Long-term trends in large-scale circulation behaviour and wind storms for North Atlantic islands: a multi-data analysis using ERA-20C and meteorological station data

Abstract

This research examines the role that large-scale circulation plays in local storminess for the North Atlantic islands of Orkney and Shetland, using the ERA-20C (1900–2009) reanalysis dataset. Automatic Lamb weather type classification is applied to daily mean sea level pressure (MSLP) data at 0.125° × 0.125° resolution to typify large-scale circulation patterns and calculate measures of storminess (frequencies of severe gale days, very severe gale days, and gale days that are not severe), calibrated using available observations from meteorological stations on the islands, which were made available by the UK Met Office. Analysis of the reanalysis-based gale day record indicates that while the frequency of cyclonic (C) weather type days does not vary over the study period, this weather type is coinciding more often with gale days and especially very severe gale days, which may indicate an increase in the intensity of cyclonic weather types in the region.