The atmospheric boundary layer over melting glaciers

Abstract

Results from a number of glacio-meteorological experiments carried out over melting glaciers are summarized. It is shown that in summer the microclimate of a glacier tongue is dominated by katabatic flow, initiated by the downward sensible heat flux. Characteristic obstacle height is an appreciable fraction (typically 0.1 to 0.5) of the height at which the wind maximum occurs, implying a serious zero-reference problem for profile analysis. Using a bulk method with roughness length estimated by a micro-topographic method appears to perform better. Analysis of the momentum and heat budgets shows that, in a first-order approximation, the dynamics of this flow can be described well by the classical Prandtl model for slope winds. The Prandtl model is extended by introducing a flow-dependent eddy viscosity. The eddy viscosity is set proportional to the maximum wind velocity (velocity scale) and the height at which the wind maximum occurs (length scale). An analytic solution can then be obtained which provides a useful description of the katabatic flow and the associated exchange of heat with the glacier surface.