A tropical Atlantic paradox: Shipboard and satellite views of a tropospheric ozone maximum and wave-one in January-February 1999.

During the Aerosols99 trans-Atlantic cruise from Norfolk, VA, to Cape Town, South Africa, daily ozonesondes were launched from the R/V Ronald H Brown between 17 January and 6 February 1999. A composite of tropospheric ozone p rofiles along the latitudinal transect shows 4 zones, nearly identical to t he ozone distribution during a January-February 1993 trans-Atlantic cruise [Weller et al., 1996]. Sondes from the cruise and Ascension Island (8S, 14. 5W), as well as the Earth-Probe (EP)/TOMS satellite instrument, show elevat ed tropospheric ozone (> 35 Dobson Units) throughout the south Atlantic in January 1999. Ozone layers associated with biomass burning north of the ITC Z (Intertropical Convergence Zone) are prominent at 0-5 km from 10-0N, but even higher ozone (100 ppbv, 5-15 km) occurred south of the ITCZ, where it was not burning - an ozone "paradox" that contributes to a wave-one zonal p attern in tropospheric ozone. Back trajectories, satellite observations and shipboard tracers suggest that the south Atlantic ozone results from a com bination of interhemispheric transport, aged stratospheric-upper tropospher ic air, and possibly from ozone supplied by lightning nitric oxide.