Modeling wind fields over complex terrain by superposition of scale-related processes and its application to the Alpine air mass exchange

Abstract

A detailed analysis of wind measurements from ground stations and upper air soundings leads to a description of the four-dimensional wind field during one day of the intensive observational phase of POLLUMET, July 5th, 1991. With a weather situation producing a countercurrent in the Swiss plateau and a high pressure situation allowing thermally induced winds to develop in the Alpine valleys, the questions of wind shear heights and overlapping of several wind regimes are analysed. An objective analysis for the regional scale wind field is supplemented by process models in order to fill the gap of knowledge at locations, where simple interpolation does not hold. The wind field obtained is validated with measurements not used as input and with constant pressure balloon flights. The identification of air masses then is realized by specifying the air mass origin for some special cases using the calculated wind field for back trajectory determination. Moreover the wind field is used to compute diurnal courses of trace gas fluxes through selected valley intersects near the entrance to the upper Reuss valley. This quantitatively specifies the exchange of air masses and their constituents between the Reuss valley and the adjacent region.

Keywords

• wind measurements
• thermally
• wind field
• air masses
• reuss valley
• switzerland
• windmessungen
• thermisch
• windfeld
• luftmassen
• reusstal
• schweiz