Improving our Understanding of Tornadic Storms using VORTEX2 Observations and Idealized Simulations

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This research is targeted to improve our understanding of the processes occurring within supercell thunderstorms that control the development of rotation at the surface, its possible intensification, and the evolution of the circulations thereafter using state-of-the-art observations from the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) and a hierarchy of numerical models. The generation of midlevel rotation in supercell storms is well understood, but there are a number of outstanding questions pertaining to the development of rotation at low levels and the subsequent intensification of that rotation to tornado strength.The main objectives of this research are- To examine how low-level circulation in supercells is controlled by the storm environment and buoyancy of the outflow- To investigate how environmental heterogeneity and storm interactions influence the development and evolution of low-level rotation- To determine how surface friction affects the development of near-surface vertical vorticity- To explore the origins of small-scale outflow "surges" and descending precipitation shafts on the supercell's rear flank and their influence on the development and evolution of low-level rotationIntellectual Merit:Despite having a good grasp of how vertical wind shear and instability in a storm's environment promote updraft rotation, scientists still lack a thorough understanding of how many other aspects of a storm's environment, including environmental heterogeneity, influence the development and maintenance of low-level rotation in supercell storms. Even less is known about how storm interactions, sudden precipitation impulses, and outflow surges affect low-level rotation. Moreover, scientists are just now scratching the surface on how surface friction might be an important source of angular momentum for developing tornadoes (as opposed to simply playing an "indirect" role in tornadogenesis by enhancing near-surface convergence of angular momentum that arises through other means).Broader Impacts:A greater understanding of tornado genesis, maintenance, and demise will have a broad impact on our ability to predict and warn of these severe weather events and to reduce casualties. The migration of National Weather Service (NWS) warning issuance from counties to more flexible polygons now affords the opportunity to tailor the size of the warning (and, implicitly, the duration of the warning) to the expected longevity of the tornado. This research may help improve the guidance that can be used by forecasters to anticipate how long a tornado might last. In addition to communicating findings to the academic community at conferences, both PIs have been directly involved with the transfer of new knowledge to the NWS via seminars. Both PIs also have been active in a wide range of outreach activities, including briefing the Congressional Natural Hazards Caucus, briefing the National Academies Board on Atmospheric Sciences and Climate, serving as science advisers for an IMAX film on tornadoes, developing K-12 educational materials, giving talks to nonscientist groups (e.g., elementary schools, storm spotters, etc.), and developing museum exhibits.