An examination of low ozone values in the Southern Hemisphere middle latitudes during 1997

Observations from both ground-based and satellite instruments show record low ozone column densities between 20S and 50S throughout 1997. The monthly averaged record from the Total Ozone Mapping Spectrometer (TOMS) shows that measurements from 1997 are lower than both the TOMS climatological mean (1979-1996) and measurements from 1998 by up to 20 Dobson units. A brief analysis of the spatial and temporal structure of total ozone in the 1997 Southern Hemisphere will be presented. To better understand the mechanisms responsible for the low ozone densities observed in 1997, and the role of chemistry versus dynamics, we employ an off-line 3D chemical transport model driven by assimilated winds from the United Kingdom Meteorological Office. Six month model simulations are performed using a simplified chemical solver for a number of years including 1997. Comparisons between model output and satellite and ground based observations will be shown. In addition, an analysis of the role dynamics played on 1997 southern hemisphere total ozone, and in particular, the influence of the quasi-biennial oscillation, will also be discussed.