Changes in storm track and cyclone activity in three SRES ensemble experiments with the ECHAM5/MPI-OM1 GCM |
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Authors: | J G Pinto U Ulbrich G C Leckebusch T Spangehl M Reyers S Zacharias |
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Institution: | 1. Institut für Geophysik und Meteorologie, Universit?t zu K?ln, Kerpener Str. 13, 50923, Cologne, Germany 2. Institut für Meteorologie, Freie Universit?t Berlin, Carl-Heinrich-Becker-Weg 6-10, 12165, Berlin, Germany
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Abstract: | Synoptic activity over the Northern Hemisphere is evaluated in ensembles of ECHAM5/MPI-OM1 simulations for recent climate
conditions (20C) and for three climate scenarios (following SRES A1B, A2, B1). A close agreement is found between the simulations
for present day climate and the respective results from reanalysis. Significant changes in the winter mid-tropospheric storm
tracks are detected in all three scenario simulations. Ensemble mean climate signals are rather similar, with particularly
large activity increases downstream of the Atlantic storm track over Western Europe. The magnitude of this signal is largely
dependent on the imposed change in forcing. However, differences between individual ensemble members may be large. With respect
to the surface cyclones, the scenario runs produce a reduction in cyclonic track density over the mid-latitudes, even in the
areas with increasing mid-tropospheric activity. The largest decrease in track densities occurs at subtropical latitudes,
e.g., over the Mediterranean Basin. An increase of cyclone intensities is detected for limited areas (e.g., near Great Britain
and Aleutian Isles) for the A1B and A2 experiments. The changes in synoptic activity are associated with alterations of the
Northern Hemisphere circulation and background conditions (blocking frequencies, jet stream). The North Atlantic Oscillation
index also shows increased values with enhanced forcing. With respect to the effects of changing synoptic activity, the regional
change in cyclone intensities is accompanied by alterations of the extreme surface winds, with increasing values over Great
Britain, North and Baltic Seas, as well as the areas with vanishing sea ice, and decreases over much of the subtropics. |
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