On surface fluxes and tropical cyclone intensification

Previous research has found that capping the wind speed dependence of the surface enthalpy flux does not inhibit tropical cyclone intensification in hurricane-in-a-box type numerical simulations with simple parameterizations. More recently, Bryan et al. (2010) modified the Emanuel maximum potential intensity theory to account for the surface wind capping. It was further suggested that limiting a single component of a multi-variable instability mechanism results in a reduction of the growth rate but not its elimination.

We continue this line of research by exploring the limiting factors in the surface enthalpy flux calculation using a three-dimensional model with varying degrees of sophistication in the environmental flow and the model physics parameterizations. We will show that when ice microphyscis and or vertical shear are introduced in wind-capped simulations, increases in the gestation period are significant and in some cases intensification is not observed. We also have conducted simulations in which the initial thermodynamic disequilibrium, measured as the difference between the saturation mixing ratio at the surface pressure and sea surface temperature and the mixing ratio of the first model level, is controlled. At sufficiently low thermodynamic disequilibrium, no intensification is observed no matter what the value of the wind speed used in the enthalpy flux calculation. We also explore the gestation period for a range of values of the capping wind-speed in a favorable thermodynamic environment with weak shear.