Latitudinal distributions of methane in the upper troposphere and marine boundary air over the Pacific in 1990

Abstract

Measurements of atmospheric methane at 11–13 km were made over the Pacific from 65°N to 65°S by two research flights (INSTAC II, February – March, 1990, and III, October, 1990). Relatively low concentrations were observed in the high latitudes, indicating intrusion of stratospheric methane at 11–13 km. Methane distributions in the tropical and subtropical regions showed north to south gradients and longitudinal gradients from west to central Pacific.During almost the same period of the INSTAC III flight, atmospheric methane in the marine boundary air was measured on boad a research vessel in the Pacific from 35°N to 20°S. In the Northern Hemisphere, methane concentrations in the marine boundary air showed relatively higher values compared with those at 11–13 km. However, the relative methane levels between lower and upper air were reversed between 10°N and the equator, where the Intertropical Convergence Zone (ITCZ) was located. Such positive vertical gradient appearing around the ITCZ was maintained to the mid‐latitudes of the Southern Hemisphere. These results strongly suggests that methane‐rich air in the Northern Hemisphere was actively transported upward at the ITCZ and then meridionally transported through the upper troposphere into the Southern Hemisphere.