Evidence of flow-splitting in the Rhine Valley during the MAP field experiment by ground-based Doppler lidar and in-situ measurements

Flow splitting in the Rhine Valley has been observed with a transportable wind lidar (TWL) during a shallow-foehn event in the framework of the Mesoscale Alpine Programme (MAP). In addition to the TWL, the boundary layer processes has been documented by means of backscatter lidars, surface meteorological stations, soundings and airborne in-situ measurements. This paper presents an analysis of the processes giving birth to flow splitting between the Seez and Rhine valleys during IOP 5 (october, 1-3, 1999) by combining the collected data with hydraulic theory. The Doppler lidar recorded in detail flow splitting, foehn wind gusts, and flow reversal. Such structures have not previously been observed with comparable detail by conventional in-situ instruments.