TITLE

Analysis of orographic flows of the international "PYREX 90" experiment based on high resolution wind profiler radar data. Thèse de l'Université Blaise Pascal; spécialité : Physique de l'Atmosphère. Clermont-Ferrand, janvier 1996, 217 p. (in french).

SUMMARY

The study of the waves over the Pyrénées range in a southeasterly to southerly flow during the IOP 9 of the Pyrex Experiment has been made using wind profiler radar data, model analysis and experimental data from the Pyrex database. The measurements, made over the Ainsa radar site in Spain, show a set of lee waves in the vertical component of the wind velocity, having a period of 3 h 30, a wavelength of about 10 km, an amplitude exceeding 5 m/s, and lasting the two days of the IOP 9. These waves appear in the morning of the 14 th of november 1990, at about 7 o'clock, in response to a wind rotation from southeasterly to southerly. These waves exhibit a non-stationary character and are non hydrostatic lee waves trapped under the 6.5 km altitude level, as deduced from the Scorer parameter profile. The resolution, with the complex coordinate method, of the "lee wave equation", valid in a linear non-hydrostatic bidimensionnel frame, allows to explain the leaky character of these trapped lee waves observed by the radars and the airplanes.

The analyses of the upstream conditions of the flow, as observed by the ST radar situated at Lannemezan in France, show some oscillations with a 8 h period and an amplitude much smaller than those observed downstream, implying a complex non-linear upstream-downstream relationship. The Froude number, calculated from the Péridot model analysis data, shows the non-linear character of the flow over the Pyrénées range, characterized by the observed upstream blocking zone, the sheltering effect and the flow splitting around the barrier.

Key words

lee wave, non-hydrostatic flow, wind profiler radar, ST radar, vertical velocity.

Y.Pointin

Début de page

Mise à jour:15 mars 1996