using a classification of circulation patterns

ABSTRACT: Several subjective and objective methods for the classification of circulation patterns into categories have been developed over the past century. In this study, we used the automated Lamb weather type (WT) classification method, based on mean sea level pressure (MSLP) to examine present and future circulation patterns above Western and Central Europe. First, the European Center for Medium-Range Weather Forecast 40-year reanalysis data (ECMWF-ERA40) is used to evaluate the occurring WTs within the newly developed ECHAM5-MPI/OM model for the period 1961–2000. Our analysis shows that the ECHAM5 model is capable of reproducing circulation patterns for the October to April season. For the remaining part of the year, there are some significant differences in eastern and western directional circulation types. Therefore, in the second part of this study, past, present and future ECHAM5 pressure fields are investigated for the autumn and winter season only. Finally, long-term trends of MSLP fields of the A1B scenario simulation using ECHAM5-MPI/OM for the period 1860–2100 show a significant increase in western circulation and anticyclonic WTs over Western and Central Europe, accompanied by a decrease in eastern circulation and cyclonic WTs. Copyright 2008 Royal Meteorological Society KEY WORDS circulation types; automatic Lamb weather type classification; a coupled general circulation model diagnosti