A Comprehensive Observational Examination of the Physical Processes that Link Tropical Cyclone Vortex Alignment to Future Intensity Change

迅速增强的热带气旋或飓风的巨大社会影响不仅因为预测不准确而加剧，给应急管理决策带来挑战，而且由于这些风暴迅速变得更具破坏性，它们也对沿海人口构成重大威胁。在经历快速强化（定义为风暴强度迅速或突然增加）之前，飓风由较弱的热带气旋发展而来，这些热带气旋最初更容易受到周围环境的有害影响。一个重要的环境影响是垂直风切变，这是风的方向或强度随着高度的增加而变化，并可能对飓风的发展产生负面影响。垂直风切变会使中高层风暴环流从低层环流中移位。这种中心的错位允许周围环境中更多不利的干燥空气进入风暴的内核，从而阻止风暴进一步加剧。因此，以前的工作强烈支持这样一种观点，即热带气旋增强的关键步骤是在整个大气深处实现中心对齐。然而，人们仍然不能很好地理解一些最初不对齐的风暴如何或为什么会转变成更垂直对齐的状态并迅速加剧。在最近一些引人注目的美国登陆飓风中，与这种结构转变相关的过程的不确定性造成了相当大的预测挑战，特别是强度变化。该项目将使用一个全面的雷达数据集，在快速增强之前和期间提供与中心对准相关的过程的见解。以前的观测案例研究和理想化的模型模拟已经确定了一个不对齐的热带气旋涡可以向对齐状态过渡的多种途径。然而，人们普遍认为对流驱动的非绝热过程在排列过程中是重要的，无论路径如何。因为所有的热带气旋都在一定程度上具有对流的特征，所以目前还不清楚与涡旋对齐事件相关的降水结构与未对齐的风暴有何精确区别。这种不确定性是这项研究的关键动力。此外，由于这些不同的走向路径只在理想化的建模系统或个别风暴的观测案例研究中被记录，关于降水，特别是弱热带气旋，如何与周围环境相互作用并影响自然界中的涡旋走向路径的可靠结论仍然不明确。因此，本项目旨在通过将涡旋、降水和与给定对齐路径相关的环境特征置于背景中来建立先前的工作。本研究的总体目标是利用一种新的机载和地面多普勒雷达数据库来研究弱热带气旋，该数据库提供了迄今为止最全面的热带气旋结构观测数据库。这种对降水结构的高分辨率评估将有助于揭示三维结构，从中可以确定负责涡旋排列的物理过程。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The vast societal impacts of rapidly intensifying tropical cyclones, or hurricanes, are exacerbated not only due to poor predictions that create challenges for emergency management decisions, but they also pose a significant threat to coastal populations as these storms quickly become more destructive. Prior to undergoing rapid intensification, which is defined as a quick or sudden increase in the strength of the storm, hurricanes develop from weaker tropical cyclones that initially are more susceptible to detrimental influences from the surrounding environment. A significant environmental influence is vertical wind shear, which is a change in the direction or strength of the wind with increasing height, and can negatively impact the development of hurricanes. Vertical wind shear can cause a displacement of the mid–upper level storm circulation from the low-level circulation. This misalignment of centers allows more unfavorable, dry air in the surrounding environment to enter a storm’s inner core, a deterrent to further intensification. Therefore, previous work strongly supports the notion that a key step for tropical cyclone intensification is achieving an alignment of centers throughout the depth of the atmosphere. However, it is still not well understood how or why some initially misaligned storms transition toward a more vertically-aligned state and rapidly intensify. In some recent, notable U.S. landfalling hurricanes, uncertainty over the processes associated with this structural transition has caused considerable forecast challenges, particularly with intensity change. This project will use a comprehensive radar dataset to provide insights on the processes associated with the alignment of centers prior to and during rapid intensification.Previous observational case studies and idealized modeling simulations have identified multiple pathways through which a misaligned tropical cyclone vortex can transition toward an aligned state. However, it is widely believed that convectively-driven diabatic processes are important in the alignment process, regardless of the pathway. Because all tropical cyclones feature convection to some degree, it is unclear how precisely precipitation structures associated with vortex alignment events differ from storms that remain misaligned. This uncertainty is a key motivator for this study. Furthermore, because these different alignment pathways have only been documented either in idealized modeling systems or in observational case studies of individual storms, robust conclusions as to how precipitation, particularly in weak tropical cyclones, interacts with the surrounding environment and affects the vortex alignment pathway in nature remains ambiguous. Therefore, this project aims to build on previous work by contextualizing the vortex, precipitation, and environmental characteristics associated with a given alignment pathway. The overall goal of this research is to investigate weak tropical cyclones using a novel airborne and ground-based Doppler radar database, which provides the most comprehensive observational database of tropical cyclone structure to date. This assessment of precipitation structure at high resolution will help reveal the three-dimensional structure, from which the physical processes responsible for vortex alignment can be determined.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.