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

这个项目的目标是从现象学的角度调查极端天气事件(EWE)，这里定义的极端天气事件是一类高影响的天气事件，从现象学的角度来看，这些事件具有社会破坏性、地理分布广泛、持续时间特别长、气候罕见等特点。假设行星尺度波的放大和破碎对于EVES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生成和反气旋生成，进而导致下游脊线的放大和阻塞，从而调节风暴路径和大气河流的位置，建立有利于EWE发生的天气尺度环境。这项拟议的研究扩展了NSF支持的对发生在北太平洋东部和北美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的Rossby波扩散动态地与北太平洋西部热带气旋(TCS)联系在一起：(I)将发生在北太平洋和北美东部的高影响天气事件的焦点缩小到自1979年以来发生在北美中部和东部的值得注意的凉季母羊，以及(Ii)扩大TCS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，在(I)中规定的母羊类别发生之前和期间，在10-20天的时间尺度上调节NPJ的演变。拟议的扩展将通过以下方式完成：(1)确定行星尺度波的放大和破裂在随后发生上述类别的母羊中的作用；(2)调查如何建立有利于上述类别的绵羊发生的天气尺度环境；(2)研究气旋发生和反气旋生成以及随后的脊脊扩大和阻断如何建立有利于上述类别的绵羊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母羊进行多尺度调查来实现，并结合这些多尺度调查，通过对几个业务全球模式(包括集合预报产品)对发生在北美中部和东部的选定的“难以预测”的凉季母羊的技术进行天气评估，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.