基态位涡径向分布对浅水涡旋系统演变的影响分析PartⅡ:扰动发展和结构变化  

Impacts of basic state Potential Vorticity(PV)profiles on the evolution of shallow-water vortices PartⅡ:Disturbance development and structural change

作　　者：刘爽 钟玮 刘宇迪 LIU Shuang;ZHONG Wei;LIU YuDi(Institutes of Meteorology and Oceanography,National University of Defense Technology of PLA, Nanjing 211101,China)

机构地区：[1]中国人民解放军国防科技大学气象海洋学院,南京211101

出　　处：《地球物理学报》2018年第9期3592-3606,共15页Chinese Journal of Geophysics

基　　金：国家重点基础研究发展计划(973)项目(2013CB430103);国家自然科学基金项目(41275002;41175089;41775055)共同资助

摘　　要：本文在基态位涡(Potential Vorticity,PV)径向分布和基态涡旋强度对热带气旋(Tropical Cyclone,TC)类涡旋系统稳定性特征影响的研究基础上,结合理想试验和数值模拟诊断分析基态PV径向分布对扰动增长和系统结构变化的影响.基于线性正压浅水模型,设计三种典型基态PV中空结构下基态涡旋强度对系统稳定性影响的敏感性试验.结果表明:基态涡旋的强度主要影响稳定性的强弱,强度越强,不稳定增长率越大,而基态PV径向分布对系统最不稳定波动性质起着决定作用.分析不同波数下扰动的发展及不同波数间扰动的相互作用可知,对于宽且实的PV环,系统稳定性主要取决于低波数不稳定,且最不稳定波数扰动的发展具有明显的优势地位;对于窄且空的PV环,系统稳定性主要取决于高波数不稳定,且多个高波数下增长最快模态的不稳定增长率值十分接近.利用模态线性叠加法讨论扰动增长对系统结构变化的影响表明:最不稳定波数的扰动发展对系统结构变化有关键影响,而多个波数的扰动不稳定增长相当时,不同波数的扰动发生相互作用从而影响系统结构变化.最后,利用实际个例模拟资料分析基态PV径向分布及其变化对TC结构和强度的影响表明:TC内核区出现的多边形眼墙结构与当前时刻基态PV径向分布所决定的最不稳定波数有很好的对应关系,同时基态PV径向分布变化所反映出的系统动力稳定性强弱与TC强度发展阶段具有很好的相关性.In previous work,the influence of the basic state Potential Vorticity(PV)profile or the strength of basic state vortex on the stability in Tropical Cyclone(TC)-like vortices has been investigated.In this study,the impact of the basic state PV profile on the perturbation growth and the structural change in vortices are further discussed using a series of numerical simulations.Sensitivity tests of intensity of the basic state vortex to the stability of the system are conducted by setting three different hollow PV structures in a two-dimensional(2D)shallow water barotropic model.The results show that the disturbance growth rates become larger with increasing strength of vortices in the same PV structure.Moreover,the shape of the PV profile is the major factor to determine the stability of a vortex.The disturbances development of different azimuthal Wavenumbers(WNs)and their interaction are analyzed.For thick and filled PV rings,the instability is more likely to occur at lower WNs and the disturbance growth of the Most Unstable Wavenumber(MUWN)is much faster than that of other WNs.For thin and hollow PV rings,the disturbance development depends mainly on the instability of higher WNs and the growth rates of the fastest growing mode(largest dimensionless growth rate)for two or more different WNs are very close.Based on the eigenmode linear superposition method,the role of disturbance growth in the intensity and structureal change in the vortex system is also discussed.It is found that the disturbance development at the MUWN plays a significant role in structural change,and the interactions of disturbance between two or more different WNs are more important as their unstable growth has little difference.To verify the aforementioned discussion,a high resolution dataset from a realistic simulation is used to examine the impacts of the evolution of PV ring on intensity and structural change of TCs.It is shown that the polygonal features appearing in the TC eyewall are highly consistent with the MUWN determined by the radi

关 键 词：基态位涡径向分布 动力不稳定 最不稳定模态 多边形眼墙 

分 类 号：P445[天文地球—大气科学及气象学]