An interhemispheric comparison of ozone mini‐hole climatologies

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Abstract
An ozone mini‐hole is a synoptic‐scale area of strongly reduced column total ozone, which undergoes a growth‐decay cycle in association with tropospheric weather systems. A climatology of mini‐hole occurrence over mid‐latitudes of the southern hemisphere is constructed, based on 13 years of daily satellite measurements from the Nimbus‐7 TOMS instrument, version 7 data. A computer‐based analytical method for searching for synoptic‐scale minima in the ozone field is employed to build up a catalogue of mini‐hole events, recording their daily locations and intensities. The resulting statistics are compared to equivalent, recently published findings for the northern hemisphere, constructed using identical procedures. Interhemispheric differences in the spatial and seasonal properties of mini‐holes are assessed. It is found that the great Antarctic ozone hole has a significant impact on mini‐hole occurrence during the southern spring since it provides an extra source of depleted ozone not generally available over the northern hemisphere. Apart from this effect, however, mini‐holes are shown to be less frequent than over the northern hemisphere.