Analysis Of Inner-core Structures Of The Rapid Intensification Of Typhoon Rammasun(2014) Based On The Numerical Simulation

The prediction of tropical cyclones intensity is always one of the difficulties in forcasting,especially the prediction of rapid intensification is a huge challenge.It`s necessary to deepen and understand the inner-core structural changes of tropical cyclones to improve the prediction of tropical cyclone intensity and disaster prevention and mitigation.In this study,the evolutions of the inner-core structure of typhoon Rammasun?2014?during its offshore rapid intensification with the finest grid size of 667 m are analysed,and compared with the axisymmetric rapid intensification processes of the simulated Hurricane Wilma?2005?,understand the evolution of the inner-core structures during the asymmetric rapid intensification processes.The results show that although typhoon Rammasun and hurricane Wilma both experienced offshore rapid intensification,the distribution of the axisymmetrical average structures during the rapid intensification processes are basically similar.However,there are still significant differences in the inner-core structures during the rapid intensification processes of Rammasun and Wilma.Wilma is a classical axisymmetric rapid intensification tropical with a weak ambient vertical wind shear,a symmetrical eyewall,a small vortex tilt,a relatively upright eyewall and axisymmetric up-level warm core during the rapid intensification process.Bsides,Wilma quickly adjusted the vortex tilt to almost aligned state before the rapid intensification occurred.However,the rapid intensification of typhoon Rammasun occurs in an environment with strong vertical wind shear(Deep vertical shear>10m s<sup>-1</sup>),and the convections are highly asymmetric with deep convections fixed on the south side of the typhoon center inner the eyewall.During rapid intensification period,Rammasun maintains a large vortex tilt and eyewall tilt in the vertical direction,and the vortex tilt of Rammasun is adjusted as the intensity develops.In addition,the asymmetric middle-level warm core is remarkable.Asymmetric eyewall convections and middle-level warm core,larger vortex tilt and eyewall tilt are the significant characteristics of Rammasun`s inner-core structure.The unique inner-core structures of Rammasun provided a model for the asymmetrical and rapid intensification of sheared typhoons in the South China Sea.Results also show that the rapid intensification process for tropical cyclones also possible occur with the asymmetric inner-core structure and the relatively tilt vertical structure.