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Étude des transferts stratosphère-troposphère
en bordure sud de la zone tropicale
et impact sur le bilan d'ozone troposphérique

Abstract : The stratosphere-troposphere exchanges induced by the polar jet-stream of the northern hemisphere are well documented. In the subtropics, since few data are available, studies of stratosphere-troposphere exchanges are limited. These exchange result from jet-stream instabilities, and also from the detrainment of stratospheric air induced by deep convection in cyclones and in the inter-tropical convergence zone.

Using the Reunion station data base of radiosoundings performed at a semi-monthly frequency, and also various other experimental data, (satellite and ECMWF global model data), a first qualitative approach based on cases study is presented. The concepts of ageostrophism, jet-streak and upper level frontogenesis, allowed to characterise and analyse the formation of several subtropical tropopause folds and cut-off lows.

A strong subsiding transfer on April 6, 1995 (300 ppbv at altitude 10 km), following from the cyclone Marlene activity, is suggested in the peripheral part of the cyclone, at approximately 1000 km of the centre of the cyclone. The dynamic analysis seems to indicate a limited horizontal extension transfer, which would involve typically dynamic meso-scale mechanisms.

To allow a better tropospheric ozone monitoring, an ozone lidar, range toping near the high tropical tropopause, has been developed and installed at Reunion university. The results, obtained within the framework of the TRACAS campaign in July 1998, evidenced very regular stratospheric ozone in the free troposphere, during the whole month of measurement. ECMWF and Meteosat analyses led evidence of a planetary-scale tropopause fold. These mechanisms are necessarily different from midlatitude folds, and could be controlled by the return flow of the Indian monsoon, and by the downward branch of the southern Hadley cell.
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Contributor : Jean-Luc Baray <>
Submitted on : Friday, February 13, 2009 - 1:38:05 PM
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Jean-Luc Baray. Étude des transferts stratosphère-troposphère
en bordure sud de la zone tropicale
et impact sur le bilan d'ozone troposphérique. Océan, Atmosphère. Université Pierre et Marie Curie - Paris VI, 1999. Français. ⟨tel-00361213⟩



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