Glacier winds and parameterisation of the related surface heat fluxes

Abstract

The katabatic flow over glaciers is studied with data from automatic weather stations (AWS). We analyse data from the Morteratschgletscher (Switzerland), Vatnajökull (Iceland) and West Greenland, and conclude that katabatic flow is very common over melting glacier surfaces and rarely disrupted by the large-scale flow. Over small and medium-size glaciers the height of the wind maximum is generally low (typically 10 m), and vertical temperature differences near the surface are very large (up to 15 K over 4 m). In glacier mass-balance models there is a great need for parameterisations of the surface heat flux. We develop a simple method to estimate the sensible heat flux Fh associated with the glacier wind. It is based on the classical Prandtl model for slope flows. We set the turbulent exchange coefficient proportional to the maximum wind speed (velocity scale) and the height of the wind maximum (length scale). The resulting theory shows that Fh increases quadratically with the temperature difference between the surface and the ambient atmosphere; Fh decreases with the square root of the potential temperature gradient of the ambient atmosphere; and Fh is independent of the surface slope.