Diagnostic studies of the Antartctic vortex during the 1987 Airborne Antarctic Ozone Experiment: Ozone miniholes

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Abstract
During the Airborne Antarctic Ozone Experiment (AAOE) localized rapid reductions in total ozone, called “miniholes”, were observed by the Total Ozone Mapping Spectrometer (TOMS) within the main ozone hole. Evolving too rapidly to be the result of chemical destruction, miniholes must be the result of atmospheric transport. An important question then is “Do miniholes represent large‐scale transport of ozone poor air into the vortex?” In this paper we examine the genesis and evolution of miniholes, and we demonstrate by the calculation of air parcel trajectories that miniholes are not the result of irreversible transport of ozone‐poor air into the polar vortex. We show instead that minihole genesis can be attributed, in large part, to synoptic‐scale tropospherically forced reversible advection (both horizontal and vertical) of low‐ozone air below the level of the main ozone depletion, resulting from the poleward penetration of an anticyclone below the main vortex. We then examine the implications of the disturbed flows associated with minihole formation. Employing differential infrared absorption laser (DIAL) data, Stratospheric Measurement (SAM) II retrievals, and United Kingdom Meteorological Office (UKMO) global analysis fields and trajectories, we highlight two aspects of minihole formation, which have important implications for both theories of photochemical ozone destruction and vortex isolation. We conclude that tropospheric forcing which reduces the ozone column through advection also forces the formation of Polar Stratospheric Clouds (PSC)s (type I and II) throughout a substantial depth of atmosphere, resulting in a large portion of the air in the vortex being exposed to heterogeneous chemistry as it passes through individual quasi‐stationary PSC regions. Finally we conclude that synoptic‐scale transport associated with these events can lead to the exchange of vortex air with air from lower latitudes. The lower limit on the mass exchange over the period of ozone depletion is estimated to be 4% of the total depleted mass, with large uncertainties.