Simulation of tropical cyclone precursors and dynamically-downscaled simulations of tropical cyclones over an Australian domain

A number of studies have suggested that tropical cyclones may become more intense in a warmer world. Over the Australian region the extent of the associated damaging winds may also affect areas further south than at present (e.g. Leslie et al., 2007). In order for models to simulate the future climate well it is necessary that they perform well when simulating the current climate. This study evaluates the performance of a number of climate models in simulating the mean climate and the generation of tropical lows over an Australian domain. Model simulations performed for the IPCC 4th Assessment report are examined, focusing on the aspects of climate that are known to influence tropical cyclone formation and intensification. Daily mean model output is then used to evaluate the numbers and locations of tropical lows in each model run. In each simulation tropical cyclones are identified and tracked based on the methodology described by Walsh et al. (2004). The ability of climate models to simulate the tropical lows is crucial to using these models to analyse the changes in tropical cyclone climatology under different emission scenarios.

The results from this model intercomparison study has allowed us to determine which models are suitable for dynamical downscaling. These models are used to force the CSIRO Conformal Cubic Atmospheric Model (CCAM; McGregor and Dix, 2008), a variable resolution regional climate model. A fine resolution version of CCAM over the Australian region is used to make an improved estimate of present-day tropical cyclone hazard. This allows us to analyse, in detail, the physics and dynamics of tropical cyclone simulations. Here we present results on the ability of climate models to simulate tropical cyclone precursors and some dynamically-downscaled simulations of tropical cyclones over the Australian region.