North Atlantic Winter Storm Activity in Modern Reanalyses and Pressure-Based Observations

Abstract

This study analyzes changes in extratropical windstorms over the North Atlantic during the last decades. We assessed and compared North Atlantic winter storm activity in a comprehensive approach from three different data sources: modern reanalysis data sets, a dynamically downscaled high-resolution global atmospheric climate simulation, and observations. The multi-decadal observations comprise both a storm index derived from geostrophic wind speed triangles and an observational record of low pressure systems counted from weather analyses. Both observational data sets have neither been compared to the most recent reanalyses nor to the downscaled global climate simulation with respect to North Atlantic winter storms before. The similarity of the geostrophic wind speed storm index to reanalyzed high wind speed percentiles and storm numbers confirms its suitability to describe storm frequencies and intensities for multi-decadal time scales. The results show that high wind speeds, storm numbers, and spatial storm track distributions are generally alike in high-resolution reanalyses and downscaled data sets and they reveal an increasing similarity to observations over time. Strong decadal and multi-decadal variability emerged in high wind speed percentiles and storm frequency, but no long-term changes for the last decades were detected.