Improved simulation of ice sheet surface albedo in the NASA GISS ModelE climate model

Processes on the surface of ice sheets play an important role in evolution of ice sheet mass balance and by extension the flux of freshwater into the ocean. It is therefore important to effectively simulate these processes in global climate models used to project future changes in the earth system including sea level and ocean circulation changes. One parameter that plays a key role in ice sheet mass balance is the albedo of snow and ice. Here we present results of simulations from the NASA Goddard Institute for Space Studies (GISS) ModelE2.1 earth system model, which now incorporates a new scheme for snow albedo over ice sheets. The scheme allows snow grain size to evolve in response to snowpack parameters, and snow albedo to evolve in response to snow grain size, snow liquid water content, and impurity concentrations, informed by a set of lookup tables derived from the SNICAR snow radiative transfer scheme. We perform a set of simulations (with winds nudged to the MERRA-2 reanalysis) in which the scheme is active with fixed dust and black carbon concentrations. Comparison between simulated and satellite-derived albedo from MODIS indicates that the scheme is an improvement over historically-employed snow-aging dependent and fixed albedo schemes. An effort to improve modeling of additional snow and ice processes over the surface of ice sheets in ModelE is also underway.