Trace gas concentrations, intertropical convergence, atmospheric fronts, and ocean currents in the tropical Pacific

Abstract

Shipboard measurements of atmospheric 222Rn, CO, and CH4 and of dissolved CO in surface waters have been carried out in the equatorial Pacific on a cruise from Ecuador to Hawaii, Tahiti and Panama in March and April of 1974, and during transit from Los Angeles to Antarctica in November and December of 1972. Trace gas results, combined with conventional meteorological data and with satellite images from Nimbus 5 and the defense meteorological satellite project (DMSP), have provided descriptions of the intertropical convergence zones (ITCZ) near 04°N, 102°W and 03°N, 154°W in March of 1974, near 04°N, 86°W in April of 1974, and near 05°N, 139°W in November of 1972. In all cases the ITCZ seems to be located north of the south equatorial current (SEC) as shown by dissolved CO peaks in surface waters. In April of 1974 a ‘second’ ITCZ was observed near 01°S, 102°W just south of the SEC. A stationary front near Hawaii (20°N, 147°W) in March of 1974 was investigated. The ITCZ was marked by light shifting winds near a zone of heavy cloud cover and precipitation. In the eastern Tropical Pacific atmospheric 222Rn increases distinctly north of the ITCZ and thus serves as an indicator for the ITCZ. CO and CH4 do not always increase coincident with atmospheric 222Rn The atmospheric features of the stationary front near Hawaii are in many ways similar to those observed for the ITCZ. The front is marked by cloud cover, precipitation zone and light shifting winds. 222Rn CO and CH4 increase significantly behind the front in subsiding air which was traced back to the Asian continent. The variation of atmospheric 222Rn, CO and CH4 with time and geographical area over the equatorial Pacific seems to be a consequence of seasonal variations of the trade wind field and long range transport to the central Pacific from Asia and to the eastern equatorial Pacific from North and Central America.