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Spatial coherency of extreme weather events in Germany and Switzerland

With a simple statistical approach, the spatial representativeness of extreme events in daily meteorological surface observations from Germany and Switzerland is analysed. A percentile‐based definition of extremes is employed, and the frequency of simultaneously occurring extreme events at different stations is used as a measure for their spatial coherency. The largest representativeness is diagnosed for daily temperature extremes, i.e. hot and cold days, which very often occur simultaneously at many stations. On the contrary, precipitation extremes usually are restricted to local or regional scales. The spatial coherency of wind gust maxima is intermediate between the other extremes and depends on station location and terrain complexity. For cold extremes, station altitude has a strong influence on the spatial coherency of the events. It is argued that the spatial representativeness of extreme weather events directly relates to the importance of a coherent large‐scale atmospheric forcing, compared to more local factors, for triggering these events. In particular, large‐scale advection is the most important driver of temperature extremes. Strong wind gusts are often caused by mid‐latitude cyclones over the North Sea. The results from this study can also be used to assess the spatial representativeness of extreme weather reconstructions from proxy data in paleoclimate studies. Copyright © 2011 Royal Meteorological Society