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A Two-Dimensional Model of the Quasi-biennial Oscillation of Ozone

L. J. GrayRutherford Appleton Laboratory, Chilton, Didcot, United Kingdom

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J. A. PylePhysical Chemistry Department, Cambridge University, Cambridge, United Kingdom

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Abstract

The stratospheric quasi-biennial oscillation (QBO) in zonal wind, temperature and column ozone has been successfully modeled in a two-dimensional dynamical/chemical model by the introduction of a parameterization scheme to model the transfer of momentum to the zonal flow associated with the damping of vertically propagating Kelvin and Rossby-gravity waves. The largest amplitudes of the observed QBO in column ozone are found in high latitudes and this must be taken into account in any explanation of the increased depletion of ozone in the southern polar spring during the 1980s. A strong QBO signal in column ozone is evident in the model at all latitudes. The largest anomalies of approximately 20 DU are present at high latitudes. The equatorial ozone QBO is out of phase with the mid- and high-latitude ozone QBO. A positive (negative) ozone anomaly at the equator coincides with the presence of equatorial westerlies (easterlies) at 50 mb, in good agreement with observations. The modeled zonal wind at the equator varies from +20 m s−1 to −18 m s−1 at 25 km. The period of the modeled QBO is just over 2 yr throughout the model run except for one event when the period extends to almost 3 yr. This anomalously long period is explained in terms of the strong interaction between the modeled QBO and the seasonal cycle; in particular, the timing of the westerly phase of the QBO is influenced by the presence of the modeled semiannual oscillation (SAO). In view of this model behavior a mechanism is proposed to explain the large variability in the period of the observed QBO.

Abstract

The stratospheric quasi-biennial oscillation (QBO) in zonal wind, temperature and column ozone has been successfully modeled in a two-dimensional dynamical/chemical model by the introduction of a parameterization scheme to model the transfer of momentum to the zonal flow associated with the damping of vertically propagating Kelvin and Rossby-gravity waves. The largest amplitudes of the observed QBO in column ozone are found in high latitudes and this must be taken into account in any explanation of the increased depletion of ozone in the southern polar spring during the 1980s. A strong QBO signal in column ozone is evident in the model at all latitudes. The largest anomalies of approximately 20 DU are present at high latitudes. The equatorial ozone QBO is out of phase with the mid- and high-latitude ozone QBO. A positive (negative) ozone anomaly at the equator coincides with the presence of equatorial westerlies (easterlies) at 50 mb, in good agreement with observations. The modeled zonal wind at the equator varies from +20 m s−1 to −18 m s−1 at 25 km. The period of the modeled QBO is just over 2 yr throughout the model run except for one event when the period extends to almost 3 yr. This anomalously long period is explained in terms of the strong interaction between the modeled QBO and the seasonal cycle; in particular, the timing of the westerly phase of the QBO is influenced by the presence of the modeled semiannual oscillation (SAO). In view of this model behavior a mechanism is proposed to explain the large variability in the period of the observed QBO.

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