SURFACE OZONE MEASUREMENTS FROM DAKSHIN GANGOTRI, ANTARCTICA

Surface ozone was measured for seven months in two spells at the Indian Antarctic station Dakshin Gangotri (70.1-degrees-S, 12-degrees-E) using the Indian electrochemical surface ozone recorder. Tropospheric ozone data from the Indian ozonesondes was also used in the analysis during the breaks in the continuous recording at surface ozone. The main objective of the measurements was to find out the nature of the variations of surface ozone during the rapid depletion and fast recovery of total ozone in late winter and early spring over the Antarctic. The surface ozone values show a summer minima of the order of 20 ppbv and a winter maxima of the order of 42 ppbv. The transition from the low summer value to the high winter value occurs during May-June. From October to November, there is a sharp fall in the surface ozone values. This sharp fall takes place at a time when the total ozone values are sharply rising from the lowest annual value. Other notable features of the surface ozone at Dakshin Gangotri during 1989 are the near absence of a diurnal variation, even during the summer months and the absence of significant changes during blizzards. The results agree fairly well with the measurements reported from Syowa in Antarctica, a station located in nearly the same latitude. Comparisons with a tropical station Pune (18.5-degrees-N, 73.8-degrees-E) bring out the sharp differences in surface ozone distribution between the two stations. Pune has the highest values when Dakshin Gangotri has the lowest and vice versa. The major difference, however, is that the systematic diurnal variation noticed at Pune almost round the year is not noticed at Dakshin Gangotri. The sharp changes noticed at Pune associated with different synoptic situations, break-up of inversions and wind changes are not noticed at Dakshin Gangotri.