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

迅速加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，而且还对沿海人口构成重大威胁，因为这些风暴很快变得更具破坏性。在经历快速增强(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，最初更容易受到周围环境的不利影响。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发生的变化，可能会对飓风的发展产生负面影响。垂直风切变可导致中高层风暴环流从低层环流移位。这种中心的错位使周围环境中更多不利的干燥空气进入风暴的核心，从而阻止了风暴的进一步加强。因此，以前的工作有力地支持了热带气旋加强的关键一步是实现整个大气深处的中心对齐的观点。然而，人们仍然不清楚一些最初错位的风暴是如何或为什么转变为更垂直排列的状态并迅速加强的。在最近一些值得注意的美国登陆飓风中，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。这个项目将使用一个全面的雷达数据集来提供与快速加强之前和期间中心对准相关的过程的洞察。以前的观测案例研究和理想化的模拟模拟已经确定了未对准的热带气旋涡旋可以通过多条路径转变为对准状态。然而，人们普遍认为对流驱动的非绝热过程在对准过程中是重要的，无论路径如何。由于所有热带气旋都有一定程度的对流特征，目前尚不清楚与涡旋排列事件相关的降水结构与仍未排列的风暴有何确切区别。这种不确定性是这项研究的一个关键动机。此外，由于这些不同的排列路径只被记录在理想化的模拟系统或个别风暴的观测案例研究中，关于降水，特别是在弱热带气旋中，如何与周围环境相互作用并影响自然界中的涡旋排列路径的可靠结论仍然不明确。因此，该项目旨在通过将与给定路线相关的涡旋、降水和环境特征联系起来，在先前工作的基础上再接再厉。这项研究的总体目标是使用一个新的机载和地面多普勒雷达数据库来调查弱热带气旋，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。这项高分辨率的降水结构评估将有助于揭示三维结构，从中可以确定导致涡旋排列的物理过程。这一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智力优势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.