The Contribution of Structure and Evolution of Potential Vorticity Tower to the Intensity Change of Hurricane Wilma (2005)
The Contribution of Structure and Evolution of Potential Vorticity Tower to the Intensity Change of Hurricane Wilma (2005)
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DOI：
10.1002/cjg2.220169
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发表时间：
2015-05
期刊：
影响因子：
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通讯作者：
Liu Shuang;Zhong Wei;Liu Ji-chen;Lu Han-cheng
中科院分区：
文献类型：
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作者：
Liu Shuang;Zhong Wei;Liu Ji-chen;Lu Han-cheng
观测和数值模拟结果表明，位涡塔及其外PV带与飓风眼壁和螺旋雨带具有较好的对应关系。因此，探索PVT的形成演变及其对飓风强度变化的影响已成为国际飓风研究的新课题。本研究采用高分辨率数值模型数据进行动态诊断和相关性分析。对飓风威尔玛（2005）的PVT特征及其演变进行了动态诊断。根据相关理论，重新定义了可定量描述PVT结构的结构参数，并将其应用于实际案例研究。本研究旨在揭示PVT结构及其演化对飓风Wilma（2005）快速强化（RI）的影响。通过对比与PV相关的物理变量变化和Wilma的强度变化，确定对流层上层的PV正异常倾向于在ri前发生。此外，PV异常在RI期随着上层暖核的下沉逐渐减弱，在RI期后消失。对流层中下层PV异常大中心的时间演变与威尔玛的强度变化具有一定的阶段性。中层正PV异常的出现与对流层上层PV异常的沉降和对流活动相关的中层潜热释放密切相关。低层PV异常大中心的强度变化满足动力不稳定判据，是飓风增强的必要条件。由此可见，飓风内核的PV强度和结构变化主要取决于上层暖核的下沉、中层潜热释放和低层动力不稳定。因此，飓风核心的PV强度和结构变化对飓风的RI具有一定的重要性。在不同的RI阶段，PVT的垂直和水平结构也被诊断。结果表明，大PV集中在眼内，且PV结构在全层呈典型的单极PVT（MPVT）特征。RI期由于高层增温、潜热释放和对流垂直混合作用下的空心PVT（HPVT）的积累，涡动力结构的变化导致了中尺度波的不稳定和威尔玛的爆发性增强。随后，大PV不断向眼内混合，径向PV混合增强。这表明眼睛两侧的大PV柱逐渐分解，HPVT转变为MPVT。与此同时，飓风开始稳定下来。综上所述，与中尺度波的传播和不稳定密切相关的低压和高压之间的转变会导致飓风眼壁和螺旋雨带的急剧变化。大PV区的位置和强度在相互转换过程中发生变化，因此在水平方向和垂直方向上都发生了PV混合。与此同时，与PV相关的动力和热力学因素变得异常，导致飓风中动量、热量和水蒸气的重新分布，最终导致飓风强度的快速变化。在模拟飓风的情况下，重新定义了两个理论结构参数：厚度和中空度，从而定量分析了PVT的结构对飓风强度变化的影响。对Wilma（2005）在RI期间的结构参数与强度变化的相关分析表明，结构参数系数与最小海面中心压力变化率均超过99%的置信水平，表明PVT结构与飓风强度变化具有高度的相关性。
Observational studies and numerical models reveal that potential vorticity tower(PVT)and its outer PV bands correspond well with eyewall and spiral rainband in hurricanes.Thus,the PVT formation and evolution and its effect on hurricane intensity change have been explored as a new task in international hurricane research.In this study,high-resolution numerical model data is used to conduct dynamic diagnosis and correlation analysis.Dynamic diagnosis is conducted to depict the characteristics and evolution of the PVT in Hurricane Wilma(2005).According to the correlation theory,the structural parameters that can be used to quantitatively describe the PVT structure are redefined and then applied into a real case study.This study aims to reveal the effect of the PVT structure and evolution on the rapid intensification(RI)of Hurricane Wilma(2005).By comparing the change of physical variables associated with the PV and the intensitychange of Wilma,it is determined that the positive PV anomaly in the upper troposphere tends to occur during the pre-RI period. Moreover,the PV anomaly gradually weakens with the subsidence of upper-level warm core during the RI period and disappears at the post-RI period.The temporal evolution of the PV anomaly large centre in the middle and lower troposphere and the intensity change of Wilma are in phase.The appearance of the mid-level positive PV anomaly is closely related to the subsidence of upper tropospheric PV anomaly and the mid-level latent heat release associated with convective activity.Furthermore,the intensity change of the lower-level PV anomaly large centre satisfies the criterion of dynamic instability,which is the necessary condition for hurricane intensification.Thus,it can be seen that the PV intensity and structural change in the inner core of the hurricane mainly depends on the subsidence of the upper-level warm-core,the mid-level latent heat release and the low-level dynamic instability.Hence,the PV intensity and structural change in the inner core of the hurricane is of some importance to the RI of hurricanes.The vertical and horizontal structures of the PVT at different stages of RI are also diagnosed.Results indicate that the large PV is concentrated in the eye,and the PV structure is characterised by typical monopole PVT(MPVT)in terms of the entire layer during the pre-RI period.As the build-up of hollow PVT(HPVT)under the effect of upper-level warming,latent heat release and vertical mixing of convection during the RI period,the changes of vortex dynamic structure result in meso-scale waves instability and the explosive intensification of Wilma.Subsequently,the large PV is continuously mixed into the eye while the radial PV mixing strengthens.This indicates that the large PV columns on either sides of the eye gradually break down,and the HPVT transforms into the MPVT.Simultaneously,the hurricane begins to stabilise.In conclusion,the transformation between the MPVT and HPVT,which is closely related to the propagation and instability of meso-scale waves,would cause a sharp change in the eyewall and spiral rainbands in hurricanes.The location and intensity of the large PV region change in the process of mutual transformation,so the PV mixing occurs in the horizontal and vertical directions.Meanwhile,the dynamic and thermodynamic factors associated with the PV become anomalous causing the redistribution of momentum,heat and water vapour in the hurricanes,and finally leading to rapid intensity change of hurricanes.Two theoretical structural parameters,thickness and hollowness,are redefined in the simulated hurricane case so that the structural effect of the PVT on the intensity change of hurricanes could be quantitatively analysed.The correlation analysis of the structural parameters and the intensity change of Wilma(2005)during the RI period show that the coefficients of the structural parameters and the change rate of minimum sea surface central pressure exceed the99% confidence level,which indicates the high dependency between the PVT structure and the intensity change of hurricanes.