of direct measurements, we used proxies that are natural or historical archives recording past climatic changes. A gridded reconstruction of spring-summer temperature was produced for Europe based on tree-rings, documentaries, pollen assemblages and ice cores. The majority of proxy series have an annual resolution. For a better inference of long-term climate variation, they were completed by low-resolution data (decadal or more), mostly on pollen and ice-core data. An original spectral analog method was devised to deal with this heterogeneous dataset, and to preserve long-term variations and the variability of temperature series. So we can replace the recent climate changes in a broader context of the past 1400 years. This preservation is possible because the method is not based on a calibration (regression) but on similarities between assemblages of proxies. The reconstruction of the April-September temperatures was validated with a Jack-knife technique. It was also compared to other spatially gridded temperature reconstructions, literature data, and glacier advance and retreat curves. We also attempted to relate the spatial distribution of European temperature anomalies to known solar and volcanic forcings. We found that our results were accurate back to 750. Cold periods prior to the 20(th) century can be explained partly by low solar activity and/or high volcanic activity. The Medieval Warm Period (MWP) could be correlated to higher solar activity. During the 20(th) century, however only anthropogenic forcing can explain the exceptionally high temperature rise. Warm periods of the Middle Age were spatially more heterogeneous than last decades, and then locally it could have been warmer. However, at the continental scale, the last decades were clearly warmer than any period of the last 1400 years. The heterogeneity of MWP versus the homogeneity of the last decades is likely an argument that different forcings could have operated. These results support the fact that we are living a climate change in Europe never seen in the past 1400 years.

Sedimentary records of trace elements from large European lakes (Switzerland) document historic to recent freshwater pollution and climate-induced runoff variations

NASA Astrophysics Data System (ADS)

Thevenon, F.; Wirth, S. B.; Fujak, M.; Poté, J.; Thierry, A.; Chiaradia, M.; Girardclos, S.

2011-12-01

Continuous sedimentary records of anthropogenic and natural trace elements determined by ICPMS, from 5 large and deep perialpine lakes from Central Europe (Switzerland), evidence the environmental impacts of industrial fossil fuel pollution. In fact, the greatest increase in heavy metal pollution was registered at all the studied sites following the European industrial revolution of ca. AD 1800; with the highest values during the middle part of the 20th century. On a regional scale, anthropogenic heavy metal input subsequently stopped increasing thanks to remediation strategies such as the implementation of wastewater treatment plants (WWTPs). On the other hand, the discharge of industrial treated wastewaters into Vidy Bay of Lake Geneva during the second part of the 20th century involved the sedimentation of highly contaminated sediments in the area surrounding the WWTP outlet pipe discharge; less than 4 km from the main supply of drinking water of Lausanne (127'000 hab.). Microbial analyses furthermore reveal i) high increase in bacterial densities following the lake eutrophication in the 1970s, and that ii) the related sediments can be considered as a reservoir of antibiotic resistant bacteria/genes (of human origin). We finally compare instrumental hydrological data over the last century with variations of lithogenic trace elements (e.g., titanium) as registered in three large lakes (Brienz, Thun and Bienne) connected by the River Aar. This task allows to better constraining the runoff variations on a regional scale over the last decades for the the River Aar, and its possible increase under warming climate conditions in the European Alps.

Monsoon climate response in Indian teak (Tectona grandis L.f.) along a transect from coast to inland

NASA Astrophysics Data System (ADS)

Sengupta, Saikat; Borgaonkar, Hemant; Joy, Reji Mariya; Ram, Somaru

2017-11-01

Indian monsoon (June-September) and post monsoon (October-November) rainfall show a distinct trend from coast to inland primarily due to moisture availability. However, the response of this synoptic-scale variation of rainfall amount to annual ring growth of Indian teak has not been studied systematically yet. The study is important as (1) ring width of Indian teak is considered as a reliable proxy for studying monsoon climate variability in multi-centennial time scale and (2) observed meteorological data show systematic changes in rainfall variation from coast to inland since last three decades. Towards this, we present here tree-ring width data from two locations—Thatibanda (1747-1979) and Nagzira (1728-2000) and use similar published data from two other locations—Allapalli (1866-1897) and Edugurapalli (1827-2000). The locations fall along a southeast northwest transect from south east Indian coast to inland. Monthly mean data from nearest observatories show an increasing trend in monsoon rainfall and a pronounced decreasing trend in post monsoon rainfall towards inland. Ring width data show moderately positive response to monsoon rainfall and negative response to summer (March-May) temperature for all stations suggesting moisture deficit in hot summer and intense precipitation in monsoon affect ring growth pattern in different ways. Ring width indices also exhibit significantly positive response with post monsoon rainfall at coastal location. The response gradually reduces towards inland. This preliminary study, thus, suggests that Indian teak has a potential to capture signals of the synoptic variation of post monsoon rainfall from coast to inland.

Mechanisms underlying recent decadal changes in subpolar North Atlantic Ocean heat content

NASA Astrophysics Data System (ADS)

Piecuch, Christopher G.; Ponte, Rui M.; Little, Christopher M.; Buckley, Martha W.; Fukumori, Ichiro

2017-09-01

The subpolar North Atlantic (SPNA) is subject to strong decadal variability, with implications for surface climate and its predictability. In 2004-2005, SPNA decadal upper ocean and sea-surface temperature trends reversed from warming during 1994-2004 to cooling over 2005-2015. This recent decadal trend reversal in SPNA ocean heat content (OHC) is studied using a physically consistent, observationally constrained global ocean state estimate covering 1992-2015. The estimate's physical consistency facilitates quantitative causal attribution of ocean variations. Closed heat budget diagnostics reveal that the SPNA OHC trend reversal is the result of heat advection by midlatitude ocean circulation. Kinematic decompositions reveal that changes in the deep and intermediate vertical overturning circulation cannot account for the trend reversal, but rather ocean heat transports by horizontal gyre circulations render the primary contributions. The shift in horizontal gyre advection reflects anomalous circulation acting on the mean temperature gradients. Maximum covariance analysis (MCA) reveals strong covariation between the anomalous horizontal gyre circulation and variations in the local wind stress curl, suggestive of a Sverdrup response. Results have implications for decadal predictability.

Form of an evolutionary tradeoff affects eco-evolutionary dynamics in a predator-prey system.

PubMed

Kasada, Minoru; Yamamichi, Masato; Yoshida, Takehito

2014-11-11

Evolution on a time scale similar to ecological dynamics has been increasingly recognized for the last three decades. Selection mediated by ecological interactions can change heritable phenotypic variation (i.e., evolution), and evolution of traits, in turn, can affect ecological interactions. Hence, ecological and evolutionary dynamics can be tightly linked and important to predict future dynamics, but our understanding of eco-evolutionary dynamics is still in its infancy and there is a significant gap between theoretical predictions and empirical tests. Empirical studies have demonstrated that the presence of genetic variation can dramatically change ecological dynamics, whereas theoretical studies predict that eco-evolutionary dynamics depend on the details of the genetic variation, such as the form of a tradeoff among genotypes, which can be more important than the presence or absence of the genetic variation. Using a predator-prey (rotifer-algal) experimental system in laboratory microcosms, we studied how different forms of a tradeoff between prey defense and growth affect eco-evolutionary dynamics. Our experimental results show for the first time to our knowledge that different forms of the tradeoff produce remarkably divergent eco-evolutionary dynamics, including near fixation, near extinction, and coexistence of algal genotypes, with quantitatively different population dynamics. A mathematical model, parameterized from completely independent experiments, explains the observed dynamics. The results suggest that knowing the details of heritable trait variation and covariation within a population is essential for understanding how evolution and ecology will interact and what form of eco-evolutionary dynamics will result.

Connecting theory and data to understand recombination rate evolution.

PubMed

Dapper, Amy L; Payseur, Bret A

2017-12-19

Meiotic recombination is necessary for successful gametogenesis in most sexually reproducing organisms and is a fundamental genomic parameter, influencing the efficacy of selection and the fate of new mutations. The molecular and evolutionary functions of recombination should impose strong selective constraints on the range of recombination rates. Yet, variation in recombination rate is observed on a variety of genomic and evolutionary scales. In the past decade, empirical studies have described variation in recombination rate within genomes, between individuals, between sexes, between populations and between species. At the same time, theoretical work has provided an increasingly detailed picture of the evolutionary advantages to recombination. Perhaps surprisingly, the causes of natural variation in recombination rate remain poorly understood. We argue that empirical and theoretical approaches to understand the evolution of recombination have proceeded largely independently of each other. Most models that address the evolution of recombination rate were created to explain the evolutionary advantage of recombination rather than quantitative differences in rate among individuals. Conversely, most empirical studies aim to describe variation in recombination rate, rather than to test evolutionary hypotheses. In this Perspective, we argue that efforts to integrate the rich bodies of empirical and theoretical work on recombination rate are crucial to moving this field forward. We provide new directions for the development of theory and the production of data that will jointly close this gap.This article is part of the themed issue 'Evolutionary causes and consequences of recombination rate variation in sexual organisms'. © 2017 The Author(s).

Spectral characteristics of background error covariance and multiscale data assimilation

DOE PAGES

Li, Zhijin; Cheng, Xiaoping; Gustafson, Jr., William I.; ...

2016-05-17

The steady increase of the spatial resolutions of numerical atmospheric and oceanic circulation models has occurred over the past decades. Horizontal grid spacing down to the order of 1 km is now often used to resolve cloud systems in the atmosphere and sub-mesoscale circulation systems in the ocean. These fine resolution models encompass a wide range of temporal and spatial scales, across which dynamical and statistical properties vary. In particular, dynamic flow systems at small scales can be spatially localized and temporarily intermittent. Difficulties of current data assimilation algorithms for such fine resolution models are numerically and theoretically examined. Ourmore » analysis shows that the background error correlation length scale is larger than 75 km for streamfunctions and is larger than 25 km for water vapor mixing ratios, even for a 2-km resolution model. A theoretical analysis suggests that such correlation length scales prevent the currently used data assimilation schemes from constraining spatial scales smaller than 150 km for streamfunctions and 50 km for water vapor mixing ratios. Moreover, our results highlight the need to fundamentally modify currently used data assimilation algorithms for assimilating high-resolution observations into the aforementioned fine resolution models. Lastly, within the framework of four-dimensional variational data assimilation, a multiscale methodology based on scale decomposition is suggested and challenges are discussed.« less

Linked hydrologic and climate variations in British Columbia and Yukon.

PubMed

Whitfield, P H

2001-01-01

Climatic and hydrologic variations between the decades 1976-1985 and 1986-1995 are examined at 34 climate stations and 275 hydrology stations. The variations in climate are distributed across a broad spatial area. Temperatures were generally warmer in the most recent decade, with many stations showing significant increases during the spring and fall. No significant decreases in temperature were found. Significant increases in temperature were more frequent in the south than in the northern portions of the region. Significant changes in precipitation were also more prevalent in the south. In coastal areas, there were significant decreases in precipitation during the dry season, and significant increases during the wet season. In the BC interior, significant precipitation decreases occurred during the fall, with significant increases during the winter and spring. In the north there were few changes in precipitation. The hydrologic responses to these variations in climate follow six distinctive patterns. The spatial distribution of these patterns suggests that in different ecozones, small variations in climate, particularly temperature, elicit different hydrologic responses.

Observations and 3D hydrodynamics-based modeling of decadal-scale shoreline change along the Outer Banks, North Carolina

USGS Publications Warehouse

Safak, Ilgar; List, Jeffrey; Warner, John C.; Kumar, Nirnimesh

2017-01-01

Long-term decadal-scale shoreline change is an important parameter for quantifying the stability of coastal systems. The decadal-scale coastal change is controlled by processes that occur on short time scales (such as storms) and long-term processes (such as prevailing waves). The ability to predict decadal-scale shoreline change is not well established and the fundamental physical processes controlling this change are not well understood. Here we investigate the processes that create large-scale long-term shoreline change along the Outer Banks of North Carolina, an uninterrupted 60 km stretch of coastline, using both observations and a numerical modeling approach. Shoreline positions for a 24-yr period were derived from aerial photographs of the Outer Banks. Analysis of the shoreline position data showed that, although variable, the shoreline eroded an average of 1.5 m/yr throughout this period. The modeling approach uses a three-dimensional hydrodynamics-based numerical model coupled to a spectral wave model and simulates the full 24-yr time period on a spatial grid running on a short (second scale) time-step to compute the sediment transport patterns. The observations and the model results show similar magnitudes (O(105 m3/yr)) and patterns of alongshore sediment fluxes. Both the observed and the modeled alongshore sediment transport rates have more rapid changes at the north of our section due to continuously curving coastline, and possible effects of alongshore variations in shelf bathymetry. The southern section with a relatively uniform orientation, on the other hand, has less rapid transport rate changes. Alongshore gradients of the modeled sediment fluxes are translated into shoreline change rates that have agreement in some locations but vary in others. Differences between observations and model results are potentially influenced by geologic framework processes not included in the model. Both the observations and the model results show higher rates of erosion (∼−1 m/yr) averaged over the northern half of the section as compared to the southern half where the observed and modeled averaged net shoreline changes are smaller (<0.1 m/yr). The model indicates accretion in some shallow embayments, whereas observations indicate erosion in these locations. Further analysis identifies that the magnitude of net alongshore sediment transport is strongly dominated by events associated with high wave energy. However, both big- and small- wave events cause shoreline change of the same order of magnitude because it is the gradients in transport, not the magnitude, that are controlling shoreline change. Results also indicate that alongshore momentum is not a simple balance between wave breaking and bottom stress, but also includes processes of horizontal vortex force, horizontal advection and pressure gradient that contribute to long-term alongshore sediment transport. As a comparison to a more simple approach, an empirical formulation for alongshore sediment transport is used. The empirical estimates capture the effect of the breaking term in the hydrodynamics-based model, however, other processes that are accounted for in the hydrodynamics-based model improve the agreement with the observed alongshore sediment transport.

Combining virtual observatory and equivalent source dipole approaches to describe the geomagnetic field with Swarm measurements

NASA Astrophysics Data System (ADS)

Saturnino, Diana; Langlais, Benoit; Amit, Hagay; Civet, François; Mandea, Mioara; Beucler, Éric

2018-03-01

A detailed description of the main geomagnetic field and of its temporal variations (i.e., the secular variation or SV) is crucial to understanding the geodynamo. Although the SV is known with high accuracy at ground magnetic observatory locations, the globally uneven distribution of the observatories hampers the determination of a detailed global pattern of the SV. Over the past two decades, satellites have provided global surveys of the geomagnetic field which have been used to derive global spherical harmonic (SH) models through some strict data selection schemes to minimise external field contributions. However, discrepancies remain between ground measurements and field predictions by these models; indeed the global models do not reproduce small spatial scales of the field temporal variations. To overcome this problem we propose to directly extract time series of the field and its temporal variation from satellite measurements as it is done at observatory locations. We follow a Virtual Observatory (VO) approach and define a global mesh of VOs at satellite altitude. For each VO and each given time interval we apply an Equivalent Source Dipole (ESD) technique to reduce all measurements to a unique location. Synthetic data are first used to validate the new VO-ESD approach. Then, we apply our scheme to data from the first two years of the Swarm mission. For the first time, a 2.5° resolution global mesh of VO time series is built. The VO-ESD derived time series are locally compared to ground observations as well as to satellite-based model predictions. Our approach is able to describe detailed temporal variations of the field at local scales. The VO-ESD time series are then used to derive global spherical harmonic models. For a simple SH parametrization the model describes well the secular trend of the magnetic field both at satellite altitude and at the surface. As more data will be made available, longer VO-ESD time series can be derived and consequently used to study sharp temporal variation features, such as geomagnetic jerks.

Robust non-Gaussian statistics and long-range correlation of total ozone

NASA Astrophysics Data System (ADS)

Toumi, R.; Syroka, J.; Barnes, C.; Lewis, P.

2001-01-01

Three long-term total ozone time series at Camborne, Lerwick and Arosa are examined for their statistical properties. Non-Gaussian behaviour is seen for all locations. There are large interannual fluctuations in the higher moments of the probability distribution. However, only the mean for all stations and summer standard deviation at Lerwick show significant trends. This suggests that there has been no long-term change in the stratospheric circulation, but there are decadal variations. The time series can be also characterised as scale invariant with a Hurst exponent of about 0.8 for all three sites. The Arosa time series was found to be weakly intermittent, in agreement with the non-Gaussian characteristics of the data set

Development of the USGS national land-cover database over two decades

USGS Publications Warehouse

Xian, George Z.; Homer, Collin G.; Yang, Limin; Weng, Qihao

2011-01-01

Land-cover composition and change have profound impacts on terrestrial ecosystems. Land-cover and land-use (LCLU) conditions and their changes can affect social and physical environments by altering ecosystem conditions and services. Information about LCLU change is often used to produce landscape-based metrics and evaluate landscape conditions to monitor LCLU status and trends over a specific time interval (Loveland et al. 2002; Coppin et al. 2004; Lunetta et al. 2006). Continuous, accurate, and up-to-date land-cover data are important for natural resource and ecosystem management and are needed to support consistent monitoring of landscape attributes over time. Large-area land-cover information at regional, national, and global scales is critical for monitoring landscape variations over large areas.

Using the Interactive Graphic Syllabus in the Teaching of Economics

ERIC Educational Resources Information Center

Moosavian, Seyyed Ali Zeytoon Nejad

2017-01-01

In the past few decades, two novel variations of syllabus have emerged: namely "the Graphic Syllabus" and "the Interactive Syllabus". Each of these two variations of syllabus has its own special advantages. The present paper argues that there could be devised a new combined version of the two mentioned variations, called…

Decadal-Scale Forecasting of Climate Drivers for Marine Applications.

PubMed

Salinger, J; Hobday, A J; Matear, R J; O'Kane, T J; Risbey, J S; Dunstan, P; Eveson, J P; Fulton, E A; Feng, M; Plagányi, É E; Poloczanska, E S; Marshall, A G; Thompson, P A

Climate influences marine ecosystems on a range of time scales, from weather-scale (days) through to climate-scale (hundreds of years). Understanding of interannual to decadal climate variability and impacts on marine industries has received less attention. Predictability up to 10 years ahead may come from large-scale climate modes in the ocean that can persist over these time scales. In Australia the key drivers of climate variability affecting the marine environment are the Southern Annular Mode, the Indian Ocean Dipole, the El Niño/Southern Oscillation, and the Interdecadal Pacific Oscillation, each has phases that are associated with different ocean circulation patterns and regional environmental variables. The roles of these drivers are illustrated with three case studies of extreme events-a marine heatwave in Western Australia, a coral bleaching of the Great Barrier Reef, and flooding in Queensland. Statistical and dynamical approaches are described to generate forecasts of climate drivers that can subsequently be translated to useful information for marine end users making decisions at these time scales. Considerable investment is still needed to support decadal forecasting including improvement of ocean-atmosphere models, enhancement of observing systems on all scales to support initiation of forecasting models, collection of important biological data, and integration of forecasts into decision support tools. Collaboration between forecast developers and marine resource sectors-fisheries, aquaculture, tourism, biodiversity management, infrastructure-is needed to support forecast-based tactical and strategic decisions that reduce environmental risk over annual to decadal time scales. © 2016 Elsevier Ltd. All rights reserved.

Solar Cycle Fine Structure and Surface Rotation from Ca II K-Line Time Series Data

NASA Astrophysics Data System (ADS)

Scargle, Jeff; Keil, Steve; Worden, Pete

2011-10-01

Analysis of three and a half decades of data from the NSO/AFRL/Sac Peak K-line monitoring program yields evidence for four components to the variation: (a) the solar cycle, with considerable fine structure and a quasi-periodicity of 122.4 days; (b) a stochastic process, faster than (a) and largely independent of it, (c) a quasi-periodic signal due to rotational modulation, and of course (d) observational errors (shown to be quite small). Correlation and power spectrum analyses elucidate periodic and aperiodic variation of these chromospheric parameters. Time-frequency analysis is especially useful for extracting information about differential rotation, and in particular elucidates the connection between its behavior and fine structure of the solar cycle on approximately one-year time scales. These results further suggest that similar analyses will be useful at detecting and characterizing differential rotation in stars from stellar light-curves such as those being produced by NASA's Kepler observatory. Component (b) consists of variations over a range of timescales, in the manner of a "1/f" random process. A time-dependent Wilson-Bappu effect appears to be present in the solar cycle variations (a), but not in the stochastic process (b). The data can be found at the National Solar Observatory web site http://nsosp.nso.edu/data/cak_mon.html, or by file transfer protocol at ftp://ftp.nso.edu/idl/cak.parameters.

Conservation genetics of extremely isolated urban populations of the northern dusky salamander (Desmognathus fuscus) in New York City

PubMed Central

Zak, Yana; Pehek, Ellen

2013-01-01

Urbanization is a major cause of amphibian decline. Stream-dwelling plethodontid salamanders are particularly susceptible to urbanization due to declining water quality and hydrological changes, but few studies have examined these taxa in cities. The northern dusky salamander (Desmognathus fuscus) was once common in the New York City metropolitan area, but has substantially declined throughout the region in recent decades. We used five tetranucleotide microsatellite loci to examine population differentiation, genetic variation, and bottlenecks among five remnant urban populations of dusky salamanders in NYC. These genetic measures provide information on isolation, prevalence of inbreeding, long-term prospects for population persistence, and potential for evolutionary responses to future environmental change. All populations were genetically differentiated from each other, and the most isolated populations in Manhattan have maintained very little genetic variation (i.e. <20% heterozygosity). A majority of the populations also exhibited evidence of genetic bottlenecks. These findings contrast with published estimates of high genetic variation within and lack of structure between populations of other desmognathine salamanders sampled over similar or larger spatial scales. Declines in genetic variation likely resulted from population extirpations and the degradation of stream and terrestrial paths for dispersal in NYC. Loss of genetic variability in populations isolated by human development may be an underappreciated cause and/or consequence of the decline of this species in urbanized areas of the northeast USA. PMID:23646283

Urn model for products’ shares in international trade

NASA Astrophysics Data System (ADS)

Barbier, Matthieu; Lee, D.-S.

2017-12-01

International trade fluxes evolve as countries revise their portfolios of trade products towards economic development. Accordingly products’ shares in international trade vary with time, reflecting the transfer of capital between distinct industrial sectors. Here we analyze the share of hundreds of product categories in world trade for four decades and find a scaling law obeyed by the annual variation of product share, which informs us of how capital flows and interacts over the product space. A model of stochastic transfer of capital between products based on the observed scaling relation is proposed and shown to reproduce exactly the empirical share distribution. The model allows analytic solutions as well as numerical simulations, which predict a pseudo-condensation of capital onto few product categories and when it will occur. At the individual level, our model finds certain products unpredictable, the excess or deficient growth of which with respect to the model prediction is shown to be correlated with the nature of goods.

Heterogeneous responses of temperate-zone amphibian populations to climate change complicates conservation planning

USGS Publications Warehouse

Muths, Erin L.; Chambert, Thierry A.; Schmidt, B. R.; Miller, D. A. W.; Hossack, Blake R.; Joly, P.; Grolet, O.; Green, D. M.; Pilliod, David S.; Cheylan, M.; Fisher, Robert N.; McCaffery, R. M.; Adams, M. J.; Palen, W. J.; Arntzen, J. W.; Garwood, J.; Fellers, Gary M.; Thirion, J. M.; Grant, Evan H. Campbell; Besnard, A.

2017-01-01

The pervasive and unabated nature of global amphibian declines suggests common demographic responses to a given driver, and quantification of major drivers and responses could inform broad-scale conservation actions. We explored the influence of climate on demographic parameters (i.e., changes in the probabilities of survival and recruitment) using 31 datasets from temperate zone amphibian populations (North America and Europe) with more than a decade of observations each. There was evidence for an influence of climate on population demographic rates, but the direction and magnitude of responses to climate drivers was highly variable among taxa and among populations within taxa. These results reveal that climate drivers interact with variation in life-history traits and population-specific attributes resulting in a diversity of responses. This heterogeneity complicates the identification of conservation ‘rules of thumb’ for these taxa, and supports the notion of local focus as the most effective approach to overcome global-scale conservation challenges.

300 Years of East African Climate Variability from Oxygen Isotopes in a Kenya Coral

NASA Astrophysics Data System (ADS)

Dunbar, R.

2003-04-01

Instrumental records of climate variability from the western Indian Ocean are relatively scarce and short. Here I present a monthly resolution stable isotopic record acquired from a large living coral head (Porites) from the Malindi Marine Reserve, Kenya (3^oS, 40^oE). The annual chronology is precise and is based on exceptionally clear high and low density growth band couplets. The record extends from 1696 to 1996 A.D., making it the longest coral climate record from the Indian Ocean and one of the longest available worldwide. We have analyzed the uppermost portion of the coral colony in triplicate, using 3 separate cores. This upper section, used for calibration purposes, also provides estimates of signal fidelity and noise in the climate recording system internal to the colony. Coral δ18O at this site primarily records SST; linear regression of monthly coral δ18O vs. SST yields a slope of -0.26 ppm δ18O per ^oC, and δ18O explains ˜57% of the SST variance. Additional isotopic variability may result from changes in seawater δ18O due to local runoff or regional evaporation/precipitation balance, but these changes are likely to be small because local rainfall δ18O is not strongly depleted relative to seawater and salinity gradients are small. The coral record indicates a clear warming trend of about 1.5^oC that accelerates in the latest 20th century, superimposed on strong decadal variability that persists throughout the record. In fact, δ18O values in the 1990's exceed the 300 year envelope (they are lower) and correspond with apparently unprecedented coral bleaching in coastal East Africa. The decadal component of the Malindi coral record reflects a regional climate signal spanning much of the western equatorial Indian Ocean. In general, East African SST and rainfall are better correlated with Pacific ENSO indicators than with the Indian Monsoon at all periods (inter-annual through multi-decadal) but the correlation weakens after 1975. One dramatic new result we report here is a strong indication of a major cool and dry period from 1750--1820 A.D. This is the single largest multi-decadal anomaly of the past 300 years and correlates perfectly in time with the historically and anecdotally defined Lapanarat Drought. Our results indicate a strong link between multi-decadal tropical cold SST anomalies And far-reaching continental droughts in East Africa. Causes and links to other climate recording systems will be explored. Interannual-decadal SST variations are strongly coherent with ENSO indices and other ENSO-sensitive coral records on decadal and interannual time scales. The decadal component of the Malindi coral record reflects a regional climate signal spanning much of the western equatorial Indian Ocean. Previous work has argued that this component likely reflects a monsoonal influence. However, decadal variance in both Malindi and Seychelles (Charles et al. 1997) coral records is more strongly coherent with ENSO indices than with the India or East Africa rain indices. The coherency of both coral records with Pacific indicators suggests instead that Indian Ocean variability reflects decadal ENSO-like variability originating in the Pacific. These records don't correlate significantly with the Pacific Decadal Oscillation implying a dominant role for the tropical Pacific (as opposed to extra-tropical regions) as a source of regional decadal variability in the western Indian Ocean. This work confirms that the tropical Pacific can act as an agent of decadal climate variability over a very large spatial scale.

OCEAN CIRCULATION. Observing the Atlantic Meridional Overturning Circulation yields a decade of inevitable surprises.

PubMed

Srokosz, M A; Bryden, H L

2015-06-19

The importance of the Atlantic Meridional Overturning Circulation (AMOC) heat transport for climate is well acknowledged. Climate models predict that the AMOC will slow down under global warming, with substantial impacts, but measurements of ocean circulation have been inadequate to evaluate these predictions. Observations over the past decade have changed that situation, providing a detailed picture of variations in the AMOC. These observations reveal a surprising degree of AMOC variability in terms of the intraannual range, the amplitude and phase of the seasonal cycle, the interannual changes in strength affecting the ocean heat content, and the decline of the AMOC over the decade, both of the latter two exceeding the variations seen in climate models. Copyright © 2015, American Association for the Advancement of Science.

Is Global Warming Accelerating?

NASA Astrophysics Data System (ADS)

Shukla, J.; Delsole, T. M.; Tippett, M. K.

2009-12-01

A global pattern that fluctuates naturally on decadal time scales is identified in climate simulations and observations. This newly discovered component, called the Global Multidecadal Oscillation (GMO), is related to the Atlantic Meridional Oscillation and shown to account for a substantial fraction of decadal fluctuations in the observed global average sea surface temperature. IPCC-class climate models generally underestimate the variance of the GMO, and hence underestimate the decadal fluctuations due to this component of natural variability. Decomposing observed sea surface temperature into a component due to anthropogenic and natural radiative forcing plus the GMO, reveals that most multidecadal fluctuations in the observed global average sea surface temperature can be accounted for by these two components alone. The fact that the GMO varies naturally on multidecadal time scales implies that it can be predicted with some skill on decadal time scales, which provides a scientific rationale for decadal predictions. Furthermore, the GMO is shown to account for about half of the warming in the last 25 years and hence a substantial fraction of the recent acceleration in the rate of increase in global average sea surface temperature. Nevertheless, in terms of the global average “well-observed” sea surface temperature, the GMO can account for only about 0.1° C in transient, decadal-scale fluctuations, not the century-long 1° C warming that has been observed during the twentieth century.

A Decadal Climate Cycle in the North Atlantic Ocean as Simulated by the ECHO Coupled GCM.

NASA Astrophysics Data System (ADS)

Grötzner, A.; Latif, M.; Barnett, T. P.

1998-05-01

In this paper a decadal climate cycle in the North Atlantic that was derived from an extended-range integration with a coupled ocean-atmosphere general circulation model is described. The decadal mode shares many features with the observed decadal variability in the North Atlantic. The period of the simulated oscillation, however, is somewhat longer than that estimated from observations. While the observations indicate a period of about 12 yr, the coupled model simulation yields a period of about 17 yr. The cyclic nature of the decadal variability implies some inherent predictability at these timescales.The decadal mode is based on unstable air-sea interactions and must be therefore regarded as an inherently coupled mode. It involves the subtropical gyre and the North Atlantic oscillation. The memory of the coupled system, however, resides in the ocean and is related to horizontal advection and to the oceanic adjustment to low-frequency wind stress curl variations. In particular, it is found that variations in the intensity of the Gulf Stream and its extension are crucial to the oscillation. Although differing in details, the North Atlantic decadal mode and the North Pacific mode described by M. Latif and T. P. Barnett are based on the same fundamental mechanism: a feedback loop between the wind driven subtropical gyre and the extratropical atmospheric circulation.

