OZONE OVER SOUTHERN AFRICA DURING SAFARI-92 TRACE-A

Characteristics of total O-3 in southern Africa and over the adjacent Atlantic during the IGAC/STARE/SAFARI-92/TRACE A (International Global Atmospheric Chemistry/South Tropical Atlantic Regional Experiment/Sou thern African Fire Atmospheric Research Initiative/Transport and Atmos pheric Chemistry near the Equator-Atlantic) field experiments are desc ribed, Most of the analysis is based on data from the Nimbus 7/total o zone mapping spectrometer (TOMS) gridded O-3 data archive (version 6.0 ), which is used to examine O-3 in terms of seasonal and interannual v ariability. Total O-3 column variability is compared to the tropospher ic O-3 column derived from balloon-borne ozonesondes at four fixed SAF ARI-92/TRACE A sites (Ascension Island, Brazzaville, Okaukuejo, and Ir ene) from September 1 to October 23, 1992. All of these sites except O kaukuejo had regular ozonesonde launches from 1990 to 1992. Total O-3 and integrated tropospheric O-3 at the sounding sites showed the expec ted September-October maxima over southern Africa and the adjacent Atl antic Ocean. Statistical analysis of the TOMS record for 1979-1992 all ows disaggregation of components contributing to total O-3 variability : Signals due to semiannual and annual cycles and the quasi-biennial o scillation are identified at the sounding sites. The tropospheric O-3 column estimated from integrated sondes (to similar to 16 km) at the f our sites ranged from 24 to 62 Dobson units (DU) (mean, 45 DU) and ave raged 15% of total O-3 at Irene (14 launches) and 19% of total O-3 at Ascension (20 launches). Tropospheric O-3 was higher at Ascension and Brazzaville than at the sites south of 15 degrees S because transport from biomass burning regions was more direct at these sites. This tran sport is seen in Hovmoller (time-longitude) plots of total O-3. A comp arison of 1990-1992 integrated tropospheric O-3 amounts with the annua l total ozone cycle shows that tropospheric ozone variations may accou nt for all of the annual signal at Ascension (8 degrees S) and Brazzav ille (4 degrees S) but only 30-40% of the seasonal total O-3 variation at Irene (26 degrees S). Hovmoller plots of daily TOMS O-3 over South ern Africa and the Atlantic show easterly flow of local O-3 maxima at 0 degrees-10 degrees S and westerly movement from 30 degrees-40 degree s S. At 0 degrees-10 degrees S the continent-ocean total O-3 gradient and Ascension and Brazzaville O-3 soundings are used to estimate a pho tochemical O-3 formation rate of 1-2 ppbv O-3/d over the Atlantic. Thi s agrees with model calculations of moderately aged biomass burning em issions from SAFARI-92/TRACE A.