Dependence of tropical cyclone intensification rate and size change on the radial tangential wind profile of the initial vortex —Results from specified diabatic heating

In this study, the influence of the initial vortex structure on the intensification rate (IR) and the inner-core size change of tropical cyclones (TCs) has been investigated based on a series of experiments with specified diabatic heating in both the Sawyer-Eliassen Equation (SEQ) and the tropical cyclone model- TCM4. The tangential wind tendency is first diagnosed based on the secondary circulation from the SEQ forced by specified diabatic heating. The results show that a larger/broader (thinner/narrower) initial vortex displays slower (faster) IR but the larger (smaller) inner-core size increase because of higher (lower) inertial stability (IS) outside the RMW. For given diabatic heating in the eyewall, higher IS outside the RMW in broader vortices slows down the low-level inflow convergence to the eyewall but intensifies the inflow outside the RWM, thus reducing the IR but increasing the storm size; and vice versa. Diabatic heating far away from the RMW has little effect on the IR or size change of a smaller/narrower initial vortex because of smaller IS and large Rossby deformation radius outside the RMW. Results from TCM4 with specified diabatic heating show features very similar to those from the SEQ. For diabatic heating in the high IS core inside the RMW, all vortices show rapid intensification but the larger IR occurs to the thinner initial vortex because of weaker IS outside the RMW. Although a broader vortex shows lower IR, higher IS outside the RMW slows down the inflow outside the RMW, thus leading to slower contraction of the RMW. Diabatic hating outside the RMW in the thinner initial vortex contributes little to the tangential wind tendency outside the RMW, suggesting that diabatic heating in spiral rainbands far away from the eyewall has little effect on TC IR. Furthermore, the IR becomes much smaller when surface friction is taken into account in TCM4, suggesting that surface friction has a negative effect on TC intensification.