MERRA-2: Greenland Ice Sheet Surface Mass Balance
Surface mass balance is the accumulated snow on the ice sheet surface minus meltwater runoff. It is thought that the Greenland Ice Sheet's contribution to sea level rise is composed of equal contributions of iceberg calving and surface mass loss, but that surface runoff will make a larger contribution in the future.
MERRA-2 is an atmospheric reanalysis product from the NASA GMAO that provides a regularly gridded, historical depiction of the global atmosphere over the satellite era. MERRA-2 combines a state-of-the-art atmospheric circulation model with available satellite and in situ observations. The MERRA-2 model includes surface hydrology processes over polar ice sheets including fractional snow cover, spatially-varying albedo, and meltwater percolation, refreezing, and runoff. A comparison of surface mass balance over the Ice Sheet shows reasonable agreement with high-resolution regional climate models. Topography is shown as dashed contours.
Snow accumulation values over the central ice sheet are very similar, and there is general agreement in the location of ablation zones along the periphery of the ice sheet. There are differences in the quantity of runoff in southwestern Greenland, which can be as large as two meters per year in the regional climate models. Nevertheless the time series of MERRA-2 runoff correlates reasonably well with the MAR regional climate model over recent years and when compared to other global analyses including the NOAA CFSR and the European reanalysis ERA-I. The time series includes the dramatic melt event in 2012 during which the entirety of the ice sheet simultaneously experienced surface melt on 11-July. MERRA-2 can be used to examine and understand conditions leading up to extreme melt events and place them in a global context.
