The effect of a regional increase in ocean surface roughness on the tropospheric circulation: a GCM experiment     

Uwe Ulbrich  Gerd Bürger  Dierk Schriever  Hans von Storch  Susanne L Weber  Gerhard Schmitz 《Climate Dynamics》1993,8(6):277-285

The sensitivity of the atmospheric circulation to an increase in ocean surface roughness in the Southern Hemisphere storm track is investigated in a paired general circulation model experiment. Such a change in sea roughness could be induced by ocean waves generated by storms. Two extended permanent-July runs are made. One with standard sea surface roughness, the other with ten times as a large surface roughness over open sea poleward of 40° S. The regional increase in ocean surface roughness significantly modifies the tropospheric circulation in the Southern Hemisphere. The strongest effect is the reduction of tropospheric winds (by 2 m/s or 10%) above the area with increased roughness. The poleward eddy momentum flux is reduced in the upper troposphere and the meridional eddy sensible heat flux is reduced in the lower troposphere. Zonal mean and eddy kinetic energy are consistently reduced.  相似文献   

Book reviews     

Martin Kaehler  H. Haefner  S. J. Prinsenberg  Pierre Biays  Konrad Murr  W. U. Ehrmann  Gerd Lüttig  Alexander Zaporozec  Peter Schröder  T. Gold  G. R. Lewthwaite  H. Hecklau  Andreas Grotewold  T. H. Elkins  K. Strobach 《GeoJournal》1988,16(3):323-329

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Meteorological features in Adélie Land during the austral summer season     

Nobuyoshi Ishikawa  Yuji Kodama  Gerd Wendler 《Pure and Applied Geophysics》1990,132(3):439-455

Intensive meteorological observations were carried out at three sites along the slope of Adélie Land, Antarctica, with the goal of documenting summertime meteorological features of the katabatic zone. Three observational sites were placed at 5 km (D10), 110 km (D47), and 210 km (D57) from the coast, and frequency distributions of meteorological parameters were obtained at each site. Some meteorological features at D47 and D57 (interior sites) were different than at D10 (the coastal site); namely, mean air temperatures averaged for the whole observational period showed more pronounced diurnal variations at the interior sites than at the coastal site. These variations could be represented by sinusoidal curves. Wind speeds also showed diurnal variations, whose extremes appeared several hours later than the temperature extremes. The prevailing wind direction for all sites was southerly, about 30° east of the fall line, with small variations in wind direction. The strength and the height of temperature inversions were examined in two different layers (0 to 50 m, 50 to 300 m) at D47. A strong, shallow inversion layer formed at night, however, completely vanished during the day. On the other hand, an upper level inversion whose strength was weak persisted. The katabatic characteristics of the surface wind found at D47 in summer could be due to this upper level temperature inversion.A contribution to I.A.G.O. (Interaction-Atmosphere-Glace-Ocean).  相似文献   

Zu den Oberflächentemperaturen der Nordsee im Jahr 1993     

Gerd Wegner 《Ocean Dynamics》1994,46(2):163-175

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Impact of Climate Change on the Regional Hydrology – Scenario-Based Modelling Studies in the German Rhine Catchment     

Lucas Menzel  Annegret H. Thieken  Daniel Schwandt  Gerd Bürger 《Natural Hazards》2006,38(1-2):45-61

The aim of the study is an impact analysis of global climate change on regional hydrology with special emphasis on discharge conditions and floods. The investigations are focussed on the major part of the German Rhine catchment with a drainage area of approx. 110,000 km². This area is subdivided into 23 subcatchments. In a first step, the hydrological model HBV-D serves to simulate runoff conditions under present climate for the individual subbasins. Simulated, large scale atmospheric fields, provided by two different Global Circulation Models (GCMs) and driven by the emission scenario IS95a (“business as usual”) are then used as input to the method of expanded downscaling (EDS). EDS delivers local time series of scenario climate as input to HBV-D. In a final step, the investigations are focussed on the assessment of possible future runoff conditions under the impact of climate change. The study indicates a potential increase in precipitation, mean runoff and flood discharge for small return intervals. However, the uncertainty range that originates from the application of the whole model chain and two different GCMs is high. This leads to high cumulative uncertainties, which do not allow conclusions to be drawn on the development of future extreme floods.  相似文献   

On the stability of geotechnical systems and its fractal progressive loss     

Gerd Gudehus  Asterios Touplikiotis 《Acta Geotechnica》2018,13(2):317-328

Geotechnical systems, consisting of soil and embedded solid structures, are practically stable if inevitable actions cause at most harmless redistributions. This kind of robustness can often be achieved with limit state design, i.e. by assuming representative snapshots of worst cases. Changes in configuration and state due to changing boundary conditions can be better judged with quasi-static numerical simulations using validated constitutive relations. The ever-present fractality of the ground may be neglected as long as the system is stable, whereas it gets dominant during a progressive loss of stability with jerky critical phenomena which elude mathematical treatment until present. In this sense geotechnical systems can be or get sensitive, i.e. further actions can trigger detrimental chain reactions with seismogeneous collapse of the soil fabric, pore pressure increase up to liquefaction, erosion, cracking of ground and structural parts and/or tilting. The geotechnical risk can be better mitigated by taking into account chain reactions with wild randomness. It can be further reduced by monitoring the seismic emission in addition to mass flows, structural deformations and pore pressures. The paper is to clarify notions and concepts.  相似文献   

