Unstable extension of Enceladus' lithosphere     

Michael T. Bland  Ross A. Beyer  Adam P. Showman 《Icarus》2007,192(1):92-105

Regions near Enceladus' equator, Sarandib and Diyar Planitia, contain extensive sets of parallel ridges and troughs that may be diagnostic of the region's formation conditions. We present photoclinometry profiles across these ridges and troughs, which indicate that they are periodic, low-slope features with dominant wavelengths of 3 to 4 km and amplitudes between 100 and 400 m. The morphology of these terrains is consistent with formation via unstable extension of the lithosphere. Our numerical modeling demonstrates that unstable extension can generate large-scale topography under Enceladus-like conditions. Comparison of our photoclinometry profiles with the dominant wavelengths produced by our numerical model permits estimation of the background heat flow at the time the Sarandib-Diyar province formed. We estimate heat flows of 110 to , suggesting that resurfacing of the planitiae was accompanied by strong, localized heating. The extension necessary to produce the ridges and troughs may have been caused by now-inactive diapirs, internal phase changes, or other mechanisms. Our heat flux estimates imply elastic thickness at the time of resurfacing of 0.4 to 1.4 km, which are sufficient to have allowed satellite reorientation if the province was underlain by a low-density region. It is therefore plausible that Enceladus has experienced multiple heating events, each leading to localized resurfacing and global reorientation.  相似文献   

Two-dimensional kinematics of SLACS lenses – II. Combined lensing and dynamics analysis of early-type galaxies at z= 0.08–0.33     

Matteo Barnabè  Oliver Czoske  Léon V. E. Koopmans  Tommaso Treu  Adam S. Bolton  Raphaël Gavazzi 《Monthly notices of the Royal Astronomical Society》2009,399(1):21-36

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Generation of equatorial jets by large-scale latent heating on the giant planets     

Yuan Lian  Adam P. Showman 《Icarus》2010,207(1):373-393

Three-dimensional numerical simulations show that large-scale latent heating resulting from condensation of water vapor can produce multiple zonal jets similar to those on the gas giants (Jupiter and Saturn) and ice giants (Uranus and Neptune). For plausible water abundances (3-5 times solar on Jupiter/Saturn and 30 times solar on Uranus/Neptune), our simulations produce ∼20 zonal jets for Jupiter and Saturn and 3 zonal jets on Uranus and Neptune, similar to the number of jets observed on these planets. Moreover, these Jupiter/Saturn cases produce equatorial superrotation whereas the Uranus/Neptune cases produce equatorial subrotation, consistent with the observed equatorial-jet direction on these planets. Sensitivity tests show that water abundance, planetary rotation rate, and planetary radius are all controlling factors, with water playing the most important role; modest water abundances, large planetary radii, and fast rotation rates favor equatorial superrotation, whereas large water abundances favor equatorial subrotation regardless of the planetary radius and rotation rate. Given the larger radii, faster rotation rates, and probable lower water abundances of Jupiter and Saturn relative to Uranus and Neptune, our simulations therefore provide a possible mechanism for the existence of equatorial superrotation on Jupiter and Saturn and the lack of superrotation on Uranus and Neptune. Nevertheless, Saturn poses a possible difficulty, as our simulations were unable to explain the unusually high speed (∼) of that planet’s superrotating jet. The zonal jets in our simulations exhibit modest violations of the barotropic and Charney-Stern stability criteria. Overall, our simulations, while idealized, support the idea that latent heating plays an important role in generating the jets on the giant planets.  相似文献   

Modeling and monitoring of mine water rebound in an abandoned coal mine complex: Siersza Mine, Upper Silesian Coal Basin, Poland   总被引：1，自引：0，他引：1  

David Banks  Adam Frolik  Grzegorz Gzyl  Marek Rogoż 《Hydrogeology Journal》2010,18(2):519-534

