Large-scale atmospheric flow conditions and sea surface temperatures associated with hazardous winds in Switzerland

Abstract

The link between hazardous winter winds in Switzerland and the large-scale atmospheric and sea surface temperature (SST) environment in the North Atlantic basin is examined. The analyses cover synoptic, interannual, and decadal time scales and are based on all ensemble members of the Twentieth Century Reanalysis dataset for 1871–2008. On the synoptic time scale, the top ten high wind events in Switzerland are analysed; on longer time scales, the variability of the integrated winter wind loss potential (WLP) in Switzerland is examined. The top ten high wind events were associated with an eastward extension of the extratropical jet, enhanced cyclone frequencies over the North Sea and Scandinavia and reduced cyclone frequencies over the Mediterranean. The events were further accompanied by positive SST anomalies in the East Atlantic and the Mediterranean, and positive lower-tropospheric temperature and atmospheric moisture anomalies over Western and Central Europe. On interannual and decadal time scales, the winter WLP variability was associated with a large-scale atmospheric and SST pattern resembling a southeastward displacement of the winter North Atlantic Oscillation (NAO) pattern. The correlation of the WLP with the NAO and the East Atlantic pattern was positive for most of the 1951–2008 period, and increased with time. The distinct eastward shift of the northern centre of action of the NAO at the end of the twentieth century may explain the improved correlation between the winter NAO variability and the WLP.