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研究极端天气事件（EWEs），这里将其定义为一类具有社会破坏性，地理分布广泛，异常持久且气候罕见的高影响天气事件。据推测，行星尺度的波放大和破碎是必要的EWEs的发生，因为由此产生的高振幅的流动模式可能会导致强烈的气旋和反气旋，并随后下游脊放大和阻塞，可以调制的位置风暴路径和大气河流，并建立天气尺度的环境有利于EWEs的发生。拟议的研究扩展了正在进行的NSF支持的调查，由PI和Co-PI对发生在北太平洋东部和北美的高影响天气事件进行调查，这些事件通过罗斯贝波分散沿着北太平洋急流（NPJ）与西北太平洋热带气旋（TC）动态相关：（i）将重点缩小到1979年以来发生在北太平洋东部和北美的高影响天气事件，以注意发生在北美中部和东部的值得注意的冷季EWE，和（ii）扩大TC和高影响天气事件之间的动力联系，以包括热带、中纬度和极地起源的先行扰动，这些扰动在（i）中指定的EWE类发生之前和期间在10-20天时间尺度上调节NPJ的演变。建议的扩展将完成：（一）确定的作用，行星尺度的波放大和打破在随后发生的上述类的EWEs;（二）调查如何气旋和反气旋，以及随后的下游脊放大和阻塞，建立天气尺度的环境有利于上述类的EWEs的发生。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，通过对几个业务全球模型（包括集合预报产品）的技能进行天气学评估，确定限制可预测性的因素，以确定发生在北美中部和东部的“难以预测”的冷季EWE。

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.