The Effect of Regional Climate Model Domain Choice on the Simulation of Tropical Cyclone-Like Vortices in the Southwestern Indian Ocean

Abstract

While GCMs do simulate tropical cyclone-like vortex tracks in the southern Indian Ocean, they do not capture well those which make landfall in southern Africa. The feasibility of using a nested modelling system to produce seasonal tropical cyclone forecasts is examined, since improved horizontal resolution may potentially improve simulated cyclone tracks. As a first approach, a regional climate model is driven by time-dependent large-scale meteorological analyses for several domain configurations. Tropical cyclones across the southern Indian Ocean are likely to be significantly affected by the large-scale zonal flow. Therefore, the effects of model domain size and the positioning of its lateral boundaries on the simulation of tropical cyclone-like vortices and their tracks on a seasonal time scale are investigated. Four tropical cyclones are studied, which occurred in January of the years 1995 to 1997. Results show that the positioning of the eastern boundary of the regional model domain is of significant importance in the life cycle of simulated tropical cyclone-like vortices: a vortex entering through the eastern boundary of the regional model is generally well simulated. It is inferred from these results that the nested approach can potentially improve upon the frequency of landfalling tracks over southern Africa simulated by GCMs