Large-scale atmospheric flow conditions and sea surface temperatures associated with hazardous winds in Switzerland
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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.
KeywordsVariability of winter storms over Switzerland Large-scale atmospheric and SST environment NAO Teleconnection patterns 20CR Objective cyclone detection
We thank two anonymous reviewers for comments which improved the quality of the manuscript. We thank H. Wernli and M. Sprenger for making their cyclone identification algorithm available. Support for the Twentieth Century Reanalysis Project dataset is provided by the U.S. Department of Energy, Office of Science Innovative and Novel Computational Impact on Theory and Experiment (DOE INCITE) program, and Office of Biological and Environmental Research (BER), and by the National Oceanic and Atmospheric Administration Climate Program Office. J. Hurrell’s station-based NAO index records are available at http://climatedataguide.ucar.edu/guidance/hurrell-north-atlantic-oscillation-nao-index-station-based (last access: December 2012). Monthly RPCA-based NA and Eurasian teleconnection pattern indices from the CPC are available at ftp://cpc.ncep.noaa.gov/wd52dg/data/indices/ (last access: December 2012). Wavelet software was provided by C. Torrence and G. Compo and is available at http://atoc.colorado.edu/research/wavelets/ (last access: March 2012).
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