Aerosol exchange in the remote troposphere

Abstract

A series of meteorological research flights were conducted over the Pacific Ocean, Antarctica, and the Antarctic seas, during the months of October, November and December, 1977, 1978 and 1980. The route of these flights was generally along an axis most distant from the temperate continents. Relatively high ozone mixing ratios were found over many oceanic areas, in agreement with GAMETAG observations. A minimum of tropospheric ozone was observed near the ITCZ, but ozone appeared to be advected into the tropical troposphere near the 500 mb level. The cumulus of the intertropical convergence zone are effective conveyors of aerosol, carrying enhanced aerosol concentrations to above the 200 mb level. The enhanced aerosol concentrations of the ITCZ were found to be transported into the adjacent tropical troposphere. The greatest aerosol concentrations were found in and near the high cumulus of the ITCZ, beneath the Southern Subtropical jet, and near stratiform clouds in the southern hemisphere. The aerosol concentration diminished steadily with increasing latitude south of the southern subtropical jet, in dry air. Uniform aerosol concentrations were observed in the Antarctic troposphere, except in the vicinity of cirrus layers aloft. and in moist or cloudy layers near the surface. Enhanced ozone mixing ratios were found in troughs about the periphery of Antarctica, and in slightly turbulent layers near mountains. Ozone and aerosol concentrations sometimes co-varied with respect to time but, no systematic variation could be shown among ozone concentration, aerosol concentration and meteorological parameters. Ozone and aerosol concentrations observed over a wide geographic area of Antarctica were stratified into two altitude classes, and the results mapped. Ozone concentrations in the mid troposphere (550 to 400 mb levels) were small and nearly invariant over the interior of Antarctica. Ozone concentrations in the upper tropospheric (400 - 300 mb) layers varied greatly, and became quite large over troughs and about the periphery of Antarctica, and in the vicinity of high mountains. Ozone exchange appears quite vigorous in the upper troposphere and frequent aerosol exchange occurs in the lower troposphere, but the stability of the middle troposphere inhibits mixing among these levels, in agreement with the hypothesis of Oltmanns and Komhyr. Vertical profiles of aerosol concentration indicate an aerosol decrease of 25 particles cm -3 Km -l in clear air over Antarctica. Moist and/or cloudy air over and near the Ross and Weddell Seas is enhanced with aerosol, relative to this dry profile. Moist layers over the interior of Antarctica are also enhanced in aerosol concentration in comparison with dry Antarctic air. DOI: 10.1111/j.1600-0889.1986.tb00187.x