Numerical Simulation of Flow Diversion around the Pyrenees: A Tramontana Case Study

Marc Georgelin Laboratoire d'Aérologie, URA CNRS 354, Université Paul Sabatier, Toulouse, France

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Evelyne Richard Laboratoire d'Aérologie, URA CNRS 354, Université Paul Sabatier, Toulouse, France

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Abstract

The intensive observing period (IOP) 6 of the Pyrenees Experiment (PYREX) has been simulated with a hydrostatic three-dimensional model. The PYREX IOP 6 was devoted to the observation of a regional wind, the tramontana, 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 long 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 observations 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 simulation, in the acceleration zone where the model gives accurate wind intensity and direction, at the land–sea transition where the development of an internal boundary layer is well predicted, and above the Mediterranean Sea where the spatial structure of the tramontana is well reproduced.

Abstract

The intensive observing period (IOP) 6 of the Pyrenees Experiment (PYREX) has been simulated with a hydrostatic three-dimensional model. The PYREX IOP 6 was devoted to the observation of a regional wind, the tramontana, 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 long 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 observations 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 simulation, in the acceleration zone where the model gives accurate wind intensity and direction, at the land–sea transition where the development of an internal boundary layer is well predicted, and above the Mediterranean Sea where the spatial structure of the tramontana is well reproduced.

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