OZONE CLIMATOLOGY AT NATAL, BRAZIL, FROM INSITU OZONESONDE DATA

Results are presented from analysis of a large ozone profile data set obtained from balloon ozonesonde soundings made at Natal, Brazil (6-degrees-S, 35-degrees-W) during the last 10 years (1978-1988). The measurements have been made through an Instituto Nacional de Pesquisas Espaciais (INPE)/NASA long-term collaboration program. The balloons were released by the Brazilian Air Force at the Natal rocket range. The data set is sufficiently large to provide useful climatology on the average ozone concentration behavior and its seasonal variation. The day-to-day ozone concentration variability in the troposphere is rather large, giving standard deviations of about 30-40% for seasonal averages. Maximum ozone concentrations occur during local spring, September-October, and minimum concentrations during late autumn, April-May. The seasonal variation in the troposphere is much larger than in the stratosphere. If there were no seasonal variation at all in the stratosphere, the seasonal variation observed in the troposphere alone would be strong enough to drive a total ozone column variation of about 5%, which is about one half the size of the variation observed in the Natal Dobson spectrophotometer data. The ozone concentration at Natal increases with height between the surface and about 500 mbar, almost linearly, from about 15 parts per billion by volume (ppbv) to about 38 ppbv, in autumn. For the spring average the ozone concentration increases from about 25 ppbv at the surface to about 66 ppbv at 500 mbar. The sonde data suggest that limitations in aneroid pressure sensors used until 1986 caused the Natal sondes to indicate too much ozone above 6 mbar. Because of the relative sparsity and uneven distribution in time of the ozone soundings, the data are not adequate to study ozone trends. The Dobson data time series shows no definitive ozone trend but displays a pronounced quasi-biennial oscillation in ozone.