Stable genetic structure and connectivity in pollution-adapted and nearby pollution-sensitive populations of Fundulus heteroclitus

PubMed Central

Biancani, Leann M.; Flight, Patrick A.; Nacci, Diane E.; Rand, David M.; Crawford, Douglas L.; Oleksiak, Marjorie F.

2018-01-01

Populations of the non-migratory estuarine fish Fundulus heteroclitus inhabiting the heavily polluted New Bedford Harbour (NBH) estuary have shown inherited tolerance to local pollutants introduced to their habitats in the past 100 years. Here we examine two questions: (i) Is there pollution-driven selection on the mitochondrial genome across a fine geographical scale? and (ii) What is the pattern of migration among sites spanning a strong pollution gradient? Whole mitochondrial genomes were analysed for 133 F. heteroclitus from seven nearby collection sites: four sites along the NBH pollution cline (approx. 5 km distance), which had pollution-adapted fish, as well as one site adjacent to the pollution cline and two relatively unpolluted sites about 30 km away, which had pollution-sensitive fish. Additionally, we used microsatellite analyses to quantify genetic variation over three F. heteroclitus generations in both pollution-adapted and sensitive individuals collected from two sites at two different time points (1999/2000 and 2007/2008). Our results show no evidence for a selective sweep of mtDNA in the polluted sites. Moreover, mtDNA analyses revealed that both pollution-adapted and sensitive populations harbour similar levels of genetic diversity. We observed a high level of non-synonymous mutations in the most polluted site. This is probably associated with a reduction in Ne and concomitant weakening of purifying selection, a demographic expansion following a pollution-related bottleneck or increased mutation rates. Our demographic analyses suggest that isolation by distance influences the distribution of mtDNA genetic variation between the pollution cline and the clean populations at broad spatial scales. At finer scales, population structure is patchy, and neither spatial distance, pollution concentration or pollution tolerance is a good predictor of mtDNA variation. Lastly, microsatellite analyses revealed stable population structure over the last decade. PMID:29892357

Soil Respiration in Tibetan Alpine Grasslands: Belowground Biomass and Soil Moisture, but Not Soil Temperature, Best Explain the Large-Scale Patterns

PubMed Central

Geng, Yan; Wang, Yonghui; Yang, Kuo; Wang, Shaopeng; Zeng, Hui; Baumann, Frank; Kuehn, Peter; Scholten, Thomas; He, Jin-Sheng

2012-01-01

The Tibetan Plateau is an essential area to study the potential feedback effects of soils to climate change due to the rapid rise in its air temperature in the past several decades and the large amounts of soil organic carbon (SOC) stocks, particularly in the permafrost. Yet it is one of the most under-investigated regions in soil respiration (Rs) studies. Here, Rs rates were measured at 42 sites in alpine grasslands (including alpine steppes and meadows) along a transect across the Tibetan Plateau during the peak growing season of 2006 and 2007 in order to test whether: (1) belowground biomass (BGB) is most closely related to spatial variation in Rs due to high root biomass density, and (2) soil temperature significantly influences spatial pattern of Rs owing to metabolic limitation from the low temperature in cold, high-altitude ecosystems. The average daily mean Rs of the alpine grasslands at peak growing season was 3.92 µmol CO2 m−2 s−1, ranging from 0.39 to 12.88 µmol CO2 m−2 s−1, with average daily mean Rs of 2.01 and 5.49 µmol CO2 m−2 s−1 for steppes and meadows, respectively. By regression tree analysis, BGB, aboveground biomass (AGB), SOC, soil moisture (SM), and vegetation type were selected out of 15 variables examined, as the factors influencing large-scale variation in Rs. With a structural equation modelling approach, we found only BGB and SM had direct effects on Rs, while other factors indirectly affecting Rs through BGB or SM. Most (80%) of the variation in Rs could be attributed to the difference in BGB among sites. BGB and SM together accounted for the majority (82%) of spatial patterns of Rs. Our results only support the first hypothesis, suggesting that models incorporating BGB and SM can improve Rs estimation at regional scale. PMID:22509373

Normalizing and scaling of data to derive human response corridors from impact tests.

PubMed

Yoganandan, Narayan; Arun, Mike W J; Pintar, Frank A

2014-06-03

It is well known that variability is inherent in any biological experiment. Human cadavers (Post-Mortem Human Subjects, PMHS) are routinely used to determine responses to impact loading for crashworthiness applications including civilian (motor vehicle) and military environments. It is important to transform measured variables from PMHS tests (accelerations, forces and deflections) to a standard or reference population, termed normalization. The transformation process should account for inter-specimen variations with some underlying assumptions used during normalization. Scaling is a process by which normalized responses are converted from one standard to another (example, mid-size adult male to large-male and small-size female adults, and to pediatric populations). These responses are used to derive corridors to assess the biofidelity of anthropomorphic test devices (crash dummies) used to predict injury in impact environments and design injury mitigating devices. This survey examines the pros and cons of different approaches for obtaining normalized and scaled responses and corridors used in biomechanical studies for over four decades. Specifically, the equal-stress equal-velocity and impulse-momentum methods along with their variations are discussed in this review. Methods ranging from subjective to quasi-static loading to different approaches are discussed for deriving temporal mean and plus minus one standard deviation human corridors of time-varying fundamental responses and cross variables (e.g., force-deflection). The survey offers some insights into the potential efficacy of these approaches with examples from recent impact tests and concludes with recommendations for future studies. The importance of considering various parameters during the experimental design of human impact tests is stressed. Published by Elsevier Ltd.

Surface temperature patterns in complex terrain: Daily variations and long-term change in the central Sierra Nevada, California

USGS Publications Warehouse

Lundquist, J.D.; Cayan, D.R.

2007-01-01

A realistic description of how temperatures vary with elevation is crucial for ecosystem studies and for models of basin-scale snowmelt and spring streamflow. This paper explores surface temperature variability using temperature data from an array of 37 sensors, called the Yosemite network, which traverses both slopes of the Sierra Nevada in the vicinity of Yosemite National Park, California. These data indicate that a simple lapse rate is often a poor description of the spatial temperature structure. Rather, the spatial pattern of temperature over the Yosemite network varies considerably with synoptic conditions. Empirical orthogonal functions (EOFs) were used to identify the dominant spatial temperature patterns and how they vary in time. Temporal variations of these surface temperature patterns were correlated with large-scale weather conditions, as described by National Centers for Environmental Prediction-National Center for Atmospheric Research Reanalysis data. Regression equations were used to downscale larger-scale weather parameters, such as Reanalysis winds and pressure, to the surface temperature structure over the Yosemite network. These relationships demonstrate that strong westerly winds are associated with relatively warmer temperatures on the east slope and cooler temperatures on the west slope of the Sierra, and weaker westerly winds are associated with the opposite pattern. Reanalysis data from 1948 to 2005 indicate weakening westerlies over this time period, a trend leading to relatively cooler temperatures on the east slope over decadal timescale's. This trend also appears in long-term observations and demonstrates the need to consider topographic effects when examining long-term changes in mountain regions. Copyright 2007 by the American Geophysical Union.

Temporal and spatial patterns of wetland extent influence variability of surface water connectivity in the Prairie Pothole Region, United States

USGS Publications Warehouse

Vanderhoof, Melanie; Alexander, Laurie C.; Todd, Jason

2016-01-01

Context. Quantifying variability in landscape-scale surface water connectivity can help improve our understanding of the multiple effects of wetlands on downstream waterways. Objectives. We examined how wetland merging and the coalescence of wetlands with streams varied both spatially (among ecoregions) and interannually (from drought to deluge) across parts of the Prairie Pothole Region. Methods. Wetland extent was derived over a time series (1990-2011) using Landsat imagery. Changes in landscape-scale connectivity, generated by the physical coalescence of wetlands with other surface water features, were quantified by fusing static wetland and stream datasets with Landsat-derived wetland extent maps, and related to multiple wetness indices. The usage of Landsat allows for decadal-scale analysis, but limits the types of surface water connections that can be detected. Results. Wetland extent correlated positively with the merging of wetlands and wetlands with streams. Wetness conditions, as defined by drought indices and runoff, were positively correlated with wetland extent, but less consistently correlated with measures of surface water connectivity. The degree of wetland-wetland merging was found to depend less on total wetland area or density, and more on climate conditions, as well as the threshold for how wetland/upland was defined. In contrast, the merging of wetlands with streams was positively correlated with stream density, and inversely related to wetland density. Conclusions. Characterizing the degree of surface water connectivity within the Prairie Pothole Region in North America requires consideration of 1) climate-driven variation in wetness conditions and 2) within-region variation in wetland and stream spatial arrangements.

Ocean time-series near Bermuda: Hydrostation S and the US JGOFS Bermuda Atlantic time-series study

NASA Technical Reports Server (NTRS)

Michaels, Anthony F.; Knap, Anthony H.

1992-01-01

Bermuda is the site of two ocean time-series programs. At Hydrostation S, the ongoing biweekly profiles of temperature, salinity and oxygen now span 37 years. This is one of the longest open-ocean time-series data sets and provides a view of decadal scale variability in ocean processes. In 1988, the U.S. JGOFS Bermuda Atlantic Time-series Study began a wide range of measurements at a frequency of 14-18 cruises each year to understand temporal variability in ocean biogeochemistry. On each cruise, the data range from chemical analyses of discrete water samples to data from electronic packages of hydrographic and optics sensors. In addition, a range of biological and geochemical rate measurements are conducted that integrate over time-periods of minutes to days. This sampling strategy yields a reasonable resolution of the major seasonal patterns and of decadal scale variability. The Sargasso Sea also has a variety of episodic production events on scales of days to weeks and these are only poorly resolved. In addition, there is a substantial amount of mesoscale variability in this region and some of the perceived temporal patterns are caused by the intersection of the biweekly sampling with the natural spatial variability. In the Bermuda time-series programs, we have added a series of additional cruises to begin to assess these other sources of variation and their impacts on the interpretation of the main time-series record. However, the adequate resolution of higher frequency temporal patterns will probably require the introduction of new sampling strategies and some emerging technologies such as biogeochemical moorings and autonomous underwater vehicles.

Response of Tropical Forests to Intense Climate Variability and Rainfall Anomaly over the Last Decade

NASA Astrophysics Data System (ADS)

Saatchi, S.; Asefi, S.

2012-04-01

During the last decade, strong precipitation anomalies resulted from increased sea surface temperature in the tropical Atlantic, have caused extensive drying trends in rainforests of western Amazonia, exerting water stress, tree mortality, biomass loss, and large-scale fire disturbance. In contrast, there have been no reports on large-scale disturbance in rainforests of west and central Africa, though being exposed to similar intensity of climate variability. Using data from Tropical Rainfall Mapping Mission (TRMM) (1999-2010), and time series of rainfall observations from meteorological stations (1971-2000), we show that both Amazonian and African rainforest experienced strong precipitation anomalies from 2005-2010. We monitored the response of forest to the climate variability by analyzing the canopy water content observed by SeaWinds Ku-band Scatterometer (QSCAT) (1999-2009) and found that more than 70 million ha of forests in western Amazonia experienced a strong water deficit during the dry season of 2005 and a closely corresponding decline in canopy backscatter that persisted until the next major drought in 2010. This decline in backscatter has been attributed to loss of canopy water content and large-scale tree mortality corroborated by ground and airborne observations. However, no strong impacts was observed on tropical forests of Africa, suggesting that the African rainforest may have more resilience to droughts. We tested this hypothesis by examining the seasonal rainfall patterns, maximum water deficit, and the surface temperature variations. Results show that there is a complex pattern of low annual rainfall, moderate seasonality, and lower surface temperature in Central Africa compared to Amazonia, indicating potentially a lower evapotranspiration circumventing strong water deficits

Response of Tropical Forests to Intense Climate Variability and Rainfall Anomaly of Last Decade

NASA Astrophysics Data System (ADS)

Saatchi, S. S.; Asefi Najafabady, S.

2011-12-01

During the last decade, strong precipitation anomalies resulted from increased sea surface temperature in the tropical Atlantic, have caused extensive drying trends in rainforests of western Amazonia, exerting water stress, tree mortality, biomass loss, and large-scale fire disturbance. In contrast, there have been no reports on large-scale disturbance in rainforests of west and central Africa, though being exposed to similar intensity of climate variability. Using data from Tropical Rainfall Mapping Mission (TRMM) (1999-2010), and time series of rainfall observations from meteorological stations (1971-2000), we show that both Amazonian and African rainforest experienced strong precipitation anomalies from 2005-2010. We monitored the response of forest to the climate variability by analyzing the canopy water content observed by SeaWinds Ku-band Scatterometer (QSCAT) (1999-2009) and found that more than 70 million ha of forests in western Amazonia experienced a strong water deficit during the dry season of 2005 and a closely corresponding decline in canopy backscatter that persisted until the next major drought in 2010. This decline in backscatter has been attributed to loss of canopy water content and large-scale tree mortality corroborated by ground and airborne observations. However, no strong impacts was observed on tropical forests of Africa, suggesting that the African rainforest may have more resilience to droughts. We tested this hypothesis by examining the seasonal rainfall patterns, maximum water deficit, and the surface temperature variations. Results show that there is a complex pattern of low annual rainfall, moderate seasonality, and lower surface temperature in Central Africa compared to Amazonia, indicating potentially a lower evapotranspiration circumventing strong water deficits.

The Impact of Climate Change on Ozone-Related Mortality in Sydney

PubMed Central

Physick, William; Cope, Martin; Lee, Sunhee

2014-01-01

Coupled global, regional and chemical transport models are now being used with relative-risk functions to determine the impact of climate change on human health. Studies have been carried out for global and regional scales, and in our paper we examine the impact of climate change on ozone-related mortality at the local scale across an urban metropolis (Sydney, Australia). Using three coupled models, with a grid spacing of 3 km for the chemical transport model (CTM), and a mortality relative risk function of 1.0006 per 1 ppb increase in daily maximum 1-hour ozone concentration, we evaluated the change in ozone concentrations and mortality between decades 1996–2005 and 2051–2060. The global model was run with the A2 emissions scenario. As there is currently uncertainty regarding a threshold concentration below which ozone does not impact on mortality, we calculated mortality estimates for the three daily maximum 1-hr ozone concentration thresholds of 0, 25 and 40 ppb. The mortality increase for 2051–2060 ranges from 2.3% for a 0 ppb threshold to 27.3% for a 40 ppb threshold, although the numerical increases differ little. Our modeling approach is able to identify the variation in ozone-related mortality changes at a suburban scale, estimating that climate change could lead to an additional 55 to 65 deaths across Sydney in the decade 2051–2060. Interestingly, the largest increases do not correspond spatially to the largest ozone increases or the densest population centres. The distribution pattern of changes does not seem to vary with threshold value, while the magnitude only varies slightly. PMID:24419047

Improving seasonal forecasts of hydroclimatic variables through the state of multiple large-scale climate signals

NASA Astrophysics Data System (ADS)

Castelletti, A.; Giuliani, M.; Block, P. J.

2017-12-01

Increasingly uncertain hydrologic regimes combined with more frequent and intense extreme events are challenging water systems management worldwide, emphasizing the need of accurate medium- to long-term predictions to timely prompt anticipatory operations. Despite modern forecasts are skillful over short lead time (from hours to days), predictability generally tends to decrease on longer lead times. Global climate teleconnection, such as El Niño Southern Oscillation (ENSO), may contribute in extending forecast lead times. However, ENSO teleconnection is well defined in some locations, such as Western USA and Australia, while there is no consensus on how it can be detected and used in other regions, particularly in Europe, Africa, and Asia. In this work, we generalize the Niño Index Phase Analysis (NIPA) framework by contributing the Multi Variate Niño Index Phase Analysis (MV-NIPA), which allows capturing the state of multiple large-scale climate signals (i.e. ENSO, North Atlantic Oscillation, Pacific Decadal Oscillation, Atlantic Multi-decadal Oscillation, Indian Ocean Dipole) to forecast hydroclimatic variables on a seasonal time scale. Specifically, our approach distinguishes the different phases of the considered climate signals and, for each phase, identifies relevant anomalies in Sea Surface Temperature (SST) that influence the local hydrologic conditions. The potential of the MV-NIPA framework is demonstrated through an application to the Lake Como system, a regulated lake in northern Italy which is mainly operated for flood control and irrigation supply. Numerical results show high correlations between seasonal SST values and one season-ahead precipitation in the Lake Como basin. The skill of the resulting MV-NIPA forecast outperforms the one of ECMWF products. This information represents a valuable contribution to partially anticipate the summer water availability, especially during drought events, ultimately supporting the improvement of the Lake Como operations.

Modeling the Influence of Hemispheric Transport on Trends in ...

EPA Pesticide Factsheets

We describe the development and application of the hemispheric version of the CMAQ to examine the influence of long-range pollutant transport on trends in surface level O3 distributions. The WRF-CMAQ model is expanded to hemispheric scales and multi-decadal model simulations were recently performed for the period spanning 1990-2010 to examine changes in hemispheric air pollution resulting from changes in emissions over this period. Simulated trends in ozone and precursor species concentrations across the U.S. and the northern hemisphere over the past two decades are compared with those inferred from available measurements during this period. Additionally, the decoupled direct method (DDM) in CMAQ is used to estimate the sensitivity of O3 to emissions from different source regions across the northern hemisphere. The seasonal variations in source region contributions to background O3 is then estimated from these sensitivity calculations and will be discussed. A reduced form model combining these source region sensitivities estimated from DDM with the multi-decadal simulations of O3 distributions and emissions trends, is then developed to characterize the changing contributions of different source regions to background O3 levels across North America. The National Exposure Research Laboratory (NERL) Computational Exposure Division (CED) develops and evaluates data, decision-support tools, and models to be applied to media-specific or receptor-specific problem areas

Influence and predictive capacity of climate anomalies on daily to decadal extremes in canopy photosynthesis.

PubMed

Desai, Ankur R

2014-02-01

Significant advances have been made over the past decades in capabilities to simulate diurnal and seasonal variation of leaf-level and canopy-scale photosynthesis in temperate and boreal forests. However, long-term prediction of future forest productivity in a changing climate may be more dependent on how climate and biological anomalies influence extremes in interannual to decadal variability of canopy ecosystem carbon exchanges. These exchanges can differ markedly from leaf level responses, especially owing to the prevalence of long lags in nutrient and water cycling. Until recently, multiple long-term (10+ year) high temporal frequency (daily) observations of canopy exchange were not available to reliably assess this claim. An analysis of one of the longest running North American eddy covariance flux towers reveals that single climate variables do not adequately explain carbon exchange anomalies beyond the seasonal timescale. Daily to weekly lagged anomalies of photosynthesis positively autocorrelate with daily photosynthesis. This effect suggests a negative feedback in photosynthetic response to climate extremes, such as anomalies in evapotranspiration and maximum temperature. Moisture stress in the prior season did inhibit photosynthesis, but mechanisms are difficult to assess. A complex interplay of integrated and lagged productivity and moisture-limiting factors indicate a critical role of seasonal thresholds that limit growing season length and peak productivity. These results lead toward a new conceptual framework for improving earth system models with long-term flux tower observations.

Spatiotemporal Divergence of the Warming Hiatus over Land Based on Different Definitions of Mean Temperature

PubMed Central

Zhou, Chunlüe; Wang, Kaicun

2016-01-01

Existing studies of the recent warming hiatus over land are primarily based on the average of daily minimum and maximum temperatures (T2). This study compared regional warming rates of mean temperature based on T2 and T24 calculated from hourly observations available from 1998 to 2013. Both T2 and T24 show that the warming hiatus over land is apparent in the mid-latitudes of North America and Eurasia, especially in cold seasons, which is closely associated with the negative North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) and cold air propagation by the Arctic-original northerly wind anomaly into mid-latitudes. However, the warming rates of T2 and T24 are significantly different at regional and seasonal scales because T2 only samples air temperature twice daily and cannot accurately reflect land-atmosphere and incoming radiation variations in the temperature diurnal cycle. The trend has a standard deviation of 0.43 °C/decade for T2 and 0.41 °C/decade for T24, and 0.38 °C/decade for their trend difference in 5° × 5° grids. The use of T2 amplifies the regional contrasts of the warming rate, i.e., the trend underestimation in the US and overestimation at high latitudes by T2. PMID:27531421

Testing the Sun-climate Connection with Paleoclimate Data

NASA Technical Reports Server (NTRS)

Crowley, Thomas J.; Howard, Matthew K.

1990-01-01

If there is a significant sun-climate connection, it should be detectable in high-resolution paleoclimate records. Of particular interest is the last few thousand years, where we have both indices of solar variability (C-14 and Be-10) and climate variations (alpine glaciers, tree rings, ice cores, corals, etc.). Although there are a few exceptions, statistical analyses of solar and climate records generally indicates a flickering relationship between the two -- sometimes it seems to be present, sometimes not. The most repeatable solar climate periods occur at approx. 120 and approx. 56 yrs, although there is also evidence for approx. 420 and approx. 200 yrs. power in some records. However, coherence between solar and climate spectra is usually low, and occurrence of solar spectra in climate records is sometimes dependent on choice of analysis program. These results suggest in general a relatively weak sun-climate link on time scales of decades to centuries. This conclusion is consistent with previous studies and with the observation that inferred climate fluctuations of 1.0 to 1.5 C on this time scale would require solar constant variations of approximately 0.5 to 1.0 percent. This change in forcing is almost an order of magnitude greater than observed changes over the last solar cycle and appears to be on the far-outer limit of acceptable changes for a Maunder Minimum-type event.

Revisiting a possible relationship between solar activity and Earth rotation variability

NASA Astrophysics Data System (ADS)

Abarca del Rio, R.; Gambis, D.

2011-10-01

A variety of studies have searched to establish a possible relationship between the solar activity and earth variations (Danjon, 1958-1962; Challinor, 1971; Currie, 1980, Gambis, 1990). We are revisiting previous studies (Bourget et al, 1992, Abarca del Rio et al, 2003, Marris et al, 2004) concerning the possible relationship between solar activity variability and length of day (LOD) variations at decadal time scales. Assuming that changes in AAM for the entire atmosphere are accompanied by equal, but opposite, changes in the angular momentum of the earth it is possible to infer changes in LOD from global AAM time series, through the relation : delta (LOD) (ms) = 1.68 10^29 delta(AAM) (kgm2/s) (Rosen and Salstein, 1983), where δ(LOD) is given in milliseconds. Given the close relationship at seasonal to interannual time's scales between LOD and the Atmospheric Angular Momentum (AAM) (see Abarca del Rio et al., 2003) it is possible to infer from century long atmospheric simulations what may have been the variability in the associated LOD variability throughout the last century. In the absence of a homogeneous century long LOD time series, we take advantage of the recent atmospheric reanalyzes extending since 1871 (Compo, Whitaker and Sardeshmukh, 2006). The atmospheric data (winds) of these reanalyzes allow computing AAM up to the top of the atmosphere; though here only troposphere data (up to 100 hPa) was taken into account.

Atmospheric River Characteristics under Decadal Climate Variability

NASA Astrophysics Data System (ADS)

Done, J.; Ge, M.

2017-12-01

How does decadal climate variability change the nature and predictability of atmospheric river events? Decadal swings in atmospheric river frequency, or shifts in the proportion of precipitation falling as rain, could challenge current water resource and flood risk management practice. Physical multi-scale processes operating between Pacific sea surface temperatures (SSTs) and atmospheric rivers over the Western U.S. are explored using the global Model for Prediction Across Scales (MPAS). A 45km global mesh is refined over the Western U.S. to 12km to capture the major terrain effects on precipitation. The performance of the MPAS is first evaluated for a case study atmospheric river event over California. Atmospheric river characteristics are then compared in a pair of idealized simulations, each driven by Pacific SST patterns characteristic of opposite phases of the Interdecadal Pacific Oscillation (IPO). Given recent evidence that we have entered a positive phase of the IPO, implications for current reservoir management practice over the next decade will be discussed. This work contributes to the NSF-funded project UDECIDE (Understanding Decision-Climate Interactions on Decadal Scales). UDECIDE brings together practitioners, engineers, statisticians, and climate scientists to understand the role of decadal climate information for water management and decisions.

Multiyear predictability of tropical marine productivity

PubMed Central

Séférian, Roland; Bopp, Laurent; Gehlen, Marion; Swingedouw, Didier; Mignot, Juliette; Guilyardi, Eric; Servonnat, Jérôme

2014-01-01

With the emergence of decadal predictability simulations, research toward forecasting variations of the climate system now covers a large range of timescales. However, assessment of the capacity to predict natural variations of relevant biogeochemical variables like carbon fluxes, pH, or marine primary productivity remains unexplored. Among these, the net primary productivity (NPP) is of particular relevance in a forecasting perspective. Indeed, in regions like the tropical Pacific (30°N–30°S), NPP exhibits natural fluctuations at interannual to decadal timescales that have large impacts on marine ecosystems and fisheries. Here, we investigate predictions of NPP variations over the last decades (i.e., from 1997 to 2011) with an Earth system model within the tropical Pacific. Results suggest a predictive skill for NPP of 3 y, which is higher than that of sea surface temperature (1 y). We attribute the higher predictability of NPP to the poleward advection of nutrient anomalies (nitrate and iron), which sustain fluctuations in phytoplankton productivity over several years. These results open previously unidentified perspectives to the development of science-based management approaches to marine resources relying on integrated physical-biogeochemical forecasting systems. PMID:25071174

The sedimentary record of climatic and anthropogenic influence on the Patuxent estuary and Chesapeake Bay ecosystems

USGS Publications Warehouse

Cronin, T. M.; Vann, C.D.

2003-01-01

Ecological and paleoecological studies from the Patuxent River mouth reveal dynamic variations in benthic ostracode assemblages over the past 600 years due to climatic and anthropogenic factors. Prior to the late 20th century, centennial-scale changes in species dominance were influenced by climatic and hydrological factors that primarily affected salinity and at times led to oxygen depletion. Decadal-scale droughts also occurred resulting in higher salinities and migration of ostracode species from the deep channel (Loxoconcha sp., Cytheromorpha newportensis) into shallower water along the flanks of the bay. During the 19th century the abundance of Leptocythere nikraveshae and Perissocytheridea brachyforma suggest increased turbidity and decreased salinity. Unprecedented changes in benthic ostracodes at the Patuxent mouth and in the deep channel of the bay occurred after the 1960s when Cytheromorpha curta became the dominant species, reflecting seasonal anoxia. The change in benthic assemblages coincided with the appearance of deformities in foraminifers. A combination of increased nitrate loading due to greater fertilizer use and increased freshwater flow explains this shift. A review of the geochemical and paleoecological evidence for dissolved oxygen indicates that seasonal oxygen depletion in the main channel of Chesapeake Bay varies over centennial and decadal timescales. Prior to 1700 AD, a relatively wet climate and high freshwater runoff led to oxygen depletion but rarely anoxia. Between 1700 and 1900, progressive eutrophication occurred related to land dearance and increased sedimentation, but this was superimposed on the oscillatory pattern of oxygen depletion most likely driven by climatological and hydrological factors. It also seems probable that the four- to five-fold increase in sedimentation due to agricultural and timber activity could have contributed to an increased natural nutrient load, likely fueling the early periods (1700-1900) of hypoxla prior to widespread fertilizer use. Twentieth-century anoxia worsened in the late 1930s-1940s and again around 1970, reaching unprecedented levels in the past few decades. Decadal and interannual variability in oxygen depletion even in the 20th century is still strongly influenced by climatic processes influencing precipitation and freshwater runoff.

Assessing Groundwater Depletion and Dynamics Using GRACE and InSAR: Potential and Limitations.

PubMed

Castellazzi, Pascal; Martel, Richard; Galloway, Devin L; Longuevergne, Laurent; Rivera, Alfonso

2016-11-01

In the last decade, remote sensing of the temporal variation of ground level and gravity has improved our understanding of groundwater dynamics and storage. Mass changes are measured by GRACE (Gravity Recovery and Climate Experiment) satellites, whereas ground deformation is measured by processing synthetic aperture radar satellites data using the InSAR (Interferometry of Synthetic Aperture Radar) techniques. Both methods are complementary and offer different sensitivities to aquifer system processes. GRACE is sensitive to mass changes over large spatial scales (more than 100,000 km 2 ). As such, it fails in providing groundwater storage change estimates at local or regional scales relevant to most aquifer systems, and at which most groundwater management schemes are applied. However, InSAR measures ground displacement due to aquifer response to fluid-pressure changes. InSAR applications to groundwater depletion assessments are limited to aquifer systems susceptible to measurable deformation. Furthermore, the inversion of InSAR-derived displacement maps into volume of depleted groundwater storage (both reversible and largely irreversible) is confounded by vertical and horizontal variability of sediment compressibility. During the last decade, both techniques have shown increasing interest in the scientific community to complement available in situ observations where they are insufficient. In this review, we present the theoretical and conceptual bases of each method, and present idealized scenarios to highlight the potential benefits and challenges of combining these techniques to remotely assess groundwater storage changes and other aspects of the dynamics of aquifer systems. © 2016, National Ground Water Association.

Dynamic evaluation of two decades of WRF-CMAQ ozone ...

