Studies of the Structure, Evolution and Dynamics of Lower Stratospheric Frontal Zones Associated with Upper-level Jet/Front Systems and their Influence on Tropopause Deformation

对流层顶的形变在各种天气系统的发展中起着重要的作用。在已知的促进局部形变和对流层顶变陡的物理和结构机制中，有高层急流/锋系统（ULJFs）的发展，极地和副热带ULJFs的叠加，以及最近的对流层顶相干扰动（CTDs）对动态对流层顶上已经存在的极地或亚热带潜在温度梯度的侵蚀。从这些角度来看，对流层顶变陡必然涉及喷射核心上方平流层下层锋面区的结构和动力学演变。据推测，这种变化会对对流层顶的局部变形产生影响，从而对对流层低层天气系统的发展产生影响。这一猜想，加上之前几乎完全缺乏对这些特征的研究，促使研究人员研究与高层急流/锋系统（ULJFs）相关的平流层低层锋区的结构、演变和生命周期，以及它们对局地对流层顶变形、温带发展、平流层/对流层交换的影响及其与对流层顶相干扰动（CTDs）的关系。调查将采用天气气候学和案例研究两种方法，使用国家环境预测中心的全球最终分析（FNL）数据，以及使用国家大气研究中心的天气研究和预报（WRF）模型对选定事件进行的精细尺度数值模拟的输出。FNL分析将用于研究极端地表气旋形成与对流层顶陡峭度之间的关系，以及研究强和极端CTDs的垂直结构，这些垂直结构被假设对平流层下层锋结构和对流层顶斜率有重要影响。利用选定的ULJF生命周期的精细尺度WRF模拟输出，将研究平流层下层锋面环流对射流核心上方对流层顶局部变形的影响。这一分析将通过分段位涡度（PV）反演得到加强，该反演使用相同的模式输出，将分别用于检查与ULJF对流层上层和平流层下层锋面区扰动PV相关的环流。将这些单独的环流分离开来，将有助于深入了解单独锋面发展的性质，了解每一种演变结构对另一种结构的影响，以及对喷流核心上下对流层顶变形的影响，以及对地表气旋形成的影响。wrf -化学模式将用于研究不同的平流层下层锋面结构及其相关环流对平流层/对流层交换程度的影响。通过涉及研究生和本科生，这项研究将促进这一子领域的发现、学习、教学、培训和多样性。研究结果将通过学术出版物和论文广泛传播。由此产生的对与超短波相关的平流层下层锋区的结构、演化和动力学的进一步了解，将为平流层下层过程在对流层顶变形中的作用提供新的见解，从而推动中纬度地区的敏感天气。因此，这项研究代表了理解一个未被充分研究的问题的第一步，这个问题对温带气旋的生命周期有直接影响。因此，对它的追求可能会通过提高与这些干扰直接或间接相关的天气预报能力，为社会带来好处。

Deformation of the tropopause plays a fundamental role in the development of a variety of weather systems. Among the physical and structural mechanisms known to promote local deformation and steepening of the tropopause are the development of upper-level jet/front systems (ULJFs), the superposition of polar and subtropical ULJFs, and, more recently, the encroachment of coherent tropopause disturbances (CTDs) upon pre-existing polar or subtropical gradients of potential temperature on the dynamic tropopause. When viewed from any of these perspectives, tropopause steepening necessarily involves structural and dynamical evolution of the lower stratospheric frontal zone above the jet core. It is hypothesized that such changes have consequences for the local deformation of the tropopause and, accordingly, for the development of lower tropospheric weather systems. This conjecture, coupled with a nearly complete absence of prior research focus on these features, motivates the research in which the structure, evolution, and life cycle of the lower stratospheric frontal zones associated with upper-level jet/front systems (ULJFs), as well as their influence on local tropopause deformation, extratropical development, stratosphere/troposphere exchange and their relationship to coherent tropopause disturbances (CTDs) will be examined. The investigation will employ both synoptic-climatological and case study approaches using the National Center for Environmental Prediction's Global Final Analysis (FNL) data as well as output from fine-scale numerical simulations of selected events performed using the National Center for Atmospheric Research's Weather Research and Forecasting (WRF) model. The FNL analysis will be used to both examine the relationship between extreme surface cyclogenesis and tropopause steepness as well as to investigate the vertical structure of strong and extreme CTDs which is hypothesized to have an important influence on lower stratospheric frontal structure and tropopause slope. Employing output from fine-scale WRF simulations of selected cases of ULJF life cycles, the influence of lower stratospheric frontal circulations on local deformation of the tropopause above the jet core will be examined. This analysis will be augmented by a piecewise potential vorticity (PV) inversion, performed using the same model output, that will be used to examine the circulations associated with the perturbation PV of the upper tropospheric and lower stratospheric frontal zones of the ULJF, respectively. Isolation of these separate circulations will lend insight into the nature of the separate frontal developments, the influence each evolving structure has on the other, on tropopause deformation above and below the jet core, as well as on surface cyclogenesis. The WRF-Chemsitry model will be used to examine the influence of varying lower stratospheric frontal structures and their associated circulations on the degree of stratosphere/troposphere exchange. By involving both graduate and undergraduate students, the research will advance discovery, learning, teaching, training and diversity within this subfield. The results of the research will be disseminated widely through scholarly publications and theses. The resulting increased understanding of the structure, evolution and dynamics of the lower stratospheric frontal zones associated with ULJFs will provide new insights into the role of lower stratospheric processes in deforming the tropopause and, consequently, in driving the sensible weather in the mid-latitudes. Thus, the research represents first steps towards understanding of an understudied problem with direct impacts on the life cycles of extratropical cyclones. As such, its pursuit potentially will provide a benefit to society by enhancing the ability to forecast weather that is directly and indirectly associated with these disturbances.