Thursday, 20 June 2002
Observations and modeling of the Mistral wind
Two Mistral events documented during the Mesoscale Alpine Program
are studied using observational data and
high resolution mesoscale model simulations.
Radiosoundings suggested that both Mistral wind events were associated
with the passage of cold fronts and post-frontal air descent. EuroSat
Rapidscan images indicated a stationary and persistent cloud edge
along the lee of Massif Central. The cloud edge marks the beginning of
Mistral flow acceleration and descent according to COAMPS simulations.
Narrow persistent cloud banners were identified trailing from Mont
Loz\'{e}re during both Mistral events.
COAMPS indicated that these cloud banners were associated with turbulence
mixing in wakes induced by mountain gravity wavebreaking. The cloud banners
and wakes defined the western boundary of the Mistral.
Analysis of dropsonde data and in-situ flight data proved the existence of a sharp shear line separating the cold violent Mistral wind from warm calm wake flow to the lee of Mountain Province. Turbulence and eddies were found along the shear line. Trajectory analysis of model data suggested that air parcels on the two sides of the shear line had different histories.
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