Strang Splitting Versus Implicit-Explicit Methods in Solving Chemistry Transport Models A contribution to subproject GLOREAM

Usually transport-chemistry models are solved by operator-splitting methods where the chemistry and the vertical transport processes are integrated in a coupled way by implicit methods of order two or higher with automatic error control. In mesoscale applications the integration intervals are relatively short and small initial transients occur for the chemistry-diffusion operator which are an artefact of the operator-splitting approach. Integration methods with error control are quite sensitive to this initial transients which results in rather small step sizes to start up the integration. However to take into account effectively changes inside the chemistry-diffusion process (sunset, sunrise, change of the mixing height) an error control is held indispensible.