The surface layer on the leeside of the Alps during foehn

Abstract

This paper describes and documents the meteorological conditions which occur in association with a cold surface layer on the northern lee side of the Alps during foehn. A climatological study using four years' rawinsonde data shows that during many foehn events a weak advection from the east occurs in the cold surface layer beneath the southerly foehn flow. Three cases of foehn in the northern Alps were studied using data taken by instrumented aircraft. The analysis of various vertical soundings between the baseline of the Alps and Munich indicate that the cold surface layer is eroded up to 50 km north of the baseline but that further north, the foehn has not touched the ground. The analysis of data taken in the urban plume west of Munich shows that the pollution is trapped by the inversion in the cold air leading to high levels of air pollution west of Munich.