Mechanisms and Variability of Tropical Cyclone Formation under the Upper-Tropospheric Influence

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。飓风和热带风暴有各种不同的发展途径。 人们对热带波浪穿越热带大西洋非常温暖的沃茨形成的风暴给予了极大的关注。 然而，对热带过渡风暴（TT）的关注较少，这种风暴形成于较低的海面温度和高空强风下。 尽管如此，这些复杂的风暴仍可能对社会产生非常大的影响，因为它们更接近美国东南部海岸线，而且通常较难预测。 这个奖项是为了研究这些热带过渡风暴。 这项研究的预期成果将提高TT风暴的预测能力，这对保护生命和财产至关重要。 该项目还将支持研究生，确保下一代科学家的培训。热带过渡风暴（TT）是由于上层槽和主要发展区（MDR）外的低层扰动相互作用而形成的，通常在较冷的沃茨。 两种相互竞争的影响影响TT风暴：阻碍热带气旋发展的高垂直风切变，以及促进对流和热带气旋生成的准地转上升。 该项目将使用观测数据（轨迹、再分析、卫星）和使用WRF-ARW模式的高分辨率数值模拟来测试一组假设，这些假设集中在导致TT风暴形成的动力学、热力学和对流演变上。 待检验的四个假设是：H1：TT第一阶段的对流演变在很大程度上受三维天气流平衡上升的控制，这受到高层和低层扰动的影响，H2：高层位涡（PV）异常和低层扰动之间的相互作用产生了袋状结构（即，H3：袋状结构的形成标志着TT第二阶段的开始，在此期间，热带气旋的形成与MDR风暴中相同的中尺度过程，袋状结构内的差异增湿在对流组织中起着重要作用，H4：一个新的成因潜力指数（GPI），它考虑了对流层的上部和下部条件，将比目前的GPI公式更好地代表TT风暴，并有助于更好地理解和预测TT风暴的变化。该奖项反映了NSF的法定使命，并被认为值得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。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Hurricanes and tropical storms have a variety of different pathways to development. Significant attention has been paid to storms developing from tropical waves crossing the very warm waters of the tropical Atlantic Ocean. However, less attention has been paid to tropical transition (TT) storms, which form over cooler sea surface temperatures and under stronger winds aloft. These complex storms are nonetheless potentially very impactful to society because they develop closer to the southeastern US coastline and are generally less predictable. This award is for the study of these tropical transition storms. The intended output from this study will be improved predictive skill of TT storms which is important for protection of life and property. The project will also support graduate students, ensuring the training of the next generation of scientists.Tropical Transition (TT) storms form due to the interaction of an upper-level trough and a low-level disturbance outside the Main Development Region (MDR), usually in cooler waters. Two competing influences impact TT storms; high vertical wind shear that hinders tropical cyclone development, and quasi-geostrophic ascent that promotes convection and tropical cyclogenesis. This project will test a set of hypotheses centered on the dynamic, thermodynamic, and convective evolution leading to the formation of a TT storm using observational data (track, reanalysis, satellite) and high-resolution numerical modeling simulations using the WRF-ARW model. The four hypotheses to be tested are: H1: Convective evolution at the first stage of TT is largely controlled by the balanced ascent of the 3D synoptic flow, which is affected by both the upper-level and the low-level disturbances, H2: The interaction between an upper-level potential vorticity (PV) anomaly and a low-level disturbance creates a pouch-like structure (i.e., a quasi-closed Lagrangian circulation) in the lower and mid-troposphere, H3: The formation of the pouch-like structure marks the onset of the second stage of TT, during which the tropical cyclone formation proceeds with the same mesoscale processes as in MDR storms and differential moistening within the pouch plays an important role in convective organization, and H4: A new Genesis Potential Index (GPI), which considers both the upper- and lower-tropospheric conditions, will better represent TT storms than the current GPI formula and can help better understand and predict the variability of TT storms.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.