A variable-volume, head-dependent mine water filling model (MIFIM) has been utilized to simulate the post-abandonment flooding of the Siersza coal mine in the Upper Silesian Coal Basin of southern Poland. It is demonstrated that desaturated pore space in the aquifer adjacent to the mine comprises a significant component of the resaturable mine-related void. The model results are very sensitive to the value of this poorly constrained parameter. Nevertheless, the model successfully predicted the first appearance of mine water in an observation well and its subsequent rise. Despite this apparent success, it is concluded that such modeling approaches generally lack predictive power for mines in permeable, porous host rocks. As real monitoring data accumulate, however, such models can be calibrated and their utility increased.  相似文献   

Sea level rise and tigers: predicted impacts to Bangladesh’s Sundarbans mangroves     

Colby Loucks  Shannon Barber-Meyer  Md. Abdullah Abraham Hossain  Adam Barlow  Ruhul Mohaiman Chowdhury 《Climatic change》2010,98(1-2):291-298

The Sundarbans mangrove ecosystem, shared by India and Bangladesh, is recognized as a global priority for biodiversity conservation. Sea level rise, due to climate change, threatens the long term persistence of the Sundarbans forests and its biodiversity. Among the forests’ biota is the only tiger (Panthera tigris) population in the world adapted for life in mangrove forests. Prior predictions on the impacts of sea level rise on the Sundarbans have been hampered by coarse elevation data in this low-lying region, where every centimeter counts. Using high resolution elevation data, we estimate that with a 28 cm rise above 2000 sea levels, remaining tiger habitat in Bangladesh’s Sundarbans would decline by 96% and the number of breeding individuals would be reduced to less than 20. Assuming current sea level rise predictions and local conditions do not change, a 28 cm sea level rise is likely to occur in the next 50–90 years. If actions to both limit green house gas emissions and increase resilience of the Sundarbans are not initiated soon, the tigers of the Sundarbans may join the Arctic’s polar bears (Ursus maritimus) as early victims of climate change-induced habitat loss.  相似文献   

Stratospheric temperature trends: impact of ozone variability and the QBO     

Mauro Dall’Amico  Lesley J. Gray  Karen H. Rosenlof  Adam A. Scaife  Keith P. Shine  Peter A. Stott 《Climate Dynamics》2010,34(2-3):381-398

In most climate simulations used by the Intergovernmental Panel on Climate Change 2007 fourth assessment report, stratospheric processes are only poorly represented. For example, climatological or simple specifications of time-varying ozone concentrations are imposed and the quasi-biennial oscillation (QBO) of equatorial stratospheric zonal wind is absent. Here we investigate the impact of an improved stratospheric representation using two sets of perturbed simulations with the Hadley Centre coupled ocean atmosphere model HadGEM1 with natural and anthropogenic forcings for the 1979–2003 period. In the first set of simulations, the usual zonal mean ozone climatology with superimposed trends is replaced with a time series of observed zonal mean ozone distributions that includes interannual variability associated with the solar cycle, QBO and volcanic eruptions. In addition to this, the second set of perturbed simulations includes a scheme in which the stratospheric zonal wind in the tropics is relaxed to appropriate zonal mean values obtained from the ERA-40 re-analysis, thus forcing a QBO. Both of these changes are applied strictly to the stratosphere only. The improved ozone field results in an improved simulation of the stepwise temperature transitions observed in the lower stratosphere in the aftermath of the two major recent volcanic eruptions. The contribution of the solar cycle signal in the ozone field to this improved representation of the stepwise cooling is discussed. The improved ozone field and also the QBO result in an improved simulation of observed trends, both globally and at tropical latitudes. The Eulerian upwelling in the lower stratosphere in the equatorial region is enhanced by the improved ozone field and is affected by the QBO relaxation, yet neither induces a significant change in the upwelling trend.  相似文献   

Climate forcings and climate sensitivities diagnosed from atmospheric global circulation models     

