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Title: Simulation of links between temperature extremes and atmospheric circulation in regional climate models Authors:  Jan Kysely - Institute of Atmospheric Physics AS CR (Czech Republic) [presenting]
Eva Plavcova - Institute of Atmospheric Physics AS CR (Czech Republic)
Abstract: Atmospheric circulation is an important driver of temperature anomalies and extreme temperature events in mid-latitudes. Since climate models suffer from biases in the simulation of temperature extremes, it is important to study whether those biases are associated with large-scale atmospheric flow. We evaluate links of summer heat waves/winter cold spells to circulation types in an ensemble of 19 EURO-CORDEX regional climate model (RCM) simulations in central Europe and compare them against observations over 1980-2005. We find that the RCMs reproduce in general the observed circulation significantly conducive to temperature extremes, with zonal flow reducing probability of extremes in both seasons, while advection of warm/cold air from the south-easterly/north-easterly quadrant playing dominant role in developing heat waves/cold spells. Because of these links, simulation of temperature extremes in the RCMs is strongly affected by biases in atmospheric circulation. For almost all examined simulations, the persistence of circulation supertypes (i.e. types with common flow characteristics grouped together) is significantly overestimated, which may contribute to enhanced tendency to group days with large temperature anomalies into sequences. This bias is manifested in development of too-long heat waves/cold spells in the RCMs, and points to limited credibility of possible future scenarios of these temperature extremes based on the RCM simulations.