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

由于环境垂直风切变对热带气旋(TC)的倾斜作用，长期以来一直被认为是热带气旋(TC)加强的主要制约因素。风切变还有利于干空气侵入热带气旋核心区，降低对流上升气流的浮力。然而，在轻到中等的剪切条件下，TCS确实发展或甚至经历了快速强化(RI)。在这样的条件下，准确预报热带气旋加强的时间和速率，特别是RI，对热带气旋的数值预报提出了巨大的挑战。因此，了解克服切变引起的热带气旋增强负面影响的物理过程对于改进热带气旋强度预报具有重要意义。到目前为止的研究表明，几个过程，例如由于表面热通量的增加而导致的通风减少和边界层恢复，可以克服切变造成的负面影响，从而导致TC涡旋的加强。然而，与这些过程相关的热带气旋能量学和热带气旋增强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切变环境中热带气旋发生阶段后强度变化的潜在机制的理解。不同切变和热力环境下TC增强率差异的关键物理过程将为TC强度变化的业务预报提供有用的指导，包括RI和缓慢增强。为了实现研究目标，本项目旨在利用理想化飓风天气研究和预报(HWRF)敏感性数值试验和HWRF集合数据同化系统(HEDAS)产生的资料，对切变环境中TC增强的关键热力学变化及其动力响应提供新的见解。HWRF集合数据同化系统(HEDAS)具有同化不同时间和空间分辨率与风暴相关的观测的能力。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)在湿静态能量(MSE)框架内分析热带气旋生成后阶段的能量学；(B)利用一种新的诊断工具探索热带气旋能量学和涡旋自旋动力学之间的联系，这可以更好地理解不平衡框架中由各种动力和热力学强迫驱动的热带气旋增强；以及(C)使用地块轨迹分析，研究减少中低空通风和边界层恢复在切变环境中TC强化中的作用的关键问题。该奖项反映了NSF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。

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.