The role of convective processes over the Zaire-Congo Basin to the southern hemispheric ozone maximum

During October, satellite measurements show that there is a region of elevated tropospheric ozone over the tropical southern Atlantic Ocean. The cause of the high ozone concentrations has been related to biomass burning in South America and Africa. In this paper, we present evidence from satellite sources, European Center for Medium-Range Weather Forecast analyses, and a mesoscale simulation during October, suggesting that afternoon and evening deep convection in central Africa is responsible for some of the abnormally high concentrations of ozone in the Tropical South Atlantic which extend southeast over southern Africa into the Indian Ocean. The mechanisms for enhancing tropospheric O₃ includes (1) the removal of ozone, NO_x, and hydrocarbon rich air from fires in eastern Africa within the planetary boundary layer to the middle and upper troposphere by deep convection; (2) the production of NO_x from lightning associated with mesoscale convective systems and the subsequent photochemical production of O₃, and (3) the entrainment of O₃ rich air from the lower stratosphere into the upper troposphere by deep convection. During the next few years an international field campaign in central Africa (the experiment for regional sources and sinks of oxidants-EXPRESSO), global lightning data, and the launch of the Tropical Rainfall Measuring Mission (TRMM) will help to identify the relative importance of each of the processes over central Africa that could be responsible for high O₃ concentrations over the tropical south Atlantic.