Assessing the role of precursor cyclones on the formation of extreme Greenland blocking episodes and their impact on summer melting across the Greenland ice sheet

A 30 year climatology of North Atlantic cyclones from 1979 to 2008 is examined within the context of extreme Greenland blocking and accelerated surface melting across the Greenland ice sheet (GrIS). A distinct class of North Atlantic cyclones, known as precursor cyclones, was identified as any extratropical cyclones originating to the west of Greenland blocks prior to the peak of blocking intensity. Composite map analysis reveals that precursor cyclones contributed to a significant intensification of extreme Greenland blocking episodes (GBEs) through the process of upper level wave amplification. Across all seasons, most extreme GBEs are associated with multiple precursor cyclones prior to peaking in intensity, and a majority of these cyclones have continental rather than oceanic origins. Over both the western and eastern sectors of Greenland, daily meltwater production simulated by the Modèle Atmosphérique Régional regional climate model is greater during extreme GBEs accompanied by precursor cyclones compared to extreme GBEs lacking a precursor cyclone. Based on an analysis of air parcel trajectories and North Atlantic SST anomalies, enhanced surface melting during the summer, particularly over southern and western Greenland, is strongly linked to the combination of vigorous adiabatic warming generated by subsiding air within the blocking anticyclones and warm air advection supplied by the precursor cyclones. With the increased frequency of extreme GBEs accompanied by precursor cyclones observed during a strong positive phase of the Atlantic Multidecadal Oscillation, recent long‐term increases in GrIS surface melting can be partially attributed to the interaction of these atmospheric and oceanic processes.