Influences Of Tropical Cyclone’s Inner-core Wind Distribution Features On Its Development

To investigate the influences of tropical cyclone’s structure on its intensification, the rapid intensification (RI) and non-rapid intensification cases are selected by using best track data from Joint Typhoon Warning Center (JTWC). Then the structure differences between these two types of cases are analyzed according to Multi-platform Tropical Cyclone Surface Wind Analysis (MTCSWA) data. Results show that:(1) the S-parameter, which is calculated according to the radius of maximum wind (RMW) and the wind speed at the radius twice as the RMW, are smaller for RI cases indicating that the structures of RI cases are more compact.(2) the azimuthally averaged surface tangential wind of RI cases has a more prominent peak district, a smaller RMW and stronger maximum wind. The significant structure differences between these two types of cases exist in the TC inner-core area, implying close connections between TC inner-core structure and its intensification.(3) because of the wind distribution features, the mean vorticity and vorticity gradient of RI cases are bigger. In other words, bigger vorticity and vorticity gradient correspond to faster intensification rate.Based on above structure features, two ideal experiments are designed in WRF model. Among them CTL experiment has bigger vorticity and vorticity gradient corresponding to RI cases. RANK experiment corresponds to non-RI cases. By comparing the model results, it is found that the merger process of convective vorticity eddies plays an important role in the early development of initial vortex. According to vorticity segregation theory, the bigger vorticity gradient in CTL experiment is helpful for the convective vorticity eddies to move towards the center, providing more chances for vorticity eddies to merger into larger vorticity. Besides, the low-level inflow in the CTL experiment is stronger and closer to typhoon center, which is also beneficial for the merger of convective vorticity eddies through the advection effect. Under the influence of these two factors, the vorticity eddies in CTL experiment move to the center more obviously. So it is more likely that these eddies will interact with each other and merger into bigger vorticities, which is beneficial for the vortex system in CTL experiment to intensify. On the other hand, it is demonstrated that the diabatic heating is also important for the TC development by the diagnosis of Sawyer-Eliassen balance equation. The vorticity of CTL experiment is larger, which means the inertial stability is larger and the Rossby deformation radius is smaller. As a result, the heating in CTL experiment tends to confined in a limited area, which is beneficial to conversion from diabatic heating to TC kinetic energy. All these factors are conducive to the development of the vortex system in CTL experiment.