Testing Weighted Splitting Schemes on a One-Column Transport-Chemistry Model

In many transport-chemistry models, a huge system of one-dimensional equations of the advection-diffusion-reaction type has to be integrated in time. Typically, this is done with the help of operator splitting. Operator splitting is attractive for complex large-scale transport-chemistry models because it can handle different processes separately in different parts of the computer program. Rosenbrock schemes combined with approximate matrix factorisation (ROS-AMF) are an alternative to operator splitting which does not suffer from splitting errors. However, since the ROS2-AMF schemes are not based on operator splitting, implementation of these methods often requires major changes in the code. In this paper we test another second-order splitting introduced by Strang in 1963, which seemed to be forgotten and rediscovered recently (partially due to its intrinsic parallelism). This splitting, called symmetrically weighted sequential (SWS) splitting, is simple and straightforward to apply, independent of the order of the operators and has an operator-level parallelism. In the experiments, the SWS scheme compares favourably with Strang splitting, but is less accurate than ROS-AMF.