Interaction between Atlantic cyclones and Eurasian atmospheric blocking drives warm extremes in the high Arctic

Atmospheric blocking can influence Arctic weather by diverting the mean westerly flow polewards, bringing warm, moist air to high latitudes. Recent studies have shown that diabatic heating processes in the ascending warm conveyor belt branch of extratropical cyclones are relevant to blocking dynamics. This leads to the question of the extent to which diabatic heating associated with mid-latitude cyclones may influence high-latitude blocking and drive Arctic warm events. In this study we investigate the dynamics behind 50 extreme warm events of wintertime high Arctic surface temperature anomalies. We find that 30 of these events are associated with “Ural” blocking, featuring negative upper-level PV anomalies over central Siberia north of the Ural Mountains. Lagrangian back-trajectory calculations show that almost 70% of the air parcels making up these negative PV anomalies experience lifting and diabatic heating (average 14,7 K) in the 9-days prior to blocking. Further, 43,4 % of the heated trajectories undergo maximum heating and lifting in a compact region of the midlatitude North Atlantic, temporally taking place between 6 and 2.5 days before arriving in the blocking region. These trajectories mainly reside in the subtropics before being advected into the lifting region. We also find anomalously high cyclonic activity (on average 3,9 cyclones within a 3,5-day window around the time of maximum lifting) within a sector northwest of the main lifting domain. This study highlights the importance of the interaction between mid-latitude cyclones and Eurasian blocking as driver for Arctic warm extremes.