Impact of the Basic-state Vortex Structure on Tropical Cyclone Structure and Intensity Change

To understand the evolutionary features of tropical cyclones (TC) with different basic state vortex structures, the 3D nonhydrostatic dry mesoscale numerical Weather Research and Forecasting (WRF) model is utilized. Two typical initial basic state vortex structures with “short and fat”, “tall and thin” are constructed, respectively. The results show that “tall and thin” vortex structure exhibits significantly greater instability than “short and fat” vortex structure.. Their large relative vorticity (RV) columns on both sides of the TC eye are first connected as a bridge near the height of 2-3 km, then the hollow RV tower (HRVT) collapses. For the former, the low-level perturbed vorticity grows slowly, and in the middle and late stages the HRVT in the low-level begins to collapse, and the large RVs in the eyewall are gradually transported to the eye center, the horizontal RV structure corresponds to the most unstable wave number 3.. For the “tall and thin” vortex structure, their asymmetric perturbations grow rapidly, and the low-level RV column structure starts to collapse in 3 hours, and the large RV in the eyewall mixes rapidly toward the eye center, and the large RV ring at the beginning shows a clear quadrilateral structure, and then collapses, four mesoscale vortices are formed and exist for a long time. By 18 hours the mesoscale vortices merge, and are finally unipolar. For the “short and fat” vortex structure, the RV mixing process have not a significant effect on the intensity change; whereas, for the “tall and thin” vortex structure, the intensity is enhanced by significant dynamical instability.