The Influence of Wave– and Zonal Mean–Ozone Feedbacks on the Quasi-biennial Oscillation

Abstract

The effects of wave and zonal mean ozone heating on the evolution of the quasi-biennial oscillation (QBO) are examined using a two-dimensional mechanistic model of the equatorial stratosphere. The model atmosphere is governed by coupled equations for the zonal mean and (linear) wave fields of ozone, temperature, and wind, and is driven by specifying the amplitudes of a Kelvin wave and a Rossby?gravity wave at the lower boundary. Wave?mean flow interactions are accounted for in the model, but not wave?wave interactions. A reference simulation (RS) of the QBO, in which ozone feedbacks are neglected, is carried out and the results compared with Upper Atmosphere Research Satellite observations. The RS is then compared with three model experiments, which examine separately and in combination the effects of wave ozone and zonal mean ozone feedbacks. Wave?ozone feedbacks alone increase the driving by the Kelvin and Rossby?gravity waves by up to 10%, producing stronger zonal wind shear zones and a stronger meridional circulation. Zonal mean?ozone feedbacks (ozone QBO) alone decrease the magnitude of the temperature QBO by up to 15%, which in turn affects the momentum deposition by the wave fields. Overall, the zonal mean?ozone feedbacks increase the magnitude of the meridional circulation by up to 30%. The combined effects of wave?ozone and ozone QBO feedbacks generally produce a larger response then either process alone. Moreover, these combined ozone feedbacks produce a temperature QBO amplitude that is up to 30% larger than simulations without the feedbacks. Correspondingly, significant changes are also observed in the zonal wind and ozone QBOs. When ozone feedbacks are included in the model, the Kelvin and Rossby?gravity wave amplitudes can be reduced by ?10% and still produce a QBO similar to simulations without ozone.