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The study examines links of summer heat waves and winter cold spells in Central Europe to atmospheric circulation and specifically its persistence in an ensemble of regional climate models (RCMs). We analyse 13 RCMs driven by the ERA-40 reanalysis and compare them against observations over reference period 1971-2000. Using objective classification of circulation types and an efficiency coefficient with a block resampling test, we identify circulation types significantly conducive to heat waves and cold spells. We show that the RCMs have a stronger tendency to group together days with very high or low temperature and tend to simulate too many heat waves and cold spells, especially those lasting 5 days and more. Circulation types conducive to heat waves in summer are characterized by anticyclonic, southerly and easterly flow, with increasing importance of warm advection during heat waves. Winter cold spells are typically associated with easterly and anticyclonic flow, and the onset of cold spells tends to be linked to northerly and cyclonic flow with cold advection. The RCMs are generally able to reproduce the links between circulation and heat waves or cold spells, including the radiation-to-advection effect for heat waves and the opposite advection-to-radiation effect for cold spells. They capture relatively well also changes of mean temperature anomalies during sequences of given circulation types, namely the tendency towards temperature increase (decrease) during those types conducive to heat waves (cold spells). Since mean lengths of all circulation supertypes are overestimated in the RCMs, we conclude that the overly persistent circulation in climate models contributes to the overestimated frequency of long heat waves and cold spells. As these biases are rather general among the examined RCMs and similar drawbacks are likely to be manifested in climate model simulations for the twenty-first century, the results also suggest that climate change scenarios for spells of days with high or low temperatures should be interpreted with a view to the models' limitations in simulating the recent climate. [ABSTRACT FROM AUTHOR]

The study investigates the relationships between large-scale atmospheric circulation (represented by circulation indices and 27 circulation types derived from gridded mean sea level pressure) and daily precipitation amounts over three regions in the Czech Republic (Central Europe) with different precipitation regimes. We examine how ENSEMBLES regional climate model ( RCM) simulations driven by re-analysis reproduce the observed links and capture differences in the links between given regions (lowland vs highlands) and seasons. We study the links of circulation to (1) mean precipitation over the regions, (2) probability of wet days, and (3) probability of extreme daily precipitation (exceeding threshold defined by a high quantile of precipitation distribution in a given season). We find quite strong links in the observed data between atmospheric circulation and these precipitation characteristics. The links are generally more pronounced for highland than lowland regions. More wet days and higher precipitation amounts are found for cyclonic and stronger flows, and for westerly and north-easterly flows. The RCMs are generally able to capture basic features of the links. They nevertheless have difficulties to reproduce some more specific features and differences in the links between the regions. Results also suggest that good performance in some precipitation characteristics may be due to compensating errors rather than model's perfection. [ABSTRACT FROM AUTHOR]