Comparing forward and inverse models to estimate the seasonal variation of hemisphere-integrated fluxes of carbonyl sulfide

[摘要] A simple inverse model is proposed to deduce hemisphere-integrated COS flux based on publishedtime series of total column COS.The global atmosphere is divided into two boxes representing theNorthern and Southern Hemispheres, and the total column COS data from several stations are usedto calculate hemispheric COS loadings.The integrated flux within each hemisphere is calculated as alinear combination of a steady-state solution and time-varying perturbation.The nature of the time-varyingperturbation is deduced using two different approaches: an analytic solution based on acosine function that was fitted to the original total column COS measurement time series and aSimplex optimization with no underlying assumption about the functional form of the total columntime series.The results suggest that there is a steady-state COS flux from the Northern to theSouthern Hemisphere.There is a seasonal variation superimposed on this flux that in the SouthernHemisphere has a maximum rate of COS input into the atmosphere around January and a maximumrate of COS removal from the atmosphere around August--September.In the NorthernHemisphere, the maximum rate of COS input into the atmosphere is around May--June, and themaximum rate of COS removal is either August or January, depending on which station in theNorthern Hemisphere is considered.The results of the inverse model are compared with theoutcome of a forward approach on the temporal and spatial variation of the dominant globalsources and sinks published earlier.In general, the deduced hemisphere-integrated flux estimatesshowed good agreement with the database estimates, though it remains uncertain whether COSremoval from the atmosphere in the Northern Hemisphere is dominated by plant and soil uptake inthe boreal summer or by oceanic uptake in boreal winter.

[学科分类] 大气科学