An examination of anomalously low column ozone in the Southern Hemisphere midlatitudes during 1997

[1] Observations from both ground-based and satellite instruments show record low column ozone abundance between 20 S and 40 S during 1997. The 1997 monthly averaged column ozone from the Total Ozone Mapping Spectrometer (TOMS) is up to 25 Dobson units (DU) lower than the TOMS climatological mean (1979–1996) and up to 20 DU below the previous record low values. Observations from the Halogen Occultation Experiment show that below average ozone concentrations during 1997 were confined primarily to the lower stratosphere. Residual circulation statistics calculated from the United Kingdom Meteorological Office temperature analyses indicate that circulation anomalies during 1997 can account for 5–10 DU/month decrease in column ozone between 20 S and 50 S. At these latitudes during 1997, structural characteristics of the ozone and residual circulation fields both suggest a connection with the equatorial quasi-biennial oscillation.