Aircraft section measurements of meteorology and ozone in northern Namibia during SAFARI-92

Ozone and meteorological data obtained via instrumented aircraft surveys over tropical southwestern Africa in the period October 8-12, 1992, are analyzed as part of the international Southern African Fire-Atmosphere Research Initiative (SAFARI) program. Twice-daily aircraft flights recorded measurements of wind, turbulence, temperature, dewpoint, and ozone at 1 Hz from 1-12 km in a series of successive profiles extending from 12° to 24°E along 18°S latitude. Wind patterns derived from aircraft and the European Centre for Medium-Range Weather Forecasts (ECMWF) highlight a quasi-permanent anticyclone in the midtroposphere over central southern Africa. Light meridional flow prevailed in the 3-7 km layer. Ozone values were in the range 40-60 parts per billion by volume (ppbv) from 1 to 4 km across the aircraft section and <20 ppbv in the surface marine layer off the west coast. In the continental air, ozone increased with height to 90 ppbv above 7 km. As a dry trough passed eastward, ozone values declined 30% in the layer above 4 km. Aircraft results indicate the presence of a potential recirculation mechanism around the midtropospheric anticyclone. Recirculation would facilitate photochemical reduction to ozone of regional pyrogenic emissions, following vertical mixing by turbulent diurnal heating. A persistent dry stable layer from 6 to 9 km may accumulate pollutants over tropical southern Africa, while upper westerly troughs could eject some of the continental air eastward.