Comparison of modelled- and remote sensing- derived daily snow line altitudes at Ulugh Muztagh,northern Tibetan Plateau   总被引：1，自引：0，他引：1  

Marinka SPIESS  Eva HUINTJES  Christoph SCHNEIDER 《山地科学学报》2016,13(4):593-613

The ice cap Ulugh Muztagh in the central Kunlun Shan at the northern fringe of the Tibetan Plateau is a very isolated region with arid cold conditions. No observational, meteorological or glaciological ground truth data is available. Using the Moderate-resolution Imaging Spectroradiometer(MODIS) Level 1 radiance Swath Data(MOD02QKM) with a spatial resolution of 250 m, transient snow lines during the months of July to September in 2001 to 2014 are derived. Results are used to calibrate the physical based Coupled Snowpack and Ice surface energy and Mass balance model(COSIMA). The model runs on a representative detail region of Ulugh Muztagh(UM) on a digital elevation model with the same spatial resolution as the MODIS bands. In the absence of field observations, the model is driven solely by dynamically downscaled global analysis data from the High Asia Refined analysis(HAR). We compare remote sensing derived and modelled mean regional transient snow line altitudes in the course of consecutive summer seasons in 2008 to 2010. The resulting snow line altitude(SLA) and annual equilibrium line altitude(ELA) proxy of both methods coincide very well in their interannual variability in accordance with interannual variability of climatic conditions. Since SLAs of both methods do notconsistently agree on a daily basis a usage of remote sensing derived SLAs for model calibration in the absence of field observation data is only limitedly feasible for daily analysis. ELA approximation using the highest SLA at the end of ablation period may not be applied to UM because the negative winter mass balance(MB) is not reflected in the summer SLA. The study reveals moderate negative MB for UM throughout the modelling period. The mean regional MB of UM accounts for-523±410 mm w.e. a-1 in the modelling period. Hence UM seems not to belong to the area of the ‘Karakorum anomaly' comprising a region of positive mass balances in recent years which has its centre presumably in the Western Kunlun Shan.  相似文献   

Significance of flow rule for the passive earth pressure problem     

Schmüdderich  Christoph  Tschuchnigg  Franz  Schweiger  Helmut F. 《Acta Geotechnica》2022,17(1):81-92

Acta Geotechnica - Determination of earth pressures is one of the fundamental tasks in geotechnical engineering. Although many different methods have been utilized to present passive earth pressure...  相似文献   

enviroCar: A Citizen Science Platform for Analyzing and Mapping Crowd‐Sourced Car Sensor Data          下载免费PDF全文

Arne Bröring  Albert Remke  Christoph Stasch  Christian Autermann  Matthes Rieke  Jakob Möllers 《Transactions in GIS》2015,19(3):362-376

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MODIS Derived Equilibrium Line Altitude Estimates for Purogangri Ice Cap,Tibetan Plateau,and their Relation to Climatic Predictors (2001–2012)          下载免费PDF全文

Marinka Spiess  Fabien Maussion  Marco Möller  Dieter Scherer  Christoph Schneider 《Geografiska Annaler: Series A, Physical Geography》2015,97(3):599-614

The variation of the equilibrium line altitude can be used as an indicator for glacier mass balance variability. Snow lines at the end of the ablation period are suitable proxies for the annual equilibrium line altitude on glaciers. We investigate snow lines at Purogangri ice cap on the central Plateau in order to study the interannual variability of glacier mass balance. Datasets of the daily Moderate Resolution Imaging Spectroradiometer snow product MOD10A1 were used to infer transient snow line variability during 2001–2012 and to derive regional‐scale, annual equilibrium line altitude. The Moderate Resolution Imaging Spectroradiometer snow albedo embedded within the snow product was compared with high‐resolution Landsat imagery. An albedo threshold was established to differentiate between ice and snow and the 13th percentile of the altitudes of snow‐covered pixels was chosen to represent the snow line altitude. The second maximum of the snow line altitudes in the ablation period was taken as a proxy for the annual equilibrium line altitude. A linear correlation analysis was carried out (1) between interannual variability of the equilibrium line altitude at Purogangri ice cap and various climate elements derived from the High Asia Reanalysis, and (2) between interannual variability of the equilibrium line altitude and the circulation indices North Atlantic Oscillation and Indian Summer Monsoon. Results suggest that air temperature and meridional wind speed above ground in July, as well as the lower tropospheric zonal wind in June and August play a crucial role in the development of the annual equilibrium line altitude.  相似文献   

Benchmarking the simulation of Cr isotope fractionation     

Christoph Wanner  Jennifer L. Druhan  Richard T. Amos  Peter Alt-Epping  Carl I. Steefel 《Computational Geosciences》2015,19(3):497-521

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Near-Surface Motion in the Nocturnal,Stable Boundary Layer Observed with Fibre-Optic Distributed Temperature Sensing   总被引：1，自引：1，他引：0  

Matthias J. Zeeman  John S. Selker  Christoph K. Thomas 《Boundary-Layer Meteorology》2015,154(2):189-205

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Effective stability around the Cassini state in the spin-orbit problem     

Marco Sansottera  Christoph Lhotka  Anne Lemaître 《Celestial Mechanics and Dynamical Astronomy》2014,119(1):75-89

