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May 30, 2024 - 12:30 pm
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School of Meteorology (Defense)Thesis Defense
Tropopause Polar Vortex Linkages to Arctic and Midlatitude Phenomena
Tomer Burg
Friday, May 30th, 2024
12:30 pm / NWC 5600
Abstract: Tropopause polar vortices (TPVs) are coherent, closed tropopause-based vortices that spend at least 60% of their lifetime poleward of 65° latitude. TPVs are most common in the Arctic, where they are often associated with Arctic cyclones (ACs) which can result in sea ice loss, and less frequently associated with polar lows (PLs), which are mesoscale, short-lived but at times intense cyclones that can result in locally significant societal impacts. TPVs on occasion exit the Arctic into the midlatitudes, where they can lead to major cold air outbreaks (CAOs).
The objective of this dissertation is to improve the knowledge of TPV linkages to ACs, PLs and CAOs, focusing on systematic TPV linkages to rapidly deepening ACs and case studies evaluating the impact of TPV intensity on an AC case, a PL case, and a major CAO. Rapidly deepening ACs were found to be commonly associated with an upstream TPV which becomes vertically aligned with the AC by the end of the rapid deepening episode, with TPVs playing a greater role in AC rapid deepening during summer than winter. Intensifying TPVs associated with an intense AC case resulted in an increased peak deepening rate and earlier peak intensity of the AC, although a smaller impact was found when intensifying a TPV associated with a downstream PL. Ensemble sensitivity analysis revealed greater sensitivity of the PL track and intensity to the environment surrounding the TPV rather than the intensity of the TPV itself.
Finally, an investigation of the role of two merging TPVs in a historic CAO in the southern Great Plains in February 2021 shows both TPVs had a direct role in the evolution of the CAO, but that air parcel trajectories were mostly associated with one TPV instead of being distributed equally between both TPVs. The impact of modifying the TPVs is nonlinear; intensifying both TPVs resulted in an earlier merger and a stronger cold pool but a slower and farther north resultant TPV, while weakening both TPVs resulted in a weaker cold pool. This result differs from past studies of TPV-CAO linkages where a single, fast-moving TPV exhibited a more direct correlation between TPV intensity and CAO magnitude.