A Satellite Emulator for Evaluating Sea Ice Volume in Coupled Earth System Models

We introduce a method for evaluating monthly to decadal sea ice volume in coupled earth system models using freeboard measurements from individual ground tracks from ICESat, Operation IceBridge (OIB), CryoSat-2, and ICESat-2. There are three facets to this work. First, spatiotemporal disparities between model grid cells and track-wise satellite observations have been overcome by exploiting scaling relationships we have discovered in freeboard measurements from ICESat and OIB. Second, we evaluate sea ice model freeboard, rather than ice thickness, to remove sources of observational error associated with snow thickness, as well as ice, snow and seawater density. We also improve the comparison of modeled and observed freeboard by exploiting accompanying research that quantifies an isostatic length scale and variable porosity of ridges in a new sea ice model ridging parameterization. Finally, we have developed a metric to quantify model skill and bias with accompanying statistical significance that indicates the contribution of both ice and snow thickness to differences between modeled and observed freeboard. A version of this `satellite emulator' is used to evaluate sea ice volume in a suite of simulations from the Regional Arctic System Model (RASM) for the entire ICESat campaign, and we present plans to make this satellite emulator available in a community sea ice code for use with ICESat-2 data from 2018 onwards.