Study of Processes Leading to Tropical Cyclone Structure and Intensity Changes

这项研究的主要目的是提高对导致热带气旋结构和强度变化的过程的理解。工作假设是：(1)任何环境气流引入准定常的非对称强迫，降低了对称环流的轴对称位势的能力，从而限制了热带气旋在有利的热带海洋条件下所能达到的最大位势强度；(2)外部强迫通过发生在内核区(距气旋中心约200公里范围内)的中尺度过程直接或间接地影响热带气旋的结构和强度变化，包括内、外螺旋雨带和眼壁对流之间的相互作用；同心眼壁循环；以及眼壁破裂和相关的混合过程。将讨论以下科学问题：a.内外螺旋雨带如何形成、传播和相互作用，并与眼壁对流相互作用，影响热带气旋的结构和强度变化？B.环境不对称强迫对热带气旋同心眼壁的形成和随后的眼壁替换有多重要？是什么决定了同心眼壁循环的时间和寿命以及相关的热带气旋强度变化？C.热带气旋的核心对环境气流的垂直切变有何反应？随后风暴结构和强度有何变化？结构和强度的变化对切变的大小和垂直剖面的敏感度如何？为了回答这些问题，首席调查员(PI)将使用其开发的四重嵌套、可移动网格、完全可压缩、非静力热带气旋模式(TCM4)进行一系列精心设计的理想化数值试验。PI将分析西北太平洋和大西洋上热带气旋的卫星和雷达数据以及全球再分析产品，以帮助设计理想的模式初始条件。将对数值结果进行全面的诊断和预算分析，以阐明物理机制。该项目的学术价值：本研究将进一步了解核心动力及其与大尺度环境的相互作用在导致热带气旋结构和强度变化中的作用，特别是它们对同心眼壁结构的形成以及眼、眼壁和风暴尺度环流大小变化的贡献。该项目的更广泛影响：热带气旋结构和强度变化的研究是美国天气研究计划(USWRP)的优先事项，该计划是一个机构间活动，旨在开展必要的研究，以提高对热带气旋运动、结构和强度的理解和预测。这项研究可能有助于更好地理解导致热带气旋结构和强度变化的物理过程，从而改进通过数值模式对热带气旋结构和强度的预测。在开展这项研究的过程中，国际热带气旋研究所将培养一名热带气旋科学方面的研究生，特别是在热带气旋模拟和数值预报领域。

The major goal of this research is to improve understanding of the processes that lead to structure and intensity changes of tropical cyclones (TC). The working hypotheses are (1) any environmental flow introduces quasi-stationary asymmetric forcing which reduce the capability of axisymmetrization potential of the symmetric circulation, and thus limiting the maximum potential intensity that the TC otherwise can achieve given favorable tropical oceanic conditions, and (2) external forcing affects tropical cyclone structure and intensity changes either directly or indirectly through the mesoscale processes occurring in the inner core region (within about 200 km from the cyclone center), including interactions among inner, outer spiral rainbands and eyewall convection; concentric eyewall cycle; and eyewall breakdown and the associated mixing process. The following scientific questions will be addressed: a. How do the inner and outer spiral rainbands form, propagate, and interact with each other and with eyewall convection, affecting tropical cyclone structure and intensity changes? b. How important is the environmental asymmetric forcing to the formation of tropical cyclone concentric eyewall and the subsequent eyewall replacement? What determines the timing and lifetime of the concentric eyewall cycle and the associated tropical cyclone intensity change? c. How does the inner core of a tropical cyclone respond to vertical shear of the environmental flow and what are the subsequent changes in storm structure and intensity? How sensitive are the structure and intensity changes to both the magnitude and vertical profile of the shear? To answer these questions, the Principal Investigator (PI) will use the quadruply nested, movable mesh, fully compressible, nonhydrostatic tropical cyclone model (TCM4) developed by the PI to conduct a series of well-designed idealized numerical experiments. The PI will analyze satellite and radar data for tropical cyclones over both the western North Pacific and Atlantic and the global reanalysis products to help design the idealized model initial conditions. Comprehensive diagnostics and budget analyses of the numerical results will be performed to elucidate the physical mechanisms. The intellectual merit of the project: This research will further understanding of the roles of inner core dynamics and their interaction with the large-scale environment in leading to the structure and intensity changes of tropical cyclones, in particular, their contributions to the formation of concentric eyewall structure and the size changes of the eye, eyewall, and the storm scale circulation. The broader impacts of the project: Research on tropical cyclone structure and intensity changes is of high priority within the U.S. Weather Research Program (USWRP), an interagency activity designed to perform research necessary to improve understanding and prediction of tropical cyclone motion, structure, and intensity. This research potentially will contribute to improved understanding of the physical processes that cause the tropical cyclone structure and intensity changes, leading to improved prediction of tropical cyclone structure and intensity by numerical models. In the process of carrying out this research, the PI will train a graduate student in the science of tropical cyclones, especially in the area of tropical cyclone modeling and numerical prediction.