Vertical ozone distribution over southern Africa and adjacent oceans during SAFARI‐92

Abstract

A set of four ozonesonde stations located at Ascension Island, Brazzaville, Okaukuejo, and Irene, operational during the TRACE A and SAFARI‐92 experiments has provided an opportunity to investigate the vertical distribution of ozone over southern Africa and adjacent oceans. All stations display a springtime maximum in tropospheric ozone. Enhanced tropospheric ozone, which occurs between June and September at Brazzaville and between July and October at Ascension Island, is linked to dry season biomass burning. The influence of tropical biomass burning is delayed until September at Okaukuejo when a sharp increase in tropospheric ozone is experienced. The biomass burning influence at Irene is less because of its more southerly location. A general tropospheric enhancement is observed at all stations. It is manifest as an enriched layer in the upper troposphere at Okaukuejo (9–12 km) and Brazzaville (11–14 km) and in the lower troposphere (2–8 km) at Ascension Island. At Ascension Island lower tropospheric ozone values are about 20 parts per billion by volume greater than elsewhere and the tropospheric component here accounts for about 18% of the total column ozone. A series of tethersonde soundings conducted at hourly intervals at Okaukuejo revealed ozone to be well mixed in the lower boundary layer during the day, but to display marked vertical stratification at night.

Tropospheric ozone over Equatorial Africa: regional aspects from the MOZAIC data

“…Convection may lift ozone and its precursors from the boundary layer over Brazil to the middle and the upper troposphere, where it is transported over the Atlantic by highlevel westerlies, and with the easterlies emanating from the St-Helene high (SASTA) centered over Namibia . This enhancement in the middle troposphere during SON is also in agreement with the analyses made by Cros et al (1992), Kirchhoff et al (1996), Nganga et al (1996), Thompson et al (1996), Diab et al (1996) and Olson et al (1996) during the TRACE-A and SAFARI 92 campaigns.…”

Classification of tropospheric ozone profiles over Johannesburg based on mozaic aircraft data

“…2e, which obscures the marked layering evident in individual profiles. All, except 2 profiles, occur in spring when tropospheric ozone values are known to be highest (for example Diab et al, 1996;Thompson et al, 1996).…”

“…Traditionally, mean profiles averaged by season or year, together with some measure of variability about these means, have been analyzed. Examples of studies that have focused on constructing an ozone climatology for particular locations, include Kirchhoff et al (1991), Diab et al (1996), Fortuin and Kelder (1998), Thouret et al (1998a), Logan (1999) and Thompson et al (2003). However, computation of the mean tends to obscure the profile micro-structure because of the many counteracting influences present in the data.…”

Stratospheric filamentation into the upper tropical troposphere

“…that stratospheric intrusions in this and other subtropical regions could also be of interest to recent discussions conserning observed tropospheric ozone and its seasonal and geographical variability [e.g., Diab et al, 1996, and references therein].…”