AN ANALYSIS OF TROPICAL TRANSPORT - INFLUENCE OF THE QUASI-BIENNIAL OSCILLATION

An analysis of over 4 years of Upper Atmosphere Research Satellite (UA RS) measurements of CH4 HF, O-3, and zonal wind are used to study the influence of the quasi-biennial oscillation (QBO) on constituent trans port in the tropics. At the equator, spectral analysis of the Halogen Occultation Experiment (HALOE) and Microwave Limb Sounder (MLS) observ ations reveals QBO signals in constituent and temperature fields at al titudes between 20 and 45 km Between these altitudes, the location of the maximum QBO amplitude roughly corresponds with the location of the largest vertical gradient in the constituent field. Thus, at 40 km wh ere CH4 and HF have strong vertical gradients, QBO signals are corresp ondingly large, while at lower altitudes where the vertical gradients are weak, so are the QBO variations, Similarly, ozone, which is largel y under dynamical control below 30 km in the tropics, has a strong QBO signal in the region of sharp vertical gradients (similar to 28 km) b elow the ozone peak. Above 35 km, annual and semi-annual variations ar e also found to be important components of the variability of long-liv ed tracers. Therefore, above 30 km, the variability in CH4 and HF at t he equator is represented by a combination of semiannual, annual, and QBO timescales. A one-dimensional vertical transport model is used to further investigate the influence of annual and QBO variations on trop ical constituent fields. QBO-induced vertical motions are calculated f rom observed high resolution Doppler imager (HRDI) zonal winds at the equator, while the mean annually varying tropical ascent rate is obtai ned from the Goddard two-dimensional model. Model simulations of tropi cal CH4 confirm the importance of both the annual cycle and the QBO in describing the HALOE CH4 observations above 30 km. Estimates of the t ropical ascent late and the variation due to the annual cycle and QBO are also discussed.