MAY 2002: Quasibiennial oscillation in tropical ozone as revealed by ozonesonde data

The Quasibiennial oscillation (QBO) is the dominant source of interannual variability in equatorial ozone. In Logan et al. [2002], we present an analysis of the QBO in tropical ozone using recent in-situ equatorial profiles made by ozonesonde, supplemented by satellite profiles and column data. Measurements from Nairobi, Kenya (1^oS, 37^oE), and San Cristobal, Galapagos (1^oS, 90^oW), provide the first in-situ profiles of ozone within 1^o of the equator. The Figure shows the time evolution of the Nairobi ozone profiles (line contours in mPa; dashed lines are interpolations) superimposed on the zonal component of the Singapore winds. The sonde data encompass one complete QBO cycle. The figure shows that the largest increase in ozone accompanies the descent of the westerly shear zone, down to 50 hPa. The amplitude of the partial pressure maximum in ozone increases by about 25% in 5 -6 months as it descends from 17 to 24 hPa (from about 14 mPa near 20 hPa in May-June 1998 to about 17 hPa at 23 hPa in September-October 1998).