Large‐scale wind and precipitation extremes in the Mediterranean: a climatological analysis for 1979–2012

Abstract

A new method for identifying high impact large‐scale wind and precipitation events in the extended Mediterranean region is outlined and applied to the European Centre for Medium‐range Weather Forecasts (ECMWF) reanalysis dataset ERA‐Interim for the years 1979–2012. The method highlights large‐scale 10 m gust and precipitation events that classify as extreme if integrated over a spatial scale of 1000 km and a temporal scale of 3 days. The method detects successfully high impact events, and reveals clear seasonal differences among the subregions of the Mediterranean. Western Mediterranean precipitation extremes are more intense, and occur mainly in autumn, while eastern Mediterranean events occur in winter. Composite dynamical analyses of large‐scale wind and precipitation extremes, and a combination of them, highlight coherent dynamical flow structures associated with the extremes in the different subregions of the Mediterranean. Precipitation events are preceded by an upper‐level trough and strong jet on its western flank, followed by cyclogenesis (mainly in the western Mediterranean), and/or a merging of the polar with the subtropical jet over northeastern Africa (in the eastern Mediterranean). Strong surface wind extremes develop around cyclones that intensify south of a deep parent cyclone near the exit of a strong anticyclonically curved jet, propagate eastwards and create a cold and dry northerly wind anomaly at the surface. Furthermore, combined large‐scale wind and precipitation extremes often occur simultaneously near cyclones, either North Atlantic cyclones, which project the wind and precipitation into the western Mediterranean, or Mediterranean cyclones. The latter produce wind extremes over a localized area, which often overlaps entirely with the region that receives extreme precipitation.