What Sets a Hurricane's Radius of Maximum Wind?

Many basic aspects controlling the steady state parameters of hurricanes are not yet understood and remain difficult to predict. For example, not much is known about what determines the Radius of Maximum Wind (RMW), one of the most important dynamical properties necessary to describe any given hurricane. Previous studies (e.g., Mallen & Montgomery, 2005) found that there is no simple correlation between RMW and other dynamical parameters (such as maximum wind speed, minimum central pressure, or environmental conditions such as sea surface temperature) within the realm of measured data.

We present here an investigation of RMW using an axisymmetric, nonhydrostatic model (ZETAC), with the objective of generating steady state hurricanes and investigating how the RMW depends on the various parameters. Our model includes interactive radiation, Lin microphysics and it fully resolves convection. The resolution of the model is 1.25 km and the domain size is 10 deg radius. Reference atmospheric profiles of temperature and humidity used in the RMW experiments were obtained by using the same model, with no initial vortex, to generate radiative-convective equilibrium states for each of an ensemble of sea surface temperatures (SST). We then performed a series of hurricane simulations, using each of the set of SSTs and their respective atmospheric profiles. For each SST, we also vary initial vortex size and initial vortex intensity in order to understand the dependence of RMW on initial conditions. Each simulation was integrated for 15 days of hurricane life. For each steady state achieved, we then consider, for example, how well the hurricane intensity is predicted by the Maximum Potential Intensity theory MPI (e.g., Emanuel, 1995), and search for correlations between MPI and RMW. Other measures and correlations are also considered. This series of simulations is intended to conclusively determine, within the context of an axisymmetric hurricane model, whether the RMW is a predictable parameter.