Effects Of Monsoon Gyre On Tropical Cyclone Genesis And Track Turning

Monsoon gyre is an important way to generate tropical cyclone. The interaction between monsoon gyre and tropical cyclone would cause the TC path to mutate. We first make a simple statistical analysis of the monsoon gyre structure corresponding to different kinds of TC paths. Secondly, on the basis of statistics, the non-hydrostatic Advanced Research Weather Research and Forecasting model(version 3.3.1) is used to simulate the process of tropical cyclogenesis and the abrupt characteristics of tropical cyclone track associated with monsoon gyre.The numerical results show that the larger environmental vorticity of the monsoon gyre is not conducive to the rapid development of tropical cyclones.Although the monsoon gyre having larger initial vorticity, the radial gradient of its vertical vorticity is relatively smaller due to its larger initial size. The radial vorticity gradient can modulate convective cells merging through "vorticity segregagation"effect in the initial phase. As the disturbance organized, the inflow advection of vorticity became more and more important. From the thermo dynamical viewpoint,relatively larger environmental relative humidity is in favor of the tropical cyclogenesis.Finally,the effect of the intensity of the monsoon gyre on the abrupt change of the tropical cyclone is simulated by changing the vertical structure of the monsoon gyre. The Fujiwara effect exists in the process of interaction between TC and the monsoon gyre. TC center and the monsoon gyre center will rotate with each other,and close to each other slowly. The TC center will coincide with the monsoon gyre center in the northward TC, but the northwestward TC will not. The symmetric circulation of the monsoon gyre can change the direction of the asymmetric steering flow. In the northward TC, the cyclonic circulation of the monsoon gyre is stronger at the initial stage, which makes the orientation of the asymmetric steering flow more west, which is beneficial to the westward movement of TC. With the continuous close of TC center and the monsoon gyre center, the symmetry of the vortex structure is strengthened, which will weaken the westward asymmetric steering flow. In addition, the coincidence of the TC center and the monsoon gyre center in the northward type will strengthen the Rossby energy dispersion in the southeastern quadrant, which will lead to strong southerly wind to help the northward turning of TC track.