REDISTRIBUTION BY DEEP CONVECTION AND LONG-RANGE TRANSPORT OF CO AND CH4 EMISSIONS FROM THE AMAZON BASIN, AS OBSERVED BY THE AIRBORNE CAMPAIGN TROPOZ-II DURING THE WET SEASON

Flights performed over South America in the Austral summer, during the airborne campaign Tropospheric Ozone Experiment (TROPOZ II, January 1 991), have shown an upper tropospheric maximum (UTM) of carbon monoxid e, methane, and relative humidity above 7 km altitude and between 30 d egrees S and 5 degrees N. The study of chemical characteristics and co nvective/transport processes associated with this UTM shows that the a ir came from the Amazon basin boundary layer, was lifted by convective processes to upper levels, and was then redistributed over South Amer ica, and even across the South Atlantic toward the African coast, by t he upper level anticyclone present during the wet season over tropical South America. The chemical composition of this UTM (high CO, CH4, an d relative humidity; medium NOy, NO, and alkanes; low ozone and acetyl ene) agrees with the observations from the Atmospheric Boundary Layer Expedition ABLE 2B over the Amazon basin during the wet season and sup ports a biogenic origin for methane and carbon monoxide. The slow (or even absent) photochemical activity associated with this UTM can be ex plained by the low levels of active hydrocarbons and reactive nitrogen species. The TROPOZ II results complete and extend observations from previous expeditions by demonstrating that large biogenic emissions of ozone precursors from the Amazon basin can enter the upper general ci rculation during the Austral summer (December-January-February) and, t hough they do not contribute significantly to the ozone budget over So uth America, on being exported to the rest of the global circulation t hey will certainly become involved in the global ozone budget.