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The high latitude middle and upper tropospheric circulation in the depth of the southern winter is significantly different from the cold season above the Arctic. The marked westerly winds high over the flanks of the Antarctic flow, more-or-less, in a circular pattern due to the 'quasi-circular' Antarctic continent lying beneath them, surrounded as it is by a circumpolar ocean. This flow has the effect of preventing any heat transport into its centre by depressions from lower latitudes - implying that stratospheric wintertime temperatures over the Antarctic are significantly colder than those in the Arctic winter stratosphere. This intense frigidity plays a crucially important role in the artificial depletion of ozone above Antarctica (see Chapter 7).