Pressure gradient force, atmospheric circulation and climate in western Europe (1899-2002)

Abstract

One mission of synoptic climatology is to quantify the link between atmospheric circulation and surface environment. The pressure gradient force (PGF) is used as a multiple index to summarize the monthly atmospheric circulation for a site in western Europe (5°E and 50°N). The study of the temporal evolution of the PGF components (direction, magnitude, X and Y components) was carried out for the period 1899-2002. The results reflect the variability in atmospheric circulation and reveal some trends. The magnitude of the PGF is particularly affected by several successive periods where the strength of the atmospheric flow was lower (negative trend) or higher (positive trend) than normal. During the last decades of the twentieth century the atmospheric flow appears stronger than before (positive trend), except in summer. As the direction of the PGF can be related to the trajectory of the flow via the Buys-Ballot law, its anomalies are directly related to anomalies in the advection of air masses. No definite trend can be detected for this variable. However, it seems that the northerly flow becomes rare in winter. The relevance of the PGF is also examined with regard to the evolution of monthly temperatures and precipitations via some series of multiple regressions. The best results are obtained for the precipitations, with an explained variance lying between 47 and 73% (respectively in May and February). For temperatures, the explained variance oscillates between 34 and 73% (in September and January). The fact that the meridional and zonal components of the PGF, and the absolute pressure at the site are explicitly taken into account, ensures a good quantification of the atmospheric circulation 'anomalies', that are largely responsible for the annual, seasonal or monthly singularities of temperature and precipitation over western Europe. Copyright © 2007 Royal Meteorological Society.