Annual, quasi‐biennial, and El Niño‐Southern Oscillation (ENSO)time‐scale variations in equatorial total ozone

Equatorial total ozone variations with time scales of annual, quasi‐biennial, and about 4‐year periodicities are described by paying attention to their longitudinal structure. Analyses are made for 11 years from 1979 to 1989, using the global total ozone data derived from the total ozone mapping spectrometer on board the Nimbus 7 satellite. Over the equator an annual cycle in total ozone is conspicuous. Zonal mean values are maximum around September and minimum around January. The longitudinal structure shows a zonal wavenumber 1 pattern with minimum values around 140°E to the date line all year‐round, indicating a close relationship to a region where the convective cloud activity is vigorous. By removing the climatological annual cycle from the original data, there appears the quasi‐biennial oscillation in total ozone. This variation is characterized by zonally uniform phase changes and is strongly coupled with the quasi‐biennial oscillation of the equatorial zonal wind in the lower stratosphere. Moreover, subtracting zonal mean values from the anomaly data mentioned above, we see an east‐west seesaw variation with a nodal longitude around the date line. This east‐west variation, having a characteristic time scale of about 4 years, is clearly related to the El Niño and the Southern Oscillation cycle. During El Niño events the longitudinal anomaly field in total ozone is positive in the western Pacific and negative in the eastern Pacific; the anomaly pattern is reversed during anti‐El Niño events. Because the active region of convective clouds is located relatively in the eastern Pacific sector during El Niño events, it is suggested that the stronger upwelling and the higher tropopause associated with the convective cloud activity bring about less total ozone.