Evaluating how photochemistry and transport determine stratospheric inorganic chlorine in coupled chemistry‐climate models

Abstract

This study examines how the stratospheric conversion of organic molecules containing chlorine (CCly) to inorganic forms (Cly) can be comprehensively evaluated in three‐dimensional coupled chemistry‐climate models (CCMs) using results from two models (SOCOL and UMETRAC) as examples. Stratospheric inorganic chlorine concentrations depend on both photochemistry and transport. The CCly to Cly conversion process is the first step towards chlorine catalyzed destruction of stratospheric ozone. It is therefore important that models used for the prediction of future stratospheric change accurately simulate this process. Also, because there are multiple processes influencing Cly in CCMs, direct comparison of Cly by itself is of limited use as a validation diagnostic for CCMs. Results show that SOCOL's representation of the photochemical conversion of CCly to Cly is more realistic than UMETRAC's. The CCly to Cly parameterization used in UMETRAC masks transport deficiencies in the model which means that Cly in the polar lower stratosphere from UMETRAC compares better with observations than SOCOL.