Collaborative Research: Understanding Tropical Cyclone Energetics and Intensification in Environmental Vertical Wind Shear

环境垂直风切变是热带气旋增强的主要抑制因素，它能使热带气旋发生倾斜。风切变也有利于干空气侵入TC核心区，降低对流上升气流的浮力。然而，在轻度到中度剪切条件下，tc确实会发展甚至经历快速强化（RI）。在这种条件下，特别是在RI条件下，准确预测TC增强的时间和速率，对TC的数值预测提出了很大的挑战。因此，了解克服剪切对TC增强的负面影响的物理过程对TC强度预测的潜在改进非常重要。迄今为止的研究表明，由于表面焓通量的增强而导致的通气减少和边界层恢复等几个过程可以克服切变带来的负面影响，从而导致TC涡的增强。然而，与这些过程相关的TC能量学和TC强化的动力学途径的细节仍然知之甚少。该项目的总体目标是促进对剪切环境中形成阶段后TC强度变化机制的理解。在不同剪切和热力学环境下区分TC增强速率的关键物理过程将为TC强度变化（包括RI和缓慢增强）的业务预测提供有用的指导。为了实现研究目标，该项目旨在利用理想的飓风天气研究与预报（HWRF）敏感性数值实验和HWRF集成数据同化系统（HEDAS）生成的数据，为剪切环境中控制TC增强的关键热力学变化及其动态响应提供新的见解，该系统具有在数值系统中吸收不同时间和空间分辨率的风暴相关观测的能力。对HEDAS数据集和HWRF理想化模拟进行了综合分析。研究活动包括：(a)在湿静态能（MSE）框架内分析发生后阶段的TC能量；(b)利用一种新的诊断工具探索热对流能量学和涡旋上升动力学之间的联系，这种工具可以更好地理解在不平衡框架中由各种动力和热力学强迫驱动的热对流增强；(c)利用包裹轨迹分析研究在剪切环境中减少中低层通风和边界层恢复在TC增强中的作用。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。

Environmental vertical wind shear has long been recognized as a major inhibiting factor for tropical cyclone (TC) intensification since it acts to tilt the vortex. The wind shear also facilitates the dry-air intrusion into the TC core region to reduce the buoyancy of convective updrafts. Yet, TCs do develop or even undergo rapid intensification (RI) in light to moderate shear conditions. An accurate prediction of both timing and rate of TC intensification in such conditions, in particular RI, poses a great challenge in numerical forecasts of TCs. Understanding the physical processes that overcome the shear induced negative effects on TC intensification is, thus, important for the potential improvement of TC intensity forecasts. Research to date showed that several processes, such as the reduction in ventilation and boundary-layer recovery due to the enhancement of surface enthalpy fluxes, could overcome the negative impacts imposed by the shear, leading to the intensification of a TC vortex. However, details in TC energetics and dynamical route to TC intensification associated with these processes remain poorly understood. The overall goal of this project is to advance the understanding of mechanisms underlying the TC intensity change after the genesis stage in a sheared environment. The identified key physical processes that differentiate the TC intensification rates in different shear and thermodynamic environments will provide useful guidance for operational forecast of TC intensity change including both RI and slow intensification.To achieve the research objectives, this project aims to provide new insights into the key thermodynamic changes and their dynamic responses that govern TC intensification in a sheared environment using idealized Hurricane Weather Research and Forecast (HWRF) sensitivity numerical experiments and the data generated by the HWRF Ensemble Data Assimilation System (HEDAS) that possesses the ability to assimilate storm-relative observations with different time and spatial resolutions in the numerical system. Comprehensive analyses on the HEDAS dataset and HWRF idealized simulations are carried out. Research activities include (a) analyses of TC energetics during post-genesis stages within the moist static energy (MSE) framework; (b) Exploration of the linkage between TC energetics and vortex spin-up dynamics using a novel diagnostic tool that can yield an improved understanding of the TC intensification driven by various dynamic and thermodynamic forcing in an unbalance framework; and (c) Investigation of key issues regarding the role of the reduction of mid- and low-level ventilation and boundary-layer recovery in TC intensification in a sheared environment using parcel trajectory analyses.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.