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151.
Glacier fluctuations between 1975 and 2008 in the Greater Himalaya Range of Zanskar, southern Ladakh
Glaciers in the Himalaya are often heavily covered with supraglacial debris,making them difficult to study with remotely-sensed imagery alone.Various methods such as band ratios can be used effectively to map clean-ice glaciers;however,a thicker layer of debris often makes it impossible to distinguish between supraglacial debris and the surrounding terrain.Previously,a morphometric mapping approach employing an ASTER-derived digital elevation model has been used to map glaciers in the Khumbu Himal and the Tien Shan.This study on glaciers in the Greater Himalaya Range in Zanskar,southern Ladakh,aims (i) to use the morphometric approach to map large debris-covered glaciers;and (ii) to use Landsat and ASTER data and GPS and field measurements to document glacier change over the past four decades.Field work was carried out in the summers of 2008.For clean ice,band ratios from the ASTER dataset were used to distinguish glacial features.For debris-covered glaciers,topographic features such as slope were combined with thermal imagery and supervised classifiers to map glacial margins.The method is promising for large glaciers,although problems occurred in the distal and lateral parts and in the fore field of the glaciers.A multi-temporal analysis of glaciers in Zanskar showed that in general they have receded since at least the mid-to late-1970s.However,some few glaciers that advanced or oscillated - probably because of specific local environmental conditions - do exist. 相似文献
152.
Dale P. Cruikshank Tobias C. Owen Thomas R. Geballe Catherine de Bergh Francois Poulet Joshua P. Emery 《Icarus》2005,175(1):268-283
We present spectra of Saturn's icy satellites Mimas, Enceladus, Tethys, Dione, Rhea, and Hyperion, 1.0-2.5 μm, with data extending to shorter (Mimas and Enceladus) and longer (Rhea and Dione) wavelengths for certain objects. The spectral resolution (R=λ/Δλ) of the data shown here is in the range 800-1000, depending on the specific instrument and configuration used; this is higher than the resolution (R=225 at 3 μm) afforded by the Visual-Infrared Mapping Spectrometer on the Cassini spacecraft. All of the spectra are dominated by water ice absorption bands and no other features are clearly identified. Spectra of all of these satellites show the characteristic signature of hexagonal H2O ice at 1.65 μm. We model the leading hemisphere of Rhea in the wavelength range 0.3-3.6 μm with the Hapke and the Shkuratov radiative transfer codes and discuss the relative merits of the two approaches to fitting the spectrum. In calculations with both codes, the only components used are H2O ice, which is the dominant constituent, and a small amount of tholin (Ice Tholin II). Tholin in small quantities (few percent, depending on the mixing mechanism) appears to be an essential component to give the basic red color of the satellite in the region 0.3-1.0 μm. The quantity and mode of mixing of tholin that can produce the intense coloration of Rhea and other icy satellites has bearing on its likely presence in many other icy bodies of the outer Solar System, both of high and low geometric albedos. Using the modeling codes, we also establish detection limits for the ices of CO2 (a few weight percent, depending on particle size and mixing), CH4 (same), and NH4OH (0.5 weight percent) in our globally averaged spectra of Rhea's leading hemisphere. New laboratory spectral data for NH4OH are presented for the purpose of detection on icy bodies. These limits for CO2, CH4, and NH4OH on Rhea are also applicable to the other icy satellites for which spectra are presented here. The reflectance spectrum of Hyperion shows evidence for a broad, unidentified absorption band centered at 1.75 μm. 相似文献
153.
Using Ockham's razor as a guide, we have tried to find the simplest model for the formation of giant planets that can explain current observations of atmospheric composition. While this “top-down” approach is far from sufficient to define such models, it establishes a set of boundary conditions whose satisfaction is necessary. Using Jupiter as the prototype, we find that a simple model for giant planet formation that begins with a solar nebula of uniform composition and relies on accretion of low temperature icy planetesimals plus collapse of surrounding solar nebula gas supplies that satisfaction. We compare the resulting predictions of elemental abundances and isotope ratios in the atmospheres of the other giants with those from contrasting models and suggest some key measurements to make further progress. 相似文献
154.
155.
Faith Vilas Kandy S. Jarvis Susan M. Lederer Michael S. Kelley Tobias C. Owen 《Icarus》2004,170(1):125-130
Narrowband reflectance spectra (0.53-1.0 μm) of Iapetus' leading and trailing sides were obtained in 2000 to test the presence of an absorption feature located near 0.67 μm seen in reflectance spectra of Iapetus' dark material and Hyperion's surface material. No feature was observed. The difference in reflectance across the UV/VIS/NIR spectral region, and the dependence of the presence or absence of this absorption feature on angular separation from the apex of Iapetus in its orbit, phase angle, and heliocentric distance (affecting temperature), were examined. A trend of increased reddening, and the presence of the absorption feature, correlate with an angular separation from the apex of ? approximately 10°. Spectral information is lost when the contribution of the bright water ice signal to the reflectance spectrum increases sufficiently. In order to optimize compositional studies of Iapetus, we encourage future ground-based and space-based spectral observations to maximize the concentration of dark material in the instrumental field of view. 相似文献
156.
157.
