Simulation Of Mesoscale Vortex Activity In Tropical Cyclogensis Within Monsoon Gyre

The formation of a tropical cyclone(TC) involves multiple scale circulations and their interactions. While much has been learned about tropical cyclogenesis, the mesoscale circulation during the genesis process is acquainted scarcely. In general, the formation of TC will be affected by large scale circulation systems. Studies show that monsoon gyre activity is closely associated with tropical cyclogenesis over the western North Pacific. In order to analyze multi-scale vortex activity during the genesis of TC with high-resolution simulation data, simulation initial time of this study starts before the formation of midlevel mesocale convective vortex (MCV), which is different from previous researches. This study mainly investigates the formation of MCV and activity of meso-y vorticity anomalies.The numerical simulation results show that low-deformation disturbance first occurred in the enhanced southwesterly flows on the southeast of monsoon gyre. The enhanced cyclonic circulation leads to the formation of MCV with horizontal scale around 200km in the low-deformation area. Further study demonstrates that the midlevel MCV formation is the result of the merging of two potential vorticity anomalies.Meso-y vorticity anomalies with 10-20km horizontal scale were also present in the low-deformation area, some of them were vertical hot towers. The favorable cyclonic environment created by MCV facilitates organization of meso-y vorticity anomalies. As a result, distribution of low-level vorticity anomalies is more concentrated and more active than mid-level distribution. The simulation result shows that the formation of tropical cyclones is associated with the transformation of midlevel and low level meso-y vorticity anomalies activity.In addition, the influence of starting up finest grid spacing at different time on tropical cyclogenesis is also discussed by numerical experiments. Compared with earlier starting-up, starting-up finest grid spacing after the formation of midlevel MCV is more beneficial for the tropical cyclogenesis, which provides a more favorable and constant humidity and heating environment, also demonstrates that midlevel MCV plays an important role on tropical cyclogenesis.