A Three-Dimensional Modeling Study of the Extratropical Quasi-Biennial Oscillation in Ozone

Abstract

The two phases of the quasi-biennial oscillation in ozone are simulated using winds generated by a three-dimensional mechanistic stratospheric model input into an off-line ozone transport model. Ozone chemistry is parameterized in the off-line model. The mechanistic model is run with either easterly or westerly zonal winds in the lower equatorial stratosphere, so as to model the equatorial wind structure during the two phases of the equatorial quasi-biennial oscillation (QBO). When forcing is applied at the lower model boundary in the winter hemisphere, the mechanistic model simulates differences in the global circulation between the easterly and westerly phases of the QBO. The resulting modeled total ozone is larger in the polar regions during the easterly phase of the QBO than during the westerly phase, in agreement with observations. Using the residual-mean formalism the authors find that the difference in the modeled budget of ozone between the two phases of the QBO is due to a modulation of the extratropical planetary wave structure, and consequently the ozone transport, by the equatorial zonal-mean winds. Differences in the residual-mean velocities between the two phases of the QBO explain most of the differences in the ozone transport.