Valentina Krysanova Michel Wortmann Tobias Bolch Bruno Merz Doris Duethmann Judith Walter 《水文科学杂志》2013,58(4):566-590
AbstractClimate variability and change play a crucial role in the vulnerable system of the Aksu River basin located in Kyrgyzstan and northwest China, providing precious water resources for the intense oasis agriculture of the Xinjiang Province (China). Ubiquitous warming and increase in precipitation (in the lower part of the basin) have been detected. Glaciers in the region are retreating. Seasonal trends in river discharge show an increase. A clear link could be demonstrated between daily temperature and lagged river discharge at two headwater stations in summer. However, the correlation breaks over short periods in the end of summer or beginning of autumn at the Xiehela station, when the high (over 95th percentile) flow peaks caused by the glacier lake outburst floods of the Merzbacher Lake occur. This feature is a challenge for the climate impact assessment in the region, as these regular outbursts have to be represented in the projections for the future as well.
Editor D. Koutsoyiannis 相似文献
158.
Serena Ceola Alberto Montanari Tobias Krueger Fiona Dyer Heidi Kreibich Ida Westerberg 《水文科学杂志》2013,58(16):2803-2817
ABSTRACTWe explore how to address the challenges of adaptation of water resources systems under changing conditions by supporting flexible, resilient and low-regret solutions, coupled with on-going monitoring and evaluation. This will require improved understanding of the linkages between biophysical and social aspects in order to better anticipate the possible future co-evolution of water systems and society. We also present a call to enhance the dialogue and foster the actions of governments, the international scientific community, research funding agencies and additional stakeholders in order to develop effective solutions to support water resources systems adaptation. Finally, we call the scientific community to a renewed and unified effort to deliver an innovative message to stakeholders. Water science is essential to resolve the water crisis, but the effectiveness of solutions depends, inter alia, on the capability of scientists to deliver a new, coherent and technical vision for the future development of water systems.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR not assigned 相似文献
159.
Stéphane Cordier Tobias Lauer Dominique Harmand Manfred Frechen Gaël Brkojewitch 《地球表面变化过程与地形》2012,37(11):1167-1175
The aim of this paper is to study a low energy fluvial system response to natural and anthropogenic forcing during the last two millennia. In contrast with longer timescales (Holocene to Quaternary), historical sedimentary archives are sparse in such systems which are typically characterized by the predominance of erosion compared with aggradation. We studied three main sections in the Moselle valley (northeastern France) by a multi‐proxy approach combining morphology, sedimentology, archaeological evidence, historical archives, and dating. The geochronological framework was based on Optically Stimulated Luminescence (OSL) and validated by independent age control. The exposed sediments were allocated to different historical periods from Roman period to present. The first results show that, in contrast with many other fluvial systems, the Moselle and its tributaries did not experience major changes during historical periods. Climatic changes such as the Little Ice Age had a minor influence on floodplain aggradation (e.g. in grain size or sedimentation rates) in the Moselle valley and were only able to affect the fluvial style. This provides evidence that the reworking of sediments is the main fluvial process at short timescales in the valley floors of the Moselle catchment. In contrast, anthropogenic forcing seems important not only during recent centuries but also since Roman times. This is suggested by the case‐study of the Metz‐Mazelle section where significant headward erosion and sedimentation were recognized, and may be related to human occupation. The results therefore point to a need for increasing geoarchaeological and geochronological research in the Moselle catchment and similar low energy fluvial systems. Such research is actually essential to improve the knowledge of the fluvial response to environmental changes during the historical periods and to recognize the respective influence of natural variability and human forcing. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
160.
Redistributing hot gas around galaxies: do cool clouds signal a solution to the overcooling problem?
Tobias Kaufmann James S. Bullock Ariyeh H. Maller Taotao Fang James Wadsley 《Monthly notices of the Royal Astronomical Society》2009,396(1):191-202
We present a pair of high-resolution smoothed particle hydrodynamics simulations that explore the evolution and cooling behaviour of hot gas around Milky Way size galaxies. The simulations contain the same total baryonic mass and are identical other than their initial gas density distributions. The first is initialized with a low-entropy hot gas halo that traces the cuspy profile of the dark matter, and the second is initialized with a high-entropy hot halo with a cored density profile as might be expected in models with pre-heating feedback. Galaxy formation proceeds in dramatically different fashion depending on the initial setup. While the low-entropy halo cools rapidly, primarily from the central region, the high-entropy halo is quasi-stable for ∼4 Gyr and eventually cools via the fragmentation and infall of clouds from ∼100 kpc distances. The low-entropy halo's X-ray surface brightness is ∼100 times brighter than current limits and the resultant disc galaxy contains more than half of the system's baryons. The high-entropy halo has an X-ray brightness that is in line with observations, an extended distribution of pressure-confined clouds reminiscent of observed populations and a final disc galaxy that has half the mass and ∼50 per cent more specific angular momentum than the disc formed in the low-entropy simulation. The final high-entropy system retains the majority of its baryons in a low-density hot halo. The hot halo harbours a trace population of cool, mostly ionized, pressure-confined clouds that contain ∼10 per cent of the halo's baryons after 10 Gyr of cooling. The covering fraction for H i and Mg ii absorption clouds in the high-entropy halo is ∼0.4 and ∼0.6, respectively, although most of the mass that fuels disc growth is ionized, and hence would be under counted in H i surveys. 相似文献