Ushuaia is less affected by the ozone hole than the three Antarctic sites due to its lower latitude (Fig. 3.6(c)). The average and 10th and 90th percentiles tend to be lower in spring than summer, as is expected from the natural annual cycle of ozone. Large UV levels may occur between September and December when the edge of the ozone hole moves over Ushuaia. During those events, the daily maximum UV Index measured in October was as high as 11.5. Historical measurements are based on the average TOMS/Nimbus-7 ozone column of the years 1978 -1981. The grey range in Fig. 3.6(c) indicates variability by clouds only. The discrepancy between recent and historical data is much smaller than for Antarctic sites. The difference for October is about 18% for the average and 25% - 30% for the 90th percentile (Fig. 3.7(c)). Some increases in the UV Index are also evident for January and February, but little change has been observed for the months March - July.
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