A comparison of anticyclone and trough influences on the vertical distribution of ozone and meteorological conditions during SAFARI‐92

Abstract

The vertical distribution of ozone recorded over northern Namibia during SAFARI‐92 is examined as a function of prevailing atmospheric circulation. Two dominant synoptic weather types, namely, anticyclonic flow and flow associated with a westerly trough, are identified and composite ozone profiles produced for each weather type. In both cases an elevated, enriched ozone layer (9–12 km), where ozone concentrations exceed 80 ppbv on average, and 100–120 ppbv on individual days, is present. Under anticyclonic conditions, ozone increases steadily from surface values of around 40 ppbv to about 60–80 ppbv throughout the troposphere. In contrast, the westerly trough is characterized by a midtropospheric (4–8 km) ozone minimum, where values are 20 ppbv lower. This gives rise to a double ozone maximum in the troposphere. The elevated, enriched layer is thought to be a pervasive layer equatorward of 20°S and to result from biomass burning.