The Atmospheric Boundary Layer Over Baltic Sea Ice   总被引：4，自引：0，他引：4  

Burghard?BrümmerEmail author  Amèlie?Kirchg??ner  Gerd?Müller 《Boundary-Layer Meteorology》2005,117(1):91-109

A new parametrization for the surface energy balance of urban areas is presented. It is shown that this new method can represent some of the important urban phenomena, such as an urban heat island and the occurrence of a near-neutral nocturnal boundary layer with associated positive turbulent heat fluxes, unlike the traditional method for representing urban areas within operational numerical weather prediction (NWP) models. The basis of the new parametrization is simple and can be applied easily within an operational NWP model. Also, it has no additional computational expense compared to the traditional scheme and is hence applicable for operational forecasting requirements. The results show that the errors for London within the Met Office operational mesoscale model have been significantly reduced since the new scheme was introduced. The bias and root-mean-square (rms) errors have been approximately halved, with the rms error now similar to the model as a whole. The results also show that a seasonal cycle still exists in the model errors, but it is suggested that this may be caused by anthropogenic heat sources that are neglected in the urban scheme.The British Crowns right to retain a non-exclusive royalty-free license in and to any copyright is acknowledged.  相似文献   

Reconstruction of palaeohydrological conditions in a lagoon during the 2nd Zechstein cycle through simultaneous use of δD values of individual n-alkanes and δ<Superscript>18</Superscript>O and δ<Superscript>13</Superscript>C values of carbonates     

Dirk?Sachse  Jens?Radke  Reinhard?Gaupp  Lorenz?Schwark  Guido?Lüniger  Gerd?GleixnerEmail author 《International Journal of Earth Sciences》2004,93(4):554-564

For the first time ¹⁸O and ¹³C values from carbonates and D values of individual n-alkanes were used to reconstruct palaeohydrological conditions in a lagoon at the southern margin of the Central European Zechstein Basin (CEZB). A 12-m core covering the complete Ca2 interval and adjacent anhydrites (A1 and A2) was analyzed for ¹⁸O and ¹³C values of dolomitized carbonates and D values of individual n-alkanes. ¹⁸O_carb values (+2 to +5 vs. VPDB) were strongly influenced by evaporation and temporal freshwater input into the lagoon. The ¹³C_carb values (–1 to +4 vs. VPDB) were controlled mainly by changes in primary production. Both isotopic ratios show an inverse relationship throughout most of the core, contradicting diagenetic alteration, since ¹³C_carb values are not altered significantly during dolomitization. Assuming a temperature range of 35–40 °C in the lagoon, ¹⁸O_carb values of +2.5 to +8 (vs. VSMOW) for the lagoonal water can be reconstructed. The lagoon may have desiccated twice during the Ca2 interval, as indicated by very high ¹⁸O_carb and low ¹³C_carb values, coinciding with increasing amount of anhydrite in the analyzed sample. These events seem to reflect not just local but a regional intra-Ca2 cyclicity. Measured D values of the short-chain n-alkanes, namely n-C₁₆ and n-C₁₈ which are widely used as indicators for photosynthetic bacterial and algal input, reflect the isotopic composition of the lagoonal water. Assuming constant fractionation during incorporation of hydrogen into lipids of –160, an average D value of +70 (vs. VSMOW) can be reconstructed for the lagoonal water, accounting for very arid conditions. The long-chain n-alkanes n-C₂₇, n-C₂₈, n-C₂₉ and n-C₃₀, thought to be derived from the leaf waxes of terrestrial higher plants, were shown to be depleted in D relative to the short-chain alkanes, therefore indicating a different hydrogen source. Terrestrial plants in arid areas mainly use water supplied by precipitation. By using a smaller fractionation of –120 due to evaporation processes in the leaves, reconstructed values vary between –74 and –9 (vs. VSMOW). These values are not indicating extremely arid conditions, implying that the long-chain n-alkanes were transported trough wind and/or rivers into the lagoon at the Zechstein Sea coast. D_water values, reconstructed using the n-C₁₆ alkane and ¹⁸O _water values, independently reconstructed on the same sample using the temperature dependant fractionation for dolomites are good agreement and suggest high amounts of evaporation affecting the coastal lagoon. Altogether, our results indicate that hydrogen isotopic ratios of n-alkanes give information on their origin and are a useful proxy for palaeoclimatic reconstruction.  相似文献   

Sea surface temperature changes in the North Sea and their causes   总被引：2，自引：0，他引：2  

Becker  Gerd A.; Pauly  Manfred 《ICES Journal of Marine Science》1996,53(6):887-898

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Thermal history of the westernmost Eastern Alps (Penninic Rhenodanubian Flysch nappes,Helvetic nappes,and Subalpine Molasse thrust sheets)     

Michael Zerlauth  Audrey Bertrand  Gerd Rantitsch  Doris Groß  Hugo Ortner  Hannah Pomella  Bernhard Fügenschuh 《International Journal of Earth Sciences》2016,105(5):1525-1547

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