EPA Pesticide Factsheets

Dynamic evaluation of the fully coupled Weather Research and Forecasting (WRF)– Community Multi-scale Air Quality (CMAQ) model ozone simulations over the contiguous United States (CONUS) using two decades of simulations covering the period from 1990 to 2010 is conducted to assess how well the changes in observed ozone air quality are simulated by the model. The changes induced by variations in meteorology and/or emissions are also evaluated during the same timeframe using spectral decomposition of observed and modeled ozone time series with the aim of identifying the underlying forcing mechanisms that control ozone exceedances and making informed recommendations for the optimal use of regional-scale air quality models. The evaluation is focused on the warm season's (i.e., May–September) daily maximum 8-hr (DM8HR) ozone concentrations, the 4th highest (4th) and average of top 10 DM8HR ozone values (top10), as well as the spectrally-decomposed components of the DM8HR ozone time series using the Kolmogorov-Zurbenko (KZ) filter. Results of the dynamic evaluation are presented for six regions in the U.S., consistent with the National Oceanic and Atmospheric Administration (NOAA) climatic regions. During the earlier 11-yr period (1990–2000), the simulated and observed trends are not statistically significant. During the more recent 2000–2010 period, all trends are statistically significant and WRF-CMAQ captures the observed trend in most regions. Given large n

Assessing groundwater depletion and dynamics using GRACE and InSAR: Potential and limitations

USGS Publications Warehouse

Castellazzi, Pascal; Martel, Richard; Galloway, Devin L.; Longuevergne, Laurent; Rivera, Alfonso

2016-01-01

In the last decade, remote sensing of the temporal variation of ground level and gravity has improved our understanding of groundwater dynamics and storage. Mass changes are measured by GRACE (Gravity Recovery and Climate Experiment) satellites, whereas ground deformation is measured by processing synthetic aperture radar satellites data using the InSAR (Interferometry of Synthetic Aperture Radar) techniques. Both methods are complementary and offer different sensitivities to aquifer system processes. GRACE is sensitive to mass changes over large spatial scales (more than 100,000 km2). As such, it fails in providing groundwater storage change estimates at local or regional scales relevant to most aquifer systems, and at which most groundwater management schemes are applied. However, InSAR measures ground displacement due to aquifer response to fluid-pressure changes. InSAR applications to groundwater depletion assessments are limited to aquifer systems susceptible to measurable deformation. Furthermore, the inversion of InSAR-derived displacement maps into volume of depleted groundwater storage (both reversible and largely irreversible) is confounded by vertical and horizontal variability of sediment compressibility. During the last decade, both techniques have shown increasing interest in the scientific community to complement available in situ observations where they are insufficient. In this review, we present the theoretical and conceptual bases of each method, and present idealized scenarios to highlight the potential benefits and challenges of combining these techniques to remotely assess groundwater storage changes and other aspects of the dynamics of aquifer systems.

Inter-decadal variation of the Tropical Atlantic-Korea (TA-K) teleconnection pattern during boreal summer season

NASA Astrophysics Data System (ADS)

Ham, Yoo-Geun; Hwang, YeonJi; Lim, Young-Kwon; Kwon, Minho

2017-12-01

The inter-decadal variation of the positive relationship between the tropical Atlantic sea surface temperature (SST) and Korean precipitation during boreal summer season during 1900-2010 is examined. The 15-year moving correlation between the Tropical Atlantic SST (TAtlSST) index (SST anomalies from 30°S to 30°N and 60°W to 20°E) and Korean precipitation (precipitation anomalies from 35°-40°N to 120°-130°E) during June-July-August exhibits strong inter-decadal variation, which becomes positive at the 95% confidence level after the 1980s. Intensification of the linkage between the TAtlSST index and Korean precipitation after the 1980s is attributed to global warming via the increased background SST. The increase in the background SST over the Atlantic provides background conditions that enhance anomalous convective activity by anomalous Atlantic SST warming. Therefore, the overall atmospheric responses associated with the tropical Atlantic SST warming could intensify. The correlation between the TAtlSST index and Korean precipitation also exhibits strong inter-decadal variation within 1980-2010, which is over 0.8 during early 2000s, while it is relative low (i.e., around 0.6) during the early 1980s. The enhanced co-variability between the tropical and the mid-latitude Atlantic SST during the early 2000s indicates the intensification of TAtlSST-related Rossby wave source over the mid-latitude Atlantic, which excites stationary waves propagated from the Atlantic to the Korean peninsula across northern Europe and northeast Asia. This Rossby-wave train induces a cyclonic flow over the northern edge of the Korea, which intensifies southwesterly and results in precipitation over Korea. This observed decadal difference is well simulated by the stationary wave model experiments with a prescribed TAtlSST-related Rossby wave source over the mid-latitude Atlantic.

Long-term wave measurements in a climate change perspective.

NASA Astrophysics Data System (ADS)

Pomaro, Angela; Bertotti, Luciana; Cavaleri, Luigi; Lionello, Piero; Portilla-Yandun, Jesus

2017-04-01

At present multi-decadal time series of wave data needed for climate studies are generally provided by long term model simulations (hindcasts) covering the area of interest. Examples, among many, at different scales are wave hindcasts adopting the wind fields of the ERA-Interim reanalysis of the European Centre for Medium-Range Weather Forecasts (ECMWF, Reading, U.K.) at the global level and by regional re-analysis as for the Mediterranean Sea (Lionello and Sanna, 2006). Valuable as they are, these estimates are necessarily affected by the approximations involved, the more so because of the problems encountered within modelling processes in small basins using coarse resolution wind fields (Cavaleri and Bertotti, 2004). On the contrary, multi-decadal observed time series are rare. They have the evident advantage of somehow representing the real evolution of the waves, without the shortcomings associated with the limitation of models in reproducing the actual processes and the real variability within the wave fields. Obviously, observed wave time series are not exempt of problems. They represent a very local information, hence their use to describe the wave evolution at large scale is sometimes arguable and, in general, it needs the support of model simulations assessing to which extent the local value is representative of a large scale evolution. Local effects may prevent the identification of trends that are indeed present at large scale. Moreover, a regular maintenance, accurate monitoring and metadata information are crucial issues when considering the reliability of a time series for climate applications. Of course, where available, especially if for several decades, measured data are of great value for a number of reasons and can be valuable clues to delve further into the physics of the processes of interest, especially if considering that waves, as an integrated product of the local climate, if available in an area sensitive to even limited changes of the large scale pattern, can provide related compact and meaningful information. In addition, the availability for the area of interest of a 20-year long dataset of directional spectra (in frequency and direction) offers an independent, but theoretically corresponding and significantly long dataset, allowing to penetrate the wave problem through different perspectives. In particular, we investigate the contribution of the individual wave systems that modulate the variability of waves in the Adriatic Sea. A characterization of wave conditions based on wave spectra in fact brings out a more detailed description of the different wave regimes, their associated meteorological conditions and their variation in time and geographical space.

Calibration of decadal ensemble predictions

NASA Astrophysics Data System (ADS)

Pasternack, Alexander; Rust, Henning W.; Bhend, Jonas; Liniger, Mark; Grieger, Jens; Müller, Wolfgang; Ulbrich, Uwe

2017-04-01

Decadal climate predictions are of great socio-economic interest due to the corresponding planning horizons of several political and economic decisions. Due to uncertainties of weather and climate, forecasts (e.g. due to initial condition uncertainty), they are issued in a probabilistic way. One issue frequently observed for probabilistic forecasts is that they tend to be not reliable, i.e. the forecasted probabilities are not consistent with the relative frequency of the associated observed events. Thus, these kind of forecasts need to be re-calibrated. While re-calibration methods for seasonal time scales are available and frequently applied, these methods still have to be adapted for decadal time scales and its characteristic problems like climate trend and lead time dependent bias. Regarding this, we propose a method to re-calibrate decadal ensemble predictions that takes the above mentioned characteristics into account. Finally, this method will be applied and validated to decadal forecasts from the MiKlip system (Germany's initiative for decadal prediction).

Can GRACE Explain Some of the Main Interannual Polar Motion Signatures?

NASA Astrophysics Data System (ADS)

Adhikari, S.; Ivins, E. R.; Larour, E. Y.

2016-12-01

GRACE has provided a series of monthly solutions for water mass transport that now span a 14-year period. A natural question to ask is how much of this mass transport information might be used to reconstruct, theoretically, the non-tidal and non-Chandlerian polar motion at interannual time scales. Reconstruction of the pole position at interannual time scales since 2002 has been performed by Chen et al. (2013, GRL) and Adhikari and Ivins (2016, Science Advances). (The main feature of polar motion that has been evolving since the mid 1990's is the increasing dominance of Greenland ice mass loss.) Here we discuss this reconstruction and the level of error that occurs because of missing information about the spherical harmonic degree 1 and 2 terms and the lack of terms associated with angular momentum transfer in the Louiville equations. Using GRACE observations and complementary solutions of self-attraction/loading problem on an elastically compressible rotating earth, we show that ice mass losses from polar ice sheets, and when combined with changes in continental hydrology, explain nearly the entire amplitude (83±23%) and mean directional shift (within 5.9±7.6°) of recently observed eastward polar motion. We also show that decadal scale pole variations are directly linked to global changes in continental hydrology. The energy sources for such motions are likely to be associated with decadal scale ocean and atmospheric oscillations that also drive 20th century continental wet-dry variability. Interannual variability in pole position, therefore, offers a tool for assessing past stability of our climate, and for the future, now faced with an increased intensity in the water cycle and more vulnerable to ice sheet instability. Figure caption: Observed and reconstructed mean annual pole positions with respect to the 2003-2015 mean position. Blue error band is associated with the reconstructed solution; red signifies additional errors that are related to uncertainty in the long-term linear trend. Notice the interannual variability during the GRACE period.

Imaging spectroscopy links aspen genotype with below-ground processes at landscape scales

PubMed Central

Madritch, Michael D.; Kingdon, Clayton C.; Singh, Aditya; Mock, Karen E.; Lindroth, Richard L.; Townsend, Philip A.

2014-01-01

Fine-scale biodiversity is increasingly recognized as important to ecosystem-level processes. Remote sensing technologies have great potential to estimate both biodiversity and ecosystem function over large spatial scales. Here, we demonstrate the capacity of imaging spectroscopy to discriminate among genotypes of Populus tremuloides (trembling aspen), one of the most genetically diverse and widespread forest species in North America. We combine imaging spectroscopy (AVIRIS) data with genetic, phytochemical, microbial and biogeochemical data to determine how intraspecific plant genetic variation influences below-ground processes at landscape scales. We demonstrate that both canopy chemistry and below-ground processes vary over large spatial scales (continental) according to aspen genotype. Imaging spectrometer data distinguish aspen genotypes through variation in canopy spectral signature. In addition, foliar spectral variation correlates well with variation in canopy chemistry, especially condensed tannins. Variation in aspen canopy chemistry, in turn, is correlated with variation in below-ground processes. Variation in spectra also correlates well with variation in soil traits. These findings indicate that forest tree species can create spatial mosaics of ecosystem functioning across large spatial scales and that these patterns can be quantified via remote sensing techniques. Moreover, they demonstrate the utility of using optical properties as proxies for fine-scale measurements of biodiversity over large spatial scales. PMID:24733949

Duration of the common cold and similar continuous outcomes should be analyzed on the relative scale: a case study of two zinc lozenge trials.

PubMed

Hemilä, Harri

2017-05-12

The relative scale has been used for decades in analysing binary data in epidemiology. In contrast, there has been a long tradition of carrying out meta-analyses of continuous outcomes on the absolute, original measurement, scale. The biological rationale for using the relative scale in the analysis of binary outcomes is that it adjusts for baseline variations; however, similar baseline variations can occur in continuous outcomes and relative effect scale may therefore be often useful also for continuous outcomes. The aim of this study was to determine whether the relative scale is more consistent with empirical data on treating the common cold than the absolute scale. Individual patient data was available for 2 randomized trials on zinc lozenges for the treatment of the common cold. Mossad (Ann Intern Med 125:81-8, 1996) found 4.0 days and 43% reduction, and Petrus (Curr Ther Res 59:595-607, 1998) found 1.77 days and 25% reduction, in the duration of colds. In both trials, variance in the placebo group was significantly greater than in the zinc lozenge group. The effect estimates were applied to the common cold distributions of the placebo groups, and the resulting distributions were compared with the actual zinc lozenge group distributions. When the absolute effect estimates, 4.0 and 1.77 days, were applied to the placebo group common cold distributions, negative and zero (i.e., impossible) cold durations were predicted, and the high level variance remained. In contrast, when the relative effect estimates, 43 and 25%, were applied, impossible common cold durations were not predicted in the placebo groups, and the cold distributions became similar to those of the zinc lozenge groups. For some continuous outcomes, such as the duration of illness and the duration of hospital stay, the relative scale leads to a more informative statistical analysis and more effective communication of the study findings. The transformation of continuous data to the relative scale is simple with a spreadsheet program, after which the relative scale data can be analysed using standard meta-analysis software. The option for the analysis of relative effects of continuous outcomes directly from the original data should be implemented in standard meta-analysis programs.

Tracking four-decade inundation changes with multi-temporal satellite images in China's largest freshwater lake

NASA Astrophysics Data System (ADS)

Wu, Guiping

2017-04-01

Poyang Lake is the largest freshwater lake in China. The lake has undergone remarkable spatio-temporal changes in both short- and long-term scales since 1970s, resulting in significant hydrological, ecological and economic consequences. Remote sensing techniques have advantages for large-scale studies, by offering images at different spatial and spectral resolutions. However, due to technical difficulties, no single satellite sensor can meet the needs for high spatio-temporal resolution required for such monitoring. In this study, using Landsat Thematic Mapper (TM) and Moderate Resolution Imaging Spectroradiometer (MODIS) images collected between 1973 and 2012, we documented and investigated the short- and long-term characteristics of lake inundation based on Normalized Difference Water Index (NDWI). First, we presented a novel downscaling method based on the NDWI statistical regression algorithm to generate small-scale resolution inundation map (30m) from coarse MODIS data (500m). The downscaling is a linear calibration of the NDWI index from MODIS imagery to Landsat imagery, which is based on the assumption that the relationships between fine resolution and coarse resolution are invariable. Second, Tupu analysis method was further performed to explore the spatial-temporal distribution and changing processes of lake inundation based on downscaling inundation maps. Then, a defined water variation rate (WVR) and inundation frequency (IF) indicator was used to reveal seasonal water surface submersion/exposure processes of lake expansion and shrinkage in different zones. Finally, mathematical statistics methods were utilized to explore the possible driving mechanisms of the revealed change patterns with meteorological data and hydrological data. The results show that, there is a high correlation (mean absolute error of 3.95% and an R2 of 0.97) between the MODIS- and Landsat-derived water surface areas in Poyang Lake. Over the past 40 years, a declining trend to a certain extent for the Poyang Lake's area could be detected. The lake surface displayed comparatively low values ( 2000 km2) in wet periods of 1980, 2006, 2009 and 2011, corresponding to severe hydrological droughts in the lake. In addition, the water surface variation in Poyang Lake had a typical seasonal behavior. It mostly followed a unimodal cycle with area peaks appeared in the wet season. The earliest beginning of the inundation cycle was emerged in 2000 and the latest in 2006. In general, the change of lake area is a synthetic result of climate change, land-cover change and construction of dykes. Our findings should be valuable to a comprehensive understanding of Poyang Lake's decadal and seasonal variation, which is critical for flood/drought prevention, land use planning and lake ecological conservation.

[Effect of climate change on the fisheries conununity pattern in the overwintering ground of open waters of northern East China Sea].

PubMed

Liu, Zun-lei; Yuan, Xing-wei; Yang, Lin-lin; Yan, Li-ping; Tian, Yong-jun; Chen, Jia-hua

2015-03-01

Data sets of 26 fisheries target species from the fishery-depen-dent and fishery-independent surveys in the overwintering ground of open waters of northern East China Sea (OW-NECS), combined sea surface temperature (SST), were used to examine the links between diversity index, pattern of common variability and climate changes based on the principal component analysis (PCA) and generalized additive model (GAM). The results showed that the shift from a cold regime to a warm regime was detected in SST during the 1970s-2011 with step changes around 1982/ 1983. SST increased during the cold regime and the warm regime before 1998 (warming trend period, 1972-1998), and decreased during the warm regime after 1998 (cooling trend period, 1999-2011). Shannon diversity index was largely dependent on the filefish, which contributed up to 50% of the total production as a single species, with low diversity in the waters of the OW-NECS, during the late 1980s and early 1990s. Excluding the filefish, the diversity index linearly increased and decreased during 1972-1998 and 1999-2011, respectively. The variation pattern generally corresponds with the trend in water temperature, strongly suggesting the effect of the SST on the diversity. The first two components (PC1 and PC2) of PCA for target species, which accounted for 32.43% of the total variance, showed evident decadal variation patterns with a step change during 1992-1999 and inter-annual variability with short-period fluctuation, respectively. It seems that PC1 was associated with large scale climatic change, while PC2 was related to inter-annual oceanographic variability such as ENSO events. Linear fitting results showed winEOF1 had significant effect on PC1, and GAM analysis for PC1 showed that winter EOF1 (winEOF1) and summer EOF2 (sumEOF2) can explain 88.9% of the total variance. Nonlinear effect was also found between PC2 and win EOF1, indicating that the fish community structure, which had predominantly decadal/inter-annual variation patterns, was influenced by inter-annual variations in oceanographic conditions.

Dynamic Evaluation of Two Decades of CMAQ Simulations over the Continental United States

EPA Science Inventory

This presentation focuses on the dynamic evaluation of the CMAQ model over the continental United States using multi-decadal simulations for the period from 1990 to 2010 to examine how well the changes in observed ozone air quality induced by variations in meteorology and/or emis...

Climate change and marine ecosystems (Invited)

NASA Astrophysics Data System (ADS)

Chavez, F.

2013-12-01

Impacts of climate variability on marine ecosystems are pervasive. Those associated with the interannual El Ni~no phenomena are the most studied and better understood. Longer term variations associated with the Atlantic Multidecadal Oscillation (AMO), the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO) have become more evident as the present-day instrumental record has increased in length. The biological (chlorophyll to fish) and chemical (nutrients, oxygen, carbon) consequences of these climate-driven variations are discussed with an emphasis on the eastern and equatorial Pacific. During warmer periods biological productivity in the eastern Pacific is reduced and larger mobile organisms dramatically change their abundance and/or geographic distributions. At the same time biological productivity in the western Pacific increases highlighting that present (and future) climate-driven changes in biological productivity and chemical distributions are not (and will not) be uniform. The presentation documents present day variations using global scale information from satellites and in situ databases, model simulations and data collected by intensive local time series. Paradoxically longer term changes associated with phenomena like the Little Ice Age (LIA), captured in the sedimentary record, do not seem to follow the same warm (poor), cold (productive) patterns in the eastern Pacific, in fact these are reversed. The presentation ends with speculation regarding long term changes associated with a warmer world.

Upper-Ocean Heat Balance Processes and the Walker Circulation in CMIP5 Model Projections

NASA Technical Reports Server (NTRS)

Robertson, F. R.; Roberts, J. B.; Funk, C.; Lyon, B.; Ricciardulli, L.

2012-01-01

Considerable uncertainty remains as to the importance of mechanisms governing decadal and longer variability of the Walker Circulation, its connection to the tropical climate system, and prospects for tropical climate change in the face of anthropogenic forcing. Most contemporary climate models suggest that in response to elevated CO2 and a warmer but more stratified atmosphere, the required upward mass flux in tropical convection will diminish along with the Walker component of the tropical mean circulation as well. Alternatively, there is also evidence to suggest that the shoaling and increased vertical stratification of the thermocline in the eastern Pacific will enable a muted SST increase there-- preserving or even enhancing some of the dynamical forcing for the Walker cell flow. Over the past decade there have been observational indications of an acceleration in near-surface easterlies, a strengthened Pacific zonal SST gradient, and globally-teleconnected dislocations in precipitation. But is this evidence in support of an ocean dynamical thermostat process posited to accompany anthropogenic forcing, or just residual decadal fluctuations associated with variations in warm and cold ENSO events and other stochastic forcing? From a modeling perspective we try to make headway on this question by examining zonal variations in surface energy fluxes and dynamics governing tropical upper ocean heat content evolution in the WCRP CMIP5 model projections. There is some diversity among model simulations; for example, the CCSM4 indicates net ocean warming over the IndoPacific region while the CSIRO model concentrates separate warming responses over the central Pacific and Indian Ocean regions. The models, as with observations, demonstrate strong local coupling between variations in column water vapor, downward surface longwave radiation and SST; but the spatial patterns of changes in the sign of this relationship differ among models and, for models as a whole, with observations. Our analysis focuses initially on probing the inter-model differences in energy fluxes / transports and Walker Circulation response to forcing. We then attempt to identify statistically the El Nino- / La Nina-related ocean heat content variability unique to each model and regress out the associated energy flux, ocean heat transport and Walker response on these shorter time scales for comparison to that of the anthropogenic signals.

Sensitivity of tree ring growth to local and large-scale climate variability in a region of Southeastern Brazil

NASA Astrophysics Data System (ADS)

Venegas-González, Alejandro; Chagas, Matheus Peres; Anholetto Júnior, Claudio Roberto; Alvares, Clayton Alcarde; Roig, Fidel Alejandro; Tomazello Filho, Mario

2016-01-01

We explored the relationship between tree growth in two tropical species and local and large-scale climate variability in Southeastern Brazil. Tree ring width chronologies of Tectona grandis (teak) and Pinus caribaea (Caribbean pine) trees were compared with local (Water Requirement Satisfaction Index—WRSI, Standardized Precipitation Index—SPI, and Palmer Drought Severity Index—PDSI) and large-scale climate indices that analyze the equatorial pacific sea surface temperature (Trans-Niño Index-TNI and Niño-3.4-N3.4) and atmospheric circulation variations in the Southern Hemisphere (Antarctic Oscillation-AAO). Teak trees showed positive correlation with three indices in the current summer and fall. A significant correlation between WRSI index and Caribbean pine was observed in the dry season preceding tree ring formation. The influence of large-scale climate patterns was observed only for TNI and AAO, where there was a radial growth reduction in months preceding the growing season with positive values of the TNI in teak trees and radial growth increase (decrease) during December (March) to February (May) of the previous (current) growing season with positive phase of the AAO in teak (Caribbean pine) trees. The development of a new dendroclimatological study in Southeastern Brazil sheds light to local and large-scale climate influence on tree growth in recent decades, contributing in future climate change studies.

Decadal-scale changes of nitrate in ground water of the United States, 1988-2004

USGS Publications Warehouse

Rupert, Michael G.

2008-01-01

This study evaluated decadal-scale changes of nitrate concentrations in groundwater samples collected by the USGS National Water-Quality Assessment Program from 495 wells in 24 well networks across the USA in predominantly agricultural areas. Each well network was sampled once during 1988-1995 and resampled once during 2000-2004. Statistical tests of decadal-scale changes of nitrate concentrations in water from all 495 wells combined indicate there is a significant increase in nitrate concentrations in the data set as a whole. Eight out of the 24 well networks, or about 33%, had significant changes of nitrate concentrations. Of the eight well networks with significant decadal-scale changes of nitrate, all except one, the Willamette Valley of Oregon, had increasing nitrate concentrations. Median nitrate concentrations of three of those eight well networks increased above the USEPA maximum contaminant level of 10 mg L-1. Nitrate in water from wells with reduced conditions had significantly smaller decadal-scale changes in nitrate concentrations than oxidized and mixed waters. A subset of wells had data on ground water recharge date; nitrate concentrations increased in response to the increase of N fertilizer use since about 1950. Determining ground water recharge dates is an important component of a ground water trends investigation because recharge dates provide a link between changes in ground water quality and changes in land-use practices. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Reduced representation approaches to interrogate genome diversity in large repetitive plant genomes.

PubMed

Hirsch, Cory D; Evans, Joseph; Buell, C Robin; Hirsch, Candice N

2014-07-01

Technology and software improvements in the last decade now provide methodologies to access the genome sequence of not only a single accession, but also multiple accessions of plant species. This provides a means to interrogate species diversity at the genome level. Ample diversity among accessions in a collection of species can be found, including single-nucleotide polymorphisms, insertions and deletions, copy number variation and presence/absence variation. For species with small, non-repetitive rich genomes, re-sequencing of query accessions is robust, highly informative, and economically feasible. However, for species with moderate to large sized repetitive-rich genomes, technical and economic barriers prevent en masse genome re-sequencing of accessions. Multiple approaches to access a focused subset of loci in species with larger genomes have been developed, including reduced representation sequencing, exome capture and transcriptome sequencing. Collectively, these approaches have enabled interrogation of diversity on a genome scale for large plant genomes, including crop species important to worldwide food security. © The Author 2014. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Extracting climate memory using Fractional Integrated Statistical Model: A new perspective on climate prediction

PubMed Central

Yuan, Naiming; Fu, Zuntao; Liu, Shida

2014-01-01

Long term memory (LTM) in climate variability is studied by means of fractional integral techniques. By using a recently developed model, Fractional Integral Statistical Model (FISM), we in this report proposed a new method, with which one can estimate the long-lasting influences of historical climate states on the present time quantitatively, and further extract the influence as climate memory signals. To show the usability of this method, two examples, the Northern Hemisphere monthly Temperature Anomalies (NHTA) and the Pacific Decadal Oscillation index (PDO), are analyzed in this study. We find the climate memory signals indeed can be extracted and the whole variations can be further decomposed into two parts: the cumulative climate memory (CCM) and the weather-scale excitation (WSE). The stronger LTM is, the larger proportion the climate memory signals will account for in the whole variations. With the climate memory signals extracted, one can at least determine on what basis the considered time series will continue to change. Therefore, this report provides a new perspective on climate prediction. PMID:25300777

Digging into the corona: A modeling framework trained with Sun-grazing comet observations

NASA Astrophysics Data System (ADS)

Jia, Y. D.; Pesnell, W. D.; Bryans, P.; Downs, C.; Liu, W.; Schwartz, S. J.

2017-12-01

Images of comets diving into the low corona have been captured a few times in the past decade. Structures visible at various wavelengths during these encounters indicate a strong variation of the ambient conditions of the corona. We combine three numerical models: a global coronal model, a particle transportation model, and a cometary plasma interaction model into one framework to model the interaction of such Sun-grazing comets with plasma in the low corona. In our framework, cometary vapors are ionized via multiple channels and then captured by the coronal magnetic field. In seconds, these ions are further ionized into their highest charge state, which is revealed by certain coronal emission lines. Constrained by observations, we apply our framework to trace back to the local conditions of the ambient corona, and their spatial/time variation over a broad range of scales. Once trained by multiple stages of the comet's journey in the low corona, we illustrate how this framework can leverage these unique observations to probe the structure of the solar corona and solar wind.

Human Y chromosome copy number variation in the next generation sequencing era and beyond.

PubMed

Massaia, Andrea; Xue, Yali

2017-05-01

The human Y chromosome provides a fertile ground for structural rearrangements owing to its haploidy and high content of repeated sequences. The methodologies used for copy number variation (CNV) studies have developed over the years. Low-throughput techniques based on direct observation of rearrangements were developed early on, and are still used, often to complement array-based or sequencing approaches which have limited power in regions with high repeat content and specifically in the presence of long, identical repeats, such as those found in human sex chromosomes. Some specific rearrangements have been investigated for decades; because of their effects on fertility, or their outstanding evolutionary features, the interest in these has not diminished. However, following the flourishing of large-scale genomics, several studies have investigated CNVs across the whole chromosome. These studies sometimes employ data generated within large genomic projects such as the DDD study or the 1000 Genomes Project, and often survey large samples of healthy individuals without any prior selection. Novel technologies based on sequencing long molecules and combinations of technologies, promise to stimulate the study of Y-CNVs in the immediate future.

Uniform Temperature Dependency in the Phenology of a Keystone Herbivore in Lakes of the Northern Hemisphere

PubMed Central

Straile, Dietmar; Adrian, Rita; Schindler, Daniel E.

2012-01-01

Spring phenologies are advancing in many ecosystems associated with climate warming causing unpredictable changes in ecosystem functioning. Here we establish a phenological model for Daphnia, an aquatic keystone herbivore based on decadal data on water temperatures and the timing of Daphnia population maxima from Lake Constance, a large European lake. We tested this model with long-term time-series data from two lakes (Müggelsee, Germany; Lake Washington, USA), and with observations from a diverse set of 49 lakes/sites distributed widely across the Northern Hemisphere (NH). The model successfully captured the observed temporal variation of Daphnia phenology in the two case study sites (r2 = 0.25 and 0.39 for Müggelsee and Lake Washington, respectively) and large-scale spatial variation in the NH (R2 = 0.57). These results suggest that Daphnia phenology follows a uniform temperature dependency in NH lakes. Our approach – based on temperature phenologies – has large potential to study and predict phenologies of animal and plant populations across large latitudinal gradients in other ecosystems. PMID:23071520

A further contribution to the seasonal variation of weighted mean temperature

NASA Astrophysics Data System (ADS)

Ding, Maohua; Hu, Wusheng

2017-12-01

The weighted mean temperature Tm is a variable parameter in the Global Navigation Satellite System (GNSS) meteorology and the Askne-Nordius zenith wet delay (ZWD) model. Some parameters about the Tm seasonal variation (e.g. the annual mean value, the annual range, the annual and semi-annual amplitudes, and the long-term trend) were discussed before. In this study, some additional results about the Tm seasonal variation on a global scale were found by using the Tm time series at 309 global radiosonde sites. Periodic signals of the annual and semi-annual variations were detected in these Tm time series by using the Lomb-Scargle periodogram. The annual variation is the main component of the periodic Tm in non-tropical regions, while the annual variation or the semiannual variation can be the main component of the periodic Tm in tropics. The mean annual Tm almost keeps constant with the increasing latitude in tropics, while it decreases with the increasing latitude in non-tropical regions. From a global perspective, Tm has an increasing trend of 0.22 K/decade on average, which may be caused by the global warming effects. The annual phase is almost found in about January for the non-tropical regions of the Southern Hemisphere and in about July for the non-tropical regions of the Northern Hemisphere, but it has no clear symmetry in tropics. Unlike the annual phase, the geographical distributions of semi-annual phase do not follow obvious rules. In non-tropical regions, the maximum and minimum Tm of the seasonal model are usually found in respective summer and winter days while the maximum and minimum Tm are distributed over a whole year but not in any fixed seasons for tropical regions. The seasonal model errors increase with the increasing value of annual amplitude. A primary reason for the irregular seasonal variation in tropics is that Tm has rather small variations in this region.

