Synoptic patterns that contribute to extremely hot days in Europe

Abstract

This paper describes a trend analysis which has been performed in the annual frequency of extremely hot days (EHD) in Europe and the identification of synoptic patterns that contribute to the generation of extreme high temperature events. In order to do this, we have used a set of daily temperature series from European Climate Assessment (ECA) and Dataset Project and subjective Hess-Brezowsky (HB) catalogue of weather types (Grosswetterlagen). The period selected for the study was from January 1, 1955 until December 31, 1998, during which it has been obtained the highest number of complete series of temperature. An EHD has been defined as one in which the maximum temperature exceeds the threshold of 95% of the distribution of daily maximum temperatures. The connection between an EHD and general circulation of the atmosphere is based on a statistical index that depending on its value, allocate one type of synoptic pattern producing maximum extreme temperature. To obtain the classification of the most important synoptic patterns, a rotated principal component analysis (RPC) has been applied. The results show an increase in the annual frequency of EHD and at the same time, significant positive trends in the frequency of synoptic situations associated with EHD for the whole Western European region.