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Abstract. Atmospheric blocking can influence Arctic weather by diverting the meanwesterly flow and steering cyclones polewards, bringing warm, moist air tohigh latitudes. Recent studies have shown that diabatic heating processes inthe ascending warm conveyor belt branch of extratropical cyclones are relevantto blocking dynamics. This leads to the question of the extent to whichdiabatic heating associated with mid-latitude cyclones may influencehigh-latitude blocking and drive Arctic warm events. In this study weinvestigate the dynamics behind 50 extreme warm events of wintertime high-Arctic temperature anomalies during 1979–2016. Classifying the warm eventsbased on blocking occurrence within three selected sectors, we find that 30 ofthese events are associated with a block over the Urals, featuring negativeupper-level potential vorticity (PV) anomalies over central Siberia north ofthe Ural Mountains. Lagrangian back-trajectory calculations show that almost60 % of the air parcels making up these negative PV anomalies experiencelifting and diabatic heating (median 11 K) in the 6 d prior to theblock. Further, almost 70 % of the heated trajectories undergo maximumheating in a compact region of the mid-latitude North Atlantic, temporallytaking place between 6 and 1 d before arriving in the blockingregion. We also find anomalously high cyclone activity (on average fivecyclones within this 5 d heating window) within a sector northwest of themain heating domain. In addition, 10 of the 50 warm events are associated withblocking over Scandinavia. Around 60 % of the 6 d back trajectoriesstarted from these blocks experience diabatic heating, of which 60 % undergomaximum heating over the North Atlantic but generally closer to the time ofarrival in the block and further upstream relative to heated trajectoriesassociated with Ural blocking. This study suggests that, in addition to theability of blocks to guide cyclones northwards, Atlantic cyclones play asignificant role in the dynamics of high-latitude blocking by providing low-PVair via moist-diabatic processes. This emphasizes the importance of the mutualinteractions between mid-latitude cyclones and Eurasian blocking forwintertime Arctic warm extremes.

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