Simulation of Tropical Cyclones with a Cloud-System Resolving Model for Different Equator-to-Pole Temperature Gradients

We study tropical cyclones in different climates using a cloud-system resolving model (SAM, Khairoutdinov and Randall 2003) configured on an idealized aqua-planet beta-plane that extends from 70N to 70S. To facilitate simulation of strong cyclones, the model employs RAVE (Reduced Acceleration in the Vertical, e.g. Kuang et al. 2005), which allows reproducing category 4 and 5 hurricanes even for the model spatial resolution of 15km. Here, we present preliminary results of these simulations in which we vary the equator-to-pole temperature gradient and focus on the key characteristics of tropical cyclones, including the total number of cyclones, their genesis, strength and latitudinal distribution, and interaction with synoptic weather systems. We find that the tropical cyclone activity changes non-monotonically with reduction in the oceanic meridional temperature gradient – for small changes the cyclone activity decreases slightly, but for larger changes it strongly increases, mainly because of the strong reduction in wind shear in mid-latitudes for weak meridional temperature gradients. The increase in tropical cyclone activity is accompanied by the merging between the characteristics of extra-tropical storms and tropical cyclones, as seen in the paths of the storms as well as their property distributions (e.g. pressure anomaly versus maximum speed). We discuss these results in the context of the current debate on future changes in tropical cyclones with global warming.