Air mass source regions associated with anomalous melting of the Greenland Ice Sheet

Abstract:

The Greenland ice sheet has experienced increased ablation and mass loss during the past two decades. Surface melt and mass balance is partially driven by large-scale changes in atmospheric circulation, which can direct anomalously warm and humid air masses over the ice sheet and lead to pulses of extensive melt and high runoff rates. However, the connection between the air mass source regions and melt pulses is poorly understood. Here we examine extreme melt pulses (>95^th percentile melt extent for 3 or more days) for topographically defined regions of the ice sheet. Daily melt extent is determined from a satellite passive microwave product. The NOAA ARL HYSPLIT model is used to calculate back-trajectories leading to melt pulses from the NASA MERRA2 atmospheric reanalysis. Potential temperatures at the top of the troposphere are used to trace atmospheric motion prior to melt pulses. Particular attention is given to extreme events in July 2012 and 2019 that led to melt at the highest elevations of the ice sheet. Results show the difference in source region east and west of the ice divide, and the important role of air mass source regions from North America and Europe.