OZONE-RICH TRANSIENTS IN THE UPPER EQUATORIAL ATLANTIC TROPOSPHERE

High concentrations of ozone are found in the Earth's stratosphere, bu t strong stratification suppresses efficient exchange of this ozone-ri ch air with the underlying troposphere. Upward transport of tropospher ic trace constituents occurs mainly through equatorial deep convective systems. In contrast, significant downward transport of ozone-rich st ratospheric air is thought to take place only outside the tropics by e xchange processes in upper-level fronts associated with strong distort ions of the tropopause(1). Ozone within the tropical troposphere is as sumed to originate predominantly from ground-based emissions of ozone precursors, particularly from biomass burning(2), rather than from a s tratospheric source. Recent measurements of ozone in the upper troposp here in convective regions over the Pacific Ocean(3) indeed reveal nea r-zero concentrations. Here we present sharply contrasting observation s: ozone-rich (100-500 parts per billion by volume) transients were fr equently encountered by specially equipped commercial aircraft at a cr uising altitude of 10-12 km (in the upper troposphere) in the vicinity of strong convective activity over the equatorial Atlantic Ocean. Thi s strongly suggests that the input of stratospheric ozone into the tro posphere can take place in the tropics. We suggest that this transport occurs either by direct downward movement of air masses or by quasi-i sentropic transport from the extratropical stratosphere.