Greenland Surface Melt Dominated by Solar and Sensible Heating

The Greenland Ice Sheet is the primary source of global Barystatic sea-level rise, and at least half of its recent mass-loss acceleration is caused by surface meltwater runoff. Previous studies on surface melt have examined various thermodynamic and dynamic drivers, yet their contributions are not compared using unified observations. We use decade-long in-situ measurements from automatic weather stations throughout the ablation zone to assess energy components and identify the leading physical processes in this area. Large melt events exceeding 3 sigma contribute only similar to 2% to total surface melt since 2007. The day-to-day variability of all melt is dominated by sensible heat exchange (31 +/- 7%) and shortwave radiation (28 +/- 5%). Sensible and solar heating correlate with the occurrence of dry and fast gravity-driven winds. These katabatic winds increase sensible heating of the surface mainly by enhancing vertical mixing that reduces the temperature inversion. The concomitant low humidity and clear skies yield increased solar heating. Plain Language Summary Greenland's surface melt is a primary contributor to global sea-level rise. However, the leading causal mechanisms are still unclear. Here, we use decade-long measurements from automatic weather stations in the most melt-susceptible regions on the Greenland Ice Sheet to identify dominant energy components and associated physical processes for surface mass loss. Surprisingly, large melt events, such as the one in 2012 during which almost the entire Greenland Ice Sheet experienced surface melt, contribute only 2% to total surface melt since 2007. The day-to-day variability of normal-rate melt events is dominated by sensible heat exchange (31%) and shortwave radiation (28%). They are likely caused by katabatic winds, a gravity-driven downslope wind that can be forceful and often associated with clear skies. In Greenland, grounds are usually colder than the air above as sunlight gets reflected by snow and ice. These katabatic winds enhance vertical mixing to bring down warm air aloft to heat grounds. With katabatic winds occurring during clear skies, they coincide with periods of increased shortwave radiation. Since high-melt regions along the ice sheet margins will typically have relatively steep slopes, these downslope winds will continue to have a large impact on Greenland's surface melt in the future.

Automated summary

The Greenland Ice Sheet is the primary source of global Barystatic sea-level rise, with at least half of its recent mass loss acceleration caused by surface meltwater runoff. Decade-long measurements from automatic weather stations in the most melt-susceptible regions identified dominant energy components and associated physical processes for surface mass loss. Surprisingly, large melt events only contribute 2% to total surface melt since 2007, with day-to-day variability dominated by sensible heat exchange and shortwave radiation.