STRATOSPHERIC OZONE VARIATIONS IN THE EQUATORIAL REGION AS SEEN IN STRATOSPHERIC AEROSOL AND GAS EXPERIMENT DATA

An analysis is made of equatorial ozone variations for 5 years, 1984-1 989, using the ozone profile data derived from the Stratospheric Aeros ol and Gas Experiment II (SAGE II) instrument. Attention is focused on the annual cycle and also on interannual variability, particularly th e quasi-biennial oscillation (QBO) and El Nifio-Southern Oscillation ( ENSO) variations in the lower stratosphere, where the largest contribu tion to total column ozone takes place. The annual variation in zonal mean total ozone around the equator is composed of symmetric and asymm etric modes with respect to the equator, with maximum contributions be ing around 19 km for the symmetric mode and around 25 km for the asymm etric mode. The persistent zonal wavenumber 1 structure observed by th e total ozone mapping spectrometer over the equator is almost missing in the SAGE-derived column amounts integrated in the stratosphere, sug gesting a significant contribution from tropospheric ozone. Interannua l variations in the equatorial ozone are dominated by the QBO above 20 km and the ENSO-related variation below 20 km. The ozone QBO is chara cterized by zonally uniform phase changes in association with the zona l wind QBO in the equatorial lower stratosphere. The ENSO-related ozon e variation consists of both the east-west vacillation and the zonally uniform phase variation. During the El Nino event, the east-west cont rast with positive (negative) deviations in the eastern (western) hemi sphere is conspicuous, while the decreasing tendency of the zonal mean values is maximum at the same time.