MODELING OZONE AND CARBON-MONOXIDE REDISTRIBUTION BY SHALLOW CONVECTION OVER THE AMAZONIAN RAIN-FOREST

During a ''locally occurring system'' (LOS) in Amazonian forest charac terized by an active mixing layer from surface to 1000 m capped by a f ossil mixed layer between 1000 and 1500 m, the vertical mixing effects of a shallow cumulus are examined. The explicit redistribution of CO and O-3 has been studied with a two-dimensional convective cloud model coupled with a chemical model including gas and aqueous phases, for a shallow convective situation taken from the GTE/ABLE 2B campaign. The chemistry describes the main oxidation chains of CH4 and CO in presen ce of low NOx concentration in a remote troposphere. Model results com pare favorably with observations obtained after development of the sha llow convection. The analysis of results explains how a growing and de caying cloud field allows exchanges between a mixing layer, a fossil m ixed layer and the free troposphere. An inert tracer study has shown t hat the layer lying between surface to 500 m is transported up to 2000 m. Even small clouds are responsible for the transport and the transf ormation of chemical species. Sensitivity tests are performed to evalu ate the relative importance of dynamical, microphysical and chemical p rocesses. The cumulus venting is the main process which modifies the t race species redistribution. The O-3 and CO amounts which are transpor ted by a fair-weather cumulus through the boundary layer and free trop osphere in the wet season, over a tropical rain forest, are respective ly 1.2 x 10(23) molecules km(-2) h(-1) and 7.7 x 10(23) molecules km(- 2) h(-1). In tropical regions, over rain forest, even with low NOx con centration, several cumulus exist every day and the vertical fluxes of some chemical species (like O-3) cannot be neglected.