The response of tropical cyclone to transient symmetric and asymmetric inner-core heating

The secondary eyewall formation and the eyewall replacement cycle are common features in intense tropical cyclones (TCs), which can play important roles in TC intensity and structure change. In this study, the WRF model is used to examine the influence of different heating patterns outside the primary eyewall on the evolution of TC structure and intensity. The symmetric and asymmetric diabatic heating with specified intensity are incorporated into a steady-state TC at different radii to mimic the role of secondary eyewall to evaluate the response in terms of TC intensity and structure. In the numerical experiments, the specified heating is added for six hours and is then turned off. Therefore, the TC intensity experiences oscillation to different degrees depending on the heating pattern. It is found that the closer the symmetric heating is set to the primary eyewall, the more significantly the primary eyewall is weakened, likely due to the cutoff of inward transport of angular momentum and moisture. When the maximum heating is located at the lower level, the vortex tends to expand the maximum radial inflow outward and have a larger eye. The budget of absolute angular momentum (AAM) indicates the primary contributor to the generation of AAM near convective heating region is the mean advection by the secondary circulation. The friction and diffusion can to a certain degree offset the AAM production.

In the experiments with the asymmetric heaing, the heating with different azimuthal wavenumbers is specified around the TC center at different radii. Results show that the asymmetric heating plays a stronger role in weakening the primary eyewall than the symmetric heating. The higher wavenumber the diabatic heating has, the more rapidly the vortex weakens. The PV fields also exhibit the corresponding asymmetric structures with filamentation features.