Dynamically Downscaled Simulations of Tropical Cyclones - A Multi-Model Approach for the Australian Region

The dramatic and damaging effects of tropical cyclones (TCs) are already clearly apparent in the current climate, making potential changes in the frequency or intensity of these storms in the future of immense interest. The spatial resolution of both global climate models (GCM) and regional climate models (RCM) is relatively coarse, so downscaling approaches must be used to investigate potential changes in the intensity of TCs in a warmer, future climate. In this presentation we present results from downscaling studies of Australian region tropical cyclones using two atmospheric models. The models used are the CSIRO Cubic-Conformal Atmospheric Model (CCAM) and the Regional Atmospheric Modeling Scheme (RAMS).

Three GCMs from the World Climate Research Programme (WCRP) Coupled Model Intercomparison Project Phase 3 (CMIP3) multi-model data set were chosen based on their ability to simulate the climatology of large-scale fields important for TC genesis and development as well as the simulation of TC-like vortices in the current climate. Initially the GCMs were used to force CCAM with a stretched grid of approximately 60 km over Australia. Tropical cyclone-like vortices from the 60 km model output were detected using the method of Walsh et al. (2004) and these individual events further downscaled: (1) with a 15 km movable mesh version of CCAM and (2) with RAMS using a 5 km grid spacing.

The modeled TC present-day climatology from both systems is evaluated and changes in future climates quantified. Results from the 2 modelling systems will be compared and projected changes in the Australian-region TC climate including intensity, size and precipitation will be summarized. Some preliminary results using the Weather Research and Forecasting (WRF) model will also be presented.