Observational And Numerical Simulation Study Of Tropical Cyclone Over The Northwestern Pacific Ocean And Northern Indian Ocean And Statistic Analysis Of Cyclogenesis

Forecasts of tropical cyclone (TC) movement have improved significantly over the last three decades due to a combination of better observations, well-improved numerical models, and in-depth understanding of physical processes and mechanisms that control the motion of tropical cyclones (TCs). By contrast, the skill level in prediction of TC structure and intensity changes remains comparatively low in spite of the application of sophisticated numerical models. One possible reason is that the physical processed associated with intensity changes are not well understood. Recent studies suggested that the changes of TC structure and intensity are affected at any time by large and complex arrays of physical mechanisms governing the inner core structure and the interactions between the storm and both the underlying ocean and its large-scale environment. Thus, the main focuses of the present thesis are on studying the changes of TC structure and intensity by using all available data and numerical modeling.Typhoon Imbudo (2003) made two landfalls in Luzon and Guangdong Province, respectively. Its intensity underwent deepening, weakening, reintensifying, reweakening, and dissipating stages. During the storm landfalling in Luzon, its eyewall firstly contracted, then displaced, broken down, and reorganized. Strong convections occurred on the left side of storm path before Imbudo landfalling in China, while strong convections occurred on the right side of storm track before it landfalling in Luzon. These asymmetric convections caused asymmetric rainfalls correspondingly. The Regional Atmospheric Modeling System (RAMS) is used to simulate the evolution process of Imbudo during its landfalling in China. The modeling captured successfully the track, intensity changes, dynamic and thermodynamic structures of inner core. The simulated clouds agreed with the satellite imagery well. Asymmetric convection was also reproduced in the modeling. By further analyzing the modeled asymmetry, it is found that the storm-scale vertical wind shear affected the distributions of rainfall. As typhoon made landfall, cold airs and potential vorticity (PV) mixing change the structure of PV, which impacted the asymmetry in the storm core. Asymmetry associated with boundary layer can alter the mean circulation of TC. Distribution of potential heat flux and land-sea contrast also plays a role to the formation of convective asymmetry. On the other hand, we performed a simulation of the eyewall evolution of Imbudo during its landfalling in Luzon, by using the Pennsylvania State University-National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5). The shrink, breakdown, and reformation of eyewall are reproduced well. It is indicated that the contraction and breakdown are related to the increase of low-level tangential winds, the diffusion caused by topography and cut-off of vapor transfer, respectively. The characteristics of vortex Rossby wave are also analyzed.The numerical simulation of Typhoon Rananim (2004) is conducted by using MM5. The...