Using variable-resolution grids to model precipitation from atmospheric rivers around the Greenland ice sheet

Abstract

Abstract. Atmospheric rivers (ARs) are synoptic-scale features that transport moisture poleward and have been shown to cause short duration, high-volume melt events on the Greenland ice sheet (GrIS). This project investigates the effectiveness of variable-resolution (VR) grids in modeling ARs and their subsequent precipitation around the GrIS using a study period of 1 January 1979 to 31 December 1998. VR simulations from the Community Earth System Model (CESM2.2) bridge the gap between limitations of global climate models and regional climate models while maximizing computational efficiency. VR grids improve the representation of ARs, in part by resolving small-scale processes. ARs from CESM2.2 simulations using three grid types (VR, latitude-longitude, and quasi-uniform) with varying resolutions are compared to output of ERA5 and MERRA2 observation-based reanalysis products. The VR grids produce ARs with smaller areal extents and lower integrated precipitation over the GrIS compared to latitude-longitude and quasi-uniform grids. We hypothesize that the smaller areal extents in VR grids are produced by the refined topography resolved in these grids. In contrast, smoothing from coarser resolution latitude-longitude and quasi-uniform grids allow ARs to penetrate further inland on the GrIS. The reduced areal extent in VR grids also likely contributes to the lower area-integrated cumulative precipitation, whereas the area-average cumulative precipitation is similar for VR, latitude-longitude, and quasi-uniform grids. The VR grids most closely match the AR overlap extent and precipitation in ERA5 and MERRA2, suggesting the most realistic behavior among the three configurations.