A modelling study of tropospheric distributions of the trace gases CFCl3 and CH3CCl3 in the 1980s

K.-Y. Wang, D. E. Shallcross
2000 Annales Geophysicae  
Interhemispheric transport is a key process aecting the accuracy of source quanti®cation for species such as methane by inverse modelling, and is a source of dierence among global three-dimensional chemistry transport models (CTMs). Here we use longterm observations of the atmospheric concentration of long-lived species such as CH 3 CCl 3 and CFCl 3 for testing three-dimensional chemistry transport models (CTMs); notably their ability to model the interhemispheric transport, distribution,
more » ... distribution, trend, and variability of trace gases in the troposphere. The very striking contrast between the inhomogeneous source distribution and the nearly homogeneous trend, observed in the global ALE/ GAGE experiments for both CH 3 CCl 3 and CFCl 3 illustrates an ecient interhemispheric transport of atmospherically long-lived chemical species. Analysis of the modelling data at two tropical stations, Barbados (13 N, 59 W) and Samoa (14 S, 124 W), show the close relationship between inter-hemispheric transport and cross-equator Hadley circulations. We found that crossequator Hadley circulations play a key role in producing the globally homogeneous observed trends. Chemically, the most rapid interaction between CH 3 CCl 3 and OH occurs in the northern summer troposphere; while the most rapid photolysis of CH 3 CCl 3 and CFCl 3 , and the chemical reactions between CFCl 3 and O( 1 D), take place in the southern summer stratosphere. Therefore, the cross-equator Hadley circulation plays a key role which regulates the southward¯ux of chemical species. The regulation by the Hadley circulations hence determines the amount of air to be processed by OH, O( 1 D), and ultraviolet photolysis, in both hemispheres. In summary, the dynamic regulation of the Hadley circulations, and the chemical processing (which crucially depends on the concentration of OH, O( 1 D), and on the intensity of solar insolation) of the air contribute to the seasonal variability and homogeneous growth rate of observed CH 3 CCl 3 and CFCl 3 .
doi:10.1007/s00585-000-0972-3 fatcat:rnr4cyzlsje5pp63opuju3ampy