Upgrading photolysis in the p-TOMCAT CTM: model evaluation and assessment of the role of clouds

[摘要] A new version of the p-TOMCAT Chemical Transport Model (CTM) which includes an improved photolysis code,Fast-JX, is validated. Through offline testing we show thatFast-JX captures well the observed J(NO₂) and J(O¹D) values obtained at Weybourne and during a flightabove the Atlantic, though with some overestimation of J(O¹D)when comparing to the aircraft data. By comparingp-TOMCAT output of CO and ozone with measurements, we find that the inclusion of Fast-JX inthe CTM strongly improves the latter's ability to capture the seasonality andlevels of tracers' concentrations. A probability distribution analysis demonstrates that photolysisrates and oxidant (OH, ozone) concentrations cover a broader range ofvalues when using Fast-JX instead of the standard photolysis scheme. This is not only driven byimprovements in the seasonality of cloudiness but also even moreby the better representation of cloud spatial variability. We use three different cloud treatments to studythe radiative effect of clouds on theabundances of a range of tracers and find only modest effects on a global scale. This is consistent with the mostrelevant recent study. The new version of the validatedCTM will be used for a variety of future studies examining the variability of tropospheric compositionand its drivers.

[学科分类] 天文学(综合)