Tropical Cyclone-like Vortices in a Limited Area Model: Comparison with Observed Climatology

Abstract

A climate simulation of a limited area model implemented over the Australian region is analyzed for the presence of low pressure systems that have some of the physical characteristics of tropical cyclones. The model is run at a horizontal resolution of 125 km and is nested within a GCM simulation of 10 Januarys. The model simulates those variables that are believed to be important for tropical cyclone formation reasonably well, as evaluated using Gray?s Seasonal Genesis Parameter. Objective criteria are used to detect tropical cyclone-like vortices (TCLVs) in the model. The composite structure of the simulated storms and the life cycle of a typical TCLV are described. Like tropical cyclones, the simulated TCLVs have warm cores, low-level wind maxima, and their tracks and regions of occurrence are similar to those observed for tropical cyclones. In general, the TCLVs simulated by the limited area model are weaker than observed, as determined by a measure of the area-averaged low-level tangential wind speed, but they are much more realistic than those vortices similarly generated by the GCM. Maximum wind speeds also occur farther from the center of the storm on average than observed. A multiply nested limited area model simulation at a horizontal resolution of 30 km shows further improvement in the TCLV simulation. While the 125-km resolution model may have some potential for predicting genesis regions, numbers, and tracks of TCLVs, it does not yet show such potential for predicting intensities.