An unusual stratospheric ozone decrease linked to isentropic air-mass transport as observed over Irene 25.5° S, 28.1° E in mid-May 2002Reportar como inadecuado




An unusual stratospheric ozone decrease linked to isentropic air-mass transport as observed over Irene 25.5° S, 28.1° E in mid-May 2002 - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

1 CNRM - Centre national de recherches météorologiques 2 Équipe Stratosphère LACy - Laboratoire de l-Atmosphère et des Cyclones 3 LACy - Laboratoire de l-Atmosphère et des Cyclones 4 SA - Service d-aéronomie 5 UKZN - University of KwaZulu-Natal

Abstract : A prominent ozone minimum of less than 240 Dobson Units DU was observed over Irene 25.5° S, 28.1° E by the Total Ozone Mapping Spectrometer TOMS during May 2002 with extremely low ozone value of less than 219 DU recorded on 12 May, as compared to a climatological mean of 249 DU for May between 1999 and 2005. In this study, the vertical structure of this ozone minimum is examined using ozonesonde measurements performed over Irene on 15 May 2002, when the total ozone as given by TOMS was about 226 DU. Indeed, it is found that the ozone minimum is of Antarctic polar origin with a low-ozone layer in the middle stratosphere above 625 K and of tropical origin with low-ozone layer between 400-K and 450-K isentropic levels in the lower stratosphere. The upper and lower depleted parts of the ozonesonde profile for 15 May, are respectively attributed to equatorward and poleward transport of low-ozone air toward the subtropics. The tropical air moving over Irene and the polar one passing over the same area associated with enhanced planetary-wave activity are simulated successfully using a high-resolution advection contour model MIMOSA of Potential Vorticity. Indeed, in mid-May 2002, MIMOSA maps show a polar vortex filament in the middle stratosphere above the 625-K isentropic level and they show also tropical air-masses moving southward over Irene in the lower stratosphere between 400-K and 450-K isentropic levels. The winter stratospheric wave driving and its associated localized isentropic mixing leading to the ozone minimum are investigated by means of two diagnostic tools: the Eliassen-Palm flux and the effective diffusivity computed from the European Center for Medium-range Weather Forecasts ECMWF fields. The unusual distribution of ozone over Irene during May 2002 in the middle stratosphere is closely connected to the anomalously pre-conditioned structure of the polar vortex at that time of the year. Indeed, the perturbed vortex was typically predisposed for easy erosion by dynamical transport processes, which have been driven by strong planetary wave activity and have eventually resulted in a very large latitudinal advection of polar air masses towards the subtropics. The exceptional presence of polar vortex air over the subtropics during May 2002 can be considered as the first sign of the particular polar vortex disturbances, which after being well reinforced, contributed to the unprecedented behavior of the Antarctic spring ozone hole observed during September 2002.





Autor: N. Semane - Hassan Bencherif - Béatrice Morel - A. Hauchecorne - R. D. Diab -

Fuente: https://hal.archives-ouvertes.fr/



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