The roles of transports in seasonal variation of total ozone amount

The seasonal variation of the meridional ozone transport and its contributions to seasonal variation of the total ozone amount are investigated in terms of mass weighted isentropic zonal means and eddies of ozone flux.

The mean ozone transport decreases the total ozone amount in the tropics and increases it in the extratropics, since the stratospheric poleward ozone transport due to the Brewer-Dobson circulation is much larger than the lower tropospheric equatorward transport. The stratospheric transport has a seasonal variation with a hemispheric asymmetry. In the northern hemisphere, the mean ozone flux convergence centered near the pole has a larger seasonal variation with a maximum in late winter. In the southern hemisphere, it is centered around 60S, outside of the polar vortex, and its seasonal variation is rather small. Also, the Brewer-Dobson circulation causes a seasonal variation of the flux divergence in the tropics, which is largest in the northern winter.

The eddy ozone transport is mostly equatorward, and decreases the total ozone amount in the extratropics and increases it in the tropics. The equatorward ozone flux results from the isentropic poleward gradient of the ozone mixing ratio in the lower stratosphere and troposphere, which is formed by the extratropical downward transport of the Brewer-Dobson circulation. The eddy transport contributes less to seasonal variation of the total ozone amount. An exception is a strong poleward eddy transport near the Antarctic in late spring. The transport characteristics are discussed in detail during and after the breakdown of the Antarctic polar vortex.