5.9 Coupled Time-Integration of Chemical and Aerosol Dynamical Processes by Using Multirate Implicit-Explicit Schemes

摘要

The application of suitable time integration schemes is especially important for highly dynamical problems like atmospheric aerosol processes. Usually, classical time integrators take the same time step over the complete domain and for all components. Consequently, the model regions and the components with the strictest time step restrictions dictate this global time step. Opposed to this, multirate schemes are employed to adapt the time step locally, so that slower components take longer and fewer time steps, which can reduce the computational costs substantially. In the paper, a new class of time integration schemes is proposed which combines the multirate approach with implicit-explicit (IMEX) methods. These schemes are applied for block-structured grids with different horizontal resolutions as well as the coupling between aerosol dynamical and gas phase chemical processes in the chemistry-transport model COSMO-MUSCAT.