Field Exploration and Life Detection Sampling Through Planetary Analogue Sampling (FELDSPAR).

NASA Technical Reports Server (NTRS)

Stockton, A.; Amador, E. S.; Cable, M. L.; Cantrell, T.; Chaudry, N.; Cullen, T.; Duca, Z.; Gentry, D. M.; Kirby, J.; Jacobsen, M.;

Multi-Decadal Aerosol Variations from 1980 to 2009: A Perspective from Observations and a Global Model

NASA Technical Reports Server (NTRS)

Chin, Mian; Diehl, T.; Tan, Q.; Prospero, J. M.; Kahn, R. A.; Remer, L. A.; Yu, H.; Sayer, A. M.; Bian, H.; Geogdzhayev, I. V.;

Interdecadal modulation of the Atlantic Multi-decadal Oscillation (AMO) on southwest China's temperature over the past 250 years

NASA Astrophysics Data System (ADS)

Fang, Keyan; Guo, Zhengtang; Chen, Deliang; Wang, Lei; Dong, Zhipeng; Zhou, Feifei; Zhao, Yan; Li, Jinbao; Li, Yingjun; Cao, Xinguang

2018-05-01

The temperature gradient between southwestern China and Indian Ocean is one key driver of the Indian Summer Monsoon, suggesting the necessity to understand temperature variability in southwestern China. Contrary to the general warming experienced in most of China, a few regions in southwestern China have undergone a cooling trend since the 1950s. To place this cooling trend in a historical context, this study develops an Abies fabri tree-ring width chronology in the Sichuan Basin, the most populated region in southwest China. The chronology spans from 1590 to 2012, with its reliable portion from 1758 to 2012, by far the longest in the Sichuan Basin. To better extract regional climate signals encoded in tree rings with strong local disturbances, we incorporate climate signals of nearby tree-ring chronologies to generate a large-scale tree-ring chronology (LSC). The LSC shows higher correlations with temperature near the sampling site on Mount Emei and sea surface temperatures of the northern Atlantic Ocean than chronologies developed using traditional methods. The highest correlations between the LSC and temperature are found from current February to July in the Sichuan Basin for the period 1901-1950 (r = 0.70), with a sharp decrease afterwards. Interdecadal variations of the LSC match well with Atlantic Multi-decadal Oscillation reconstructions, except for the late nineteenth century and after 1980s. This study provides evidence that southwest China is a transitional region both affected by the interdecadal temperature variations of the northern Atlantic and Asian areas, although their influences weakened in recent possible due to enhanced human activities.

Interannual to Decadal SST Variability in the Tropical Indian Ocean

NASA Astrophysics Data System (ADS)

Wang, G.; Newman, M.; Han, W.

2017-12-01

The Indian Ocean has received increasing attention in recent years for its large impacts on regional and global climate. However, due mainly to the close interdependence of the climate variation within the Tropical Pacific and the Indian Ocean, the internal sea surface temperature (SST) variability within the Indian Ocean has not been studied extensively on longer time scales. In this presentation we will show analysis of the interannual to decadal SST variability in the Tropical Indian Ocean in observations and Linear Inverse Model (LIM) results. We also compare the decoupled Indian Ocean SST variability from the Pacific against fully coupled one based on LIM integrations, to test the factors influence the features of the leading SST modes in the Indian Ocean. The result shows the Indian Ocean Basin (IOB) mode, which is strongly related to global averaged SST variability, passively responses to the Pacific variation. Without tropical Indo-Pacific coupling interaction, the intensity of IOB significantly decreases by 80%. The Indian Ocean Dipole (IOD) mode demonstrates its independence from the Pacific SST variability since the IOD does not change its long-term characteristics at all without inter-basin interactions. The overall SSTA variance decreases significantly in the Tropical Indian Ocean in the coupling restricted LIM runs, especially when the one-way impact from the Pacific to the Indian Ocean is turned off, suggesting that most of the variability in the Indian Ocean comes from the Pacific influence. On the other hand, the Indian Ocean could also transport anomalies to the Pacific, making the interaction a complete two-way process.

Bivalves as indicators of environmental variation and potential anthropogenic impacts in the southern Barents Sea

PubMed Central

Carroll, Michael L.; Johnson, Beverly J.; Henkes, Gregory A.; McMahon, Kelton W.; Voronkov, Andrey; Ambrose, William G.; Denisenko, Stanislav G.

2009-01-01

Identifying patterns and drivers of natural variability in populations is necessary to gauge potential effects of climatic change and the expected increases in commercial activities in the Arctic on communities and ecosystems. We analyzed growth rates and shell geochemistry of the circumpolar Greenland smooth cockle, Serripes groenlandicus, from the southern Barents Sea over almost 70 years between 1882 and 1968. The datasets were calibrated via annually-deposited growth lines, and growth, stable isotope (δ18O, δ13C), and trace elemental (Mg, Sr, Ba, Mn) patterns were linked to environmental variations on weekly to decadal scales. Standardized growth indices revealed an oscillatory growth pattern with a multi-year periodicity, which was inversely related to the North Atlantic Oscillation Index (NAO), and positively related to local river discharge. Up to 60% of the annual variability in the Ba/Ca could be explained by variations in river discharge at the site closest to the rivers, but the relationship disappeared at a more distant location. Patterns of δ18O, δ13C, and Sr/Ca together provide evidence that bivalve growth ceases at elevated temperatures during the fall and recommences at the coldest temperatures in the early spring, with the implication that food, rather than temperature, is the primary driver of bivalve growth. The multi-proxy approach of combining the annually integrated information from the growth results and higher resolution geochemical results yielded a robust interpretation of biophysical coupling in the region over temporal and spatial scales. We thus demonstrate that sclerochronological proxies can be useful retrospective analytical tools for establishing a baseline of ecosystem variability in assessing potential combined impacts of climatic change and increasing commercial activities on Arctic communities. PMID:19394657

Terrestrial Feedbacks Incorporated in Global Vegetation Models through Observed Trait-Environment Responses

NASA Astrophysics Data System (ADS)

Bodegom, P. V.

2015-12-01

Most global vegetation models used to evaluate climate change impacts rely on plant functional types to describe vegetation responses to environmental stresses. In a traditional set-up in which vegetation characteristics are considered constant within a vegetation type, the possibility to implement and infer feedback mechanisms are limited as feedback mechanisms will likely involve a changing expression of community trait values. Based on community assembly concepts, we implemented functional trait-environment relationships into a global dynamic vegetation model to quantitatively assess this feature. For the current climate, a different global vegetation distribution was calculated with and without the inclusion of trait variation, emphasizing the importance of feedbacks -in interaction with competitive processes- for the prevailing global patterns. These trait-environmental responses do, however, not necessarily imply adaptive responses of vegetation to changing conditions and may locally lead to a faster turnover in vegetation upon climate change. Indeed, when running climate projections, simulations with trait variation did not yield a more stable or resilient vegetation than those without. Through the different feedback expressions, global and regional carbon and water fluxes were -however- strongly altered. At a global scale, model projections suggest an increased productivity and hence an increased carbon sink in the next decades to come, when including trait variation. However, by the end of the century, a reduced carbon sink is projected. This effect is due to a downregulation of photosynthesis rates, particularly in the tropical regions, even when accounting for CO2-fertilization effects. Altogether, the various global model simulations suggest the critical importance of including vegetation functional responses to changing environmental conditions to grasp terrestrial feedback mechanisms at global scales in the light of climate change.

Predation and infanticide influence ideal free choice by a parrot occupying heterogeneous tropical habitats.

PubMed

Bonebrake, Timothy C; Beissinger, Steven R

2010-06-01

The ideal free distribution (IFD) predicts that organisms will disperse to sites that maximize their fitness based on availability of resources. Habitat heterogeneity underlies resource variation and influences spatial variation in demography and the distribution of populations. We relate nest site productivity at multiple scales measured over a decade to habitat quality in a box-nesting population of Forpus passerinus (green-rumped parrotlets) in Venezuela to examine critical IFD assumptions. Variation in reproductive success at the local population and neighborhood scales had a much larger influence on productivity (fledglings per nest box per year) than nest site or female identity. Habitat features were reliable cues of nest site quality. Nest sites with less vegetative cover produced greater numbers of fledglings than sites with more cover. However, there was also a competitive cost to nesting in high-quality, low-vegetative cover nest boxes, as these sites experienced the most infanticide events. In the lowland local population, water depth and cover surrounding nest sites were related with F. passerinus productivity. Low vegetative cover and deeper water were associated with lower predation rates, suggesting that predation could be a primary factor driving habitat selection patterns. Parrotlets also demonstrated directional dispersal. Pairs that changed nest sites were more likely to disperse from poor-quality nest sites to high-quality nest sites rather than vice versa, and juveniles were more likely to disperse to, or remain in, the more productive of the two local populations. Parrotlets exhibited three characteristics fundamental to the IFD: habitat heterogeneity within and between local populations, reliable habitat cues to productivity, and active dispersal to sites of higher fitness.

Modulation of quasi-biennial ozone oscillations in the equatorial stratosphere by the solar cycle

NASA Astrophysics Data System (ADS)

Bezverkhnii, Viacheslav; Gruzdev, Aleksandr

Analysis of variation in ozone concentration, temperature, and zonal wind velocity in the equatorial stratosphere at the quasi-biennial (QB) and quasi-decadal (QD) time scales and their relation to the QB and 11-year variations in solar activity is made with the help of wavelet, cross-wavelet and cross-spectral techniques using SBUV/SBUV 2 (ozone), NMC, ERA-40, ERA-Interim (wind and temperature), and radiosonde (wind) data. Sunspot number and 10.7 cm solar radio flux data are used as indices of solar activity. The QD mode with the mean period of 128 months and the QB mode with 28-29 month period are derived from variations in ozone concentration , ozone meridional gradient, temperature and wind velocity. Local maxima of amplitudes of the QD variation in the ozone meridional gradient occur in 4-5 and 20-30 hPa layers. The amplitude of the QB mode of the ozone meridional gradient in 30-50 hPa layer is modulated by the solar cycle in such a way that the amplitude maximum corresponds approximately to the solar cycle maximum. Similar modulation is not found in the QB mode of ozone concentration. While the QD variations in ozone and zonal wind velocity are weak compared to the QB oscillation, the amplitudes of the QD and QB modes of temperature oscillations in the lower and middle stratosphere are close to each other. The modulation of the QB oscillations in the ozone meridional gradient in the lower stratosphere by the 11-year solar cycle is an additional evidence of solar activity influence on the stratosphere, which extends results by Soukharev and Hood (2001), Bezverkhnii and Gruzdev (2007), and Gruzdev and Bezverkhnii (2010). References: 1. Bezverkhnii, V.A., and A.N. Gruzdev. Relation between quasi-decadal and quasi-biennial oscillations of solar activity and the equatorial stratospheric wind. Doklady Earth Sciences, 2007, Vol. 415A, No 6, pp. 970-974. 2. Gruzdev, A.N., and V.A. Bezverkhnii. Possible ozone influence on the quasi-biennial oscillation in the equatorial stratosphere. Doklady Earth Sciences, 2010, Vol. 434, Part 1, pp. 1279-1284. 3. Soukharev, B.E., and L.L. Hood. Possible solar modulation of the equatorial quasi-biennisl oscillation: Additional statistical evidence. J. Geophys. Res., 2001, Vol. 106, No D14, pp. 14855-14868.

Climate variability in China during the last millennium based on reconstructions and simulations

NASA Astrophysics Data System (ADS)

García-Bustamante, E.; Luterbacher, J.; Xoplaki, E.; Werner, J. P.; Jungclaus, J.; Zorita, E.; González-Rouco, J. F.; Fernández-Donado, L.; Hegerl, G.; Ge, Q.; Hao, Z.; Wagner, S.

2012-04-01

Multi-decadal to centennial climate variability in China during the last millennium is analysed. We compare the low frequency temperature and precipitation variations from proxy-based reconstructions and palaeo-simulations from climate models. Focusing on the regional responses to the global climate evolution is of high relevance due to the complexity of the interactions between physical mechanisms at different spatio-temporal scales and the potential severity of the derived multiple socio-economic impacts. China stands out as a particularly interesting region, not only due to its complex climatic features, ranging from the semiarid northwestern Tibetan Plateau to the tropical monsoon southeastern climates, but also because of its wealth of proxy data. However, comprehensive assessments of proxy- and model-based information about palaeo-climatic variations in China are, to our knowledge, still lacking. In addition, existing studies depict a general lack of agreement between reconstructions and model simulations with respect to the amplitude and/or occurrence of warmer/colder and wetter/drier periods during the last millennium and the magnitude of the 20th century warming trend. Furthermore, these works are mainly focused on eastern China regions that show a denser proxy data coverage. We investigate how last millennium palaeo-runs compare to independent evidences from an unusual large number of proxy reconstructions over the study area by employing state-of-the-art palaeo-simulations with multi-member ensembles from the CMIP5/PMIP3 project. This shapes an ideal frame for the evaluation of the uncertainties associated to internal and intermodel model variability. Preliminary results indicate that despite the strong regional and seasonal dependencies, temperature reconstructions in China evidence coherent variations among all regions at centennial scale, especially during the last 500 years. The spatial consistency of low frequency temperature changes is an interesting aspect and of relevance for the assessment of forced climatic responses in China. The comparison between reconstructions and simulations from climate models show that, apart from the 20th century warming trend, the variance of the reconstructed mean China temperature lies in the envelope (uncertainty range) spanned by the temperature simulations. The uncertainty arises from the internal (multi-member ensembles) and the inter-model variability. Centennial variations tend to be broadly synchronous in the reconstructions and the simulations. However, the simulations show a delay of the warm period 1000-1300 AD. This warm medieval period both in the simulations and the reconstructions is followed by cooling till 1800 AD. Based on the simulations, the recent warming is not unprecedented and is comparable to the medieval warming. Further steps of this study will address the individual contribution of anthropogenic and natural forcings on climate variability and change during the last millennium in China. We will make use of of models that provide runs including single forcings (fingerprints) for the attribution of climate variations from decadal to multi-centennial time scales. With this aim, we will implement statistical techniques for the detection of optimal signal-to-noise-ratio between external forcings and internal variability of reconstructed temperatures and precipitation. To apply these approaches the uncertainties associated with both reconstructions and simulations will be estimated. The latter will shed some light into the mechanisms behind current climate evolution and will help to constrain uncertainties in the sensitivity of model simulations to increasing CO2 scenarios of future climate change. This work will also contribute to the overall aims of the PAGES 2k initiative in Asia (http://www.pages.unibe.ch/workinggroups/2k-network)

Arctic sea ice variability in the context of recent atmospheric circulation trends

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

Deser, C.; Walsh, J.E.; Timlin, M.S.

Sea ice is a sensitive component of the climate system, influenced by conditions in both the atmosphere and ocean. Variations in sea ice may in turn modulate climate by altering the surface albedo; the exchange of heat, moisture, and momentum between the atmosphere and ocean; and the upper ocean stratification in areas of deep water formation. The surface albedo effect is considered to be one of the dominant factors in the poleward amplification of global warming due to increased greenhouse gas concentrations simulated in many climate models. Forty years (1958--97) of reanalysis products and corresponding sea ice concentration data aremore » used to document Arctic sea ice variability and its association with surface air temperature (SAT) and sea level pressure (SLP) throughout the Northern Hemisphere extratropics. The dominant mode of winter (January-March) sea ice variability exhibits out-of-phase fluctuations between the western and eastern North Atlantic, together with a weaker dipole in the North Pacific. The time series of this mode has a high winter-to-winter autocorrelation (0.69) and is dominated by decadal-scale variations and a longer-term trend of diminishing ice cover east of Greenland and increasing ice cover west of Greenland. Associated with the dominant pattern of winter sea ice variability are large-scale changes in SAT and SLP that closely resemble the North Atlantic oscillation. The associated SAT and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the trends of ice coverage have been greatest, although the well-documented warming of the northern continental regions is also apparent. the temporal and spatial relationships between the SLP and ice anomaly fields are consistent with the notion that atmospheric circulation anomalies force the sea ice variations. However, there appears to be a local response of the atmospheric circulation to the changing sea ice variations. However, there appears to be a local response of the atmospheric circulation to the changing sea ice cover east of Greenland. Specifically, cyclone frequencies have increased and mean SLPs have decreased over the retracted ice margin in the Greenland Sea, and these changes differ from those associated directly with the North Atlantic oscillation. The dominant mode of sea ice variability in summer (July-September) is more spatially uniform than that in winter. Summer ice extent for the Arctic as a whole has exhibited a nearly monotonic decline (-4% decade{sup {minus}1}) during the past 40 yr. Summer sea ice variations appear to be initiated by atmospheric circulation anomalies over the high Arctic in late spring. Positive ice-albedo feedback may account for the relatively long delay (2--3 months) between the time of atmospheric forcing and the maximum ice response, and it may have served to amplify the summer ice retreat.« less

Evolutionary implications of mitochondrial genetic variation: mitochondrial genetic effects on OXPHOS respiration and mitochondrial quantity change with age and sex in fruit flies.

PubMed

Wolff, J N; Pichaud, N; Camus, M F; Côté, G; Blier, P U; Dowling, D K

2016-04-01

The ancient acquisition of the mitochondrion into the ancestor of modern-day eukaryotes is thought to have been pivotal in facilitating the evolution of complex life. Mitochondria retain their own diminutive genome, with mitochondrial genes encoding core subunits involved in oxidative phosphorylation. Traditionally, it was assumed that there was little scope for genetic variation to accumulate and be maintained within the mitochondrial genome. However, in the past decade, mitochondrial genetic variation has been routinely tied to the expression of life-history traits such as fertility, development and longevity. To examine whether these broad-scale effects on life-history trait expression might ultimately find their root in mitochondrially mediated effects on core bioenergetic function, we measured the effects of genetic variation across twelve different mitochondrial haplotypes on respiratory capacity and mitochondrial quantity in the fruit fly, Drosophila melanogaster. We used strains of flies that differed only in their mitochondrial haplotype, and tested each sex separately at two different adult ages. Mitochondrial haplotypes affected both respiratory capacity and mitochondrial quantity. However, these effects were highly context-dependent, with the genetic effects contingent on both the sex and the age of the flies. These sex- and age-specific genetic effects are likely to resonate across the entire organismal life-history, providing insights into how mitochondrial genetic variation may contribute to sex-specific trajectories of life-history evolution. © 2016 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2016 European Society For Evolutionary Biology.

Determining the contributions of urbanisation and climate change to NPP variations over the last decade in the Yangtze River Delta, China.

PubMed

Wu, Shaohua; Zhou, Shenglu; Chen, Dongxiang; Wei, Zongqiang; Dai, Liang; Li, Xingong

2014-02-15

Terrestrial net primary production (NPP) is an important measure of global change, and identifying the relative contributions of urbanisation and climate change to NPP is important for understanding the impact of human and natural influences on terrestrial systems and the carbon cycle. The objective of this study was to reveal how urbanisation and climate drive changes in NPP. Satellite-based estimates of NPP collected over a 12-year period (1999-2010) were analysed to identify NPP variations in the Yangtze River Delta. Temporal and spatial analysis methods were used to identify the relationships among NPP, nighttime light urbanisation index values, and climatic factors from pixel to regional scales. The NPP of the entire Yangtze River Delta decreased slightly at a rate of -0.5 g C m(-2)a(-1) from 1999 to 2010, but this change was not significant. However, in the urban region, NPP decreased significantly (p<0.05) at a rate of -4.7 g C m(-2)a(-1) due to urbanisation processes. A spatially explicit method was proposed to partition the relative contributions of urbanisation and climate change to NPP variation. The results revealed that the urbanisation factor is the main driving force for NPP change in high-speed urbanisation areas, and the factor accounted for 47% of the variations. However, in the forest and farm regions, the NPP variation was mainly controlled by climate change and residual factors. Copyright © 2013 Elsevier B.V. All rights reserved.

Climate sensitivity to the lower stratospheric ozone variations

NASA Astrophysics Data System (ADS)

Kilifarska, N. A.

2012-12-01

The strong sensitivity of the Earth's radiation balance to variations in the lower stratospheric ozone—reported previously—is analysed here by the use of non-linear statistical methods. Our non-linear model of the land air temperature (T)—driven by the measured Arosa total ozone (TOZ)—explains 75% of total variability of Earth's T variations during the period 1926-2011. We have analysed also the factors which could influence the TOZ variability and found that the strongest impact belongs to the multi-decadal variations of galactic cosmic rays. Constructing a statistical model of the ozone variability, we have been able to predict the tendency in the land air T evolution till the end of the current decade. Results show that Earth is facing a weak cooling of the surface T by 0.05-0.25 K (depending on the ozone model) until the end of the current solar cycle. A new mechanism for O3 influence on climate is proposed.

NDVI indicated long-term interannual changes in vegetation activities and their responses to climatic and anthropogenic factors in the Three Gorges Reservoir Region, China.

PubMed

Wen, Zhaofei; Wu, Shengjun; Chen, Jilong; Lü, Mingquan

2017-01-01

Natural and social environmental changes in the China's Three Gorges Reservoir Region (TGRR) have received worldwide attention. Identifying interannual changes in vegetation activities in the TGRR is an important task for assessing the impact these changes have on the local ecosystem. We used long-term (1982-2011) satellite-derived Normalized Difference Vegetation Index (NDVI) datasets and climatic and anthropogenic factors to analyze the spatiotemporal patterns of vegetation activities in the TGRR, as well as their links to changes in temperature (TEM), precipitation (PRE), downward radiation (RAD), and anthropogenic activities. At the whole TGRR regional scale, a statistically significant overall uptrend in NDVI variations was observed in 1982-2011. More specifically, there were two distinct periods with different trends split by a breakpoint in 1991: NDVI first sharply increased prior to 1991, and then showed a relatively weak rate of increase after 1991. At the pixel scale, most parts of the TGRR experienced increasing NDVI before the 1990s but different trend change types after the 1990s: trends were positive in forests in the northeastern parts, but negative in farmland in southwest parts of the TGRR. The TEM warming trend was the main climate-related driver of uptrending NDVI variations pre-1990s, and decreasing PRE was the main climate factor (42%) influencing the mid-western farmland areas' NDVI variations post-1990s. We also found that anthropogenic factors such as population density, man-made ecological restoration, and urbanization have notable impacts on the TGRR's NDVI variations. For example, large overall trend slopes in NDVI were more likely to appear in TGRR regions with large fractions of ecological restoration within the last two decades. The findings of this study may help to build a better understanding of the mechanics of NDVI variations in the periods before and during TGDP construction for ongoing ecosystem monitoring and assessment in the post-TGDP period. Copyright © 2016 Elsevier B.V. All rights reserved.

Genome-wide investigation of genetic changes during modern breeding of Brassica napus.

PubMed

Wang, Nian; Li, Feng; Chen, Biyun; Xu, Kun; Yan, Guixin; Qiao, Jiangwei; Li, Jun; Gao, Guizhen; Bancroft, Ian; Meng, Jingling; King, Graham J; Wu, Xiaoming

2014-08-01

Considerable genome variation had been incorporated within rapeseed breeding programs over past decades. In past decades, there have been substantial changes in phenotypic properties of rapeseed as a result of extensive breeding effort. Uncovering the underlying patterns of allelic variation in the context of genome organisation would provide knowledge to guide future genetic improvement. We assessed genome-wide genetic changes, including population structure, genetic relatedness, the extent of linkage disequilibrium, nucleotide diversity and genetic differentiation based on F ST outlier detection, for a panel of 472 Brassica napus inbred accessions using a 60 k Brassica Infinium® SNP array. We found genetic diversity varied in different sub-groups. Moreover, the genetic diversity increased from 1950 to 1980 and then remained at a similar level in China and Europe. We also found ~6-10 % genomic regions revealed high F ST values. Some QTLs previously associated with important agronomic traits overlapped with these regions. Overall, the B. napus C genome was found to have more high F ST signals than the A genome, and we concluded that the C genome may contribute more valuable alleles to generate elite traits. The results of this study indicate that considerable genome variation had been incorporated within rapeseed breeding programs over past decades. These results also contribute to understanding the impact of rapeseed improvement on available genome variation and the potential for dissecting complex agronomic traits.

MiKlip-PRODEF: Probabilistic Decadal Forecast for Central and Western Europe

NASA Astrophysics Data System (ADS)

Reyers, Mark; Haas, Rabea; Ludwig, Patrick; Pinto, Joaquim

2013-04-01

The demand for skilful climate predictions on time-scales of several years to decades has increased in recent years, in particular for economic, societal and political terms. Within the BMBF MiKlip consortium, a decadal prediction system on the global to local scale is currently being developed. The subproject PRODEF is part of the MiKlip-Module C, which aims at the regionalisation of decadal predictability for Central and Western Europe. In PRODEF, a combined statistical-dynamical downscaling (SDD) and a probabilistic forecast tool are developed and applied to the new Earth system model of the Max-Planck Institute Hamburg (MPI-ESM), which is part of the CMIP5 experiment. Focus is given on the decadal predictability of windstorms, related wind gusts as well as wind energy potentials. SDD combines the benefits of both high resolution dynamical downscaling and purely statistical downscaling of GCM output. Hence, the SDD approach is used to obtain a very large ensemble of highly resolved decadal forecasts. With respect to the focal points of PRODEF, a clustering of temporal evolving atmospheric fields, a circulation weather type (CWT) analysis, and a storm damage indices analysis is applied to the full ensemble of the decadal hindcast experiments of the MPI-ESM in its lower resolution (MPI-ESM-LR). The ensemble consists of up to ten realisations per yearly initialised decadal hindcast experiments for the period 1960-2010 (altogether 287 realisations). Representatives of CWTs / clusters and single storm episodes are dynamical downscaled with the regional climate model COSMO-CLM with a horizontal resolution of 0.22°. For each model grid point, the distributions of the local climate parameters (e.g. surface wind gusts) are determined for different periods (e.g. each decades) by recombining dynamical downscaled episodes weighted with the respective weather type frequencies. The applicability of the SDD approach is illustrated with examples of decadal forecasts of the MPI-ESM. We are able to perform a bias correction of the frequencies of large scale weather types and to quantify the uncertainties of decadal predictability on large and local scale arising from different initial conditions. Further, probability density functions of local parameters like e.g. wind gusts for different periods and decades derived from the SDD approach is compared to observations and reanalysis data. Skill scores are used to quantify the decadal predictability for different leading time periods and to analyse whether the SDD approach shows systematic errors for some regions.

Dynamic Evaluation of Two Decades of CMAQ Simulations over the Continental United States (book chapter)

EPA Science Inventory

This paper focuses on dynamic evaluation of the CMAQ model over the continental United States using multi-decadal simulations for the period from 1990 to 2010 to examine how well the changes in observed ozone air quality induced by variations in meteorology and/or emissions are s...

Reduction of initial shock in decadal predictions using a new initialization strategy

NASA Astrophysics Data System (ADS)

He, Yujun; Wang, Bin; Liu, Mimi; Liu, Li; Yu, Yongqiang; Liu, Juanjuan; Li, Ruizhe; Zhang, Cheng; Xu, Shiming; Huang, Wenyu; Liu, Qun; Wang, Yong; Li, Feifei

2017-08-01

A novel full-field initialization strategy based on the dimension-reduced projection four-dimensional variational data assimilation (DRP-4DVar) is proposed to alleviate the well-known initial shock occurring in the early years of decadal predictions. It generates consistent initial conditions, which best fit the monthly mean oceanic analysis data along the coupled model trajectory in 1 month windows. Three indices to measure the initial shock intensity are also proposed. Results indicate that this method does reduce the initial shock in decadal predictions by Flexible Global Ocean-Atmosphere-Land System model, Grid-point version 2 (FGOALS-g2) compared with the three-dimensional variational data assimilation-based nudging full-field initialization for the same model and is comparable to or even better than the different initialization strategies for other fifth phase of the Coupled Model Intercomparison Project (CMIP5) models. Better hindcasts of global mean surface air temperature anomalies can be obtained than in other FGOALS-g2 experiments. Due to the good model response to external forcing and the reduction of initial shock, higher decadal prediction skill is achieved than in other CMIP5 models.

Impacts of Wildfire on Interception Losses and Net Precipitation in a Sub-Alpine Rocky Mountain Watershed in Alberta, Canada.

NASA Astrophysics Data System (ADS)

Williams, C.; Silins, U.; Wagner, M. J.; Bladon, K. D.; Martens, A. M.; Anderson, A.; Stone, M.; Emelko, M. B.

2014-12-01

Interception of precipitation in sub-alpine forests is likely to be strongly reduced after wildfire, potentially producing large increases in net precipitation. Objectives of this study were to describe changes in rainfall and snow interception, and net precipitation after the severe 2003 Lost Creek wildfire as part of the Southern Rockies Watershed Project in the south-west Rocky Mountains of Alberta, Canada. Throughfall troughs and stemflow gauges were used to explore relationships between throughfall, stemflow, and net rainfall with variation in gross rainfall in burned and undisturbed stands during the summers of 2006-2008. These relationships were used to scale the effects of the wildfire on net rainfall for the first decade after the wildfire (2004-2013) using a 10 year rainfall record in the watershed. Annual snowpack surveys (5 snow courses in each of burned and reference stands) measured peak snowpack depth, density, and snow water equivalent (SWE) for this same period. Mean annual P was 1140 mm (684-1519 mm) during the first 10 years after the wildfire, with 61% falling as snow. Throughfall and stemflow in the burned forest accounted for 86% and 7% of gross rainfall, respectively, compared with 53% and 0.002% in the unburned stands in the summers of 2006-2008. Scaled rainfall interception relationships (=f(rainfall event size)) indicated annual increases in net rainfall were 192 mm/yr (133-347 mm) for 10 years after the fire. Similarly, mean increases in peak SWE were 134 mm/yr (93-216 mm). Collectively, the mean increase in net precipitation was 325 mm/yr (226-563 mm; 29%) for the first decade after the wildfire. Hydrologic forcing by increased net precipitation may be a particularly important element of wildfire impacts on sub-alpine watersheds. Furthermore, because of the very slow growth rates of sub-alpine forests, increases in net precipitation are likely to persist and affect precipitation-runoff relationships for decades in these environments.

