Future Changes in the Quasi-Biennial Oscillation Under a Greenhouse Gas Increase and Ozone Recovery in Transient Simulations by a Chemistry-Climate Model

In the equatorial stratosphere, the zonal wind direction changes from westward to eastward and vice versa at intervals of from less than two to about three years and centered at about 28 months (Reed et al., 1961; Veryard & Ebdon, 1961). This phenomenon is called the quasibiennial oscillation (QBO) from the length of its period (Angell & Korshover, 1964). The QBO initiates in the upper stratosphere, then descends gradually at a rate of about 1 km per month with an amplitude of about 20 ms-1, and diminishes near the tropopause (~16 km). The QBO structure for zonal wind and temperature is highly symmetric in longitude and latitude with a half-width of about 12° latitude, and the QBO dominates the annual and semiannual cycles in the equatorial stratosphere (e.g., Baldwin et al., 2001; Pascoe et al., 2005). The QBO can also be seen in changes in the abundances of ozone (e.g., Angell & Korshover, 1964; Randel & Wu, 1996) and other trace gases (e.g., Luo et al., 1997; Dunkerton, 2001) because their transport and chemistry are strongly dependent on the wind and temperature fields, respectively.