Possible long-term changes in stratospheric circulation: evidence from total ozone measurements at the edge of the Antarctic vortex in early winter

Measurements of total ozone in Antarctica during early winter show an increase, consistent with the observed descent of stratospheric air and the convergence that accompanies descent. Measurements in the vortex edge region at Faraday (65°S) show that the rate of increase has on average doubled between the 1960s and the 1990s. We speculate that this increase in rate of ozone change is caused by an increase in convergence. If so, it suggests that the strength of the Brewer–Dobson residual stratospheric circulation, which brings tropospheric air into the stratosphere with its accompanying chlorofluorocarbons and greenhouse gases, increased significantly. There is no obvious explanation for an increase in the circulation. Models predict that an ozone hole increases vortex strength, but only later in the spring. Models also predict that increased greenhouse gases increase the circulation, but the convergence did not increase gradually whereas greenhouse gases did. Some of the measurements in the 1990s are able to distinguish the different rates of increase of ozone in individual years, which show considerable variability, as expected following the eruption of Pinatubo.

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