Human genetics and genomics a decade after the release of the draft sequence of the human genome.

PubMed

Naidoo, Nasheen; Pawitan, Yudi; Soong, Richie; Cooper, David N; Ku, Chee-Seng

2011-10-01

Substantial progress has been made in human genetics and genomics research over the past ten years since the publication of the draft sequence of the human genome in 2001. Findings emanating directly from the Human Genome Project, together with those from follow-on studies, have had an enormous impact on our understanding of the architecture and function of the human genome. Major developments have been made in cataloguing genetic variation, the International HapMap Project, and with respect to advances in genotyping technologies. These developments are vital for the emergence of genome-wide association studies in the investigation of complex diseases and traits. In parallel, the advent of high-throughput sequencing technologies has ushered in the 'personal genome sequencing' era for both normal and cancer genomes, and made possible large-scale genome sequencing studies such as the 1000 Genomes Project and the International Cancer Genome Consortium. The high-throughput sequencing and sequence-capture technologies are also providing new opportunities to study Mendelian disorders through exome sequencing and whole-genome sequencing. This paper reviews these major developments in human genetics and genomics over the past decade.

Human genetics and genomics a decade after the release of the draft sequence of the human genome

PubMed Central

2011-01-01

Substantial progress has been made in human genetics and genomics research over the past ten years since the publication of the draft sequence of the human genome in 2001. Findings emanating directly from the Human Genome Project, together with those from follow-on studies, have had an enormous impact on our understanding of the architecture and function of the human genome. Major developments have been made in cataloguing genetic variation, the International HapMap Project, and with respect to advances in genotyping technologies. These developments are vital for the emergence of genome-wide association studies in the investigation of complex diseases and traits. In parallel, the advent of high-throughput sequencing technologies has ushered in the 'personal genome sequencing' era for both normal and cancer genomes, and made possible large-scale genome sequencing studies such as the 1000 Genomes Project and the International Cancer Genome Consortium. The high-throughput sequencing and sequence-capture technologies are also providing new opportunities to study Mendelian disorders through exome sequencing and whole-genome sequencing. This paper reviews these major developments in human genetics and genomics over the past decade. PMID:22155605

A Review of Pacific Interdecadal Climate Variability: Possible Mechanisms and Surface Climate Signatures in the Pacific Sector

NASA Astrophysics Data System (ADS)

Mantua, N. J.

2004-12-01

Many investigators have examined historical surface climate records from the Pacific sector and identified a relatively small number of spatial patterns varying at decadal to interdecadal time scales. "Pacific Decadal Variability" (PDV) is a label that has been used to describe this family of climate variations. Some patterns of PDV are contained completely within the northern extratropics, while others have signatures throughout the Pacific hemisphere on both sides of the equator. Mechanisms for observed patterns of PDV are not yet known, though a wide variety of hypotheses have been proposed. Various ocean-atmosphere mechanisms for PDV are contained within the extratropics, others within the tropics, while others involve tropical-extratropical interactions. Some investigators have proposed external forcing (solar, lunar, or volcanic) as potentially important for driving PDV. A relatively simple hypothesis couples ENSO forcing with upper ocean heat storage for extratropical PDV, and it suggests PDV predictability may be limited to ~2 year lead times. Paleo-PDV reconstructions have been based on materials throughout the Pacific sector using such things as extratropical tree-rings, tropical corals, extratropical clam shell growth rings, and ice cores. These different proxy records have generally provided different perspectives on paleo-PDV behavior.

Geodynamo Modeling of Core-Mantle Interactions

NASA Technical Reports Server (NTRS)

Kuang, Wei-Jia; Chao, Benjamin F.; Smith, David E. (Technical Monitor)

2001-01-01

Angular momentum exchange between the Earth's mantle and core influences the Earth's rotation on time scales of decades and longer, in particular in the length of day (LOD) which have been measured with progressively increasing accuracy for the last two centuries. There are four possible coupling mechanisms for transferring the axial angular momentum across the core-mantle boundary (CMB): viscous, magnetic, topography, and gravitational torques. Here we use our scalable, modularized, fully dynamic geodynamo model for the core to assess the importance of these torques. This numerical model, as an extension of the Kuang-Bloxham model that has successfully simulated the generation of the Earth's magnetic field, is used to obtain numerical results in various physical conditions in terms of specific parameterization consistent with the dynamical processes in the fluid outer core. The results show that depending on the electrical conductivity of the lower mantle and the amplitude of the boundary topography at CMB, both magnetic and topographic couplings can contribute significantly to the angular momentum exchange. This implies that the core-mantle interactions are far more complex than has been assumed and that there is unlikely a single dominant coupling mechanism for the observed decadal LOD variation.

Decadal predictions of the North Atlantic CO2 uptake.

PubMed

Li, Hongmei; Ilyina, Tatiana; Müller, Wolfgang A; Sienz, Frank

2016-03-30

As a major CO2 sink, the North Atlantic, especially its subpolar gyre region, is essential for the global carbon cycle. Decadal fluctuations of CO2 uptake in the North Atlantic subpolar gyre region are associated with the evolution of the North Atlantic Oscillation, the Atlantic meridional overturning circulation, ocean mixing and sea surface temperature anomalies. While variations in the physical state of the ocean can be predicted several years in advance by initialization of Earth system models, predictability of CO2 uptake has remained unexplored. Here we investigate the predictability of CO2 uptake variations by initialization of the MPI-ESM decadal prediction system. We find large multi-year variability in oceanic CO2 uptake and demonstrate that its potential predictive skill in the western subpolar gyre region is up to 4-7 years. The predictive skill is mainly maintained in winter and is attributed to the improved physical state of the ocean.

Arctic Ocean Freshwater Content and Its Decadal Memory of Sea-Level Pressure

NASA Astrophysics Data System (ADS)

Johnson, Helen L.; Cornish, Sam B.; Kostov, Yavor; Beer, Emma; Lique, Camille

2018-05-01

Arctic freshwater content (FWC) has increased significantly over the last two decades, with potential future implications for the Atlantic meridional overturning circulation downstream. We investigate the relationship between Arctic FWC and atmospheric circulation in the control run of a coupled climate model. Multiple linear lagged regression is used to extract the response of total Arctic FWC to a hypothetical step increase in the principal components of sea-level pressure. The results demonstrate that the FWC adjusts on a decadal timescale, consistent with the idea that wind-driven ocean dynamics and eddies determine the response of Arctic Ocean circulation and properties to a change in surface forcing, as suggested by idealized models and theory. Convolving the response of FWC to a change in sea-level pressure with historical sea-level pressure variations reveals that the recent observed increase in Arctic FWC is related to natural variations in sea-level pressure.

Adaptive diversification of growth allometry in the plant Arabidopsis thaliana.

PubMed

Vasseur, François; Exposito-Alonso, Moises; Ayala-Garay, Oscar J; Wang, George; Enquist, Brian J; Vile, Denis; Violle, Cyrille; Weigel, Detlef

2018-03-27

Seed plants vary tremendously in size and morphology; however, variation and covariation in plant traits may be governed, at least in part, by universal biophysical laws and biological constants. Metabolic scaling theory (MST) posits that whole-organismal metabolism and growth rate are under stabilizing selection that minimizes the scaling of hydrodynamic resistance and maximizes the scaling of resource uptake. This constrains variation in physiological traits and in the rate of biomass accumulation, so that they can be expressed as mathematical functions of plant size with near-constant allometric scaling exponents across species. However, the observed variation in scaling exponents calls into question the evolutionary drivers and the universality of allometric equations. We have measured growth scaling and fitness traits of 451 Arabidopsis thaliana accessions with sequenced genomes. Variation among accessions around the scaling exponent predicted by MST was correlated with relative growth rate, seed production, and stress resistance. Genomic analyses indicate that growth allometry is affected by many genes associated with local climate and abiotic stress response. The gene with the strongest effect, PUB4 , has molecular signatures of balancing selection, suggesting that intraspecific variation in growth scaling is maintained by opposing selection on the trade-off between seed production and abiotic stress resistance. Our findings suggest that variation in allometry contributes to local adaptation to contrasting environments. Our results help reconcile past debates on the origin of allometric scaling in biology and begin to link adaptive variation in allometric scaling to specific genes. Copyright © 2018 the Author(s). Published by PNAS.

Adaptive diversification of growth allometry in the plant Arabidopsis thaliana

PubMed Central

Vasseur, François; Ayala-Garay, Oscar J.; Wang, George; Enquist, Brian J.; Vile, Denis; Violle, Cyrille

2018-01-01

Seed plants vary tremendously in size and morphology; however, variation and covariation in plant traits may be governed, at least in part, by universal biophysical laws and biological constants. Metabolic scaling theory (MST) posits that whole-organismal metabolism and growth rate are under stabilizing selection that minimizes the scaling of hydrodynamic resistance and maximizes the scaling of resource uptake. This constrains variation in physiological traits and in the rate of biomass accumulation, so that they can be expressed as mathematical functions of plant size with near-constant allometric scaling exponents across species. However, the observed variation in scaling exponents calls into question the evolutionary drivers and the universality of allometric equations. We have measured growth scaling and fitness traits of 451 Arabidopsis thaliana accessions with sequenced genomes. Variation among accessions around the scaling exponent predicted by MST was correlated with relative growth rate, seed production, and stress resistance. Genomic analyses indicate that growth allometry is affected by many genes associated with local climate and abiotic stress response. The gene with the strongest effect, PUB4, has molecular signatures of balancing selection, suggesting that intraspecific variation in growth scaling is maintained by opposing selection on the trade-off between seed production and abiotic stress resistance. Our findings suggest that variation in allometry contributes to local adaptation to contrasting environments. Our results help reconcile past debates on the origin of allometric scaling in biology and begin to link adaptive variation in allometric scaling to specific genes. PMID:29540570

An observation-based progression modeling approach to spring and autumn deciduous tree phenology

NASA Astrophysics Data System (ADS)

Yu, Rong; Schwartz, Mark D.; Donnelly, Alison; Liang, Liang

2016-03-01

It is important to accurately determine the response of spring and autumn phenology to climate change in forest ecosystems, as phenological variations affect carbon balance, forest productivity, and biodiversity. We observed phenology intensively throughout spring and autumn in a temperate deciduous woodlot at Milwaukee, WI, USA, during 2007-2012. Twenty-four phenophase levels in spring and eight in autumn were recorded for 106 trees, including white ash, basswood, white oak, boxelder, red oak, and hophornbeam. Our phenological progression models revealed that accumulated degree-days and day length explained 87.9-93.4 % of the variation in spring canopy development and 75.8-89.1 % of the variation in autumn senescence. In addition, the timing of community-level spring and autumn phenophases and the length of the growing season from 1871 to 2012 were reconstructed with the models developed. All simulated spring phenophases significantly advanced at a rate from 0.24 to 0.48 days/decade ( p ≤ 0.001) during the 1871-2012 period and from 1.58 to 2.00 days/decade ( p < 0.02) during the 1970-2012 period; two simulated autumn phenophases were significantly delayed at a rate of 0.37 (mid-leaf coloration) and 0.50 (full-leaf coloration) days/decade ( p < 0.01) during the 1970-2012 period. Consequently, the simulated growing season lengthened at a rate of 0.45 and 2.50 days/decade ( p < =0.001), respectively, during the two periods. Our results further showed the variability of responses to climate between early and late spring phenophases, as well as between leaf coloration and leaf fall, and suggested accelerating simulated ecosystem responses to climate warming over the last four decades in comparison to the past 142 years.

An observation-based progression modeling approach to spring and autumn deciduous tree phenology.

PubMed

Yu, Rong; Schwartz, Mark D; Donnelly, Alison; Liang, Liang

2016-03-01

It is important to accurately determine the response of spring and autumn phenology to climate change in forest ecosystems, as phenological variations affect carbon balance, forest productivity, and biodiversity. We observed phenology intensively throughout spring and autumn in a temperate deciduous woodlot at Milwaukee, WI, USA, during 2007-2012. Twenty-four phenophase levels in spring and eight in autumn were recorded for 106 trees, including white ash, basswood, white oak, boxelder, red oak, and hophornbeam. Our phenological progression models revealed that accumulated degree-days and day length explained 87.9-93.4 % of the variation in spring canopy development and 75.8-89.1 % of the variation in autumn senescence. In addition, the timing of community-level spring and autumn phenophases and the length of the growing season from 1871 to 2012 were reconstructed with the models developed. All simulated spring phenophases significantly advanced at a rate from 0.24 to 0.48 days/decade (p ≤ 0.001) during the 1871-2012 period and from 1.58 to 2.00 days/decade (p < 0.02) during the 1970-2012 period; two simulated autumn phenophases were significantly delayed at a rate of 0.37 (mid-leaf coloration) and 0.50 (full-leaf coloration) days/decade (p < 0.01) during the 1970-2012 period. Consequently, the simulated growing season lengthened at a rate of 0.45 and 2.50 days/decade (p < =0.001), respectively, during the two periods. Our results further showed the variability of responses to climate between early and late spring phenophases, as well as between leaf coloration and leaf fall, and suggested accelerating simulated ecosystem responses to climate warming over the last four decades in comparison to the past 142 years.

A Reconstruction of Subtropical Western North Pacific SST Variability Back to 1578, Based on a Porites Coral Sr/Ca Record from the Northern Ryukyus, Japan

NASA Astrophysics Data System (ADS)

Kawakubo, Y.; Alibert, C.; Yokoyama, Y.

2017-12-01

We present a seasonal reconstruction of sea surface temperature (SST) from 1578 to 2008, based on a Porites coral Sr/Ca record from the northern Ryukyus, within the Kuroshio southern recirculation gyre. Interannual SST anomalies are generally 0.5°C, making Sr/Ca-derived SST reconstructions a challenging task. Replicate measurements along adjacent coral growth axes, enabled by the laser ablation inductively coupled plasma mass spectrometry technique used here, give evidence of rather large uncertainties. Nonetheless, derived winter SST anomalies are significantly correlated with the Western Pacific atmospheric pattern which has a dominant influence on winter temperature in East Asia. Annual mean SSTs show interdecadal variations, notably cold intervals between 1670 and 1700 during the Maunder Minimum (MM) and between 1766 and 1788 characterized by a negative phase of the North Atlantic Oscillation. Cold summers in 1783 and 1784 coincide with the long-lasting Laki eruption that had a profound impact on the Northern Hemisphere climate, including the severe "Tenmei" famine in Japan. The decades between 1855 and 1900 are significantly cooler than the first half of the twentieth century, while those between 1700 and 1765, following the MM, are warmer than average. SST variability in the Ryukyus is only marginally influenced by the Pacific Decadal Oscillation, so that external forcing remains the main driver of low-frequency temperature changes. However, the close connection between the Kuroshio extension (KE) and its recirculation gyre suggests that decadal SST anomalies associated with the KE front also impact the Ryukyus, and there is a possible additional role for feedback of the Kuroshio-Oyashio variability to the large-scale atmosphere at decadal timescale.

Response of African humid tropical forests to recent rainfall anomalies

PubMed Central

Asefi-Najafabady, Salvi; Saatchi, Sassan

2013-01-01

During the last decade, strong negative rainfall anomalies resulting from increased sea surface temperature in the tropical Atlantic have caused extensive droughts in rainforests of western Amazonia, exerting persistent effects on the forest canopy. In contrast, there have been no significant impacts on rainforests of West and Central Africa during the same period, despite large-scale droughts and rainfall anomalies during the same period. Using a combination of rainfall observations from meteorological stations from the Climate Research Unit (CRU; 1950–2009) and satellite observations of the Tropical Rainfall Measuring Mission (TRMM; 1998–2010), we show that West and Central Africa experienced strong negative water deficit (WD) anomalies over the last decade, particularly in 2005, 2006 and 2007. These anomalies were a continuation of an increasing drying trend in the region that started in the 1970s. We monitored the response of forests to extreme rainfall anomalies of the past decade by analysing the microwave scatterometer data from QuickSCAT (1999–2009) sensitive to variations in canopy water content and structure. Unlike in Amazonia, we found no significant impacts of extreme WD events on forests of Central Africa, suggesting potential adaptability of these forests to short-term severe droughts. Only forests near the savanna boundary in West Africa and in fragmented landscapes of the northern Congo Basin responded to extreme droughts with widespread canopy disturbance that lasted only during the period of WD. Time-series analyses of CRU and TRMM data show most regions in Central and West Africa experience seasonal or decadal extreme WDs (less than −600 mm). We hypothesize that the long-term historical extreme WDs with gradual drying trends in the 1970s have increased the adaptability of humid tropical forests in Africa to droughts. PMID:23878335

Response of African humid tropical forests to recent rainfall anomalies.

PubMed

Asefi-Najafabady, Salvi; Saatchi, Sassan

2013-01-01

During the last decade, strong negative rainfall anomalies resulting from increased sea surface temperature in the tropical Atlantic have caused extensive droughts in rainforests of western Amazonia, exerting persistent effects on the forest canopy. In contrast, there have been no significant impacts on rainforests of West and Central Africa during the same period, despite large-scale droughts and rainfall anomalies during the same period. Using a combination of rainfall observations from meteorological stations from the Climate Research Unit (CRU; 1950-2009) and satellite observations of the Tropical Rainfall Measuring Mission (TRMM; 1998-2010), we show that West and Central Africa experienced strong negative water deficit (WD) anomalies over the last decade, particularly in 2005, 2006 and 2007. These anomalies were a continuation of an increasing drying trend in the region that started in the 1970s. We monitored the response of forests to extreme rainfall anomalies of the past decade by analysing the microwave scatterometer data from QuickSCAT (1999-2009) sensitive to variations in canopy water content and structure. Unlike in Amazonia, we found no significant impacts of extreme WD events on forests of Central Africa, suggesting potential adaptability of these forests to short-term severe droughts. Only forests near the savanna boundary in West Africa and in fragmented landscapes of the northern Congo Basin responded to extreme droughts with widespread canopy disturbance that lasted only during the period of WD. Time-series analyses of CRU and TRMM data show most regions in Central and West Africa experience seasonal or decadal extreme WDs (less than -600 mm). We hypothesize that the long-term historical extreme WDs with gradual drying trends in the 1970s have increased the adaptability of humid tropical forests in Africa to droughts.

Decadal application of WRF/Chem for regional air quality and climate modeling over the U.S. under the representative concentration pathways scenarios. Part 1: Model evaluation and impact of downscaling

NASA Astrophysics Data System (ADS)

Yahya, Khairunnisa; Wang, Kai; Campbell, Patrick; Chen, Ying; Glotfelty, Timothy; He, Jian; Pirhalla, Michael; Zhang, Yang

2017-03-01

An advanced online-coupled meteorology-chemistry model, i.e., the Weather Research and Forecasting Model with Chemistry (WRF/Chem), is applied for current (2001-2010) and future (2046-2055) decades under the representative concentration pathways (RCP) 4.5 and 8.5 scenarios to examine changes in future climate, air quality, and their interactions. In this Part I paper, a comprehensive model evaluation is carried out for current decade to assess the performance of WRF/Chem and WRF under both scenarios and the benefits of downscaling the North Carolina State University's (NCSU) version of the Community Earth System Model (CESM_NCSU) using WRF/Chem. The evaluation of WRF/Chem shows an overall good performance for most meteorological and chemical variables on a decadal scale. Temperature at 2-m is overpredicted by WRF (by ∼0.2-0.3 °C) but underpredicted by WRF/Chem (by ∼0.3-0.4 °C), due to higher radiation from WRF. Both WRF and WRF/Chem show large overpredictions for precipitation, indicating limitations in their microphysics or convective parameterizations. WRF/Chem with prognostic chemical concentrations, however, performs much better than WRF with prescribed chemical concentrations for radiation variables, illustrating the benefit of predicting gases and aerosols and representing their feedbacks into meteorology in WRF/Chem. WRF/Chem performs much better than CESM_NCSU for most surface meteorological variables and O3 hourly mixing ratios. In addition, WRF/Chem better captures observed temporal and spatial variations than CESM_NCSU. CESM_NCSU performance for radiation variables is comparable to or better than WRF/Chem performance because of the model tuning in CESM_NCSU that is routinely made in global models.

MODIS Snow Cover Recovery Using Variational Interpolation

NASA Astrophysics Data System (ADS)

Tran, H.; Nguyen, P.; Hsu, K. L.; Sorooshian, S.

2017-12-01

Cloud obscuration is one of the major problems that limit the usages of satellite images in general and in NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) global Snow-Covered Area (SCA) products in particular. Among the approaches to resolve the problem, the Variational Interpolation (VI) algorithm method, proposed by Xia et al., 2012, obtains cloud-free dynamic SCA images from MODIS. This method is automatic and robust. However, computational deficiency is a main drawback that degrades applying the method for larger scales (i.e., spatial and temporal scales). To overcome this difficulty, this study introduces an improved version of the original VI. The modified VI algorithm integrates the MINimum RESidual (MINRES) iteration (Paige and Saunders., 1975) to prevent the system from breaking up when applied to much broader scales. An experiment was done to demonstrate the crash-proof ability of the new algorithm in comparison with the original VI method, an ability that is obtained when maintaining the distribution of the weights set after solving the linear system. After that, the new VI algorithm was applied to the whole Contiguous United States (CONUS) over four winter months of 2016 and 2017, and validated using the snow station network (SNOTEL). The resulting cloud free images have high accuracy in capturing the dynamical changes of snow in contrast with the MODIS snow cover maps. Lastly, the algorithm was applied to create a Cloud free images dataset from March 10, 2000 to February 28, 2017, which is able to provide an overview of snow trends over CONUS for nearly two decades. ACKNOWLEDGMENTSWe would like to acknowledge NASA, NOAA Office of Hydrologic Development (OHD) National Weather Service (NWS), Cooperative Institute for Climate and Satellites (CICS), Army Research Office (ARO), ICIWaRM, and UNESCO for supporting this research.

Fine-scale environmental specialization of reef-building corals might be limiting reef recovery in the Florida Keys.

PubMed

Kenkel, Carly D; Almanza, Albert T; Matz, Mikhail V

2015-12-01

Despite decades of monitoring global reef decline, we are still largely unable to explain patterns of reef deterioration at local scales, which precludes the development of effective management strategies. Offshore reefs of the Florida Keys, USA, experience milder temperatures and lower nutrient loads in comparison to inshore reefs yet remain considerably more degraded than nearshore patch reefs. A year-long reciprocal transplant experiment of the mustard hill coral (Porites astreoides) involving four source and eight transplant locations reveals that corals adapt and/or acclimatize to their local habitat on a < 10-km scale. Surprisingly, transplantation to putatively similar environmental types (e.g., offshore corals moved to a novel offshore site, or along-shore transplantation) resulted in greater reductions in fitness proxies, such as coral growth, than cross-channel transplantation between inshore and offshore reefs. The only abiotic factor showing significantly greater differences between along-shore sites was daily temperature range extremes (rather than the absolute high or low temperatures reached), providing a possible explanation for this pattern. Offshore-origin corals exhibited significant growth reductions at sites with greater daily temperature ranges, which explained up to 39% of the variation in their mass gain. In contrast, daily temperature range explained at most 9% of growth variation in inshore-origin corals, suggesting that inshore corals are more tolerant of high-frequency temperature fluctuations. Finally, corals incur trade-offs when specializing to their native reef. Across reef locations the coefficient of selection against coral transplants was 0.07 ± 0.02 (mean ± SE). This selection against immigrants could hinder the ability of corals to recolonize devastated reefs, whether through assisted migration efforts or natural recruitment events, providing a unifying explanation for observed patterns of coral decline in this reef system.

An analytical approach to separate climate and human contributions to basin streamflow variability

NASA Astrophysics Data System (ADS)

Li, Changbin; Wang, Liuming; Wanrui, Wang; Qi, Jiaguo; Linshan, Yang; Zhang, Yuan; Lei, Wu; Cui, Xia; Wang, Peng

2018-04-01

Climate variability and anthropogenic regulations are two interwoven factors in the ecohydrologic system across large basins. Understanding the roles that these two factors play under various hydrologic conditions is of great significance for basin hydrology and sustainable water utilization. In this study, we present an analytical approach based on coupling water balance method and Budyko hypothesis to derive effectiveness coefficients (ECs) of climate change, as a way to disentangle contributions of it and human activities to the variability of river discharges under different hydro-transitional situations. The climate dominated streamflow change (ΔQc) by EC approach was compared with those deduced by the elasticity method and sensitivity index. The results suggest that the EC approach is valid and applicable for hydrologic study at large basin scale. Analyses of various scenarios revealed that contributions of climate change and human activities to river discharge variation differed among the regions of the study area. Over the past several decades, climate change dominated hydro-transitions from dry to wet, while human activities played key roles in the reduction of streamflow during wet to dry periods. Remarkable decline of discharge in upstream was mainly due to human interventions, although climate contributed more to runoff increasing during dry periods in the semi-arid downstream. Induced effectiveness on streamflow changes indicated a contribution ratio of 49% for climate and 51% for human activities at the basin scale from 1956 to 2015. The mathematic derivation based simple approach, together with the case example of temporal segmentation and spatial zoning, could help people understand variation of river discharge with more details at a large basin scale under the background of climate change and human regulations.

The Lamu Basin deepwater fold-and-thrust belt: An example of a margin-scale, gravity-driven thrust belt along the continental passive margin of East Africa

NASA Astrophysics Data System (ADS)

Cruciani, Francesco; Barchi, Massimiliano R.

2016-03-01

In recent decades, advances in seismic processing and acquisition of new data sets have revealed the presence of many deepwater fold-and-thrust belts (DW-FTBs), often developing along continental passive margins. These kinds of tectonic features have been intensively studied, due to their substantial interest. This work presents a regional-scale study of the poorly explored Lamu Basin DW-FTB, a margin-scale, gravity-driven system extending for more than 450 km along the continental passive margin of Kenya and southern Somalia (East Africa). A 2-D seismic data set was analyzed, consisting of both recently acquired high-quality data and old reprocessed seismic profiles, for the first detailed structural and stratigraphic interpretation of this DW-FTB. The system originated over an Early to mid-Cretaceous shale detachment due to a mainly gravity-spreading mechanism. Analysis of synkinematic strata indicates that the DW-FTB was active from the Late Cretaceous to the Early Miocene, but almost all of the deformation occurred before the Late Paleocene. The fold-and-thrust system displays a marked N-S variation in width, the northern portion being more than 150 km wide and the southern portion only a few dozen kilometers wide; this along-strike variation is thought to be related to the complex tectonosedimentary evolution of the continental margin at the Somalia-Kenya boundary, also reflected in the present-day bathymetry. Locally, a series of volcanic edifices stopped the basinward propagation of the DW-FTB. A landward change in the dominant structural style, from asymmetric imbricate thrust sheets to pseudo-symmetric detachment folds, is generally observed, related to the landward thickening of the detached shales.

The impact of AMO and NAO in Western Iberia during the Late Holocene

NASA Astrophysics Data System (ADS)

Hernandez, A.; Leira, M.; Trigo, R.; Vázquez-Loureiro, D.; Carballeira, R.; Sáez, A.

2016-12-01

High mountain lakes in the Iberian Peninsula are particularly sensitive to the influence of North Atlantic large-scale modes of climate variability due to their geographical position and the reduced anthropic disturbances. In this context, Serra da Estrela (Portugal), the westernmost range of the Sistema Central, constitutes a physical barrier to air masses coming from the Atlantic Ocean. However, long-term climate reconstructions have not yet been conducted. We present a climate reconstruction of this region based on facies analysis, X-ray fluorescence core scanning, elemental and isotope geochemistry on bulk organic matter and a preliminary study of diatom assemblages from the sedimentary record of Lake Peixão (1677 m a.s.l.; Serra da Estrela) for the last ca. 3500 years. A multivariate statistical analysis has been performed to recognize the main environmental factors controlling the sedimentary infill. Our results reveal that two main processes explain the 70% of the total variance. Thus, changes in primary productivity, reflected in organic matter accumulation, and variations in runoff, related to external particles input, explain 53% and 17% respectively. Additionally, evidence of changes in productivity and water level regime recorded as variations in diatom assemblages correlate well with our interpretations. A comparison between the lake productivity changes and previous Atlantic Multidecadal Oscillation (AMO) reconstructions shows a good correlation, suggesting this climate mode as the main driver over lacustrine primary productivity at multi-decadal scales. In turn, changes in terrigenous inputs, linked to precipitation, seem to be more influenced by the winter North Atlantic Oscillation (NAO) variability. Hence, our results highlight that although the climate regime in this area is clearly influenced by the NAO, the AMO also plays a key role at long-term time-scales.

Twentieth century sea surface temperature and salinity variations at Timor inferred from paired coral δ18O and Sr/Ca measurements

NASA Astrophysics Data System (ADS)

Cahyarini, Sri Yudawati; Pfeiffer, Miriam; Nurhati, Intan Suci; Aldrian, Edvin; Dullo, Wolf-Christian; Hetzinger, Steffen

2014-07-01

The Indonesian Throughflow (ITF), which represents the global ocean circulation connecting the Pacific Warm Pool to the Indian Ocean, strongly influences the Indo-Pacific climate. ITF monitoring since the late 1990s using mooring buoys have provided insights on seasonal and interannual time scales. However, the absence of longer records limits our perspective on its evolution over the past century. Here, we present sea surface temperature (SST) and salinity (SSS) proxy records from Timor Island located at the ITF exit passage via paired coral δ18O and Sr/Ca measurements spanning the period 1914-2004. These high-resolution proxy based climate data of the last century highlights improvements and cautions when interpreting paleoclimate records of the Indonesian region. If the seasonality of SST and SSS is not perfectly in phase, the application of coral Sr/Ca thermometry improves SST reconstructions compared to estimates based on coral δ18O only. Our records also underline the importance of ocean advection besides rainfall on local SSS in the region. Although the El Niño/Southern Oscillation (ENSO) causes larger anomalies relative to the Indian Ocean Dipole (IOD), Timor coral-based SST and SSS records robustly correlate with IOD on interannual time scales, whereas ENSO only modifies Timor SST. Similarly, Timor SST and SSS are strongly linked to Indian Ocean decadal-scale variations that appear to lead Timor oceanographic conditions by about 1.6-2 years. Our study sheds new light on the complex signatures of Indo-Pacific climate modes on SST and SSS dynamics of the ITF. This article was corrected on 8 AUG 2014. See the end of the full text for details.

