Momentum Budget of the Atmospheric Boundary Layer over the Greenland Ice Sheet and its surrounding seas

The circulation patterns over the Greenland Ice Sheet and its surrounding seas are studied by explicitly calculating the momentum budget components, using data of a high-resolution regional atmospheric climate model. In winter (DJF), the katabatic pressure gradient force (PGF) dominates the momentum budget of the atmospheric boundary layer (ABL) over the ice sheet. Over the western slopes of the ice sheet, the large scale PGF acts in the same direction as the katabatic PGF, resulting in a strong southerly jet of up to 12 m s^-1. In winter, the accumulation of cold air over the sea ice along the northeast coast leads to a thermally induced northerly flow. This circulation facilitates southward sea ice transport in this area, and is enhanced by the large scale circulation. Along the west coast, a similar west-east temperature gradient also forces a northerly flow. In the summer months, sea ice is absent and thermal wind forcing is largely reduced over the ocean. Summer insolation also reduces katabatic forcing, the large scale forcing dominates the ABL momentum budget over the ice sheet. Heating of the ABL over the snow free tundra induces thermal contrasts with the ice sheet and ocean, forcing barrier winds in the coastal regions. Throughout the year, strong surface layer winds along the southeast coast of Greenland are forced by the large scale PGF. The figure displays averages for the winter months for a transect through North Greenland; a: potential temperature and wind speed, b: momentum budget components in the lowest model layer (~7 m).The two katabatic jets over the ice sheet are clearly visible as well as the ABL jet over the sea ice covered ocean along the east coast.