Wintertime temperature extremes in the high Arctic: drivers, statistics and implications for the mid-latitudes

Temperature extremes in the high Arctic have made the headlines in recent years, with wintertime warm spells approaching 0 °C at the North Pole. In the first part of this presentation, I will outline some salient large-scale and synoptic atmospheric drivers of wintertime warm and cold spells in the high Arctic. The warm spells are systematically associated with a large-scale circulation pattern that creates a natural pathway for extreme moisture intrusions from the Atlantic sector into the Arctic. Anomalies in the distribution of synoptic cyclones then favour 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 central-northern Eurasia. On the contrary, cold Arctic extremes are associated with a persistent low-pressure system over the pole. This effectively isolates the high latitudes from mid-latitude air masses, favouring an intense radiative cooling of the polar region. In the second part of the presentation, I will discuss return times of the wintertime warm spells, using a novel approach grounded in extreme value theory. This approach explicitly takes into account the spatial structure of the moisture intrusions driving the temperature extremes, and I will try to convince you that it provides a more realistic set of estimates than conventional return-time algorithms.