Sensitivity of Hurricane Intensity Change to Outflow Interactions with the Environment

热带气旋(TC)预报通常分为两个部分：(1)热带气旋路径的预报，定义为气旋中心移动时经过的路径；(2)热带气旋强度的预报，由眼壁底部附近最大持续地面风的强度定义。尽管对热带气旋路径的预报有了很大的改进，但对热带气旋强度和强度变化的准确预报仍然是一个特别具有挑战性的预报问题。热带气旋强度与风暴中心的最低地面气压有关，也与倾覆(即垂直)质量环流有关。翻转环流是指在地面摩擦的作用下流入热带气旋眼壁底部，在对流层上部/平流层下部高空上升，然后流出热带气旋，有效地将地球自转汇聚到眼壁中，形成大风。传统上，热带气旋的强度被解释为风暴中心由高层潜热维持的低地面气压的影响，从而驱动了翻转的环流。这项研究首次将热带气旋强度作为对热带气旋翻转环流强度变化的直接动力响应，并将地面气压变化视为对这些过程的动态响应，而不是原因。这种方法打开了一种真正的可能性，即环境对颠覆环流的抵抗或鼓励是热带气旋加强或挣扎的核心，最终将热带气旋的强化与环境相互作用联系在一起。这项研究的预期成果包括：(1)更深入地了解热带气旋翻转环流如何与热带气旋周围环境中的天气现象相互作用；(2)确定飓风飞机侦察应在何时何地观测热带气旋，以改进对热带气旋强度变化的数值预报指导；(3)在影响沿海社区和海洋利益之前，更好地理解限制热带气旋强度可预测性的因素。该项目将通过云解模拟来研究翻转质量环流强度与TC强度之间的关系。然后，通过伴随敏感性的新应用，TC强度将与流出层环境条件的扰动有关，这些扰动被假设为驱动TC强度变化。该研究将引入新的伴随适当响应函数，作为TC强度和翻转环流强度的度量，明确监测翻转环流与环境的耦合以及翻转环流与TC强度之间的关系。伴随模式输出的评估将通过诊断伴随导出的初始条件扰动的演变来执行，该初始条件扰动被优化配置以激发沿预报轨迹的热带气旋增强。将寻找热带气旋颠覆环流与环境环流的任何耦合的证据，特别是那些先前存在的热带气旋。该项目将在威斯康星大学麦迪逊分校培养本科生和研究生，开发一门新的动态气象学和气候学课程，并在美国气象学会年会上贡献一堂课。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。

Tropical cyclone (TC) prediction is often divided into two components: (1) the prediction of the TC track, defined as the path that the center of the cyclone traces as it moves, and (2) the prediction of the TC intensity, defined by the strength of the maximum sustained surface wind near the base of the eye wall. Despite substantial improvement in the prediction of TC track, the accurate prediction of TC intensity and intensity change remains a particularly challenging forecast problem. TC intensity is related to the minimum surface pressure at the center of the storm, as well as to an overturning (i.e. vertical) mass circulation. The overturning circulation, comprised of inflow into the base of the TC eyewall driven by the effects of surface friction, ascent in the inner eyewall and then outflow away from the TC at high levels in the upper troposphere/lower stratosphere effectively converges the Earth’s spin into the eyewall creating the high winds. Traditionally the intensity of the TC has been explained as an effect of the low surface pressure at the center of the storm, maintained by upper-level latent heating, that consequently drives the overturning circulation. This study for the first time will approach TC intensity as a direct dynamic response to the changing strength of overturning circulation of the TC and treat the surface pressure change as a dynamic response to these processes rather than the cause. This approach opens the real possibility that environmental resistance to, or encouragement of the overturning circulation, is at the core of why a TC intensifies or struggles, ultimately attaching TC intensification to environmental interaction. Anticipated outcomes of this research include: (1) an improved understanding of how the tropical cyclone overturning circulation interacts with weather phenomena in the environment surrounding the TC; (2) identification when and where hurricane aircraft reconnaissance should make observations of tropical cyclones to improve numerical forecast guidance of TC intensity change; (3) greater understanding of factors limiting predictability of TC intensity prior to impacts on coastal communities and marine interests.The project will examine, through use of cloud resolving simulations, the relationships between the strength of the overturning mass circulation and TC intensity. Then, through the novel application of adjoint sensitivities, TC intensity will be related to perturbations made to environmental conditions in the outflow layer that are hypothesized to be driving TC intensity changes. The study will introduce new adjoint-appropriate response functions as measures of TC intensity and the strength of the overturning circulation that explicitly monitor the coupling of the overturning circulation to the environment and the relationship between the overturning circulation and the TC intensity. Evaluation of the adjoint model output will be performed by diagnosis of the evolution of adjoint-derived initial condition perturbations, optimally configured to excite TC intensification along the forecast trajectory. Evidence of any coupling of the TC overturning circulation to environmental circulations, particularly those pre-existing the TC will be sought. The project will train undergraduate and graduate students at University of Wisconsin - Madison, develop a new course of Dynamic Meteorology and Climatology, and contribute a session in American Meteorological Society’s annual meeting.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.