Bruce T. Anderson  Jeff R. Knight  Mark A. Ringer  Clara Deser  Adam S. Phillips  Jin-Ho Yoon  Annalisa Cherchi 《Climate Dynamics》2010,35(7-8):1461-1475

Understanding the historical and future response of the global climate system to anthropogenic emissions of radiatively active atmospheric constituents has become a timely and compelling concern. At present, however, there are uncertainties in: the total radiative forcing associated with changes in the chemical composition of the atmosphere; the effective forcing applied to the climate system resulting from a (temporary) reduction via ocean-heat uptake; and the strength of the climate feedbacks that subsequently modify this forcing. Here a set of analyses derived from atmospheric general circulation model simulations are used to estimate the effective and total radiative forcing of the observed climate system due to anthropogenic emissions over the last 50 years of the twentieth century. They are also used to estimate the sensitivity of the observed climate system to these emissions, as well as the expected change in global surface temperatures once the climate system returns to radiative equilibrium. Results indicate that estimates of the effective radiative forcing and total radiative forcing associated with historical anthropogenic emissions differ across models. In addition estimates of the historical sensitivity of the climate to these emissions differ across models. However, results suggest that the variations in climate sensitivity and total climate forcing are not independent, and that the two vary inversely with respect to one another. As such, expected equilibrium temperature changes, which are given by the product of the total radiative forcing and the climate sensitivity, are relatively constant between models, particularly in comparison to results in which the total radiative forcing is assumed constant. Implications of these results for projected future climate forcings and subsequent responses are also discussed.  相似文献   

Origin and contrasting succession pathways of the Western Carpathian calcareous fens revealed by plant and mollusc macrofossils     

Petra Hájková  Michal Horsák  Michal Hájek  Adam Lacina  Hana Buchtová  Barbora Pelánková 《Boreas: An International Journal of Quaternary Research》2012,41(4):690-706

Calcareous fens are unique environments whose history is almost unexplored. The radiocarbon dates of the basal layers of 49 undisturbed calcareous fens showed that in the Western Carpathians (central Europe) many of the extant fen sites originated fairly recently, with two peaks in the High Middle and Roman Ages, the former corresponding to human‐induced changes of the landscape. Conspicuous number of fens also appeared in the Lateglacial and later in the Bronze Age owing to suitable environmental conditions. The Lateglacial calcareous fens were of semi‐open character with coniferous trees, a heliophilous understorey, and mollusc communities composed of several snail species typical of glacial landscapes. We found wood of Taxus baccata in six localities between 7390 and 600 cal. a BP, suggesting that calcareous fens could have represented a refugial habitat for this red‐listed species during the middle Holocene. Using plant macrofossil and mollusc analyses of three representative profiles we illustrate the most common developmental types: (i) fens originating in the Lateglacial, having an open or semi‐open character during the whole Holocene; (ii) open fens originating as wooded wetlands; and (iii) open fens starting their development de novo in the late Holocene. Human activities were responsible for the formation of a high number of calcareous fens, especially in the Outer Western Carpathians, and became important drivers of fen biodiversity development. Only a few recently existing calcareous fens contain old sequences of calcareous deposits. They represent unique natural archives and harbour highly endangered relic populations of fen specialists, making their strict protection urgent.  相似文献   

Patterns of hydrologic connectivity in the McMurdo Dry Valleys,Antarctica: a synthesis of 20 years of hydrologic data          下载免费PDF全文

Adam N. Wlostowski  Michael N. Gooseff  Diane M. McKnight  Christopher Jaros  W. Berry Lyons 《水文研究》2016,30(17):2958-2975

