Phenomenological Studies of Cool-Season Extreme Weather Events over Central and Eastern North America on Intraseasonal Time Scales

该项目的目标是从现象学的角度调查极端天气事件（ewe），这里将其定义为一类具有社会破坏性、地理广泛性、异常持久和气候学罕见的高影响天气事件。我们假设，行星尺度的波浪放大和破裂对于EWEs的发生是必要的，因为由此产生的高振幅流型可能导致强烈的气旋形成和反气旋形成，并随后导致下游脊的放大和阻塞，从而可以调节风暴路径和大气河流的位置，并建立有利于EWEs发生的天气尺度环境。拟议的研究扩展了由美国国家科学基金会支持的PI和Co-PI正在进行的关于北太平洋东部和北美发生的高影响天气事件的调查，这些天气事件通过沿北太平洋急流（NPJ）的罗斯比波弥散与北太平洋西部热带气旋（tc）动态相关：(i)将对发生在北太平洋东部和北美的高影响天气事件的关注范围缩小到1979年以来发生在北美中部和东部的值得注意的冷季ewe，以及（ii）扩大tc与高影响天气事件之间的动力联系，包括热带、中纬度、以及在(i)中规定的ewe类别发生之前和期间在10-20天时间尺度上调节NPJ演变的极地起源。拟议的扩展将通过以下方式完成：(i)确定行星尺度波的放大和破裂在随后发生的上述类ewe中所起的作用；（ii）研究气旋形成和反气旋形成以及随后的下游高压脊放大和阻塞如何建立有利于上述类型EWEs发生的天气尺度环境。这些目标将通过使用最先进的全球网格再分析对ewe进行多尺度调查来实现，并与这些多尺度调查相结合，通过对几个运行的全球模式的技能进行综合评估，包括对发生在北美中部和东部的“难以预测”的冷季ewe的综合预测产品，确定限制可预测性的因素。

The goal of this project is to investigate extreme weather events (EWEs), defined here as a category of high-impact weather events that are societally disruptive, geographically widespread, exceptionally prolonged, and climatologically infrequent, from a phenomenological perspective. It is hypothesized that planetary-scale wave amplification and breaking are necessary for the occurrence of EWEs, because the resulting high-amplitude flow patterns may lead to intense cyclogenesis and anticyclogenesis, and subsequently to downstream ridge amplification and blocking, that can modulate the positions of storm tracks and atmospheric rivers and establish synoptic-scale environments favorable for the occurrence of EWEs. The proposed research extends the ongoing NSF-supported investigation by the PI and Co-PI of high-impact weather events occurring over the eastern North Pacific and North America that are linked dynamically to western North Pacific tropical cyclones (TCs) through Rossby wave dispersion along the North Pacific jet stream (NPJ) by: (i) narrowing the focus on high-impact weather events occurring over the eastern North Pacific and North America to noteworthy cool-season EWEs occurring over central and eastern North America since 1979, and (ii) broadening the dynamical linkages between TCs and high-impact weather events to include antecedent disturbances of tropical, midlatitude, and polar origin that modulate the evolution of the NPJ on 10-20 day time scales prior to and during the occurrence of the class of EWEs specified in (i). The proposed extensions will be accomplished by: (i) determining the role of planetary-scale wave amplification and breaking in the subsequent occurrence of the aforementioned class of EWEs; (ii) investigating how cyclogenesis and anticyclogenesis, and subsequent downstream ridge amplification and blocking, establish synoptic-scale environments conducive to the occurrence of the aforementioned class of EWEs. These goals will be addressed by conducting multiscale investigations of EWEs using state-of-the-art global gridded reanalyses and, in conjunction with these multiscale investigations, identifying factors limiting predictability through the synoptic evaluation of the skill of several operational global models, including ensemble forecast products, for selected "hard-to-predict" cool-season EWEs occurring over central and eastern North America.