Observations of thermally induced flows during MAP

The main objective of the Mesoscale Alpine Programme (MAP) field study conducted in the Brenner Pass area was to study foehn and gap wind events (occurring under conditions of strong mechanical forcing). A sequence of fine weather days provided the opportunity to obtain detailed observations of themally driven flows over a single slope facet in steep topography. High spatial resolution wind measurements were obtained with the NOAA/ETL Doppler lidar, wherby the narrow beam and the precise pointing capabilities of the lidar allowed a detailed view of the flow layer adjacent to the terrain. Vertical wind and temperature profiles were taken with a tethered balloon, which was stationed on the mountain slope and within the volume scanned by the Doppler lidar.

This paper presents results of an analysis of that data. The Doppler lidar and tethered balloon measurements are compared to allow inferences about the interaction between valley and upslope flows. Analyses of the turbulence structure of the flow, variation in flow structure with upslope distance, and the sensitivity of flow to ambient stratification are discussed.