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.
