An empirical classification of weather types in the Mediterranean Basin and their interrelation with rainfall

Abstract

This paper presents a classification of weather types in the Mediterranean Basin based on cluster analysis of the daily occurrences of several surface pressure centers and the subjective identification of 500 hPa trough axis positions (1992–1996). The procedure results in 20 types that explain 69% of overall pressure center variance and which are consistent with the seasonal succession of regional circulation. The development of weather types in winter is primarily controlled by the eastward propagation of barotropic waves while departures from the zonal flow pattern in summer tend to be linked to blocked stationary pools. H1-types with anticyclonic circulation in the Western Mediterranean and cyclonic flow in the eastern part are well interrelated with zonal and anticyclonic general weather types in Central Europe. H2-types featuring a weak Azores Anticyclone interrelate with a variety of meridional circulation types after the Hess and Brezowski (1969) classification. The 20 types explain rainfall variance in the core Mediterranean regions (as defined by principal components) to a high degree while rainfall variance in marginal regions is influenced by circulation patterns not being typical for the Mediterranean Basin.