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Schimanke S.,Swedish Meteorological and Hydrological Institute | Schimanke S.,Free University of Berlin | Spangehl T.,Free University of Berlin | Huebener H.,Free University of Berlin | And 2 more authors.
Climate Dynamics | Year: 2013

Ensemble simulations with a coupled ocean-troposphere-stratosphere model for the pre-industrial era (1860 AD), late twentieth century (1990 AD) greenhouse gas (GHG) concentrations, the SRES scenarios B1, A1B, A2, as well as stabilization experiments up to the Twenty-third century with B1 and A1B scenario GHG concentrations at their values at 2100, have been analyzed with regard to the occurrence of major sudden stratospheric warmings (SSWs). An automated algorithm using 60°N and 10 hPa zonal wind and the temperature gradient between 60°N and the North Pole is used to identify this phenomenon in the large data set. With 1990 CO2 concentrations (352 ppmv), the frequency of simulated SSWs in February and March is comparable to observation, but they are underestimated during November to January. All simulations show an increase in the number of SSWs from the pre-industrial period to the end of the twenty-first century, indicating that the increase of GHG is also reflected in the number of sudden warmings. However, a high variability partially masks the underlying trend. Multi-century averages during the stabilization periods indicate that the increase of SSWs is linear to the applied radiative forcing. A doubling of SSWs occurs when the GHG concentration reaches the level of the A2 scenario at the end of the twenty-first century (836 ppmv). The increase in SSWs in the projections is caused by a combination of increased wave flux from the troposphere and weaker middle atmospheric zonal winds. © 2012 The Author(s).

Lauer T.,Leibniz Institute for Applied Geophysics | Frechen M.,Leibniz Institute for Applied Geophysics | Hoselmann C.,Hessian Agency for Environment and Geology | Tsukamoto S.,Leibniz Institute for Applied Geophysics
Proceedings of the Geologists' Association | Year: 2010

The Upper Rhine Graben (URG) is characterized by a thickness of up to 500. m of unconsolidated Quaternary sediments, providing excellent records of the Rhine river system and its responses to tectonic and climatic changes. The most complete Quaternary sequence of fluvial and limnic-fluvial deposits is found in the Heidelberg Basin, due to its long-term subsidence since the mid-Eocene. The aim of this study is to provide a chronological framework using optically stimulated luminescence (OSL) dating of aeolian and fluvial sands derived from the upper 33. m of a sediment core, which was drilled into the Heidelberg Basin infill close to the village of Viernheim, Germany. The OSL ages demonstrate that the dated fluvial sediments were deposited during the last glacial period (Weichselian) and that there were at least three aggradation periods during this episode. The coversands that cap the sequence were emplaced during the early Holocene. © 2009 The Geologists' Association.

Friedrich R.,Lamont Doherty Earth Observatory | Vero G.,Hessian Agency for Environment and Geology | von Rohden C.,University of Heidelberg | Lessmann B.,Hessian Agency for Environment and Geology | And 3 more authors.
Applied Geochemistry | Year: 2013

SF6 and 3H-3He dating were used to investigate groundwater of the Odenwald/Germany. The application of SF6 dating is not possible in certain areas due to high SF6 excess. High SF6 is clearly linked to the lithology of the sampled area. The SF6 excess is of terrigenic origin, radio-chemically produced in the subsurface. The mountainous Odenwald region in the federal state of Hesse/Germany is one of the main recharge areas for groundwater of the surrounding depressions, where substantial extraction for public water supply takes place. We investigated the groundwater to study residence times and mixing ratios of groundwater of different ages, define regions of groundwater recharge and understand the groundwater inflow from the Odenwald to the surrounding areas. This multi-tracer study included stable and radioactive gas and isotope tracers such as 2H, 18O, 3H, noble gases (He, Ne, Ar, Kr, Xe), 222Rn and SF6. Noble gases were used to calculate recharge temperatures of the groundwater and to correct all gas tracers for so called "excess air". Comparing the results of the two independent dating methods - SF6 and 3H-3He - reveals that dating with SF6 is not possible in the crystalline region of the Odenwald, while the 3H-3He method gives robust groundwater ages. The results indicate that SF6 is influenced by a terrigenic source in the subsurface that varies with lithology. 222Rn data from part of the wells seem to be related to the terrigenic SF6, consistent with the idea of radiochemical SF6 production in rocks and release from the aquifer matrix. © 2013 Elsevier Ltd.

Huebener H.,Hessian Agency for Environment and Geology | Sanderson M.G.,UK Met Office | Hoschel I.,Free University of Berlin | Korper J.,Free University of Berlin | And 16 more authors.
Climatic Change | Year: 2013

Climate change impacts on the regional hydrological cycle are compared for model projections following an ambitious emissions-reduction scenario (E1) and a medium-high emissions scenario with no mitigation policy (A1B). The E1 scenario is designed to limit global annual mean warming to 2 °C or less above pre-industrial levels. A multi-model ensemble consisting of ten coupled atmosphere-ocean general circulation models is analyzed, which includes five Earth System Models containing interactive carbon cycles. The aim of the study is to assess the changes that could be mitigated under the E1 scenario and to identify regions where even small climate change may lead to strong changes in precipitation, cloud cover and evapotranspiration. In these regions the hydrological cycle is considered particularly vulnerable to climate change, highlighting the need for adaptation measures even if strong mitigation of climate change would be achieved. In the A1B projections, there are significant drying trends in sub-tropical regions, precipitation increases in high latitudes and some monsoon regions, as well as changes in cloudiness and evapotranspiration. These signals are reduced in E1 scenario projections. However, even under the E1 scenario, significant precipitation decrease in the subtropics and increase in high latitudes are projected. Particularly the Amazon region shows strong drying tendencies in some models, most probably related to vegetation interaction. Where climate change is relatively small, the E1 scenario tends to keep the average magnitude of potential changes at a level comparable to current intra-seasonal to inter-annual variability at that location. Such regions are mainly located in the mid-latitudes. © 2013 Springer Science+Business Media Dordrecht.

Korper J.,Free University of Berlin | Hoschel I.,Free University of Berlin | Lowe J.A.,UK Met Office | Hewitt C.D.,UK Met Office | And 12 more authors.
Climate Dynamics | Year: 2013

With an increasing political focus on limiting global warming to less than 2 °C above pre-industrial levels it is vital to understand the consequences of these targets on key parts of the climate system. Here, we focus on changes in sea level and sea ice, comparing twenty-first century projections with increased greenhouse gas concentrations (using the mid-range IPCC A1B emissions scenario) with those under a mitigation scenario with large reductions in emissions (the E1 scenario). At the end of the twenty-first century, the global mean steric sea level rise is reduced by about a third in the mitigation scenario compared with the A1B scenario. Changes in surface air temperature are found to be poorly correlated with steric sea level changes. While the projected decreases in sea ice extent during the first half of the twenty-first century are independent of the season or scenario, especially in the Arctic, the seasonal cycle of sea ice extent is amplified. By the end of the century the Arctic becomes sea ice free in September in the A1B scenario in most models. In the mitigation scenario the ice does not disappear in the majority of models, but is reduced by 42 % of the present September extent. Results for Antarctic sea ice changes reveal large initial biases in the models and a significant correlation between projected changes and the initial extent. This latter result highlights the necessity for further refinements in Antarctic sea ice modelling for more reliable projections of future sea ice. © 2012 The Author(s).

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