On the reduced sensitivity of the Atlantic overturning to Greenland ice sheet melting in projections: a multi-model assessment     

Didier Swingedouw  Christian B. Rodehacke  Steffen M. Olsen  Matthew Menary  Yongqi Gao  Uwe Mikolajewicz  Juliette Mignot 《Climate Dynamics》2015,44(11-12):3261-3279

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The radiation budget in a regional climate model   总被引：3，自引：2，他引：1  

Steffen Kothe  A. Dobler  A. Beck  B. Ahrens 《Climate Dynamics》2011,36(5-6):1023-1036

The long- and short-wave components of the radiation budget are among the most important quantities in climate modelling. In this study, we evaluated the radiation budget at the earth??s surface and at the top of atmosphere over Europe as simulated by the regional climate model CLM. This was done by comparisons with radiation budgets as computed by the GEWEX/SRB satellite-based product and as realised in the ECMWF re-analysis ERA40. Our comparisons show that CLM has a tendency to underestimate solar radiation at the surface and the energy loss by thermal emission. We found a clear statistical dependence of radiation budget imprecision on cloud cover and surface albedo uncertainties in the solar spectrum. In contrast to cloud fraction errors, surface temperature errors have a minor impact on radiation budget uncertainties in the long-wave spectrum. We also evaluated the impact of the number of atmospheric layers used in CLM simulations. CLM simulations with 32 layers perform better than do those with 20 layers in terms of the surface radiation budget components but not in terms of the outgoing long-wave radiation and of radiation divergence. Application of the evaluation approach to similar simulations with two additional regional climate models confirmed the results and showed the usefulness of the approach.  相似文献   

Sclerochronological oxygen and carbon isotope ratios in Radix (Gastropoda) shells indicate changes of glacial meltwater flux and temperature since 4,200 cal yr BP at Lake Karakul,eastern Pamirs (Tajikistan)     

Linda Taft  Steffen Mischke  Uwe Wiechert  Christian Leipe  Ilhomjon Rajabov  Frank Riedel 《Journal of Paleolimnology》2014,52(1-2):27-41

We report δ¹⁸O and δ¹³C values of 21 fossil shells from the aquatic gastropod Radix from a sediment core taken in the eastern basin of Lake Karakul, Tajikistan (38.86–39.16°N, 73.26–73.56°E, 3,928 m above sea level) and covering the last 4,200 cal yr BP. The lake is surrounded by many palaeoshorelines evidencing former lake-level changes, most likely triggered by changes in meltwater flux. This hypothesis was tested by interpreting the isotope ratios of Radix shells together with δ¹⁸O values of Ostracoda and of authigenic aragonite. The mean δ¹⁸O values of Radix and Ostracoda fall along the same long-term trend indicating a change in the isotopic composition of precipitation, which contributed to the glaciers in the catchment as snow and finally as melt water to the lake. The sclerochronological δ¹⁸O and δ¹³C patterns in Radix shells provide seasonal weather information, which is discussed in context with previously proposed climatic changes during the last 4,200 cal yr BP. The period between ~4,200 and 3,000 cal yr BP was characterized by stepwise glacier advance in the catchment most likely due to a precipitation surplus. Subsequently the climate remained relatively cold but the lake level fluctuated, as indicated by ostracod shell isotope data. From ~1,800 cal yr BP the sclerochronological patterns provide evidence for increasing melt water flux and transport of allochthonous carbon into the lake, most likely due to an accelerated glacier retreat. The period around 1,500 cal yr BP was characterized by strong warming, increasing meltwater flux, glacier retreat and an increasing lake level. Warm conditions continued until ~500 cal yr ΒP probably representing the end of the Medieval Warm Period. A short relatively cold (dry?) period and a lower lake level are assumed for ~350 cal yr BP, possibly an analogue to the Maunder Minimum cooling in the North Atlantic region. Our results show that the lake system is complex, and that changes were triggered by external forcing and feedbacks. The similarity of δ¹⁸O values in Radix and ostracod shells demonstrates that both archives provide complementary information.  相似文献   

