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

Abstract

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 profiles along the latitudinal transect shows 4 zones, nearly identical to the 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 elevated tropospheric ozone (>35 Dobson Units) throughout the south Atlantic in January 1999. Ozone layers associated with biomass burning north of the ITCZ (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 pattern in tropospheric ozone. Back trajectories, satellite observations and shipboard tracers suggest that the south Atlantic ozone results from a combination of interhemispheric transport, aged stratospheric-upper tropospheric air, and possibly from ozone supplied by lightning nitric oxide.