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

对流层顶的变形在各种天气系统的发展中起着基本的作用。已知的促进对流层顶局部变形和陡化的物理和结构机制包括高层急流/锋面系统(ULJF)的发展、极地和亚热带ULJF的叠加，以及最近相干对流层顶扰动(CTD)侵占动态对流层顶上先前存在的极地或亚热带位温梯度。从任何一个角度来看，对流层顶变陡必然涉及急流核心上方平流层下部锋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，从而对低对流层天气系统的发展产生影响。这一猜想，加上几乎完全缺乏对这些特征的先前研究，促使研究与高层急流/锋面系统(ULJF)有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/对流层交换以及它们与相干对流层顶扰动(CTD)的关系的影响。调查将使用天气气候学和案例研究方法，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天气研究和预报(WRF)模型对选定事件进行的精细数值模拟的输出。FNL分析将被用来研究极端地面气旋发生和对流层顶陡度之间的关系，以及研究强和极端CTD的垂直结构，假设这对平流层低层锋面结构和对流层顶坡度有重要影响。利用选定的ULJF生命周期实例的WRF细尺度模拟结果，将研究平流层低层锋面环流对急流核心上方对流层顶局部变形的影响。这一分析将通过使用相同的模式输出进行的分段位涡(PV)反演得到加强，该位涡将分别用于检查与ULJF的对流层上层和平流层下部锋区的扰动PV有关的环流。分离这些单独的环流将有助于了解单独锋面发展的性质，每个演变结构对彼此的影响，对急流核心上方和下方对流层顶变形的影响，以及对地面气旋发生的影响。WRF-Chemsitry模式将用来研究平流层低层锋面结构的变化及其相关环流对平流层/对流层交换程度的影响。通过包括研究生和本科生，这项研究将促进这一子领域内的发现、学习、教学、培训和多样性。研究成果将通过学术出版物和论文广泛传播。由此产生的对与超低频辐射有关的平流层低层锋区的结构、演变和动力学的进一步了解，将为了解平流层低层过程在使对流层顶变形，从而推动中纬度地区的敏感天气方面的作用提供新的见解。因此，这项研究是朝着理解一个对温带气旋生命周期有直接影响的未被研究的问题迈出的第一步。因此，它的追求可能会通过提高预报与这些干扰直接或间接相关的天气的能力，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.