Exploring the Links in Monthly to Decadal Variability of the Atmospheric Water Balance Over the Wettest Regions in ERA-20C

NASA Astrophysics Data System (ADS)

Nogueira, M.

2017-10-01

Monthly-to-decadal variability of the regional precipitation over Intertropical Convergence Zone and north-Atlantic and north-Pacific storm tracks was investigated using ERA-20C reanalysis. Satellite-based precipitation (P) and evaporation (E) climatological patterns were well reproduced by ERA-20C. Regional P and E monthly time series displayed 20% differences, but these decreased rapidly with time scale ( 10% at yearly time scales). Spectral analysis showed good scale-by-scale statistical agreement between ERA-20C and observations. Using ERA-Interim showed no improvement despite the much wider range of information assimilated (including satellites). Remarkably high Detrended Cross-Correlation Analysis coefficients (ρDCCA > 0.7 and often ρDCCA > 0.9) revealed tight links between the nonperiodic variability of P, moisture divergence (DIV), and pressure velocity (ω) at monthly-to-decadal time scales over all the wet regions. In contrast, ρDCCA was essentially nonsignificant between nonperiodic P and E or sea surface temperature (SST). Thus, the nonperiodic monthly-to-decadal variability of precipitation in these regions is almost fully controlled by dynamics and not by local E or SST (suggested by Clausius-Clapeyron relation). Analysis of regional nonperiodic standard deviations and power spectra (and respective spectral exponents, β) provided further robustness to this conclusion. Finally, clear transitions in β for P, DIV, and ω between tropical and storm track regions were found. The latter is dominated by transient storms, with energy accumulation at synoptic scales and β < 0.1 at monthly-to-decadal time scales, implying that variability and information creation decrease rapidly with time scale. Larger β values (0.2 to 0.4) were found in the tropics, implying longer-range autocorrelations and slower decreasing variability and information creation with time scale, consistent with the important forcing from internal modes of variability (e.g., El Niño-Southern Oscillation).

North Pacific decadal climate variability since 1661

USGS Publications Warehouse

Biondi, Franco; Gershunov, Alexander; Cayan, Daniel R.

2001-01-01

Climate in the North Pacific and North American sectors has experienced interdecadal shifts during the twentieth century. A network of recently developed tree-ring chronologies for Southern and Baja California extends the instrumental record and reveals decadal-scale variability back to 1661. The Pacific decadal oscillation (PDO) is closely matched by the dominant mode of tree-ring variability that provides a preliminary view of multiannual climate fluctuations spanning the past four centuries. The reconstructed PDO index features a prominent bidecadal oscillation, whose amplitude weakened in the late l700s to mid-1800s. A comparison with proxy records of ENSO suggests that the greatest decadal-scale oscillations in Pacific climate between 1706 and 1977 occurred around 1750, 1905, and 1947.

Impact of decadal cloud variations on the Earth’s energy budget

DOE PAGES

Zhou, Chen; Zelinka, Mark D.; Klein, Stephen A.

2016-10-31

Feedbacks of clouds on climate change strongly influence the magnitude of global warming. Cloud feedbacks, in turn, depend on the spatial patterns of surface warming, which vary on decadal timescales. Therefore, the magnitude of the decadal cloud feedback could deviate from the long-term cloud feedback. We present climate model simulations to show that the global mean cloud feedback in response to decadal temperature fluctuations varies dramatically due to time variations in the spatial pattern of sea surface temperature. Here, we find that cloud anomalies associated with these patterns significantly modify the Earth’s energy budget. Specifically, the decadal cloud feedback betweenmore » the 1980s and 2000s is substantially more negative than the long-term cloud feedback. This is a result of cooling in tropical regions where air descends, relative to warming in tropical ascent regions, which strengthens low-level atmospheric stability. Under these conditions, low-level cloud cover and its reflection of solar radiation increase, despite an increase in global mean surface temperature. Our results suggest that sea surface temperature pattern-induced low cloud anomalies could have contributed to the period of reduced warming between 1998 and 2013, and o er a physical explanation of why climate sensitivities estimated from recently observed trends are probably biased low.« less

Impact of decadal cloud variations on the Earth’s energy budget

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

Zhou, Chen; Zelinka, Mark D.; Klein, Stephen A.

Feedbacks of clouds on climate change strongly influence the magnitude of global warming. Cloud feedbacks, in turn, depend on the spatial patterns of surface warming, which vary on decadal timescales. Therefore, the magnitude of the decadal cloud feedback could deviate from the long-term cloud feedback. We present climate model simulations to show that the global mean cloud feedback in response to decadal temperature fluctuations varies dramatically due to time variations in the spatial pattern of sea surface temperature. Here, we find that cloud anomalies associated with these patterns significantly modify the Earth’s energy budget. Specifically, the decadal cloud feedback betweenmore » the 1980s and 2000s is substantially more negative than the long-term cloud feedback. This is a result of cooling in tropical regions where air descends, relative to warming in tropical ascent regions, which strengthens low-level atmospheric stability. Under these conditions, low-level cloud cover and its reflection of solar radiation increase, despite an increase in global mean surface temperature. Our results suggest that sea surface temperature pattern-induced low cloud anomalies could have contributed to the period of reduced warming between 1998 and 2013, and o er a physical explanation of why climate sensitivities estimated from recently observed trends are probably biased low.« less

Impact of decadal cloud variations on the Earth's energy budget

NASA Astrophysics Data System (ADS)

Zhou, Chen; Zelinka, Mark D.; Klein, Stephen A.

2016-12-01

Feedbacks of clouds on climate change strongly influence the magnitude of global warming. Cloud feedbacks, in turn, depend on the spatial patterns of surface warming, which vary on decadal timescales. Therefore, the magnitude of the decadal cloud feedback could deviate from the long-term cloud feedback. Here we present climate model simulations to show that the global mean cloud feedback in response to decadal temperature fluctuations varies dramatically due to time variations in the spatial pattern of sea surface temperature. We find that cloud anomalies associated with these patterns significantly modify the Earth's energy budget. Specifically, the decadal cloud feedback between the 1980s and 2000s is substantially more negative than the long-term cloud feedback. This is a result of cooling in tropical regions where air descends, relative to warming in tropical ascent regions, which strengthens low-level atmospheric stability. Under these conditions, low-level cloud cover and its reflection of solar radiation increase, despite an increase in global mean surface temperature. These results suggest that sea surface temperature pattern-induced low cloud anomalies could have contributed to the period of reduced warming between 1998 and 2013, and offer a physical explanation of why climate sensitivities estimated from recently observed trends are probably biased low.

Temporal variations of cosmic rays over a variety of time scales

NASA Technical Reports Server (NTRS)

Jokipii, J. R.; Marti, K.

1986-01-01

The variation of the intensity of Galactic cosmic rays in the inner solar system over a wide variety of time scales is discussed, and the generally accepted physical model which can account quantitatively for these modulations is reviewed. The use of direct measurements and of nuclear reactions to study the temporal intensity variations is summarized. It is demonstrated that all of the observed variations could easily be the result of solar variations on long and short time scales.

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.

Decadal stability in genetic variation and structure in the intertidal seaweed Fucus serratus (Heterokontophyta: Fucaceae).

PubMed

Jueterbock, Alexander; Coyer, James A; Olsen, Jeanine L; Hoarau, Galice

2018-06-15

The spatial distribution of genetic diversity and structure has important implications for conservation as it reveals a species' strong and weak points with regard to stability and evolutionary capacity. Temporal genetic stability is rarely tested in marine species other than commercially important fishes, but is crucial for the utility of temporal snapshots in conservation management. High and stable diversity can help to mitigate the predicted northward range shift of seaweeds under the impact of climate change. Given the key ecological role of fucoid seaweeds along rocky shores, the positive effect of genetic diversity may reach beyond the species level to stabilize the entire intertidal ecosystem along the temperate North Atlantic. In this study, we estimated the effective population size, as well as temporal changes in genetic structure and diversity of the seaweed F. serratus using 22 microsatellite markers. Samples were taken across latitudes and a range of temperature regimes at seven locations with decadal sampling (2000 and 2010). Across latitudes, genetic structure and diversity remained stable over 5-10 generations. Stable small-scale structure enhanced regional diversity throughout the species' range. In accordance with its biogeographic history, effective population size and diversity peaked in the species' mid-range in Brittany (France), and declined towards its leading and trailing edge to the north and south. At the species' southern edge, multi-locus-heterozygosity displayed a strong decline from 1999 to 2010. Temporally stable genetic structure over small spatial scales is a potential driver for local adaptation and species radiation in the genus Fucus. Survival and adaptation of the low-diversity leading edge of F. serratus may be enhanced by regional gene flow and 'surfing' of favorable mutations or impaired by the accumulation of deleterious mutations. Our results have clear implications for the conservation of F. serratus at its genetically unique southern edge in Northwest Iberia, where increasing temperatures are likely the major cause for the decline not only of F. serratus, but also other intertidal and subtidal macroalgae. We expect that F. serratus will disappear from Northwest Iberia by 2100 if genetic rescue is not induced by the influx of genetic variation from Brittany.

SOM Stability under Long-term Recovery from Acidic Deposition in a Northern Hardwood Forest

NASA Astrophysics Data System (ADS)

Marinos, R.; Bernhardt, E. S.; Groffman, P. M.; Likens, G.; Rosi-Marshall, E. J.

2016-12-01

Forested ecosystems in the Northeast U.S.A. are currently recovering from decades of acidic deposition that decreased soil pH, leached base cations, and increased soluble aluminum (Al) in soils. Because most research examining SOM dynamics in these ecosystems has taken place against a background of acidic deposition, it remains poorly understood how SOM pools will change as a result of the long-term trajectory of recovery from acidic deposition throughout the region. These potential changes may alter soil fertility status as well as the chemistry of receiving freshwater bodies. Watershed-scale experiments that increase soil pH and base cation status may provide insight into how SOM pools in these recovering ecosystems will respond on timescales of decades to centuries, but results from these experiments have been equivocal. At Hubbard Brook Experimental Forest in New Hampshire, a watershed-scale acid remediation treatment of calcium silicate caused a 40% decline of SOM pools in the humic (Oa) soil horizon, in addition to increasing soil pH and base saturation. We sought to understand the mechanisms driving this substantial loss of SOM. We found that, in the Oa horizon of the treatment watershed, respiration and nitrogen (N) mineralization were significantly, positively correlated with exchangeable calcium (Ca) and uncorrelated with soil pH; in a linear regression, exchangeable Ca explained 76% of the variation in respiration and 74% of the variation in nitrogen mineralization in the treatment soils. These metrics were uncorrelated in soils from a nearby reference watershed, where Ca is uniformly low. This suggests that the rate and magnitude of soil Ca changes during recovery from acid deposition may provide an important long-term control on the stability of SOM in these ecosystems. Additionally, we found substantially enhanced in-stream biotic uptake of the inorganic N released from this enhanced SOM decomposition, with growing-season N flux from the treatment watershed attenuated by 15-55% due to in-stream uptake. This suggests that receiving headwaters undergoing recovery from acid deposition have the capacity to mitigate enhanced nutrient efflux due to increased SOM decomposition.

Monsoon-Enso Relationships: A New Paradigm

NASA Technical Reports Server (NTRS)

Lau, K. M.; Einaudi, Franco (Technical Monitor)

2000-01-01

This article is partly a review and partly a new research paper on monsoon-ENSO relationship. The paper begins with a discussion of the basic relationship between the Indian monsoon and ENSO dating back to the work of Sir Gilbert Walker up to research results in more recent years. Various factors that may affect the monsoon-ENSO, relationship, including regional coupled ocean-atmosphere processes, Eurasian snow cover, land-atmosphere hydrologic feedback, intraseasonal oscillation, biennial variability and inter-decadal variations, are discussed. The extreme complex and highly nonlinear nature of the monsoon-ENSO relationship is stressed. We find that for regional impacts on the monsoon, El Nino and La Nina are far from simply mirror images of each other. These two polarities of ENSO can have strong or no impacts on monsoon anomalies depending on the strength of the intraseasonal oscillations and the phases of the inter-decadal variations. For the Asian-Australian monsoon (AAM) as a whole, the ENSO impact is effected through a east-west shift in the Walker Circulation. For rainfall anomalies over specific monsoon areas, regional processes play important roles in addition to the shift in the Walker Circulation. One of the key regional processes identified for the boreal summer monsoon is the anomalous West Pacific Anticyclone (WPA). This regional feature has similar signatures in interannual and intraseasonal time scales and appears to determine whether the monsoon-ENSO relationship is strong or weak in a given year. Another important regional feature includes a rainfall and SST dipole across the Indian Ocean, which may have strong impact on the austral summer monsoon. Results are shown indicating that monsoon surface wind forcings may induce a strong biennial signal in ENSO and that strong monsoon-ENSO coupling may translate into pronounced biennial variability in ENSO. Finally, a new paradigm is proposed for the study of monsoon variability. This paradigm provides a unified framework in which monsoon predictability, the role of regional vs. basin-scale processes, its relationship with different climate subsystems, and causes of secular changes in monsoon-ENSO relationship can be investigated.

Climate change and observed climate trends in the fort cobb experimental watershed.

PubMed

Garbrecht, J D; Zhang, X C; Steiner, J L

2014-07-01

Recurring droughts in the Southern Great Plains of the United States are stressing the landscape, increasing uncertainty and risk in agricultural production, and impeding optimal agronomic management of crop, pasture, and grazing systems. The distinct possibility that the severity of recent droughts may be related to a greenhouse-gas induced climate change introduces new challenges for water resources managers because the intensification of droughts could represent a permanent feature of the future climate. Climate records of the Fort Cobb watershed in central Oklahoma were analyzed to determine if recent decade-long trends in precipitation and air temperature were consistent with climate change projections for central Oklahoma. The historical precipitation record did not reveal any compelling evidence that the recent 20-yr-long decline in precipitation was related to climate change. Also, precipitation projections by global circulation models (GCMs) displayed a flat pattern through the end of the 21st century. Neither observed nor projected precipitation displayed a multidecadal monotonic rising or declining trend consistent with an ongoing warming climate. The recent trend in observed annual precipitation was probably a decade-scale variation not directly related to the warming climate. On the other hand, the observed monotonic warming trend of 0.34°C decade that started around 1978 is consistent with GCM projections of increasing temperature for central Oklahoma. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Revisiting surface albedo changes over Greenland since 1980s using satellite data from GLASS, CLARA, MODIS, and Landsat

NASA Astrophysics Data System (ADS)

He, T.; Liang, S.; Zhang, Y.

2017-12-01

Massive melting events over Greenland have been observed over the past few decades. Accompanying the melting events are the surface albedo changes, which had temporal and spatial variations. Albedo changes over Greenland during the past few decades have been reported in previous studies with the help of satellite observations; however, magnitudes and timing in albedo trends differ greatly in those studies. This has limited our understanding of albedo change mechanisms over Greenland. In this study, we present an analysis of surface albedo change over Greenland since 1980s combining four satellite albedo datasets, namely MODIS, GLASS, CLARA, and Landsat. MODIS, GLASS, and CLARA albedo data are publicly available and Landsat albedos were derived in our earlier study trying to bridge the scale difference between coarse resolution data and ground measurements available from early 1980s. Inter-comparisons were made among the satellite albedos and against ground measurements. We have several new findings. First, trends in surface albedo change among the satellite albedo datasets generally agree with each other and with ground measurements. Second, all datasets showed negative albedo trends after 2000, but magnitudes differ greatly. Third, trends before 2000 from coarse resolution data are not significant but Landsat data observed positive albedo changes. Fourth, the turning point of albedo trend was found to be earlier than 2000. Those findings may bring new research topics on timing and magnitude, and an improved understanding mechanisms of the albedo changes over Greenland during the past few decades.

Scaling up functional traits for ecosystem services with remote sensing: concepts and methods.

PubMed

Abelleira Martínez, Oscar J; Fremier, Alexander K; Günter, Sven; Ramos Bendaña, Zayra; Vierling, Lee; Galbraith, Sara M; Bosque-Pérez, Nilsa A; Ordoñez, Jenny C

2016-07-01

Ecosystem service-based management requires an accurate understanding of how human modification influences ecosystem processes and these relationships are most accurate when based on functional traits. Although trait variation is typically sampled at local scales, remote sensing methods can facilitate scaling up trait variation to regional scales needed for ecosystem service management. We review concepts and methods for scaling up plant and animal functional traits from local to regional spatial scales with the goal of assessing impacts of human modification on ecosystem processes and services. We focus our objectives on considerations and approaches for (1) conducting local plot-level sampling of trait variation and (2) scaling up trait variation to regional spatial scales using remotely sensed data. We show that sampling methods for scaling up traits need to account for the modification of trait variation due to land cover change and species introductions. Sampling intraspecific variation, stratification by land cover type or landscape context, or inference of traits from published sources may be necessary depending on the traits of interest. Passive and active remote sensing are useful for mapping plant phenological, chemical, and structural traits. Combining these methods can significantly improve their capacity for mapping plant trait variation. These methods can also be used to map landscape and vegetation structure in order to infer animal trait variation. Due to high context dependency, relationships between trait variation and remotely sensed data are not directly transferable across regions. We end our review with a brief synthesis of issues to consider and outlook for the development of these approaches. Research that relates typical functional trait metrics, such as the community-weighted mean, with remote sensing data and that relates variation in traits that cannot be remotely sensed to other proxies is needed. Our review narrows the gap between functional trait and remote sensing methods for ecosystem service management.

Current Challenges in Plant Eco-Metabolomics

PubMed Central

Peters, Kristian; Worrich, Anja; Alka, Oliver; Balcke, Gerd; Bruelheide, Helge; Dietz, Sophie; Dührkop, Kai; Heinig, Uwe; Kücklich, Marlen; Müller, Caroline; Poeschl, Yvonne; Pohnert, Georg; Ruttkies, Christoph; Schweiger, Rabea; Shahaf, Nir; Tortosa, Maria; Ueberschaar, Nico; Velasco, Pablo; Weiß, Brigitte M.; van Dam, Nicole M.

2018-01-01

The relatively new research discipline of Eco-Metabolomics is the application of metabolomics techniques to ecology with the aim to characterise biochemical interactions of organisms across different spatial and temporal scales. Metabolomics is an untargeted biochemical approach to measure many thousands of metabolites in different species, including plants and animals. Changes in metabolite concentrations can provide mechanistic evidence for biochemical processes that are relevant at ecological scales. These include physiological, phenotypic and morphological responses of plants and communities to environmental changes and also interactions with other organisms. Traditionally, research in biochemistry and ecology comes from two different directions and is performed at distinct spatiotemporal scales. Biochemical studies most often focus on intrinsic processes in individuals at physiological and cellular scales. Generally, they take a bottom-up approach scaling up cellular processes from spatiotemporally fine to coarser scales. Ecological studies usually focus on extrinsic processes acting upon organisms at population and community scales and typically study top-down and bottom-up processes in combination. Eco-Metabolomics is a transdisciplinary research discipline that links biochemistry and ecology and connects the distinct spatiotemporal scales. In this review, we focus on approaches to study chemical and biochemical interactions of plants at various ecological levels, mainly plant–organismal interactions, and discuss related examples from other domains. We present recent developments and highlight advancements in Eco-Metabolomics over the last decade from various angles. We further address the five key challenges: (1) complex experimental designs and large variation of metabolite profiles; (2) feature extraction; (3) metabolite identification; (4) statistical analyses; and (5) bioinformatics software tools and workflows. The presented solutions to these challenges will advance connecting the distinct spatiotemporal scales and bridging biochemistry and ecology. PMID:29734799

Scaling Coastal Ecosystems to Oceanographic and Climatic Drivers: Making Sense of Community Variation on Rocky Shores Using the Comparative-Experimental Approach in Upwelling and Downwelling Systems

NASA Astrophysics Data System (ADS)

Menge, B. A.; Gouhier, T.; Chan, F.; Hacker, S.; Menge, D.; Nielsen, K. J.

2016-02-01

Ecology focuses increasingly on the issue of matching spatial and temporal scales responsible for ecosystem pattern and dynamics. Benthic coastal communities traditionally were studied at local scales using mostly short-term research, while environmental (oceanographic, climatic) drivers were investigated at large scales (e.g., regional to oceanic, mostly offshore) using combined snapshot and monitoring (time series) research. The comparative-experimental approach combines local-scale studies at multiple sites spanning large-scale environmental gradients in combination with monitoring of inner shelf oceanographic conditions including upwelling/downwelling wind forcing and their consequences (e.g., temperature), and inputs of subsidies (larvae, phytoplankton, detritus). Temporal scale varies depending on the questions, but can extend from years to decades. We discuss two examples of rocky intertidal ecosystem dynamics, one at a regional scale (California Current System, CCS) and one at an interhemispheric scale. In the upwelling-dominated CCS, 52% and 32% of the variance in local community structure (functional group abundances at 13 sites across 725 km) was explained by external factors (ecological subsidies, oceanographic conditions, geographic location), and species interactions, respectively. The interhemispheric study tested the intermittent upwelling hypothesis (IUH), which predicts that key ecological processes will vary unimodally along a persistent downwelling to persistent upwelling gradient. Using 14-22 sites, unimodal relationships between ecological subsidies (phytoplankton, prey recruitment), prey responses (barnacle colonization, mussel growth) and species interactions (competition rate, predation rate and effect) and the Bakun upwelling index calculated at each site accounted for 50% of the variance. Hence, external factors can account for about half of locally-expressed community structure and dynamics.

Trends in upper gastrointestinal diagnosis over four decades in Lusaka, Zambia: a retrospective analysis of endoscopic findings.

PubMed

Kayamba, Violet; Sinkala, Edford; Mwanamakondo, Stayner; Soko, Rose; Kawimbe, Boniface; Amadi, Beatrice; Zulu, Isaac; Nzaisenga, Jean-Baptiste; Banda, Themba; Mumbwe, Chipasha; Phiri, Evans; Munkonge, Philip; Kelly, Paul

2015-10-06

There a shortage of robust information about profiles of gastrointestinal disease in sub-Saharan Africa. The endoscopy unit of the University Teaching Hospital in Lusaka has been running without interruption since 1977 and this 38-year record is largely intact. We report an analysis of endoscopic findings over this period. Written endoscopy records from 29th September 1977 to 16th December 2014 were recovered, computerised, coded by two experienced endoscopists and analysed. Temporal trends were analysed using tables, graphs, and unconditional logistic regression, with age, sex of patient, decade, and endoscopist as independent variables to adjust for inter-observer variation. Sixteen thousand nine hundred fifty-three records were identified and analysed. Diagnosis of gastric ulcer rose by 22 %, and that of duodenal ulcer fell by 14 % per decade. Endoscopically diagnosed oesophageal cancer increased by 32 % per decade, but gastric cancer rose only in patients under 60 years of age (21 % per decade). Oesophageal varices were the commonest finding in patients presenting with haematemesis, increasing by 14 % per decade in that patient group. Two HIV-related diagnoses, oesophageal candidiasis and Kaposi's sarcoma, rose from almost zero to very high levels in the 1990s but fell substantially after 2005 when anti-retroviral therapy became widely available. This useful dataset suggests that there are important trends in some endoscopic findings over four decades. These trends are not explained by inter-observer variation. Reasons for the divergent trends in incidence of peptic ulceration and apparent trends in diagnosis of upper gastrointestinal cancers merit further exploration.

Space climate implications from substorm frequency

NASA Astrophysics Data System (ADS)

Newell, P. T.; Gjerloev, J. W.; Mitchell, E. J.

2013-10-01

solar wind impacting the Earth varies over a wide range of time scales, driving a corresponding range of geomagnetic activity. Past work has strongly indicated that the rate of merging on the frontside magnetosphere is the most important predictor for magnetospheric activity, especially over a few hours. However, the magnetosphere exhibits variations on other time scales, including UT, seasonal, and solar cycle variations. Much of this geomagnetic variation cannot be reasonably attributed to changes in the solar wind driving—that is, it is not created by the original Russell-McPherron effect or any generalization thereof. In this paper we examine the solar cycle, seasonal, and diurnal effects based upon the frequency of substorm onsets, using a data set of 53,000 substorm onsets. These were identified through the SuperMAG collaboration and span three decades with continuous coverage. Solar cycle variations include a profound minimum in 2009 (448 substorms) and peak in 2003 (3727). The magnitude of this variation (a factor of 8.3) is not explained through variations in estimators of the frontside merging rate (such as dΦMP/dt), even when the more detailed probability distribution functions are examined. Instead, v, or better, n1/2v2 seems to be implicated in the dramatic difference between active and quiet years, even beyond the role of velocity in modulating merging. Moreover, we find that although most substorms are preceded by flux loading (78.5% are above the mean and 83.8% above median solar wind driving), a high solar wind v is almost as important (68.3% above mean, 74.8% above median). This and other evidence suggest that either v or n1/2v2 (but probably not p) plays a strong secondary role in substorm onset. As for the seasonal and diurnal effects, the elliptical nature of the Earth's orbit, which is closest to the Sun in January, leads to a larger solar wind driving (measured by Bs, vBs, or dΦMP/dt) in November, as is confirmed by 22 years of solar wind observations. However, substorms peak in October and March and have a UT dependence best explained by whether a conducting path established by solar illumination exists in at least one hemisphere in the region where substorm onsets typically occur.

The impact of inter-annual rainfall variability on food production in the Ganges basin

NASA Astrophysics Data System (ADS)

Siderius, Christian; Biemans, Hester; van Walsum, Paul; hellegers, Petra; van Ierland, Ekko; Kabat, Pavel

2014-05-01

Rainfall variability is expected to increase in the coming decades as the world warms. Especially in regions already water stressed, a higher rainfall variability will jeopardize food security. Recently, the impact of inter-annual rainfall variability has received increasing attention in regional to global analysis on water availability and food security. But the description of the dynamics behind it is still incomplete in most models. Contemporary land surface and hydrological models used for such analyses describe variability in production primarily as a function of yield, a process driven by biophysical parameters, thereby neglecting yearly variations in cropped area, a process driven largely by management decisions. Agricultural statistics for northern India show that the latter process could explain up to 40% of the observed inter-annual variation in food production in various states. We added a simple dynamic land use decision module to a land surface model (LPJmL) and analyzed to what extent this improved the estimation of variability in food production. Using this improved modelling framework we then assessed if and at which scale rainfall variability affects meeting the food self-sufficiency threshold. Early results for the Ganges Basin indicate that, while on basin level variability in crop production is still relatively low, several districts and states are highly affected (RSTD > 50%). Such insight can contribute to better recommendations on the most effective measures, at the most appropriate scale, to buffer variability in food production.

[Influence of land use change on dissolved organic carbon export in Naoli River watershed. Northeast China].

PubMed

Yin, Xiao-min; Lyu, Xian-guo; Liu, Xing-tu; Xue, Zhen-shan

2015-12-01

The present study was conducted to evaluate the influence of land use change on dissolved organic carbon (DOC) export in Naoli River watershed, Northeast China. Seasonal variation of DOC concentrations of the river water and its relationship with land use in the whole watershed and 100 m riparian zone at the annual average scale were analyzed using the method of field sampling, laboratory analysis, GIS and statistics analysis. The results showed that the concentrations of DOC under base flow conditions in spring and summer were significantly higher than that in fall in the study watershed. The seasonal trend of DOC concentrations in wetland-watersheds was similar to that in all the sub-watersheds, while significantly different from that in non-wetland watersheds. On the annual average scale, percentage of wetland in the whole watershed and paddy field in the 100 m riparian zone had positive relationship with the DOC concentration in the river water, while percentage of forest in the whole watershed had negative relationship with it (P < 0.05). It indicated that wetland in the sub-watershed played a significant role in the seasonal variation of DOC in river water of Naoli River watershed. Wetland in the watershed and paddy field in the 100 m riparian zone significantly promoted DOC export, while forest alleviated it. Land use change in the watershed in the past few decades dramatically changed the DOC balance of river water.

Temporal variability of the Antarctic Ice sheet observed from space-based geodesy

NASA Astrophysics Data System (ADS)

Memin, A.; King, M. A.; Boy, J. P.; Remy, F.

2017-12-01

Quantifying the Antarctic Ice Sheet (AIS) mass balance still remains challenging as several processes compete to differing degrees at the basin scale with regional variations, leading to multiple mass redistribution patterns. For instance, analysis of linear trends in surface-height variations from 1992-2003 and 2002-2006 shows that the AIS is subject to decimetric scale variability over periods of a few years. Every year, snowfalls in Antarctica represent the equivalent of 6 mm of the mean sea level. Therefore, any fluctuation in precipitation can lead to changes in sea level. Besides, over the last decade, several major glaciers have been thinning at an accelerating rate. Understanding the processes that interact on the ice sheet is therefore important to precisely determine the response of the ice sheet to a rapid changing climate and estimate its contribution to sea level changes. We estimate seasonal and interannual changes of the AIS between January 2003 and October 2010 and to the end of 2016 from a combined analysis of surface-elevation and surface-mass changes derived from Envisat data and GRACE solutions, and from GRACE solutions only, respectively. While we obtain a good correlation for the interannual signal between the two techniques, important differences (in amplitude, phase, and spatial pattern) are obtained for the seasonal signal. We investigate these discrepancies by comparing the crustal motion observed by GPS and those predicted using monthly surface mass balance derived from the regional atmospheric climate model RACMO.

