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1. Introduction

Negative trends of atmospheric column ozone have been detected globally already for two decades [WMO, 1999]. The reduction is characterised by an increasingly heavy chemical ozone loss during late winter and spring in the Southern Hemisphere (SH) polar vortex and a lesser and a more varying loss during late winter and spring in the Northern Hemisphere polar vortex. The reasons to these negative trends are rather well understood. There is nevertheless a lesser negative trend detected also in the mid-latitude lower stratosphere, which is not yet understood. Several possible explanations have been introduced.

These include:

1) heterogenic chemistry on sulphate particle surface,
2) dilution and mixing of processed and ozone poor air from a polar vortex towards mid-latitudes [Brasseur et al., 1997; Eckman et al., 1996],
3) formation of PSC-clouds just outside a polar vortex,
4) homogenic chemistry still missing in the models [Solomon et al, 1994] and natural variation in the stratospheric circulation [Callis et al., 1997; Jackman et al., 1996; Schneider et al., 1991; Hadjinicolaou et al., 1997]. Dilution is believed to happen after the breakdown of a polar vortex in late spring. Mixing is suggested to happen at some extent through the edge of a polar vortex and to a larger extent below the edge of a vortex at the lowermost stratosphere. Better understanding about the chemical and physical structure and mixing properties of the vortex edge region is thus needed.

In Antarctica an abrupt ozone depletion is observed starting in August [e.g. Uchino et al., 1999]. Vömel et al. [1995] and Roscoe et al. [1997] nevertheless reported evidence for an early start already in June of ozone destruction over Antarctica. According to Lee et al. [2000] this gradually progressing depletion starts and stays confined in the edge region of the vortex until the end of July.

In this study, vertical distribution of ozone in Antarctic peninsula station of Marambio is presented. Annual behaviour and long-term ozone changes during 1987-1999 of ozone inside, outside and on the edge region of the SH polar vortex are studied.

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