RADIATIVE FLUXES AND THEIR IMPACT ON THE ENERGY-BALANCE OF THE GREENLAND ICE-SHEET

A meteorological experiment was carried out- during the summer months of 1990 and 1991 near the mean equilibrium-line altitude (ELA) on the western slope of the Greenland ice sheet (ETH Camp, 69 degrees 34'N, 4 9 degrees 17'W; 1155 m a.s.l.). As a part of the project, the energy f luxes at the surface, including all components of the radiation balanc e, atmospheric profiles with a tower and radiosondes, and the cloud co nditions were investigated in detail. Results from the radiative fluxe s are compared with observations made at other locations in order to d erive general characteristics of the radiation conditions on the Green land ice sheet and their relation to the climate of the ice sheet. At ETH Camp, albedo values obtained at ground level (2 m) and from a high tower (27 m) are similar during the melt season (late May to mid-Augu st) and slightly of inhomogeneous radiation due to increasing cloud am ount is compensated for by an increase in longwave incoming radiation. Because of the steady values of longwave outgoing radiation, net radi ation at the surface is characterized mainly by the albedo and its var iation. The regional net radiation for summer months on the Greenland ice sheet is determined mainly by three facts: (1) a strong increase i n albedo from the ablation area to the ELA and a smaller increase from the ELA to the accumulation area; (2) a large increase in longwave ou tgoing radiation in the ablation area and at the ELA in June and July compared to the accumulation areal; (3) a larger amount of cloud of th e stratus type at lower areas.