Open AccessObservations of an atmospheric chemical equator and its implications for the tropical warm pool region
Author(s) -
Hamilton Jacqueline F.,
Allen Grant,
Watson Nicola M.,
Lee James D.,
Saxton Julie E.,
Lewis Alastair C.,
Vaughan Geraint,
Bower Keith N.,
Flynn Michael J.,
Crosier Jonathan,
Carver Glenn D.,
Harris Neil R. P.,
Parker Robert J.,
Remedios John J.,
Richards Nigel A. D.
Publication year - 2008
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2008jd009940
Subject(s) - equator , intertropical convergence zone , atmospheric sciences , southern hemisphere , troposphere , chemical transport model , climatology , aerosol , environmental science , context (archaeology) , convection , chemical composition , tropopause , geology , latitude , meteorology , geography , chemistry , geodesy , precipitation , paleontology , organic chemistry
This paper reports observations of a tropospheric chemical equator in the Western Pacific region during the Austral monsoon season, separating the polluted Northern Hemisphere from the cleaner Southern Hemisphere. Measurements of carbon monoxide, ozone, aerosol size/composition, and non‐methane hydrocarbons were made from aircraft, flying north from Darwin, Australia as part of the Aerosol and Chemical Transport In tropical conVEction (ACTIVE) campaign. A chemical equator, defined as a sharp gradient in the chemical background, was found not to be coincident with the Intertropical Convergence Zone during this period. A pronounced interfacial region was identified between 8.5 and 10°S, where tracer mixing ratios increased rapidly within the boundary layer, e.g. CO from 40 ppbv to 160 ppbv within 0.5° latitude (50 km), with inhibited inter‐hemispheric mixing. These measurements are discussed in context using a combination of meteorological and Earth‐observing satellite imagery, back trajectory analysis and chemical model data with the conclusion that air flowing into and subsequently uplifted by the active convection of the Tropical Warm Pool (TWP) region in the Western Pacific is likely to be highly polluted, and will perturb the composition of the Tropical Tropopause Layer. The main source of CO and other pollutants within the TWP region is expected to be biomass burning, with extensive fires in North Sumatra and Thailand during this period. The sharp gradient in composition at the chemical equator seen here results from extensive burning to the north, contrasting with pristine maritime air advected from the Southern Indian Ocean by a strong land‐based cyclone over the Northern Territory of Australia.