Sensitivity of tropical cyclone intensification to perturbations in the surface drag coefficient

Abstract

The recent studies of the sensitivity of tropical-cyclone intensification to the surface drag coefficient in a three-dimensional model by Montgomery et al. and Smith et al. are extended to include perturbations of the surface drag coefficient in one of four boundary-layer parametrization schemes: the bulk scheme, the Blackadar scheme, the MRF scheme, and the Gayno–Seaman scheme. The schemes are slightly modified to have the same drag coefficient formulation and the same constant exchange coefficients for sensible heat and moisture.We find that the intensification rate and mature intensity are essentially unaltered when the drag coefficient is perturbed randomly by variations of up to 60%. The results, in conjunction with an analysis of coherent drag coefficient variations for a moving vortex, question the notion that coupled wind–wave models are necessary to accurately forecast tropical-cyclone intensification and mature intensity.