Model Spatial Resolution and Snowfall on Ice Sheets

Abstract:

The surface mass balance (SMB) is the primary steering factor for the evolution of ice sheets. For mountain glaciers, the SMB gradient is largely determined by elevation. However, for ice sheets the relation between elevation and mass balance is more complex, which is only partly due to the nonlinear feedback between snowmelt and albedo. On ice sheets, precipitation is the main cause of the complex relation between elevation and SMB. Most precipitation on an ice sheet is generated through orographic lift, and high precipitation rates are thus found on locations with on average upslope atmospheric circulation. Similarly steep lee slopes receive much less moisture. Therefore, precipitation and elevation are regionally poorly correlated with elevation such that statistical downscaling of accumulation is hardly possible. That is why the resolution of precipitation fields in coupled GCM-ice sheet models remains for now limited by the resolution of the GCM. This resolution matters most along the ice sheet margins where the spatial accumulation gradients are largest.

In this presentation, we will focus on southeast Greenland. This rugged region of Greenland has very sharp SMB gradients, ranging from ablation to over 3 m of annul accumulation. We will present results of a new RACMO2 simulation on various resolutions. These results are used to discuss which spatial resolution is required to model the SMB in this region correctly.