THE OZONE HOLE OVER PUNTA-ARENAS, CHILE

Three fundamental questions are addressed for the location of Punta Ar enas (53.0 degrees S, 70.9 degrees W), Chile: Does the Antarctic ozone hole extend over the city? If so, at what height is most of the ozone depleted? And by how much does the UVB radiation increase under ozone hole conditions? It is shown that Punta Arenas is affected by the Ant arctic ozone hole, even though it is a considerable distance away from the pole. In comparison with the average global trend of -0.25% per y ear, the downward ozone trend at Punta Arenas is -0.5% per year (twice as large as the global average) and -1.2% per year (almost 5 times la rger than the global average) using the monthly October averages. To o btain these figures, an ozone climatology of TOMS (Total Ozone Mapping Spectrometer) data from 1979 to 1992 has been used. Observations of t he ozone hole over Punta Arenas are described during the austral sprin g periods of 1992, 1993, and 1994. Systematic observations with a Brew er spectrophotometer have been made in order to measure the vertical c olumn of ozone and the simultaneous variations in UVB radiation. In ad dition, the vertical distribution of ozone has been investigated durin g ozone hole conditions, by using ozone ECC (Electrochemical Concentra tion Cell) sondes launched on balloons, in order to determine at which height the ozone is reduced most. Using the 220 DU (Dobson Units) thr eshold as reference, we identified the ozone hole over Punta Arenas on five occasions during the 3 year period of these observations, Septem ber 1993, October 1992, 1994; and November 1993 and 1994. The vertical distribution of ozone during ozone hole conditions shows maximum ozon e destruction efficiency near 15-17 km, where ozone nearly vanishes co mpletely, on several occasions. The largest amount of ozone depletion, however, occurs above this height, just under and at the main ozone p eak, where it may reach about 50%. The UVB radiation in small spectral bands may increase dramatically during ozone hole events; at 295-297 nm the observed factors of increase for Punta Arenas were between 10 a nd 38. The maximum integrated/weighted intensities in October, during hole events increased over background values between 2 and 3 times, wh ich represent values near the local summer maximum but not yet beyond levels normally observed at low-latitude stations.