Precipitation in Europe in relation to circulation patterns at the 500 hPa level

Abstract

The relationships of circulation patterns defined as rotated principal components of the 500 hPa geopotential heights in the Euro-Atlantic sector to precipitation distribution in Europe during the winter months (from December to March) were investigated. In each month, four to five patterns are distinguished: the North Atlantic Oscillation (NAO), Scandinavian, Central European, East European and East Atlantic. The first four are present each month, while the East Atlantic pattern is present only in December and March. Rotated principal components are used as indicators of circulation type intensity. The precipitation data consist of 321 series of monthly totals for the years 1951–1990. Maps of linear correlation coefficients between precipitation series and rotated principal components show the areas where precipitation is influenced by particular circulation types. The NAO has the greatest influence on precipitation in Western Europe; it enhances precipitation from France across the British Isles to Scandinavia and is a reason for low totals in Spain. The anticyclone over Scandinavia results in wet conditions in the Central Mediterranean and dry weather in northern Europe. The blocking phase of the Central European pattern combines with very low precipitation in Central Europe and higher-than-usual totals in the north. The East European pattern brings above-normal precipitation in north-eastern and south-western Europe, and below-normal precipitation in north-western and south-eastern areas in the phase when the geopotential level is low over the east Atlantic. Copyright © 1999 Royal Meteorological Society