Current and Future Perspectives on North American Polar–Subtropical Jet Superposition Events

Among Daniel Keyser’s many professional accomplishments are his contributions towards improved understanding of frontal dynamics and upper-level jet streaks. Indeed, Daniel’s comprehensive review with Mel Shapiro on upper-level fronts and jet streaks remains one of the leading texts on these features within the synoptic-dynamic community, and is a mainstay of any curriculum in synoptic meteorology. In this presentation, I will review the key dynamical processes that lead to the development of upper-level fronts and jet streaks in the context of a unique subset of jet streaks known as polar–subtropical jet superpositions. Polar–subtropical jet superpositions are unique due to their association with a steep, single-step tropopause structure, enhanced tropospheric baroclinicity, anomalously strong wind speeds, and their potential to induce a variety of high-impact weather events. I will then explore future changes in jet superposition dynamics as a result of anthropogenic climate change, and the resultant potential for those dynamics to induce high-impact sensible weather. In all facets of the presentation, I will reflect on Daniel’s influential approach to mentorship and scholarship, and the lessons that approach can offer to future generations of atmospheric scientists.