Abstract
Abstract. Record-low ozone column densities (with a minimum of 212 DU) persisted over three weeks at the Río Gallegos NDACC (Network for the Detection of Atmospheric Composition Change) station (51.5° S, 69.3° W) in November 2009. Total ozone remained two standard deviations below the climatological mean for five consecutive days during this period. The statistical analysis of 30 years of satellite data from the Multi Sensor Reanalysis (MSR) database for Río Gallegos revealed that such a long-lasting low-ozone episode is a rare occurrence. The event is examined using height-resolved ozone lidar measurements at Río Gallegos, and observations from satellite and ground-based instruments. The computed relative difference between the measured total ozone and the climatological monthly mean shows reductions varying between 10 and 30% with an average decrease of 25%. The mean absolute difference of total ozone column with respect to climatological monthly mean ozone column is around 75 DU. Extreme values of the UV index (UVI) were measured at the ground for this period, with the daily maximum UVI of around 13 on 15 and 28 November. The high-resolution MIMOSA-CHIM (Modélisation Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection) model was used to interpret the ozone depletion event. An ozone decrease of about 2 ppmv was observed in mid-November at the 550 K isentropic level (~22 km). The position of Río Gallegos relative to the polar vortex was classified using equivalent latitude maps. During the second week of November, the vortex was over the station at all isentropic levels, but after 20 November and until the end of the month, only the 10 lower levels in the stratosphere were affected by vortex overpasses with ozone poor air masses. A rapid recovery of the ozone column density was observed later, due to an ozone rich filament moving over Río Gallegos between 18 and 24 km in the first two weeks of December 2009.
Highlights
The Antarctic ozone hole is one of the most important perturbations that human activities have provoked in our atmosphere (WMO Report, 2007)
The objective of this paper is to make a multi-instrument study of this unique event by the use of different groundbased instruments operating at the CEILAP Rıo Gallegos site, focusing on ozone profiles measured by the NDACC (Network for the Detection of Atmospheric Composition Change) ozone differential absorption lidar (DIAL)
Note that at the end of September and beginning of October, the edge of the Antarctic vortex passed over the Rıo Gallegos region twice, which resulted in small O3 www.ann-geophys.net/30/1435/2012/
Summary
The Antarctic ozone hole is one of the most important perturbations that human activities have provoked in our atmosphere (WMO Report, 2007). The daily movement of the vortex combined with this particular shape induces overpasses of the ozone hole over the continental part of South America. In these situations large inhabitant cities like Punta Arenas (119 496 inhabitants), Rıo Gallegos (79 144 inhabitants), and Ushuaia (56 825 inhabitants) are under the influence of the ozone hole or near its border, causing an increase of solar UV radiation at these locations (Pazmino et al, 2005; Wolfram et al, 2008)
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