Numerical Studies of Tropical Cyclogenesis and Hurricane Andrew (1992)

充分了解热带气旋的成因和核心结构是美国气象研究计划的重点研究领域。在过去的几十年里，虽然已经有许多关于热带气旋发生的研究，但很少有人研究中尺度对流系统(MCSs)的气旋发生和飓风的核心结构。因此，本研究的目的是：a)检验在最佳环境条件下，对流产生的中层中涡能诱发热带气旋发生的假设；b)模拟和研究1992年安德鲁飓风的核心结构和演变。为了深入了解热带气旋发生的性质，将重点放在a)导致热带风暴中层中涡的低层气旋涡度产生和放大的过程，以及b)从具有低层冷池的MCSs转变为以深暖核结构为特征的强烈中气旋的机制。最后，基于模式的诊断将考察海-气相互作用、云-辐射相互作用和中-大尺度相互作用在MCSs向热带风暴转化过程中的作用。具体地说，1)将利用安德鲁和SSM/I资料快速加强期间的飞机观测，通过将模式积分推向预报期内的观测，帮助了解内核结构的可预报性；2)将进行更高分辨率(即2-3公里)的显式模拟，以演示再现内核结构和强度的能力，从而洞察与风暴迅速衰减和爆炸性加深有关的双眼墙周期；3)耦合一个先进的海洋和大气中尺度模式，以研究局地海面温度变化对热带气旋核心结构发展的影响；4)进行各种敏感性模拟，以考察不同的积云参数化方案、浅对流、云微物理过程(水与冰)、云-辐射相互作用和海气相互作用对风暴模拟的影响。令人满意的结果可能为热带气旋发生研究和改进飓风及其登陆结构的数值预报开辟一个新的重要时代。

Adequate understanding of the genesis and inner core structure of tropical cyclones is a high priority research area under the U.S. Weather Research Program. Although there have been numerous studies of tropical cyclogenesis in the past decades, little work has been done to investigate cyclogenesis from mesoscale convective systems (MCSs) and the inner-core structures of hurricanes. Thus, the objectives of this research are to a) test the hypothesis that convectively generated mid-level mesovortices could induce tropical cyclogenesis under optimum environmental conditions; and b) simulate and investigate the inner-core structures and evolution of Hurricane Andrew (1992). To gain insight into the nature of tropical cyclogenesis, emphasis will be placed on a) the processes leading to the generation and amplification of lower-level cyclonic vorticity in tropical storms in relation to mid-level mesovortices, and b) the mechanisms responsible for the transformation from MCSs with a low-level cold pool into intense mesocyclones that are characterized by deep warm-cored structures. Finally, model-based diagnosis will be performed to examine the roles of air-sea interaction, cloud-radiation interaction and meso-larger scale interaction in the transformation from MCSs to tropical storms.For the second objective, numerical studies of hurricane intensity will be performed. Specifically, 1) aircraft observations during the rapid intensification of Andrew and SSM/I data will be used to help understand the predictability of the inner-core structures by nudging the model integration towards the observations during a pre-forecast period; 2) higher resolution (i.e. 2 - 3 km) explicit simulations will be conducted to demonstrate the capability of reproducing inner-core structure and intensity and, thereby, gain insight into the double eyewall cycle that is associated with the rapid decay followed by explosive deepening of the storm; 3) an advanced oceanic and atmospheric mesoscale model will be coupled in order to study the impact of local sea-surface temperature changes on the development of inner-core structures; and 4) various sensitivity simulations will be performed to examine the effects of different cumulus parameterization schemes, shallow convection, cloud microphysical processes (water vs. ice), cloud-radiation interaction and air-sea interaction on the simulation of the storm.Successful completion of the proposed tasks will provide a better understanding of the dynamic effects of MCSs on larger-scale flows, the processes leading to tropical cyclogenesis from MCSs, the inner-core structures of hurricanes and various processes during rapid deepening. Satisfying results may open a new important era for tropical cyclogenesis research and for improving the numerical prediction of hurricanes and their structure at landfall.