An unusual stratospheric ozone decrease in the Southern Hemisphere subtropics linked to isentropic air-mass transport as observed over Irene (25.5 S, 28.1 E) in mid-May 2002

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Semane, N., Bencherif, Hassan, Morel, Béatrice, Hauchecorne, Alain, Diab, R.D.
• Other Authors: Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Laboratoire de l'Atmosphère et des Cyclones (LACy), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, Université de La Réunion - Faculté des Sciences et Technologies (FST), Université de La Réunion (UR), Service d'aéronomie (SA), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), University of KwaZulu-Natal Durban, Afrique du Sud (UKZN)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2006
• Subjects: [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; Antarctic; Antarc*
• Online Access: https://hal.science/hal-00083644; https://hal.science/hal-00083644/document; https://hal.science/hal-00083644/file/acp-6-1927-2006.pdf; https://doi.org/10.5194/acp-6-1927-2006

International audience A prominent ozone minimum of less than 240 Dobson Units (DU) was observed over Irene (25.5 S, 28.1 E), a subtropical site in the Southern Hemisphere, by the Total Ozone Mapping Spectrometer (TOMS) during May 2002 with an extremely low ozone value of less than 219DU recorded on 12 May, as compared to the climatological mean value of 249DU 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 226DU. It is shown that this ozone minimum is of Antarctic polar origin with a low-ozone layer in the middle stratosphere above 625K (where the climatological ozone gradient points equatorward), and is of tropical origin with a low-ozone layer in the lower stratosphere between the 400-K and 450-K isentropic levels (where the climatological ozone gradient is reversed). The upper and lower depleted parts of the ozonesonde profile for 15 May are then respectively attributed to equatorward and poleward transport of low-ozone air toward the subtropics in the Southern Hemisphere. The tropical air moving over Irene and the polar one passing over the same area associated with enhanced planetary-wave activity are successfully simulated using the high-resolution advection contour model of Ertel's potential vorticity MIMOSA. The unusual distribution of ozone over Irene during May 2002 in the middle stratosphere is connected to the anomalously pre-conditioned structure of the polar vortex at that time of the year. The winter stratospheric wave driving leading to the ozone minimum is investigated by means of the Eliassen-Palm flux computed from the European Center for Medium-range Weather Forecasts (ECMWF) ERA40 reanalyses.