Roles of transport in the seasonal variation of the total ozone amount

Abstract

Seasonal variations of the meridional ozone transport and their contributions to the total ozone amount are investigated in terms of mass‐weighted isentropic zonal means and eddies of ozone flux. Three‐dimensional data obtained using a chemical transport model are used to estimate transport fluxes. 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 greater than the lower tropospheric equatorward transport. The mean ozone flux convergence centered near the pole in the Northern Hemisphere has considerable seasonal variation with a maximum in late winter. The flux convergence is centered outside of the polar vortex in the Southern Hemisphere, and its seasonal variation is somewhat small. In addition, the Brewer‐Dobson circulation causes a seasonal variation of the tropical divergence, which is greatest in the northern winter. The eddy ozone transport is mostly equatorward in the lower stratosphere and troposphere, since the extratropical downward transport forms the isentropic poleward gradient of the ozone mixing ratio. It decreases the total ozone amount in the extratropics and increases it in the tropics. The eddy transport contributes less to seasonal variation of the total ozone amount; however, a strong poleward eddy transport increases it near the Antarctic in late spring. The transport characteristics are discussed in detail during and after breakdown of the Antarctic polar vortex.