Decadal and longer changes of the winter sea level pressure fields and related synoptic activity over the North Atlantic

Abstract

Long-term intensity changes in the winter synoptic activity over the North Atlantic are studied in relation to changes of the winter mean sea level pressure (SLP) fields. Analysis of linear trends has revealed a good agreement between long-term (interdecadal) changes in the intensity of synoptic processes and variations of the winter SLP. On the contrary, no such agreement was found between detrended and low-pass filtered anomalies. There are periods, that are characterised by the enhanced (reduced) synoptic activity attributed to the low (high) index of the North Atlantic Oscillation (NAO). It appears that low-passed anomalies of intramonthly root mean square deviations (RMSD) of SLP are negatively correlated with NAO and East Atlantic (EA) teleconnection patterns over most of the North Atlantic. The low-passed winter SLP anomalies demonstrate both propagating and standing patterns. The latter have a period of about 8 years. While meridional dipole-like structures formed by the winter SLP anomalies are shifted to the west (east) of the North Atlantic, the related anomalies of synoptic activity tend to be located in the eastern (western) part of the region. When decadally averaged, anomalies in the intensity of synoptic activity are strongly linked to the North Atlantic storm track position. The exception is the 1980–1990 decade, characterised by a very high NAO index. During this decade, enhanced synoptic activity is observed to the south of the North Atlantic storm track. Copyright © 1999 Royal Meteorological Society