LAUSR

AbstractWe characterise wintertime warm and cold spells in the High Arctic and investigate the drivers of these anomalies. The analysis is based on the European Centre for Medium-Range Weather Forecasts’ interim reanalysis dataset. We find that the warm spells are systematically associated with an intense sea-level pressure and geopotential height anomaly dipole, displaying a low over the Arctic basin and a high over northern Eurasia. This configuration creates a natural pathway for extreme moisture influx episodes from the Atlantic sector into the Arctic (here termed moisture intrusions). Anomalous cyclone frequency at the pole (due largely to local cyclogenesis) then favours a deep penetration of these intrusions across the Arctic Basin. The large-scale circulation pattern associated with the warm spells further favours the advection of cold air across Siberia, leading to the so-called Warm Arctic – Cold Eurasia pattern previously discussed in the literature. On the contrary, cold Arctic extremes are as...