Identifying the Dominant Energy Components and the Associated Physical Processes of Greenland's Surface Melt
Using decade-long in-situ measurements from automatic weather stations throughout the ablation zone of Greenland, the scientists from UCI and the Geological Survey of Denmark and Greenland (GEUS) found that the major contributor to the total surface mass loss is not large melt events, dominated by the greenhouse effects of clouds, but the day-to-day melt variability, dominated by sensible and solar heating. These two energy components are likely enhanced by the prevailing katabatic winds in this area.
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. Our study is the most comprehensive investigation of surface ablation processes on the Greenland Ice Sheet based on long-term in-situ measurements. Our findings indicate that solar and sensible heating rather than longwave heating (the currently prevailing hypothesis) contribute the most to Greenland’s surface melt. Since high-melt regions along the ice sheet margins will typically have relatively steep slopes, this wind-driven melt mechanism will continue to have a large impact on Greenland’s surface melt in the future.
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 exceeding 3σ 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.