Geostandards and Geoanalytical Research Bibliographic Review 2010     

Klaus Peter Jochum  Xiaohong Wang  Uwe Nohl  Steffen Schmidt  Beate Schwager  Brigitte Stoll  Qichao Yang  Ulrike Weis 《Geostandards and Geoanalytical Research》2011,35(4):485-488

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Comparison of approaches for the characterization of contamination at rural megasites     

Arno Rein  Steffen Popp  Steffen Zacharias  Carsten Leven  Martin Bittens  Peter Dietrich 《Environmental Earth Sciences》2011,63(6):1239-1249

The present work focuses on approaches for the characterization of subsurface contamination, which need to be reliable and cost-effective, particularly for extended and remote areas aimed at being redeveloped. Requirements are discussed with respect to specific conditions at megasites, in order to enable site valorization. In a case study, two approaches are compared, comprising (1) conventional site investigation based on historical surveys and concentration measurements at monitoring wells installed in areas suspected of being polluted and (2) the use of direct push (DP) methods covering the complete area. The DP investigation provided information on the contamination distribution and yielded also important information on hydraulic conditions. Statistical analysis of the results applying indicator kriging revealed that the conventional approach is markedly risky when decision-making relies solely on historical and sparse data. The DP campaign remarkably reduced the uncertainty concerning the estimated occurrence of polluted groundwater at the whole site. Furthermore, monitoring measurements are analyzed showing the possible importance of temporal variability. Taking economical consideration into account, DP-based groundwater screening is recommended to obtain either first or complementary information on the entire site. Based on these data, also locations for a long-term monitoring could be selected if temporal variability is assumed relevant.  相似文献   

Testing different sorting techniques in macroinvertebrate samples from running waters     

Peter Haase  Steffen Pauls  Andrea Sundermann  Armin Zenker 《Limnologica》2004,34(4):366-378

With the aim of finding an efficient, standardised and practical protocol for sorting macroinvertebrate samples for water management practice, three different sorting techniques were tested: RIVPACS sorting, a modified AQEM/STAR (MAS) sorting protocol and a Live-sorting method. Based on the same AQEM/STAR sample to ensure comparable results, we compared RIVPACS and MAS sorting for 20 samples, and Live-sorting and MAS for a different set of 20 samples. Comparisons were based on both ecological and financial parameters relevant for the implementation of the EU Water Framework Directive in Germany. Parameters include recently developed multimetric assessment indices, their stream type specific core metric results, time effort and costs. While RIVPACS and MAS sorting produced similar results in terms of ecological assessment, time effort and costs, Live-sorting differed notably in all three respects. Live-sorting is the quickest and least expensive protocol, but shows higher variability than the other protocols. We discuss the differences and the level of standardisation for each of these methods.  相似文献   

The climate sensitive zone along an altitudinal gradient in central Himalayan rivers: a useful concept to monitor climate change impacts in mountain regions     

Ram Devi Tachamo Shah  Subodh Sharma  Peter Haase  Sonja C. Jähnig  Steffen U. Pauls 《Climatic change》2015,132(2):265-278

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In (pre-) Olympic spirit: Assembling the global economic geography community in Beijing, 2007     

Steffen Wetzstein 《New Zealand geographer》2008,64(1):72-72

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Jet cocoons in rotating Seyfert galaxies: adaptive three-dimensional hydrodynamics     

Andrew J. Lim  Wolfgang Steffen 《Monthly notices of the Royal Astronomical Society》2001,322(1):166-176

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OSL quartz age underestimation due to unstable signal components     

Damian Steffen  Frank Preusser  Fritz Schlunegger   《Quaternary Geochronology》2009,4(5):353-362

When measuring samples from southern Peru, we discovered an age offset between feldspar infrared-stimulated luminescence (IRSL) and quartz optically stimulated luminescence (OSL) ages. This age offset was not only found in these particular samples but was also observed in samples from a range of geographical localities. Extensive analysis revealed that it is actually the quartz age that underestimates the true depositional age, and this is due to a very weak fast component combined with other thermally unstable OSL signal components. We discuss properties of these poorly behaving samples and how to detect such samples prior to the OSL single-aliquot regenerative-dose (SAR) measurement. Finally, existing approaches to improve equivalent dose (D_e) determination are discussed for samples from southern Peru.  相似文献