Influence of the Indian monsoon and the subtropical jet on climate change on the Tibetan Plateau since the late Pleistocene

NASA Astrophysics Data System (ADS)

Hou, Juzhi; D'Andrea, William J.; Wang, Mingda; He, Yue; Liang, Jie

2017-05-01

Precipitation atop the Tibetan Plateau (TP) is delivered by the Indian summer monsoon, the Asian summer monsoon, and weather systems associated with the subtropical westerly jet. Variations in the relative importance of the monsoon systems and the westerly jet are hypothesized to have occurred at decadal, millennial and glacial-interglacial scales. However, paleoclimate observations based on explicit climate proxies are still scarce, limiting our understanding of the mechanisms of Holocene climate variability on the Tibetan Plateau (TP). Here we present three independently dated compound specific hydrogen isotope records of sedimentary leaf waxes from lakes on the TP, Bangong Co, Lake Qinghai and Linggo Co. The leaf wax δD records reflect isotopes in precipitation, and we combine these observations with existing isotopic and hydrological data to investigate variations in the influence of the summer monsoon and the westerly jet on the moisture budget of the TP since the Late Pleistocene. δD values of precipitation at all three lakes were relatively positive during the Late Pleistocene indicating a weakened summer monsoon. During the early and mid-Holocene, δD values of precipitation at the three lakes were relatively negative, suggesting the importance of summer monsoon. During the middle to late Holocene, δD values at Bangong Co and Lake Qinghai gradually increased with superimposed episodes of short term of δD variability. However, at Linggo Co in the northern TP, periods of more positive δD values of precipitation correspond to wetter intervals inferred from lake level high stands, and likely reflect variations in moisture associated with the westerly jet. Thus, the δD records at Linggo Co imply the lesser importance of summer monsoon moisture in the hydrologic budget of the northern TP. Collectively, the hydrogen isotope records at these three lakes document millennial and centennial scale variations in the strength of the summer monsoon systems and concurrent changes in the westerly jet. Furthermore, millennial-scale fluctuations in the δD records at the three lakes during the middle to late Holocene suggest episodes of reduced summer monsoonal moisture delivery to these regions, and correspond with intervals of cool sea surface temperatures in the North Atlantic.

Changes in lead and zinc lability during weathering-induced acidification of desert mine tailings: Coupling chemical and micro-scale analyses.

PubMed

Hayes, Sarah M; White, Scott A; Thompson, Thomas L; Maier, Raina M; Chorover, Jon

2009-12-01

Desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through-flux rates. Along with other constraints, metal toxicity precludes natural plant colonization even over decadal time scales. Since unconsolidated particles can be subjected to transport by wind and water erosion, potentially resulting in direct human and ecosystem exposure, there is a need to know how the lability and form of metals change in the tailings weathering environment. A combination of chemical extractions, X-ray diffraction, micro-X-ray fluorescence spectroscopy, and micro-Raman spectroscopy were employed to study Pb and Zn contamination in surficial arid mine tailings from the Arizona Klondyke State Superfund Site. Initial site characterization indicated a wide range in pH (2.5 to 8.0) in the surficial tailings pile. Ligand-promoted (DTPA) extractions, used to assess plant-available metal pools, showed decreasing available Zn and Mn with progressive tailings acidification. Aluminum shows the inverse trend, and Pb and Fe show more complex pH dependence. Since the tailings derive from a common source and parent mineralogy, it is presumed that variations in pH and "bioavailable" metal concentrations result from associated variation in particle-scale geochemistry. Four sub-samples, ranging in pH from 2.6 to 5.4, were subjected to further characterization to elucidate micro-scale controls on metal mobility. With acidification, total Pb (ranging from 5 - 13 g kg(-1)) was increasingly associated with Fe and S in plumbojarosite aggregates. For Zn, both total (0.4 - 6 g kg(-1)) and labile fractions decreased with decreasing pH. Zinc was found to be primarily associated with the secondary Mn phases manjiroite and chalcophanite. The results suggest that progressive tailings acidification diminishes the overall lability of the total Pb and Zn pools.

Changes in lead and zinc lability during weathering-induced acidification of desert mine tailings: Coupling chemical and micro-scale analyses

PubMed Central

Hayes, Sarah M.; White, Scott A.; Thompson, Thomas L.; Maier, Raina M.; Chorover, Jon

2009-01-01

Desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through-flux rates. Along with other constraints, metal toxicity precludes natural plant colonization even over decadal time scales. Since unconsolidated particles can be subjected to transport by wind and water erosion, potentially resulting in direct human and ecosystem exposure, there is a need to know how the lability and form of metals change in the tailings weathering environment. A combination of chemical extractions, X-ray diffraction, micro-X-ray fluorescence spectroscopy, and micro-Raman spectroscopy were employed to study Pb and Zn contamination in surficial arid mine tailings from the Arizona Klondyke State Superfund Site. Initial site characterization indicated a wide range in pH (2.5 to 8.0) in the surficial tailings pile. Ligand-promoted (DTPA) extractions, used to assess plant-available metal pools, showed decreasing available Zn and Mn with progressive tailings acidification. Aluminum shows the inverse trend, and Pb and Fe show more complex pH dependence. Since the tailings derive from a common source and parent mineralogy, it is presumed that variations in pH and “bioavailable” metal concentrations result from associated variation in particle-scale geochemistry. Four sub-samples, ranging in pH from 2.6 to 5.4, were subjected to further characterization to elucidate micro-scale controls on metal mobility. With acidification, total Pb (ranging from 5 – 13 g kg−1) was increasingly associated with Fe and S in plumbojarosite aggregates. For Zn, both total (0.4 – 6 g kg−1) and labile fractions decreased with decreasing pH. Zinc was found to be primarily associated with the secondary Mn phases manjiroite and chalcophanite. The results suggest that progressive tailings acidification diminishes the overall lability of the total Pb and Zn pools. PMID:20161492

Micro-scale environmental variation amplifies physiological variation among individual mussels.

PubMed

Jimenez, Ana Gabriela; Jayawardene, Sarah; Alves, Shaina; Dallmer, Jeremiah; Dowd, W Wesley

2015-12-07

The contributions of temporal and spatial environmental variation to physiological variation remain poorly resolved. Rocky intertidal zone populations are subjected to thermal variation over the tidal cycle, superimposed with micro-scale variation in individuals' body temperatures. Using the sea mussel (Mytilus californianus), we assessed the consequences of this micro-scale environmental variation for physiological variation among individuals, first by examining the latter in field-acclimatized animals, second by abolishing micro-scale environmental variation via common garden acclimation, and third by restoring this variation using a reciprocal outplant approach. Common garden acclimation reduced the magnitude of variation in tissue-level antioxidant capacities by approximately 30% among mussels from a wave-protected (warm) site, but it had no effect on antioxidant variation among mussels from a wave-exposed (cool) site. The field-acclimatized level of antioxidant variation was restored only when protected-site mussels were outplanted to a high, thermally stressful site. Variation in organismal oxygen consumption rates reflected antioxidant patterns, decreasing dramatically among protected-site mussels after common gardening. These results suggest a highly plastic relationship between individuals' genotypes and their physiological phenotypes that depends on recent environmental experience. Corresponding context-dependent changes in the physiological mean-variance relationships within populations complicate prediction of responses to shifts in environmental variability that are anticipated with global change. © 2015 The Author(s).

Oxygenation variability in Mejillones Bay, off northern Chile, during the last two centuries

NASA Astrophysics Data System (ADS)

Díaz-Ochoa, J. A.; Pantoja, S.; de Lange, G. J.; Lange, C. B.; Sánchez, G. E.; Acuña, V. R.; Muñoz, P.; Vargas, G.

2011-01-01

The Peru Chile Current ecosystem is characterized by high biological productivity and important fisheries. Although this system is likely to be severely affected by climate change, its response to current global warming is still uncertain. In this paper, we analyze 10-166 year-old sediments in two cores collected from Mejillones Bay, an anoxic sedimentary setting favorable for the preservation of proxies. Based on a 166-year chronology, we used proxies of bottom-water oxygenation (Mo, V, S, and the (lycopane + n-C35)/n-C31 ratio) and surface water productivity (biogenic opal, counts of diatom valves, biogenic Ba, organic carbon, and chlorins) to reconstruct environmental variations in Mejillones Bay. During the last two centuries, a shift took place in the coastal marine ecosystem of Bahia Mejillones at decadal scales. This shift was characterized by intense ENSO-like activity, large-scale fluctuations in biological export productivity and bottom water oxygenation, and increased eolian activity (inferred from Ti/Al and Zr/Al). This short-term variability was accompanied by a gradual increase of sulfidic conditions that has intensified since the early 1960s.

Large-scale patterns of turnover and Basal area change in Andean forests.

PubMed

Báez, Selene; Malizia, Agustina; Carilla, Julieta; Blundo, Cecilia; Aguilar, Manuel; Aguirre, Nikolay; Aquirre, Zhofre; Álvarez, Esteban; Cuesta, Francisco; Duque, Álvaro; Farfán-Ríos, William; García-Cabrera, Karina; Grau, Ricardo; Homeier, Jürgen; Linares-Palomino, Reynaldo; Malizia, Lucio R; Cruz, Omar Melo; Osinaga, Oriana; Phillips, Oliver L; Reynel, Carlos; Silman, Miles R; Feeley, Kenneth J

2015-01-01

General patterns of forest dynamics and productivity in the Andes Mountains are poorly characterized. Here we present the first large-scale study of Andean forest dynamics using a set of 63 permanent forest plots assembled over the past two decades. In the North-Central Andes tree turnover (mortality and recruitment) and tree growth declined with increasing elevation and decreasing temperature. In addition, basal area increased in Lower Montane Moist Forests but did not change in Higher Montane Humid Forests. However, at higher elevations the lack of net basal area change and excess of mortality over recruitment suggests negative environmental impacts. In North-Western Argentina, forest dynamics appear to be influenced by land use history in addition to environmental variation. Taken together, our results indicate that combinations of abiotic and biotic factors that vary across elevation gradients are important determinants of tree turnover and productivity in the Andes. More extensive and longer-term monitoring and analyses of forest dynamics in permanent plots will be necessary to understand how demographic processes and woody biomass are responding to changing environmental conditions along elevation gradients through this century.

Large-Scale Patterns of Turnover and Basal Area Change in Andean Forests

PubMed Central

Blundo, Cecilia; Aguilar, Manuel; Aguirre, Nikolay; Aquirre, Zhofre; Álvarez, Esteban; Cuesta, Francisco; Farfán-Ríos, William; García-Cabrera, Karina; Grau, Ricardo; Linares-Palomino, Reynaldo; Malizia, Lucio R.; Cruz, Omar Melo; Osinaga, Oriana; Reynel, Carlos; Silman, Miles R.

2015-01-01

General patterns of forest dynamics and productivity in the Andes Mountains are poorly characterized. Here we present the first large-scale study of Andean forest dynamics using a set of 63 permanent forest plots assembled over the past two decades. In the North-Central Andes tree turnover (mortality and recruitment) and tree growth declined with increasing elevation and decreasing temperature. In addition, basal area increased in Lower Montane Moist Forests but did not change in Higher Montane Humid Forests. However, at higher elevations the lack of net basal area change and excess of mortality over recruitment suggests negative environmental impacts. In North-Western Argentina, forest dynamics appear to be influenced by land use history in addition to environmental variation. Taken together, our results indicate that combinations of abiotic and biotic factors that vary across elevation gradients are important determinants of tree turnover and productivity in the Andes. More extensive and longer-term monitoring and analyses of forest dynamics in permanent plots will be necessary to understand how demographic processes and woody biomass are responding to changing environmental conditions along elevation gradients through this century. PMID:25973977

Tail reconnection in the global magnetospheric context: Vlasiator first results

NASA Astrophysics Data System (ADS)

Palmroth, Minna; Hoilijoki, Sanni; Juusola, Liisa; Pulkkinen, Tuija I.; Hietala, Heli; Pfau-Kempf, Yann; Ganse, Urs; von Alfthan, Sebastian; Vainio, Rami; Hesse, Michael

2017-11-01

The key dynamics of the magnetotail have been researched for decades and have been associated with either three-dimensional (3-D) plasma instabilities and/or magnetic reconnection. We apply a global hybrid-Vlasov code, Vlasiator, to simulate reconnection self-consistently in the ion kinetic scales in the noon-midnight meridional plane, including both dayside and nightside reconnection regions within the same simulation box. Our simulation represents a numerical experiment, which turns off the 3-D instabilities but models ion-scale reconnection physically accurately in 2-D. We demonstrate that many known tail dynamics are present in the simulation without a full description of 3-D instabilities or without the detailed description of the electrons. While multiple reconnection sites can coexist in the plasma sheet, one reconnection point can start a global reconfiguration process, in which magnetic field lines become detached and a plasmoid is released. As the simulation run features temporally steady solar wind input, this global reconfiguration is not associated with sudden changes in the solar wind. Further, we show that lobe density variations originating from dayside reconnection may play an important role in stabilising tail reconnection.

The University of Utah Urban Undertaking (U4)

NASA Astrophysics Data System (ADS)

Lin, J. C.; Mitchell, L.; Bares, R.; Mendoza, D. L.; Fasoli, B.; Bowling, D. R.; Garcia, M. A.; Buchert, M.; Pataki, D. E.; Crosman, E.; Horel, J.; Catharine, D.; Strong, C.; Ehleringer, J. R.

2015-12-01

The University of Utah is leading efforts to understand the spatiotemporal patterns in both emissions and concentrations of greenhouse gases (GHG) and criteria pollutants within urban systems. The urbanized corridor in northern Utah along the Wasatch Front, anchored by Salt Lake City, is undergoing rapid population growth that is projected to double in the next few decades. The Wasatch Front offers multiple advantages as an unique "urban laboratory": urban regions in multiple valleys spanning numerous orders of magnitude in population, each with unique airsheds, well-defined boundary conditions along deserts and tall mountains, strong signals during cold air pool events, seasonal contrasts in pollution, and a legacy of productive partnerships with local stakeholders and governments. We will show results from GHG measurements from the Wasatch Front, including one of the longest running continuous CO2 records in urban areas. Complementing this record are comprehensive meteorological observations and GHG/pollutant concentrations on mobile platforms: light rail, helicopter, and research vans. Variations in the GHG and pollutant observations illustrate human behavior and the resulting "urban metabolism" taking place on hourly, weekly, and seasonal cycles, resulting in a coupling between GHG and criteria pollutants. Moreover, these observations illustrate systematic spatial gradients in GHG and pollutant distributions between and within urban areas, traced to underlying gradients in population, energy use, terrain, and land use. Over decadal time scales the observations reveal growth of the "urban dome" due to expanding urban development. Using numerical models of the atmosphere, we further link concentrations of GHG and air quality-relevant pollutants to underlying emissions at the neighborhood scale as well as urban planning considerations.

Variation Scenarios in System Deployments for the GGOS2020 Space Geodesy Network

NASA Astrophysics Data System (ADS)

Pavlis, Erricos C.; Kuzmicz-Cieslak, Magdalena; MacMillan, Daniel S.

2017-04-01

Simulation studies have so far determined an approximate size and station density for the Space Geodetic Network that will meet the requirements recommended by the U.S. National Research Council report "Precise Geodetic Infrastructure: National Requirements for a Shared Resource" (2010). A network of about 30 globally distributed "core" observatories with state of the art equipment needs to be deployed over the next decade. Subsequently, GGOS—the Global Geodetic Observing System issued a "Call for Proposals for the expansion and update of the network, to which several countries committed to contribute. The renewal process will not happen instantly and for a long time, the network will comprise legacy and next generation equipment. We conducted a new batch of simulation studies using the proposed site locations and the proposed equipment at each site, to gauge the contribution of specific systems and locations to the global results. The majority of the examined sites are well-established future sites, some of which are even close to completion. Despite the good intentions of the contributing agencies/countries, in some cases we have identified regional gaps in coverage with either SLR or VLBI systems. We have characterized the effect of these gaps on the quality of the final TRF. We present the results of these simulation studies and rank the examined cases according to the likelihood that the designed network will successfully meet the GGOS goals of 1 mm accuracy (decadal scale) and a temporal stability on the order of 0.1 mm/y, with similar numbers for the scale and orientation components of the TRF.

GGOS2020 Space Geodesy Network: Variations in System Deployment Scenarios

NASA Astrophysics Data System (ADS)

Pavlis, E. C.; Koenig, D.; Kuzmicz-Cieslak, M.; MacMillan, D. S.

2016-12-01

Simulation studies have so far determined an approximate size and station density for the Space Geodetic Network that will meet the requirements recommended by the U.S. National Research Council report "Precise Geodetic Infrastructure: National Requirements for a Shared Resource" (2010). A network of about 30 globally distributed "core" observatories with state of the art equipment needs to be deployed over the next decade. Subsequently, GGOS—the Global Geodetic Observing System issued a "Call for Proposals for the expansion and update of the network, to which several countries committed to contribute. The renewal process will not happen instantly and for a long time, the network will comprise legacy and next generation equipment. We conducted a new batch of simulation studies using the proposed site locations and the proposed equipment at each site, to gauge the contribution of specific systems and locations to the global results. The majority of the examined sites are well-established future sites, some of which are even close to completion. Despite the good intentions of the contributing agencies/countries, in some cases we have identified regional gaps in coverage with either SLR or VLBI systems. We have characterized the effect of these gaps on the quality of the final TRF. We present the results of these simulation studies and rank the examined cases according to the likelihood that the designed network will successfully meet the GGOS goals of 1 mm accuracy (decadal scale) and a temporal stability on the order of 0.1 mm/y, with similar numbers for the scale and orientation components of the TRF.

Decoding the spatial signatures of multi-scale climate variability - a climate network perspective

NASA Astrophysics Data System (ADS)

Donner, R. V.; Jajcay, N.; Wiedermann, M.; Ekhtiari, N.; Palus, M.

2017-12-01

During the last years, the application of complex networks as a versatile tool for analyzing complex spatio-temporal data has gained increasing interest. Establishing this approach as a new paradigm in climatology has already provided valuable insights into key spatio-temporal climate variability patterns across scales, including novel perspectives on the dynamics of the El Nino Southern Oscillation or the emergence of extreme precipitation patterns in monsoonal regions. In this work, we report first attempts to employ network analysis for disentangling multi-scale climate variability. Specifically, we introduce the concept of scale-specific climate networks, which comprises a sequence of networks representing the statistical association structure between variations at distinct time scales. For this purpose, we consider global surface air temperature reanalysis data and subject the corresponding time series at each grid point to a complex-valued continuous wavelet transform. From this time-scale decomposition, we obtain three types of signals per grid point and scale - amplitude, phase and reconstructed signal, the statistical similarity of which is then represented by three complex networks associated with each scale. We provide a detailed analysis of the resulting connectivity patterns reflecting the spatial organization of climate variability at each chosen time-scale. Global network characteristics like transitivity or network entropy are shown to provide a new view on the (global average) relevance of different time scales in climate dynamics. Beyond expected trends originating from the increasing smoothness of fluctuations at longer scales, network-based statistics reveal different degrees of fragmentation of spatial co-variability patterns at different scales and zonal shifts among the key players of climate variability from tropically to extra-tropically dominated patterns when moving from inter-annual to decadal scales and beyond. The obtained results demonstrate the potential usefulness of systematically exploiting scale-specific climate networks, whose general patterns are in line with existing climatological knowledge, but provide vast opportunities for further quantifications at local, regional and global scales that are yet to be explored.

Historical Variations in Inner Core Rotation and Polar Motion at Decade Timescales

NASA Astrophysics Data System (ADS)

Dumberry, M.

2005-12-01

Exchanges of angular momentum between the mantle, the fluid core and the solid inner core result in changes in the Earth's rotation. Torques in the axial direction produce changes in amplitude, or changes in length of day, while torques in the equatorial direction lead to changes in orientation of the rotation vector with respect to the mantle, or polar motion. In this work, we explore the possibility that a combination of electromagnetic and gravitational torques on the inner core can reproduce the observed decadal variations in polar motion known as the Markowitz wobble. Torsional oscillations, which involve azimuthal motions in the fluid core with typical periods of decades, entrain the inner core by electromagnetic traction. When the inner core is axially rotated, its surfaces of constant density are no longer aligned with the gravitational potential from mantle density heterogeneities, and this results in a gravitational torque between the two. The axial component of this torque has been previously described and is believed to be partly responsible for decadal changes in length of day. In this work, we show that it has also an equatorial component, which produces a tilt of the inner core and results in polar motion. The polar motion produced by this mechanism depends on the density structure in the mantle, the rheology of the inner core, and the time-history of the angle of axial misalignment between the inner core and the mantle. We reconstruct the latter using a model of torsional oscillations derived from geomagnetic secular variation. From this time-history, and by using published models of mantle density structure, we show that we can reproduce the salient characteristics of the Markowitz wobble: an eccentric decadal polar motion of 30-50 milliarcsecs oriented along a specific longitude. We discuss the implications of this result, noting that a match in both amplitude and phase of the observed Markowitz wobble allows the recovery of the historical rotational variations of the inner core, and also provides constraints on structure, rheology and dynamics of the Earth's deep interior that cannot be observed directly.

Multi-year predictability in a coupled general circulation model

NASA Astrophysics Data System (ADS)

Power, Scott; Colman, Rob

2006-02-01

Multi-year to decadal variability in a 100-year integration of a BMRC coupled atmosphere-ocean general circulation model (CGCM) is examined. The fractional contribution made by the decadal component generally increases with depth and latitude away from surface waters in the equatorial Indo-Pacific Ocean. The relative importance of decadal variability is enhanced in off-equatorial “ wings” in the subtropical eastern Pacific. The model and observations exhibit “ENSO-like” decadal patterns. Analytic results are derived, which show that the patterns can, in theory, occur in the absence of any predictability beyond ENSO time-scales. In practice, however, modification to this stochastic view is needed to account for robust differences between ENSO-like decadal patterns and their interannual counterparts. An analysis of variability in the CGCM, a wind-forced shallow water model, and a simple mixed layer model together with existing and new theoretical results are used to improve upon this stochastic paradigm and to provide a new theory for the origin of decadal ENSO-like patterns like the Interdecadal Pacific Oscillation and Pacific Decadal Oscillation. In this theory, ENSO-driven wind-stress variability forces internal equatorially-trapped Kelvin waves that propagate towards the eastern boundary. Kelvin waves can excite reflected internal westward propagating equatorially-trapped Rossby waves (RWs) and coastally-trapped waves (CTWs). CTWs have no impact on the off-equatorial sub-surface ocean outside the coastal wave guide, whereas the RWs do. If the frequency of the incident wave is too high, then only CTWs are excited. At lower frequencies, both CTWs and RWs can be excited. The lower the frequency, the greater the fraction of energy transmitted to RWs. This lowers the characteristic frequency (reddens the spectrum) of variability off the equator relative to its equatorial counterpart. At low frequencies, dissipation acts as an additional low pass filter that becomes more effective, as latitude increases. At the same time, ENSO-driven off-equatorial surface heating anomalies drive mixed layer temperature responses in both hemispheres. Both the eastern boundary interactions and the accumulation of surface heat fluxes by the surface mixed layer act to low pass filter the ENSO-forcing. The resulting off-equatorial variability is therefore more coherent with low pass filtered (decadal) ENSO indices [e.g. NINO3 sea-surface temperature (SST)] than with unfiltered ENSO indices. Consequently large correlations between variability and NINO3 extend further poleward on decadal time-scales than they do on interannual time-scales. This explains why decadal ENSO-like patterns have a broader meridional structure than their interannual counterparts. This difference in appearance can occur even if ENSO indices do not have any predictability beyond interannual time-scales. The wings around 15-20°S, and sub-surface variability at many other locations are predictable on interannual and multi-year time-scales. This includes westward propagating internal RWs within about 25° of the equator. The slowest of these take up to 4 years to reach the western boundary. This sub-surface predictability has significant oceanographic interest. However, it is linked to only low levels of SST variability. Consequently, extrapolation of delayed action oscillator theory to decadal time-scales might not be justified.

Decadal-scale changes in forest soil carbon and nitrogen storage are influenced by organic matter removal during timber harvest

Treesearch

Ryan M. Mushinski; Thomas W. Boutton; D. Andrew Scott

2017-01-01

This study investigates whether different intensities of organic matter removal associated with timber harvest influence decadal-scale storage of soil organic carbon (SOC) and total nitrogen (TN) in the top 1 m of mineral soil 18 years postharvest in a Pinus taeda L. forest in the Gulf Coastal Plain. We quantified forest harvest-related changes in...

Linking climate projections to performance: A yield-based decision scaling assessment of a large urban water resources system

NASA Astrophysics Data System (ADS)

Turner, Sean W. D.; Marlow, David; Ekström, Marie; Rhodes, Bruce G.; Kularathna, Udaya; Jeffrey, Paul J.

2014-04-01

Despite a decade of research into climate change impacts on water resources, the scientific community has delivered relatively few practical methodological developments for integrating uncertainty into water resources system design. This paper presents an application of the "decision scaling" methodology for assessing climate change impacts on water resources system performance and asks how such an approach might inform planning decisions. The decision scaling method reverses the conventional ethos of climate impact assessment by first establishing the climate conditions that would compel planners to intervene. Climate model projections are introduced at the end of the process to characterize climate risk in such a way that avoids the process of propagating those projections through hydrological models. Here we simulated 1000 multisite synthetic monthly streamflow traces in a model of the Melbourne bulk supply system to test the sensitivity of system performance to variations in streamflow statistics. An empirical relation was derived to convert decision-critical flow statistics to climatic units, against which 138 alternative climate projections were plotted and compared. We defined the decision threshold in terms of a system yield metric constrained by multiple performance criteria. Our approach allows for fast and simple incorporation of demand forecast uncertainty and demonstrates the reach of the decision scaling method through successful execution in a large and complex water resources system. Scope for wider application in urban water resources planning is discussed.

Influence of core flows on the decade variations of the polar motion

NASA Astrophysics Data System (ADS)

Hulot, G.; Le Huy, M.; Le Mouël, J.-L.

We address the possibility for the core flows that generate the geomagnetic field to contribute significantly to the decade variations of the mean pole position (generally called the Markowitz wobble). This assumption is made plausible by the observation that the flow at the surface of the core-estimated from the geomagnetic secular variation models-experiences important changes on this time scale. We discard the viscous and electromagnetic core-mantle couplings and consider only the pressure torque pf resulting from the fluid flow overpressure acting on the non-spherical core-mantle boundary (CMB) at the bottom of the mantle, and the gravity torque gf due to the density heterogeneity driving the core flow. We show that forces within the core balance each other on the time scale considered and, using global integrals over the core, the mantle and the whole Earth, we write Euler's equation for the mantle in terms of two more useful torques Pgeo and . The "geostrophic torque", γ Pgeo incorporates γpf and part of γgf, while γ is another fraction of γgf. We recall how the geostrophic pressure pgeo, and thus γPgeo for a given topography, can be derived from the flow at the CMB and compute the motion of the mean pole from 1900 to 1990, assuming in a first approach that the unknown γ can be neglected. The amplitude of the computed pole motion is three to ten times less than the observed one and out of the phase with it. In order to estimate the possible contribution of γ we then use a second approach and consider the case in which the reference state for the Earth is assumed to be the classical axisymmetric ellipsoidal figure with an almost constant ellipticity within the core. We show that (γPgeo + γ) is then equal to a pseudo-electromagnetic torque γL3, the torque exerted on the core by the component of the Lorentz force along the axis of rotation (this torque exists even though the mantle is assumed insulating). This proves that, at least in this case and probably in the more general case of a bumpy CMB, γ is not negligible compared with γ Pgeo. Eventually, we estimate the order of magnitude of γL3, show that it is likely to be small and conclude with further possibilities for the Markowitz wobble to be excited from within the core.

Multidecadal climate variability of global lands and oceans

USGS Publications Warehouse

McCabe, G.J.; Palecki, M.A.

2006-01-01

Principal components analysis (PCA) and singular value decomposition (SVD) are used to identify the primary modes of decadal and multidecadal variability in annual global Palmer Drought Severity Index (PDSI) values and sea-surface temperature (SSTs). The PDSI and SST data for 1925-2003 were detrended and smoothed (with a 10-year moving average) to isolate the decadal and multidecadal variability. The first two principal components (PCs) of the PDSI PCA explained almost 38% of the decadal and multidecadal variance in the detrended and smoothed global annual PDSI data. The first two PCs of detrended and smoothed global annual SSTs explained nearly 56% of the decadal variability in global SSTs. The PDSI PCs and the SST PCs are directly correlated in a pairwise fashion. The first PDSI and SST PCs reflect variability of the detrended and smoothed annual Pacific Decadal Oscillation (PDO), as well as detrended and smoothed annual Indian Ocean SSTs. The second set of PCs is strongly associated with the Atlantic Multidecadal Oscillation (AMO). The SVD analysis of the cross-covariance of the PDSI and SST data confirmed the close link between the PDSI and SST modes of decadal and multidecadal variation and provided a verification of the PCA results. These findings indicate that the major modes of multidecadal variations in SSTs and land-surface climate conditions are highly interrelated through a small number of spatially complex but slowly varying teleconnections. Therefore, these relations may be adaptable to providing improved baseline conditions for seasonal climate forecasting. Published in 2006 by John Wiley & Sons, Ltd.

Using decadal climate prediction to characterize and manage changing drought and flood risks in Colorado

NASA Astrophysics Data System (ADS)

Lazrus, H.; Done, J.; Morss, R. E.

2017-12-01

A new branch of climate science, known as decadal prediction, seeks to predict the time-varying trajectory of climate over the next 3-30 years and not just the longer-term trends. Decadal predictions bring climate information into the time horizon of decision makers, particularly those tasked with managing water resources and floods whose master planning is often on the timescale of decades. Information from decadal predictions may help alleviate some aspects of vulnerability by helping to inform decisions that reduce drought and flood exposure and increase adaptive capacities including preparedness, response, and recovery. This presentation will highlight an interdisciplinary project - involving atmospheric and social scientists - on the development of decadal climate information and its use in decision making. The presentation will explore the skill and utility of decadal drought and flood prediction along Colorado's Front Range, an area experiencing rapid population growth and uncertain climate variability and climate change impacts. Innovative statistical and dynamical atmospheric modeling techniques explore the extent to which Colorado precipitation can be predicted on decadal scales using remote Pacific Ocean surface temperature patterns. Concurrently, stakeholder interviews with flood managers in Colorado are being used to explore the potential utility of decadal climate information. Combining the modeling results with results from the stakeholder interviews shows that while there is still significant uncertainty surrounding precipitation on decadal time scales, relevant and well communicated decadal information has potential to be useful for drought and flood management.

