Winter anticyclonic blocking effects over Europe during 1960-2000 from an ensemble of regional climate models

Abstract

Anticyclonic blocking is an important factor for mid-latitude climate variability and is considered to play a key role in anomalous and extreme events. In this study we present an ana lysis of atmospheric blocking events on the output of a multi-model ensemble of regional climate model (RCM) simulations. The ensemble consists of a set of 13 RCMs, nested in the European domain with a resolution of 50 × 50 km. All RCM simulations were driven by similar lateral boundary conditions, namely, the ERA-40 reanalysis for the period 1961-2000, as part of the European project ENSEMBLES. The aim was to investigate the ability of the different RCMs to reproduce the anticyclonic blocking events of the forcing reanalysis fields. When the atmo - spheric blocking events were examined in terms of their frequency in the RCM outputs, we found that the longitudinal dependence of the frequency in ERA-40 is reproduced by all RCMs. The composite map of the 500 hPa geopotential height for the days central to blocking episodes calculated for the RCM ensemble was found to be similar in pattern and magnitude to the respective composite map from ERA-40 reanalysis. Related effects of the blocking events on daily average temperature and precipitation were studied in the RCM simulations and compared with respective observational (E-OBS) and reanalysis (ERA-40) gridded data sets. The results of this process-oriented evaluation study indicated a rather good ability of the different RCMs to reproduce the anticyclonic blocking events of the forcing reanalysis, as well as their influence on temperature and precipitation anomalies. © Inter-Research 2013.