The radiative-dynamical effects of high cloud on global ozone distribution

Previous studies (e.g., Dessler et al., 1996; Haigh, 1984) have discussed t he effect of cloud on modelled ozone distribution through changes in the ra diative heating in the lower stratosphere. Here the relationship is investi gated using an interactive chemical-radiative-transport 2D model. It is sho wn that, while similar cooling in the lower stratosphere due to high cloud is found, the effect on ozone is not as previously expected. The inclusion of high cloud is found to bring about a warming of the troposphere, resulti ng in a net heating in the lower stratosphere. This strengthens the circula tion, leading to a decrease in total tropical ozone. Importantly, the effec t of the cloud-induced temperature changes on heating rates does not combin e linearly with the direct radiative effect of cloud changes. The possibili ty of a link between the high cloud increases and total ozone decreases obs erved in some regions during strong El Nino episodes is investigated. The p ossible impact on ozone of a global trend in high cloud cover is also discu ssed.