Observations of vertical distribution of tropospheric ozone over Indian Ocean and its comparison with continental profiles during INDOEX FFP-1998 and IFP-1999

Abstract

The vertical distribution of ozone over the Indian Ocean was measured during the first field phase (FFP) of Indian Ocean experiment from 15°N to 20°S in February/ March 1998. Similar but exhaustive observation was taken during INDOEX-IFP in January/March 1999. A pocket of low ozone (~ 10 ppbv) was observed near the surface in addition to high ozone concentration observed at 8–12 km within the region of 5–15°S during both INDOEX FFP-98 and INDOEX IFP-99. However, the north-south gradient in ozone concentration and the layered structure at 5–8 km as observed in INDOEX FFP-98 are not prominent during INDOEX IFP-99. East-west cross-section of ozone concentration in the troposphere along 20°S and 15°N may be characterized as the background value of pristine and continental air on the northern and southern side of the equator, respectively. Though back trajectory analysis indicates that flow of air masses is mostly from the Indian subcontinent as well as south-east Asian region, it is difficult to distinguish the degree of relative contribution of continental flow to ozone concentration over the Indian Ocean. The comparison between marine and continental ozone profiles suggests that the northern side of the Inter Tropical Convergence Zone (ITCZ) resembles the continental profiles as observed over the Indian subcontinent and African region, rather than east Asian region.