Diagnosis of the Sensitivity of Type B Cyclones to the Structure and Evolution of Their Upper-Tropospheric Precursors

中纬度地面气旋是地面天气图上常见的“低气压系统”，是降水、强风和气温快速变化的重要组织者和生产者。在这些地面气旋的发展和随后的加强(气旋发生)之前，通常会在地表(即对流层上层和平流层下层)上方9-13公里处发展一个扰动。对气旋发生的研究揭示了两个阶段：第一，与风切变有关的对流层上层锋面的发展和平流层空气向对流层上部和中部的挤压。第二，在气旋发生过程中切变转变为曲率的发展阶段。结果表明，平流层空气进入对流层上层的挤压过程和随后这两个步骤的转换不仅对配置随后气旋发生的上层槽很重要，而且对形成随后气旋的加强速率也很重要。目前还不清楚这些过程是如何协同作用的，也不清楚这些过程中的每个过程在气旋发生过程中各自承担的重要性。该项目将探讨对模拟的上对流层气旋前体初始条件的微小变化如何影响地面气旋的演变。这一拟议项目的结果将使人们深入了解气旋发生之前在对流层上层发生的关键过程的时间和地点，并有可能使人们深入了解在减少与预报这些天气事件强度有关的不确定性方面的改进。该项目进行的基础研究与美国国家科学基金会推动科学进步的使命是一致的。拟议活动的更广泛影响包括培训研究生，组织和主办一次研讨会，以探索气旋及其生命周期的可预测性，并在美国气象学会2022年年会上组织一次关于中纬度生命周期的会议。这项研究建议在模拟观测到的气旋发生事件的案例研究框架内，通过解决温带气旋发展对上层气旋发生前兆演变的敏感性，来调查中纬度气旋发生事件的动力学。该项目结合了两种成熟的诊断技术(即准地转(QG)诊断和伴随得出的预报敏感性)，以了解与中纬度气旋发生有关的一个悬而未决的问题：B型气旋生命周期对气旋上对流层气旋发生前兆扰动的敏感性。诊断方法的独特组合使以前未曾探索过的研究得以了解上层对流层、前气旋发生、正压和斜压增长过程在调节地面气旋生命周期中的单独和相互作用。我们将使用一种新的实验方法，称为灵敏度-扰动-响应-诊断(SPRD)过程。SPRD使用伴随导出的个别情况的灵敏度梯度来构造最佳扰动，以在模拟的气旋生命周期中引起特定的、规定的响应，其中对扰动的气旋演变进行天气尺度QG和位涡(PV)反演诊断。采用这一程序将导致对影响气旋发展的最佳初始时间扰动的结构和演变进行全面检查，并测试伴随模型中的简化假设对每个特定情况的适当性。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。

Mid-latitude surface cyclones, the familiar "low-pressure systems" seen on surface weather maps, are significant organizers and producers of precipitation, strong winds, and rapid changes in temperature. The development and subsequent intensification of these surface cyclones (cyclogenesis) is often preceded by the development of a disturbance 9-13 kilometers above the surface (i.e., the upper-troposphere and lower-stratosphere). Studies of cyclogenesis have revealed two stages: First, development of an upper-tropospheric front and associated extrusion of stratospheric air into the upper and mid-troposphere associated with wind shear in cyclogenesis. Second, a period of development during which shear is converted to curvature in cyclogenesis. It has been shown that processes of extrusion of stratospheric air into the upper-troposphere and the subsequent conversion of these two steps are not only important in configuring the upper-trough for subsequent cyclogenesis, but also in shaping the subsequent intensification rate of the cyclone. It is unclear how these processes synergistically interact or what individual importance each of these processes assumes in cyclogenesis. This project will explore how small changes to the initial conditions of simulated upper-tropospheric cyclone precursors impacts the evolution of the surface cyclone. The results of this proposed project will provide insight into the timing and location of critical processes occurring in the upper-troposphere prior to cyclogenesis and potentially offer insight into improvements in reducing the uncertainty associated with predictions of the intensity of these weather events. The fundamental research conducted in this project is consistent with NSF's mission of promoting the progress of science. The broader impacts of the proposed activity include the training of graduate students, the organization and hosting of a workshop to explore the predictability of cyclones and their lifecycles, and the organization of a session on mid-latitude lifecycles at the 2022 annual meeting of the American Meteorological Society.This study proposes to investigate the dynamics of midlatitude cyclogenesis events by addressing the sensitivity of extratropical cyclone development to the evolution of the upper tropospheric cyclogenetic precursor (UTCP) within the framework of case studies of simulated observed cyclogenesis events. The project combines two well-developed diagnostic techniques (i.e., quasi-geostrophic (QG) diagnostics and adjoint-derived forecast sensitivities) to understand an outstanding issue related to mid-latitude cyclogenesis: the sensitivity of the Type-B cyclone lifecycles to perturbations to the cyclones' upper-tropospheric cyclogenetic precursors. The unique combination of the diagnostic approaches allows for previously unexplored research into understanding the separate and interactive roles of upper-tropospheric, pre-cyclogenetic, barotropic and baroclinic growth processes in modulating surface cyclone lifecycles. We will use a novel experimental approach termed the sensitivity-perturbation-response-diagnosis (SPRD) procedure. SPRD employs adjoint-derived sensitivity gradients for individual cases to construct optimal perturbations that elicit particular, prescribed responses in the simulated cyclone life cycle for which synoptic-scale QG and potential vorticity (PV) inversion diagnostics of the perturbed cyclone evolutions are performed. Employment of this procedure will result in a comprehensive examination of the structure and evolution of optimal initial-time perturbations influencing the cyclone's development, as well as a test of the appropriateness of the simplifying assumptions in the adjoint model to each particular case.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.