Streams in the McMurdo Dry Valleys (MDVs) of Antarctica moderate an important hydrologic and biogeochemical connection between upland alpine glaciers, valley‐bottom soils, and lowland closed‐basin lakes. Moreover, MDV streams are simple but dynamic systems ideal for studying interacting hydrologic and ecological dynamics. This work synthesizes 20 years of hydrologic data, collected as part of the MDVs Long‐Term Ecological Research project, to assess spatial and temporal dynamics of hydrologic connectivity between glaciers, streams, and lakes. Long‐term records of stream discharge (Q), specific electrical conductance (EC), and water temperature (T) from 18 streams were analysed in order to quantify the magnitude, duration, and frequency of hydrologic connections over daily, annual, and inter‐annual timescales. At a daily timescale, we observe predictable diurnal variations in Q, EC, and T. At an annual timescale, we observe longer streams to be more intermittent, warmer, and have higher median EC values, compared to shorter streams. Longer streams also behave chemostatically with respect to EC, whereas shorter streams are more strongly characterized by dilution. Inter‐annually, we observe significant variability in annual runoff volumes, likely because of climatic variability over the 20 record years considered. Hydrologic connections at all timescales are vital to stream ecosystem structure and function. This synthesis of hydrologic connectivity in the MDVs provides a useful end‐member template for assessing hydrologic connectivity in more structurally complex temperate watersheds. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Agricultural cropland extent and areas of South Asia derived using Landsat satellite 30-m time-series big-data using random forest machine learning algorithms on the Google Earth Engine cloud   总被引：1，自引：0，他引：1  

Murali Krishna Gumma  Pardhasaradhi G. Teluguntla  Adam Oliphant  Jun Xiong  Chandra Giri 《地理信息系统科学与遥感》2020,57(3):302-322

ABSTRACT

The South Asia (India, Pakistan, Bangladesh, Nepal, Sri Lanka and Bhutan) has a staggering 900 million people (~43% of the population) who face food insecurity or severe food insecurity as per United Nations, Food and Agriculture Organization’s (FAO) the Food Insecurity Experience Scale (FIES). The existing coarse-resolution (≥250-m) cropland maps lack precision in geo-location of individual farms and have low map accuracies. This also results in uncertainties in cropland areas calculated from such products. Thereby, the overarching goal of this study was to develop a high spatial resolution (30-m or better) baseline cropland extent product of South Asia for the year 2015 using Landsat satellite time-series big-data and machine learning algorithms (MLAs) on the Google Earth Engine (GEE) cloud computing platform. To eliminate the impact of clouds, 10 time-composited Landsat bands (blue, green, red, NIR, SWIR1, SWIR2, Thermal, EVI, NDVI, NDWI) were derived for each of the three time-periods over 12 months (monsoon: Days of the Year (DOY) 151–300; winter: DOY 301–365 plus 1–60; and summer: DOY 61–150), taking the every 8-day data from Landsat-8 and 7 for the years 2013–2015, for a total of 30-bands plus global digital elevation model (GDEM) derived slope band. This 31-band mega-file big data-cube was composed for each of the five agro-ecological zones (AEZ’s) of South Asia and formed a baseline data for image classification and analysis. Knowledge-base for the Random Forest (RF) MLAs were developed using spatially well spread-out reference training data (N = 2179) in five AEZs. The classification was performed on GEE for each of the five AEZs using well-established knowledge-base and RF MLAs on the cloud. Map accuracies were measured using independent validation data (N = 1185). The survey showed that the South Asia cropland product had a producer’s accuracy of 89.9% (errors of omissions of 10.1%), user’s accuracy of 95.3% (errors of commission of 4.7%) and an overall accuracy of 88.7%. The National and sub-national (districts) areas computed from this cropland extent product explained 80-96% variability when compared with the National statistics of the South Asian Countries. The full-resolution imagery can be viewed at full-resolution, by zooming-in to any location in South Asia or the world, at www.croplands.org and the cropland products of South Asia downloaded from The Land Processes Distributed Active Archive Center (LP DAAC) of National Aeronautics and Space Administration (NASA) and the United States Geological Survey (USGS): https://lpdaac.usgs.gov/products/gfsad30saafgircev001/.  相似文献