During the SOP period (9/15-11/15, 1999) of the Mesoscale Alpine Program (MAP), two Mistral events were observed. The first event occurred on 1 October, when a shallow Mistral flow developed in association with the passage of a short-wave trough in the Alpine region. Two research aircraft flew a vertical box pattern across the Mistral near the French coast and over Mediterranean Sea. The strong Mistral flow, a well defined shear zone, and reversed flow in the lee of western Alps were well documented. The second event occurred on 6 November, when a deep Mistral flow developed as an intense north Atlantic short wave trough moved into the western Alps region, and a Mediterranean cut-off low moved slowly toward the southeast. This time, four aircraft flew vertical stacks across the same section as on October 1st. This second event had a narrow shear zone and persistent strong Mistral wind as well. During both events, intensive radio-sounding and rapid-scanning by MeteoSat were conducted.
In this study, the flow structure in the Mistral and its dynamical aspects were examined based on the analysis of data (i.e. flight level data, drop-sounds, satellite images, SABL images, and radio-sounding), numerical modeling, and scale analysis.
Two issues are addressed in this case study: a) the mechanism of Mistral formation such as the effect of low level inversion and/or dip of tropopause, streamline splitting, flow turning, flow acceleration, and geostrophic adjustment processes; b) the structure of the Mistral such as the vertical momentum distribution, shear zone formation, and potential vorticity generation.
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