Tree-ring based reconstructions of interannual to decadal scale precipitation variability for northeastern Utah since 1226 A.D.

USGS Publications Warehouse

Gray, S.T.; Jackson, S.T.; Betancourt, J.L.

2004-01-01

Samples from 107 pin??on pines (Pinus edulis) at four sites were used to develop a proxy record of annual (June to June) precipitation spanning the 1226 to 2001 AD interval for the Uinta Basin Watershed of northeastern Utah. The reconstruction reveals significant precipitation variability at interannual to decadal scales. Single-year dry events before the instrumental period tended to be more severe than those after 1900. In general, decadal scale dry events were longer and more severe prior to 1900. In particular, dry events in the late 13th, 16th, and 18th Centuries surpass the magnitude and duration of droughts seen in the Uinta Basin after 1900. The last four decades of the 20th Century also represent one of the wettest periods in the reconstruction. The proxy record indicates that the instrumental record (approximately 1900 to the Present) underestimates the potential frequency and severity of severe, sustained droughts in this area, while over representing the prominence of wet episodes. In the longer record, the empirical probability of any decadal scale drought exceeding the duration of the 1954 through 1964 drought is 94 percent, while the probability for any wet event exceeding the duration of the 1965 through 1999 wet spell is only 1 percent. Hence, estimates of future water availability in the Uinta Basin and forecasts for exports to the Colorado River, based on the 1961 to 1990 and 1971 to 2000 "normal" periods, may be overly optimistic.

Origins and interrelationship of Intraseasonal rainfall variations around the Maritime Continent during boreal winter

NASA Astrophysics Data System (ADS)

Cao, Xi; Wu, Renguang

2018-04-01

Large intraseasonal rainfall variations are identified over the southern South China Sea (SSCS), tropical southeastern Indian Ocean (SEIO), and east coast of the Philippines (EPHI) in boreal winter. The present study contrasts origins and propagations and investigates interrelations of intraseasonal rainfall variations on the 10-20- and 30-60-day time scales in these regions. Different origins are identified for intraseasonal rainfall anomalies over the SSCS, SEIO, and EPHI on both time scales. On the 10-20-day time scale, strong northerly or northeasterly wind anomalies related to the East Asian winter monsoon (EAWM) play a major role in intraseasonal rainfall variations over the SSCS and EPHI. On the 30-60-day time scale, both the intraseasonal signal from the tropical Indian Ocean and the EAWM-related wind anomalies contribute to intraseasonal rainfall variations over the SSCS, whereas the EAWM-related wind anomalies have a major contribution to the intraseasonal rainfall variations over the EPHI. No relation is detected between the intraseasonal rainfall variations over the SEIO and the EAWM on both the 10-20-day and 30-60-day time scales. The anomalies associated with intraseasonal rainfall variations over the SSCS and EPHI propagate northwestward and northeastward, respectively, on the 10-20- and 30-60-day time scales. The intraseasonal rainfall anomalies display northwestward and northward propagation over the Bay of Bengal, respectively, on the 10-20- and 30-60-day time scales.

Temperature changes of the past 2000 yr in China and comparison with Northern Hemisphere

NASA Astrophysics Data System (ADS)

Ge, Q.; Hao, Z.; Zheng, J.; Shao, X.

2013-01-01

In this paper, we use principal components and partial least squares regression analysis to reconstruct a composite profile of temperature variations in China, and the associated uncertainties, at a decadal resolution over the past 2000 yr. Our aim is to contribute a new temperature time series to the paleoclimatic strand of the Asia2K working group, which is part of the PAGES (Past Global Changes) project. The reconstruction was developed using proxy temperature data, with relatively high confidence levels, from five locations across China, and an observed temperature dataset provided by Chinese Meteorological Administration covering the decades from the 1870s to the 1990s. Relative to the 1870s-1990s climatology, our two reconstructions both show three warm intervals during the 270s-390s, 1080s-1210s, and after the 1920s; temperatures in the 260s-400s, 560s-730s and 970s-1250s were comparable with those of the Present Warm Period. Temperature variations over China are typically in phase with those of the Northern Hemisphere (NH) after 1100, a period which covers the Medieval Climate Anomaly, Little Ice Age, and Present Warm Period. The recent rapid warming trend that developed between the 1840s and the 1930s occurred at a rate of 0.91° C/100 yr. The temperature difference between the cold spell (-0.74° C in the 1650s) during the Little Ice Age, and the warm peak of the Present Warm Period (0.08° C in the 1990s) is 0.82° C at a centennial time scale.

Fin whales as bioindicators of multi-decadal change in carbon and oxygen stable isotope shifts in the North Atlantic.

PubMed

Borrell, A; Saiz, L; Víkingsson, G A; Gaufier, P; López Fernández, A; Aguilar, A

2018-07-01

Global changes, and particularly the massive release of CO 2 to the atmosphere and subsequent global warming, have altered the baselines of carbon and oxygen stable isotopic ratios. Temporal shifts in these baselines can be advantageously monitored through cetacean skin samples because these animals are highly mobile and therefore integrate in their tissues the heterogeneity of local environmental signals. In this study, we examine variation of δ 13 C and δ 18 O values in the skin of fin whales sampled over three decades in two different North Atlantic feeding grounds: west Iceland and northwest Spain. These locations are situated about 2700 km apart and thus represent a wide latitudinal range within the North Atlantic Ocean. The δ 13 C decrease in both areas is attributed to the burning of fossil fuels and increased deforestation worldwide, the so-called Suess effect. The dissimilarity in the magnitude of the shift between the two areas is coincidental with previous information on local shifts and lies within the ranges of variation observed. δ 18 O values experienced a minimal, yet significant change in fin whales from W Iceland (a decline of -0.44‰ between 1986 and 2013) but not in those from NW Spain. This is in concordance with a higher rise in temperatures in the former area than in the latter. The study validates the use of cetacean skin to monitor temporal and geographical shifts in stable isotopic values and alerts that, when applying this tool to ecological research, comparisons between sample sets should take into account temporal and latitudinal scales. Copyright © 2018 Elsevier Ltd. All rights reserved.

Surface Deformation Caused by Pressure Changes in the Fluid Core

NASA Technical Reports Server (NTRS)

Fang, Ming; Hager, Bradford H.; Herring, Thomas A.

1995-01-01

Pressure load Love numbers are presented for the mantle deformation induced by the variation of the pressure field at the core mantle boundary (CNB). We find that the CMB geostrophic pressure fields, derived from 'frozen-flux' core surface flow estimates at epochs 1965 and 1975, produce a relative radial velocity (RRV) field in the range of 3mm/decade with uplift near the equator and subsidence near the poles. The contribution of this mechanism to the change in the length of day (l.o.d) is small --- about 2.3 x 10(exp -2) ms/decade. The contribution to the time variation of the ellipticity coefficient is more important --- -1.3 x 10(exp -11)/yr.

The many possible climates from the Paris Agreement's aim of 1.5 °C warming.

PubMed

Seneviratne, Sonia I; Rogelj, Joeri; Séférian, Roland; Wartenburger, Richard; Allen, Myles R; Cain, Michelle; Millar, Richard J; Ebi, Kristie L; Ellis, Neville; Hoegh-Guldberg, Ove; Payne, Antony J; Schleussner, Carl-Friedrich; Tschakert, Petra; Warren, Rachel F

2018-06-01

The United Nations' Paris Agreement includes the aim of pursuing efforts to limit global warming to only 1.5 °C above pre-industrial levels. However, it is not clear what the resulting climate would look like across the globe and over time. Here we show that trajectories towards a '1.5 °C warmer world' may result in vastly different outcomes at regional scales, owing to variations in the pace and location of climate change and their interactions with society's mitigation, adaptation and vulnerabilities to climate change. Pursuing policies that are considered to be consistent with the 1.5 °C aim will not completely remove the risk of global temperatures being much higher or of some regional extremes reaching dangerous levels for ecosystems and societies over the coming decades.

Multiscale Dynamics of Aseismic Slip on Central San Andreas Fault

NASA Astrophysics Data System (ADS)

Khoshmanesh, M.; Shirzaei, M.

2018-03-01

Understanding the evolution of aseismic slip enables constraining the fault's seismic budget and provides insight into dynamics of creep. Inverting the time series of surface deformation measured along the Central San Andreas Fault obtained from interferometric synthetic aperture radar in combination with measurements of repeating earthquakes, we constrain the spatiotemporal distribution of creep during 1992-2010. We identify a new class of intermediate-term creep rate variations that evolve over decadal scale, releasing stress on the accelerating zone and loading adjacent decelerating patches. We further show that in short-term (<2 year period), creep avalanches, that is, isolated clusters of accelerated aseismic slip with velocities exceeding the long-term rate, govern the dynamics of creep. The statistical properties of these avalanches suggest existence of elevated pore pressure in the fault zone, consistent with laboratory experiments.

Measuring Skin Temperatures with the IASI Hyperspectral Mission

NASA Astrophysics Data System (ADS)

Safieddine, S.; George, M.; Clarisse, L.; Clerbaux, C.

2017-12-01

Although the role of satellites in observing the variability of the Earth system has increased in recent decades, remote-sensing observations are still underexploited to accurately assess climate change fingerprints, in particular temperature variations. The IASI - Flux and Temperature (IASI-FT) project aims at providing new benchmarks for temperature observations using the calibrated radiances measured twice a day at any location by the IASI thermal infrared instrument on the suite of MetOp satellites (2006-2025). The main challenge is to achieve the accuracy and stability needed for climate studies, particularly that required for climate trends. Time series for land and sea skin surface temperatures are derived and compared with in situ measurements and atmospheric reanalysis. The observed trends are analyzed at seasonal and regional scales in order to disentangle natural (weather/dynamical) variability and human-induced climate forcings.

The Sun and climate

USGS Publications Warehouse

,

2000-01-01

Many geologic records of climatic and environmental change based on various proxy variables exhibit distinct cyclicities that have been attributed to extraterrestrial forcing. The best known of these are the changes in Earth’s orbital geometry called Milankovitch Cycles, with periodicities of tens to hundreds of thousands of years. However, many cycles seem to have subMilankovitch periodicities, commonly on decadal and centennial scales, similar to those of known solar cycles. A direct connection between solar irradiance (solar constant) and weather and climate has been suggested for more than 100 years but generally rejected by most scientists, who assume that the effect of solar variations would be small. However, recent satellite radiometer measurements and modeling studies indicate that small changes in total solar irradiance could produce global temperature changes of the magnitude suggested for climatic events such as the Little Ice Age (A.D. 1550–1700).

Changes of the Oceanic Long-term and seasonal variation in a Global-warming Climate

NASA Astrophysics Data System (ADS)

Xia, Q.; He, Y.; Dong, C.

2015-12-01

Abstract: Gridded absolute dynamic topography (ADT) from AVISO and outputs of sea surface height above geoid from a series of climate models run for CMIP5 are used to analysis global sea level variation. Variance has been calculated to determine the magnitude of change in sea level variation over two decades. Increasing trend of variance of ADT suggests an enhanced fluctuation as well as geostrophic shear of global ocean. To further determine on what scale does the increasing fluctuation dominate, the global absolute dynamic topography (ADT) has been separated into two distinguished parts: the global five-year mean sea surface (MSS) and the residual absolute dynamic topography (RADT). Increased variance of MSS can be ascribed to the nonuniform rising of global sea level and an enhancement of ocean gyres in the Pacific Ocean. While trend in the variance of RADT is found to be close to zero which suggests an unchanged ocean mesoscale variability. The Gaussian-like distribution of global ADT are used to study the change in extreme sea levels. Information entropy has also been adapted in our study. Increasing trend of information entropy which measures the degree of dispersion of a probability distribution suggests more appearance of extreme sea levels. Extreme high sea levels are increasing with a higher growing rate than the mean sea level rise.

Periodic and quiescent solar activity effects in the low ionosphere, using SAVNET data

NASA Astrophysics Data System (ADS)

Bertoni, F. C. P.; Raulin, J.-P.; Gavilan, H. R.; Kaufmann, P.; Raymundo, T. E.

2010-10-01

Important results have been acquired using the measurements of VLF amplitude and phase signals from the South America VLF Network (SAVNET) stations. This network is an international project coordinated by CRAAM, Brazil in cooperation with Peru and Argentina. It started operating in April 2006, and now counts on eight stations (Atibaia, Palmas, Santa Maria and Estaça~o Antártica Comandante Ferraz in Brazil; Piura, Punta-Lobos and Ica, in Peru; CASLEO, in Argentina). Researches, through the last decades, have demonstrated the versatility of the VLF technique for many scientific and technological purposes. In this work, we summarize some recent results using SAVNET data base. We have obtained daily maximum diurnal amplitude time series that exhibited behavior patterns in different time scales: 1) 1ong term variations indicating the solar activity level control of the low ionosphere; 2) characteristic periods of alternated slow and fast variations, the former being related to solar illumination conditions, and the latter that have been associated with the winter anomaly at high latitudes; 3) 27-days period related to the solar rotation and consequently associated to the solar Lyman-α radiation flux variations, reinforcing earlier theories about the importance of this spectral line for the D-region formation. Finally, we conclude presenting preliminary results of simulation using LWPC, which showed very good agreement at times of observed modal amplitude minima for a given VLF propagation path.

Glacial Isostatic Adjustment and Contemporary Sea Level Rise: An Overview

NASA Astrophysics Data System (ADS)

Spada, Giorgio

2017-01-01

Glacial isostatic adjustment (GIA) encompasses a suite of geophysical phenomena accompanying the waxing and waning of continental-scale ice sheets. These involve the solid Earth, the oceans and the cryosphere both on short (decade to century) and on long (millennia) timescales. In the framework of contemporary sea-level change, the role of GIA is particular. In fact, among the processes significantly contributing to contemporary sea-level change, GIA is the only one for which deformational, gravitational and rotational effects are simultaneously operating, and for which the rheology of the solid Earth is essential. Here, I review the basic elements of the GIA theory, emphasizing the connections with current sea-level changes observed by tide gauges and altimetry. This purpose is met discussing the nature of the "sea-level equation" (SLE), which represents the basis for modeling the sea-level variations of glacial isostatic origin, also giving access to a full set of geodetic variations associated with GIA. Here, the SLE is employed to characterize the remarkable geographical variability of the GIA-induced sea-level variations, which are often expressed in terms of "fingerprints". Using harmonic analysis, the spatial variability of the GIA fingerprints is compared to that of other components of contemporary sea-level change. In closing, some attention is devoted to the importance of the "GIA corrections" in the context of modern sea-level observations, based on tide gauges or satellite altimeters.

Crustal Movements and Gravity Variations in the Southeastern Po Plain, Italy

NASA Astrophysics Data System (ADS)

Zerbini, S.; Bruni, S.; Errico, M.; Santi, E.; Wilmes, H.; Wziontek, H.

2014-12-01

At the Medicina observatory, in the southeastern Po Plain, in Italy, we have started a project of continuous GPS and gravity observations in mid 1996. The experiment, focused on a comparison between height and gravity variations, is still ongoing; these uninterrupted time series certainly constitute a most important data base to observe and estimate reliably long-period behaviors but also to derive deeper insights on the nature of the crustal deformation. Almost two decades of continuous GPS observations from two closely located receivers have shown that the coordinate time series are characterized by linear and non-linear variations as well as by sudden jumps. Both over long- and short-period time scales, the GPS height series show signals induced by different phenomena, for example, those related to mass transport in the Earth system. Seasonal effects are clearly recognizable and are mainly associated with the water table seasonal behavior. To understand and separate the contribution of different forcings is not an easy task; to this end, the information provided by the superconducting gravimeter observations and also by absolute gravity measurements offers a most important means to detect and understand mass contributions. In addition to GPS and gravity data, at Medicina, a number of environmental parameters time series are also regularly acquired, among them water table levels. We present the results of study investigating correlations between height, gravity and environmental parameters time series.

Robustness of observation-based decadal sea level variability in the Indo-Pacific Ocean

NASA Astrophysics Data System (ADS)

Nidheesh, A. G.; Lengaigne, M.; Vialard, J.; Izumo, T.; Unnikrishnan, A. S.; Meyssignac, B.; Hamlington, B.; de Boyer Montegut, C.

2017-07-01

We examine the consistency of Indo-Pacific decadal sea level variability in 10 gridded, observation-based sea level products for the 1960-2010 period. Decadal sea level variations are robust in the Pacific, with more than 50% of variance explained by decadal modulation of two flavors of El Niño-Southern Oscillation (classical ENSO and Modoki). Amplitude of decadal sea level variability is weaker in the Indian Ocean than in the Pacific. All data sets indicate a transmission of decadal sea level signals from the western Pacific to the northwest Australian coast through the Indonesian throughflow. The southern tropical Indian Ocean sea level variability is associated with decadal modulations of ENSO in reconstructions but not in reanalyses or in situ data set. The Pacific-independent Indian Ocean decadal sea level variability is not robust but tends to be maximum in the southwestern tropical Indian Ocean. The inconsistency of Indian Ocean decadal variability across the sea level products calls for caution in making definitive conclusions on decadal sea level variability in this basin.

Decadal Variations in Surface Solar Radiation

NASA Astrophysics Data System (ADS)

Wild, M.

2007-05-01

Satellite estimates provide some information on the amount of solar radiation absorbed by the planet back to the 1980s. The amount of solar radiation reaching the Earth surface can be traced further back in time, untill the 1960s at widespread locations and into the first half of the 20th Century at selected sites. These surface sites suggest significant decadal variations in solar radiation incident at the surface, with indication for a widespread dimming from the 1960s up to the mid 1980s, and a recovery thereafter. Indications for changes in surface solar radiation may also be seen in observatinal records of diurnal temperature range, which provide a better global coverage than the radiation measurrements. Trends in diurnal temperature ranges over global land surfaces show, after decades of decline, a distinct tendency to level off since the mid 1980s. This provides further support for a significant shift in surface solar radiation during the 1980s. There is evidence that the changes in surface solar radiation are linked to associated changes in atmospheric aerosol. Variations in scattering sulfur and absorbing black carbon aerosols are in line with the variations in surface solar radiation. This suggests that at least a part of the variations in surface solar radiation should also be seen in the clear sky planetary albedo. Model simulations with a GCM which includes a sophisticated interactive treatment of aerosols and their emission histories (ECHAM5 HAM), can be used to address this issue. The model is shown to be capable of reproducing the reversal from dimming to brightening under cloud-free conditions in many parts of the world, in line with observational evidence. Associated changes can also be seen in the clear sky planetary albedo, albeit of smaller magnitude.

Investigating the variation of terrestrial water storage under changing climate and land cover

NASA Astrophysics Data System (ADS)

Fang, Y.; Niu, G. Y.; Zhang, X.; Troch, P. A. A.

2015-12-01

Terrestrial water storage (TWS) consists of groundwater, soil moisture, snow and ice, lakes and rivers and water contained in biomass. The water storage, especially the subsurface storage, is an essential property of the catchment, which controls climate, hydrological and biogeochemical processes at different scales. During the past decades, climate and land cover change has been proved to exert significant influences on hydrological processes which in turn alters the TWS variation. In order to better understand the interaction and feedback mechanism between TWS and earth system, it is necessary to quantify the effects of climate and land cover change on TWS variation. Direct estimation of total TWS has been made possible by the Gravity Recovery And Climate Experiment (GRACE) satellites that measures the earth gravity field. At present, few efforts were made to explicitly investigate the TWS variation under changing climate and land cover. GRACE data has its own limitations. One is its temporal coverage is short, it's only available since 2002, which is not sufficient to reflect the trend due to climate and land cover change. The other reason is that it cannot distinguish different components contributing to TWS. The limitation of TWS observation data can be overcame by numerical models developed to reproduce or to predict different earth system processes. After calibration and validation, with limited observations, these models can be trusted to extend our knowledge to where observations are not available both in time and space. In this study, based on Noah-MP LSM and satellite and ground data, we aim to: (1) Investigate the variation of total TWS as well as its components over Upper Colorado River Basin from 1990 to 2014. (2) Identify the major factors that control the TWS variation. (3) Quantify how the changing climate and land cover affect TWS variation in the same period.

Temporal patterns in adult salmon migration timing across southeast Alaska

USGS Publications Warehouse

Kovach, Ryan P.; Ellison, Stephen; Pyare, Sanjay; Tallmon, David

2015-01-01

Pacific salmon migration timing can drive population productivity, ecosystem dynamics, and human harvest. Nevertheless, little is known about long-term variation in salmon migration timing for multiple species across broad regions. We used long-term data for five Pacific salmon species throughout rapidly warming southeast Alaska to describe long-term changes in salmon migration timing, interannual phenological synchrony, relationships between climatic variation and migratory timing, and to test whether long-term changes in migration timing are related to glaciation in headwater streams. Temporal changes in the median date of salmon migration timing varied widely across species. Most sockeye populations are migrating later over time (11 of 14), but pink, chum, and especially coho populations are migrating earlier than they did historically (16 of 19 combined). Temporal trends in duration and interannual variation in migration timing were highly variable across species and populations. The greatest temporal shifts in the median date of migration timing were correlated with decreases in the duration of migration timing, suggestive of a loss of phenotypic variation due to natural selection. Pairwise interannual correlations in migration timing varied widely but were generally positive, providing evidence for weak region-wide phenological synchrony. This synchrony is likely a function of climatic variation, as interannual variation in migration timing was related to climatic phenomenon operating at large- (Pacific decadal oscillation), moderate- (sea surface temperature), and local-scales (precipitation). Surprisingly, the presence or the absence of glaciers within a watershed was unrelated to long-term shifts in phenology. Overall, there was extensive heterogeneity in long-term patterns of migration timing throughout this climatically and geographically complex region, highlighting that future climatic change will likely have widely divergent impacts on salmon migration timing. Although salmon phenological diversity will complicate future predictions of migration timing, this variation likely acts as a major contributor to population and ecosystem resiliency in southeast Alaska.

Satellite-based studies of maize yield spatial variations and their causes in China

NASA Astrophysics Data System (ADS)

Zhao, Y.

2013-12-01

Maize production in China has been expanding significantly in the past two decades, but yield has become relatively stagnant in the past few years, and needs to be improved to meet increasing demand. Multiple studies found that the gap between potential and actual yield of maize is as large as 40% to 60% of yield potential. Although a few major causes of yield gap have been qualitatively identified with surveys, there has not been spatial analysis aimed at quantifying relative importance of specific biophysical and socio-economic causes, information which would be useful for targeting interventions. This study analyzes the causes of yield variation at field and village level in Quzhou county of North China Plain (NCP). We combine remote sensing and crop modeling to estimate yields in 2009-2012, and identify fields that are consistently high or low yielding. To establish the relationship between yield and potential factors, we gather data on those factors through a household survey. We select targeted survey fields such that not only both extremes of yield distribution but also all soil texture categories in the county is covered. Our survey assesses management and biophysical factors as well as social factors such as farmers' access to agronomic knowledge, which is approximated by distance to the closest demonstration plot or 'Science and technology backyard'. Our survey covers 10 townships, 53 villages and 180 fields. Three to ten farmers are surveyed depending on the amount of variation present among sub pixels of each field. According to survey results, we extract the amount of variation within as well as between villages and or soil type. The higher within village or within field variation, the higher importance of management factors. Factors such as soil type and access to knowledge are more represented by between village variation. Through regression and analysis of variance, we gain more quantitative and thorough understanding of causes to yield variation at village scale, which further explains the gap between average and highest achieved yield.

Impact of volcanic eruptions on the climate of the 1st millennium AD in a comprehensive climate simulation

NASA Astrophysics Data System (ADS)

Wagner, Sebastian; Zorita, Eduardo

2015-04-01

The climate of the 1st millennium AD shows some remarkable differences compared to the last millennium concerning variation in external forcings. Together with an orbitally induced increased solar insolation during the northern hemisphere summer season and a general lack of strong solar minima, the frequency and intensity of large tropical and extratropical eruptions is decreased. Here we present results of a new climate simulation carried out with the comprehensive Earth System Model MPI-ESM-P forced with variations in orbital, solar, volcanic and greenhouse gas variations and land use changes for the last 2,100 years. The atmospheric model has a horizontal resolution of T63 (approx. 125x125 km) and therefore also allows investigations of regional-to-continental scale climatic phenomena. The volcanic forcing was reconstructed based on a publication by Sigl et al. (2013) using the sulfate records of the NEEM and WAIS ice cores. To obtain information on the aerosol optical depth (AOD) these sulfate records were scaled to an established reconstruction from Crowley and Unterman (2010), which is also a standard forcing in the framework of CMIP5/PMIP3. A comparison between the newly created data set with the Crowley and Unterman dataset reveals that the new reconstruction shows in general weaker intensities, especially of the large tropical outbreaks and fewer northern hemispheric small-to-medium scale eruptions. However, the general pattern in the overlapping period is similar. A hypothesis that can be tested with the simulation is whether the reduced volcanic intensity of the 1st millennium AD contributed to the elevated temperature levels over Europe, evident within a new proxy-based reconstruction. On the other hand, the few but large volcanic eruptions, e.g. the 528 AD event, also induced negative decadal-scale temperature anomalies. Another interesting result of the simulation relates to the 79 AD eruption of the Vesuvius, which caused the collapse of the city of Pompeii and its surroundings. Despite its severe local effects the eruption does not show a clear-cut hemispheric or global cooling. Therefore the simulation allows investigations on the effect of individual and clustered eruptions on the climate in the 1st millennium AD and its potential influence to human induced migration periods and decay of cultures in different regions.

Solar Activity and the Sea-surface Temperature Record-evidence of a Long-period Variation in Solar Total Irradiance

NASA Technical Reports Server (NTRS)

Reid, George C.

1990-01-01

There have been many suggestions over the years of a connection between solar activity and the Earth's climate on time scales long compared to the 11-year sunspot cycle. They have remained little more than suggestions largely because of the major uncertainties in the climate record itself, and the difficulty in trying to compile a global average from an assembly of measurements that are uneven in both quality and distribution. Different climate time response to solar activity, some suggesting a positive correlation, some a negative correlation, and some no correlation at all. The only excuse for making yet another such suggestion is that much effort has been devoted in recent years to compiling climate records for the past century or more that are internally consistent and believable, and that a decadal-scale record of solar total irradiance is emerging from spacecraft measurements, and can be used to set limits on the variation that is likely to have occurred on these time scales. The work described here was originally inspired by the observation that the time series of globally averaged sea-surface temperatures over the past 120 years or so, as compiled by the British Meteorological Office group (Folland and Kates, 1984), bore a resonable similarity to the long-term average sunspot number, which is an indicator of the secular variability of solar activity. The two time series are shown where the sunspot number is shown as the 135-month running mean, and the SST variation is shown as the departure from an arbitrary average value. The simplest explanation of the similarity, if one accepts it as other than coincidental, is that the sun's luminosity may have been varying more or less in step with the level of solar activity, or in other words that there is a close coupling between the sun's magnetic condition and its radiative output on time scales longer than the 11-year cycle. Such an idea is not new, and in fact the time series shown can be regarded as a modern extension of the proposal put forward by Eddy (1977) to explain the covariance between various global climate indicators and solar activity as revealed by the C-14 record over the past millenium.

Grazing moderates increases in C3 grass abundance over seven decades across a soil texture gradient in shortgrass steppe

USDA-ARS?s Scientific Manuscript database

Questions: How does long-term grazing exclusion influence plant community composition in a semiarid grassland? Can spatial variation in the effects of grazing exclusion be explained by variation in soil texture? Location: The shortgrass steppe of northeastern Colorado, USA, located in the North Amer...

Investigating different filter and rescaling methods on simulated GRACE-like TWS variations for hydrological applications

NASA Astrophysics Data System (ADS)

Zhang, Liangjing; Dobslaw, Henryk; Dahle, Christoph; Thomas, Maik; Neumayer, Karl-Hans; Flechtner, Frank

2017-04-01

By operating for more than one decade now, the GRACE satellite provides valuable information on the total water storage (TWS) for hydrological and hydro-meteorological applications. The increasing interest in use of the GRACE-based TWS requires an in-depth assessment of the reliability of the outputs and also its uncertainties. Through years of development, different post-processing methods have been suggested for TWS estimation. However, since GRACE offers an unique way to provide high spatial and temporal scale TWS, there is no global ground truth data available to fully validate the results. In this contribution, we re-assess a number of commonly used post-processing methods using a simulated GRACE-type gravity field time-series based on realistic orbits and instrument error assumptions as well as background error assumptions out of the updated ESA Earth System Model. Three non-isotropic filter methods from Kusche (2007) and a combined filter from DDK1 and DDK3 based on the ground tracks are tested. Rescaling factors estimated from five different hydrological models and the ensemble median are applied to the post-processed simulated GRACE-type TWS estimates to correct the bias and leakage. Time variant rescaling factors as monthly scaling factors and scaling factors for seasonal and long-term variations separately are investigated as well. Since TWS anomalies out of the post-processed simulation results can be readily compared to the time-variable Earth System Model initially used as "truth" during the forward simulation step, we are able to thoroughly check the plausibility of our error estimation assessment (Zhang et al., 2016) and will subsequently recommend a processing strategy that shall also be applied for planned GRACE and GRACE-FO Level-3 products for terrestrial applications provided by GFZ. Kusche, J., 2007:Approximate decorrelation and non-isotropic smoothing of time-variable GRACE-type gravity field models. J. Geodesy, 81 (11), 733-749, doi:10.1007/s00190-007-0143-3. Zhang L, Dobslaw H, Thomas M (2016) Globally gridded terrestrial water storage variations from GRACE satellite gravimetry for hydrometeorological applications. Geophysical Journal International 206(1):368-378, DOI 10.1093/gji/ggw153.