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

对流层顶的变形对各种天气系统的发展起着基础性的作用。在已知的物理和结构机制，以促进当地的变形和陡峭的对流层顶的上层急流/锋系统（ULJFs）的发展，极地和副热带ULJFs的叠加，以及最近，相干对流层顶扰动（CTD）的侵犯上预先存在的极地或副热带的位温梯度的动态对流层顶。当从任何这些角度来看，对流层顶陡化必然涉及结构和动力学的演变平流层下部锋区上方的急流核心。据推测，这种变化的对流层顶的局部变形的后果，因此，对流层低层天气系统的发展。这一猜想，加上以前几乎完全没有对这些特征的研究，激发了对与高空急流/锋面系统（ULJF）相关的平流层下部锋面区的结构，演变和生命周期的研究，以及它们对当地对流层顶变形，对流层外发展，平流层/对流层交换及其与相干对流层顶扰动（CTD）的关系。调查将采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的天气研究和预报（WRF）模型对选定事件进行精细尺度数值模拟的输出。FNL分析将用于检验极端地面气旋生成和对流层顶陡度之间的关系，以及调查强和极端CTD的垂直结构，假设其对平流层下部锋面结构和对流层顶斜率具有重要影响。利用细尺度WRF模拟ULJF生命周期的选定案例的输出，低平流层锋面环流对急流核心上方对流层顶局部变形的影响将被检查。这种分析将增加分段位涡（PV）反演，使用相同的模式输出，将被用来检查与扰动PV的ULJF的对流层上部和平流层下部锋区，分别环流。分离这些单独的环流将有助于深入了解单独的锋面发展的性质，每个演变的结构对其他结构的影响，对急流核心上方和下方的对流层顶变形，以及对表面气旋生成的影响。WRF-Chemsitry模式将用于研究平流层下部锋面结构及其相关环流的变化对平流层/对流层交换程度的影响。通过涉及研究生和本科生，研究将推进发现，学习，教学，培训和多样性在这个子领域。研究结果将通过学术出版物和论文广泛传播。由此增加的结构，演变和动力学的平流层较低的锋区与ULJFs的了解将提供新的见解平流层较低的过程中变形对流层顶的作用，因此，在驱动中纬度地区的明智的天气。因此，这项研究代表了理解一个未充分研究的问题的第一步，该问题对热带气旋的生命周期有直接影响。因此，它的追求可能会通过提高预测与这些干扰直接或间接相关的天气的能力而为社会带来好处。

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.