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

This paper presents: a classification of weather types in the Mediterranean Basin based on cluster analysis of the daily occurrences of several surfac e pressure centers and the subjective identification of 500hPa trough axis positions (1992-1996). The procedure results in 20 types that explain 69% o f overall pressure center variance and which are consistent with the season al succession of regional circulation. The development of weather types in winter is primarily controlled by the eastward propagation of barotropic wa ves while departures from the zonal Row 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 inter related with zonal and anticyclonic general weather types in Central Europe . H2-types featuring a weak Azores Anticyclone interrelate with a variety o f meridional circulation types after the Hess and Brezowski (1969) classifi cation. The 20 types explain rainfall variance in the core Mediterranean re gions las defined by principal components) to a high degree while rainfall variance in marginal regions is influenced by circulation patterns not bein g typical fur the Mediterranean Basin.