Momentum, Heat, and Moisture Budgets of the Katabatic Wind Layer over a Midlatitude Glacier in Summer

Abstract

In the summer of 1994, meteorological measurements were performed on Pasterze Glacier in the eastern Alps. One of the most remarkable observations concerning the observed climate was the persistent glacier wind. On the relatively large glacier, which has a length of 9.6 km, the gravity wind at the lower parts of the glacier is well developed and has a thickness of about 100 m. To determine the mechanisms that cause the steady-state glacier wind, the author calculated its vertically integrated budgets of momentum, heat, and moisture at a spot on the lower glacier tongue. It was found that the sum of interfacial and surface friction account for only half of the momentum dissipation of the glacier wind; the rest of the katabatic force is most probably balanced by the mesoscale pressure gradient that drives the valley wind above the katabatic layer. The heat and moisture budgets of the boundary layer show simple two-term balances: heat is lost through the turbulent flux of sensible heat at the surface (on average 50 W m?2) and gained by the downward transport of air. Moisture is added to the katabatic layer by entrainment and lost through condensation at the surface, but on average the moisture fluxes are small. The entrainment velocity, averaged over the length of the glacier, was estimated to be 2.4 cm s?1; it reduces to 0.7 cm s?1 at the glacier tongue, which was estimated by closing the local moisture budget.