Fohn flow and stable air mass in the Rhine valley: The beginning of a MAP event

摘要

The fohn event of the 8th Intensive Observation Period (20-21 October 1999) of the Mesoscale Alpine programme is examined at small scale with the help of both instrumental data (especially from a ground-based Doppler lidar) and of high-resolution simulation performed with the non-hydrostatic model meso-NH. The three-dimensional characteristics of the flow in the Rhine valley at the beginning of the event arc studied. Special attention is given to the interaction between the fohn and a stable air mass, whose presence drives the penetration of the warm and turbulent fohn air ro the ground. A quantification of the simulated features of the flow is given in terms of mass budgets over the target area, and a three-dimensional picture representing the arrival of the fohn air in the Rhine valley area is proposed.