Kinetic energy efficiencies of an idealized developing tropical cyclone

Forecast skill for tropical cyclone intensification remains relatively poor. Part of the problem results from gaps in our understanding of the basic internal dynamics of tropical cyclones. It is hoped that a better physical understanding of the role that the structure of a cyclone has on its own intensification will eventually lead to improvements in intensity prediction. In this study, we utilize a dry, linear model to investigate the intensification of an idealized, symmetric, hurricane-like vortex. A stable, balanced vortex is initialized from a mean tropical sounding and a gaussian vorticity profile chosen to provide a specified radius of maximum winds and maximum tangential velocity. A small heating perturbation is then introduced, and the vortex is allowed to evolve until it again reaches a balanced state. We define the Kinetic Energy Efficiency (KEE) to be the change in the kinetic energy of the symmetric wind field per unit heating associated with the initial perturbation. This process is repeated for perturbations introduced separately into each point in the (r,z) plane, thus showing how intensification varies with the location of heating. Many experiments were performed to determine the sensitivity of KEE to various parameters that characterize the vortex. It was found that the most important parameter is the maximum wind speed, with a 3-fold increase in KEE for a doubling of wind speed from 15m/s to 30m/s. Variations in the coriolis parameter were also found to be significant, with KEE increasing with increased latitude. KEE also generally increases with increasing radius of maximum winds. Conclusions based on more realistic and observed hurricane wind profiles will also be presented.