AERODYNAMIC STABILITY AND TURBULENT SENSIBLE-HEAT FLUX OVER A MELTING ICE SURFACE, THE GREENLAND ICE-SHEET

The turbulent sensible-heat flux to a melting ice surface is calculated from wind speed and air temperature at 2m over the ice surface, assuming a cel tain wind profile with the appropriate surface roughness. The aerodynamic stability of the boundary layer over melting ice is examined by comparing sensible-heat fluxes for logarithmic and log-linear wind profiles; where the logarithmic profile is strictly valid only for neutral conditions. Increasing stability reduces the sensible-heat flux to the glacier surface and introduces a non-linear relation between heat flux and air temperature. The stability effect is greatest at low wind speeds and fairly small at the high wind speeds that are common over the ice sheet. Earlier estimates of ablation by energy-balance modelling may be too large due to neglect of stability but this was almost offset by using a surface roughness that was too small. The log-linear wind profile should be used in future energy-balance models to take account of stability but more research is needed on the parameters of the profile, as well as on the sur face roughness.