Unstable near-surface boundary conditions in summer on top of the Greenland ice sheet

The surface energy balance for the interior of the Greenland ice sheet in summer 2000 is described. The most important feature of the energy balance is that net all-wave radiation is positive. Peak global radiation values of 800 W m(-2) provide energy at the snow surface that results in the turbulent fluxes of sensible and latent heat being directed into the atmosphere. Heating at the surface gives rise to unstable near-surface atmospheric conditions, with sensible heat fluxes typically between 10-20 W m(-2). Daily mean values of the subsurface heat flux are small and directed downwards from the surface as the snow cover warms during the summer season. Analysis-of-the gradient Richardson number for the past three summers shows that unstable conditions are common, with frequencies between 11-43% for a 2.5 month period. The unstable conditions in summer appear to be important in controlling katabatic forcing over the ice sheet.