We investigate the long-time stability in the neighborhood of the Cassini state in the conservative spin-orbit problem. Starting with an expansion of the Hamiltonian in the canonical Andoyer-Delaunay variables, we construct a high-order Birkhoff normal form and give an estimate of the effective stability time in the Nekhoroshev sense. By extensively using algebraic manipulations on a computer, we explicitly apply our method to the rotation of Titan. We obtain physical bounds of Titan’s latitudinal and longitudinal librations, finding a stability time greatly exceeding the estimated age of the Universe. In addition, we study the dependence of the effective stability time on three relevant physical parameters: the orbital inclination, $i$ , the mean precession of the ascending node of Titan orbit, $\dot{\varOmega }$ , and the polar moment of inertia, $C$ .  相似文献   

Trading more food: Implications for land use,greenhouse gas emissions,and the food system     

Christoph Schmitz  Anne Biewald  Hermann Lotze-Campen  Alexander Popp  Jan Philipp Dietrich  Benjamin Bodirsky  Michael Krause  Isabelle Weindl 《Global Environmental Change》2012,22(1):189-209

The volume of agricultural trade increased by more than ten times throughout the past six decades and is likely to continue with high rates in the future. Thereby, it largely affects environment and climate. We analyse future trade scenarios covering the period of 2005–2045 by evaluating economic and environmental effects using the global land-use model MAgPIE (“Model of Agricultural Production and its Impact on the Environment”). This is the first trade study using spatially explicit mapping of land use patterns and greenhouse gas emissions. We focus on three scenarios: the reference scenario fixes current trade patterns, the policy scenario follows a historically derived liberalisation pathway, and the liberalisation scenario assumes a path, which ends with full trade liberalisation in 2045.Further trade liberalisation leads to lower global costs of food. Regions with comparative advantages like Latin America for cereals and oil crops and China for livestock products will export more. In contrast, regions like the Middle East, North Africa, and South Asia face the highest increases of imports. Deforestation, mainly in Latin America, leads to significant amounts of additional carbon emissions due to trade liberalisation. Non-CO₂ emissions will mostly shift to China due to comparative advantages in livestock production and rising livestock demand in the region. Overall, further trade liberalisation leads to higher economic benefits at the expense of environment and climate, if no other regulations are put in place.  相似文献   

High-resolution isotope records of early Holocene rapid climate change from two coeval stalagmites of Katerloch Cave,Austria     

Ronny Boch  Christoph Spötl  Jan Kramers 《Quaternary Science Reviews》2009,28(23-24):2527-2538

Two coeval stalagmites from Katerloch Cave show pronounced intervals of low δ¹⁸O values around 8.2, 9.1, and 10.0 kyr (all ages are reported before the year 2000 AD) and represent an inorganic U–Th dated climate archive from the southeast of the European Alps, a region where only very few well-dated climate records exist. The O isotope curves, providing near-annual resolution, allow a direct comparison to the Greenland ice core records, as temperature was the primary factor controlling the O isotopic composition of Katerloch speleothems.The 8.2 kyr climate anomaly lasted about one century, from 8196 to 8100 yr, with a maximum amplitude of 1.1‰ at 8175 yr. The event is characterized by a rapid onset and a more gradual demise and U–Th data as well as annual lamina counting support a rapid climate change towards cooler conditions within 10–20 yr. There is no strong evidence that the 8.2 kyr anomaly was superimposed on a pronounced longer-term cooling episode, nor do the new data support two separate cooling events within the 8.2 kyr event as reported by other studies. Our record also shows a distinct climate anomaly around 9.1 kyr, which lasted 70–110 yr and showed a maximum amplitude of 1.0‰, i.e. it had a similar duration and amplitude as the (central) 8.2 kyr event. Compared to the 8.2 kyr event, the 9.1 kyr anomaly shows a more symmetrical structure, but onset and demise still occurred within a few decades only. The different progression of the 8.2 (asymmetrical) and 9.1 kyr anomaly (symmetrical) suggests a fundamental difference in the trigger and/or the response of the climate system. Moreover, both stalagmites show evidence of a climate anomaly around 10.0 kyr, which was of comparable magnitude to the two subsequent events.Using a well constrained modern calibration between air temperature and δ¹⁸O of precipitation for the study area and cave monitoring data (confirming speleothem deposition in Katerloch reflecting cave air temperature), a maximum cooling by ca 3 °C can be inferred at 8.2 and 9.1 kyr, which is similar to other estimates, e.g., from Lake Ammersee north of the Alps. The O isotopic composition of meteoric precipitation, however, is a complex tracer of the hydrological cycle and these temperature estimates do not take into account additional effects such as changes in the source area or synoptic shifts. Apart from that, the relative thickness of the seasonally controlled lamina types in the Katerloch stalagmites remains rather constant across the intervals comprising the isotopic anomalies, i.e. the stalagmite petrography argues against major shifts in seasonality during the early Holocene climate excursions.  相似文献   

A conservative, unconditionally stable, second-order three-point differencing scheme for the diffusion–convection equation     

Christoph Clauser  Stefan Kiesner 《Geophysical Journal International》1987,91(3):557-568

A three-point differencing scheme for the diffusion–convection equation is presented that offers all the advantages of both the central and the one-sided ('upwind') differencing scheme without suffering from their drawbacks. Specifically, the scheme is conservative, unconditionally stable, and second-order-accurate in space. It is free of oscillations and over- or undershoots, simple to code, and requires essentially no more computing time than the one-sided scheme. Although known for a relatively long time in numerical mathematics, the scheme apparently has not received sufficient attention from modellers of hydrothermal systems or contaminant transport in the geosciences. In order to fill this gap a comparison is made between this scheme and the widely used one-sided scheme for the transient diffusion–convection equation in different time discretizations. The results are discussed taking into account other approaches towards minimizing numerical diffusion.  相似文献