NUMERICAL-SIMULATION OF FLOW DIVERSION AROUND THE PYRENEES - A TRAMONTANA CASE-STUDY

The intensive observing period (IOP) 6 of the Pyrenees Experiment (PYR EX) has been simulated with a hydrostatic three-dimensional model. The PYREX IOP 6 was devoted to the observation of a regional wind, the tr amontana, which blows in the vicinity of the Pyrenees Mountains at the French-Spanish border. Under northerly synoptic wind conditions, the low-level flow frequently splits around the Pyrenees barrier (400 km l ong and 3000 m high), with the eastern branch of the flow, favored by Coriolis effect, forming the tramontana. Model results are consistent with the tramontana climatology and in good agreement with the PYREX o bservations at all the different stages of the tramontana development: in the blocking zone where the model reproduces the observed reversed flow as well as its disappearance later in the course of the simulati on, in the acceleration zone where the model gives accurate wind inten sity and direction, at the land-sea transition where the development o f an internal boundary layer is well predicted, and above the Mediterr anean Sea where the spatial structure of the tramontana is well reprod uced.