Diagnosis of Meridional Ozone Transport Based on Mass-Weighted Isentropic Zonal Means

Abstract

Abstract A transport equation based on mass-weighted isentropic zonal means applies to the diagnosis for the meridional ozone transport in the troposphere and stratosphere. The mean and eddy ozone fluxes are estimated from the global distributions of the temperature, wind, and ozone. In comparison with the conventional Eulerian mean and transformed Eulerian mean (TEM), the present diagnosis has advantages for the expression of eddy transport terms. The adiabatic eddy flux is separated from the diabatic eddy flux, which is parallel to the isentropic surface. The analysis shows that the eddy flux is almost adiabatic except that it is significantly affected by diabatic effects near the lower troposphere. Another advantage lies in the mean meridional transport. Although it is almost similar to the TEM, significant differences can be found near the Antarctic polar vortex due to nongeostrophic effects. Furthermore, the isentropic diagnosis expresses a strong equatorward flux near the lower boundary, while the TEM hardly does this because of inadequate treatment of the lower-boundary conditions. The life cycle of ozone can be understood through the exact estimation of the transport terms. Although the stratospheric meridional transport is mainly performed by the Brewer–Dobson circulation, the strong poleward eddy ozone flux is caused by planetary wave breaking, especially in the winter hemisphere. In the extratropics, the ozone subsides from the stratosphere to the troposphere by mean downward motions, mainly diffused to the lower latitudes probably due to strong baroclinic waves and effectively lost through chemical processes in the lower troposphere.