Momentum budget of the atmospheric boundary layer over the Greenland ice sheet and its surrounding seas

Abstract

The atmospheric circulation patterns over the Greenland ice sheetand its surrounding seas are studied by explicitly calculating themomentum budget components, using data of a high-resolution regionalatmospheric climate model. In winter (DJF), the katabatic pressuregradient force (PGF) dominates the momentum budget of the atmosphericboundary layer (ABL) over the ice sheet. Over the western slopesof the ice sheet, the large-scale PGF acts in the same directionas the katabatic PGF, resulting in a strong southerly jet of up to12 m s−1. In winter, the accumulation of cold air over thesea ice along the northeast coast leads to a thermally induced northerlyflow. This circulation facilitates southward sea ice transport inthis area and is enhanced by the large-scale circulation. Along thewest coast, a similar west-east temperature gradient also forcesa northerly flow. In the summer months, sea ice is absent, and thermalwind forcing is largely reduced over the ocean. Summer insolationalso reduces katabatic forcing; the large-scale forcing dominatesthe ABL momentum budget over the ice sheet. Heating of the ABL overthe snow-free tundra induces thermal contrasts with the ice sheetand ocean, forcing barrier winds in the coastal regions. Throughoutthe year, strong surface layer winds along the southeast coast ofGreenland are forced by the large-scale PGF.