ANALYSIS OF THE DISTRIBUTION OF OZONE OVER THE SOUTHERN ATLANTIC REGION

Tropospheric ozone data measured by ozonesondes during the Transport a nd Atmospheric Chemistry Near the Equator-Atlantic (TRACE A) field mis sion and the multiyear pre-TRACE A program are analyzed jointly with t ropospheric ozone amounts derived from remote satellite data (''residu als''), We present here the first detailed analysis of the entire Asce nsion Island pre-TRACE A data set, Data from the three pre-TRACE A ozo nesonde sites are used to establish a coherent spatial and temporal cl imatology of ozone in the southern tropical Atlantic region. This anal ysis shows a significant ozone seasonality over the Atlantic region, w ith a period of maximum values that extends from the austral winter th rough at least October at Natal, Brazil, and Ascension Island. Concent rations begin to decline somewhat earlier at Brazzaville, Congo, espec ially at lower altitudes. Although Natal exhibits a significantly lowe r annual average than Ascension Island or Brazzaville by about 4 Dobso n Units (DU), the magnitude of the seasonal amplitude at Natal is the largest of the three stations. Additionally, more of the seasonal ampl itude at Natal is due to a contribution from ozone in the middle and u pper troposphere than at either Ascension Island or Brazzaville, Ampli tudes as large as 15 DU are measured at individual sites, and the resi duals show an average amplitude over the southern tropical Atlantic re gion of 10-12 DU. Statistical comparison of the residuals to the ozone sonde climatology show that while the residuals tend to underpredict b oth the means and the seasonal amplitudes compared to the in situ data , they provide a good representation of the variance of ozone in this region and predict the local annual and seasonal means to within bette r than 10% and seasonal amplitudes to within 15%.