Springtime Stratospheric Ozone Over Marambio, Antarctic During 1990–1998

Abstract

Negative trends of atmospheric column ozone have been detected globally already for two decades. 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, 3) formation of PSC-clouds just outside a polar vortex and 4) homogenic chemistry still missing in the models (1). 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.