The Vorticity Dynamics of Tornadoes: Formation and Maintenance Mechanisms

Texas Tech University, Lubbock TX

Investigators

Abstract

Decades of research on tornadoes has resulted in significant progress in the understanding of how tornadoes form in supercell thunderstorms. However, there are still important questions that have not been answered conclusively. This award will address processes that are related to the development and maintenance of strong near-ground rotation though the use of sophisticated numerical models. The downstream impact of the work is related to improving the ability of weather forecasters to provide more accurate warnings of tornadic activity. The award also provides funding for the training of a postdoctoral researcher and outreach to enhance public understanding of science. The goal of this project is to analyze the various mechanisms that lead to tornado intensification and maintenance. The research team plan to develop an improved theory for tornadogenesis and demonstrate a direct link between the ambient wind profile and the rotation of a tornado. The research pursues two objectives. The first is related to the intensification of the vortex during the transition of the near-ground vorticity dynamics recently discovered by the research team’s group, while the second explores the possibility of ambient vorticity being utilized directly by the tornado. The project will be modelling-based, using the CM1 numerical model at 50m resolution for tornado simulations and 100m resolution for supercell simulations. Six hypotheses would be addressed, 4 related to tornado intensification and 2 regarding the environmental source of vorticity: • The transition toward the in-and-up mechanism results in rapid intensification of the vortex. • This transition is accompanied by a feedback loop at the scale of the vortex. • Whether or not the transition occurs depends on the strength of the initial vortex patch. • Once the in-and-up mechanism is active, the influx of vertical vorticity is no longer required (but not harmful) for vortex maintenance. However, continued influx of vertical vorticity may influence the diameter and intensity of the vortex. • In cases where there is large ambient storm-relative streamwise vorticity at the origin height of the relevant parcels, the barotropic vorticity reinforces, or sometimes dominates, the horizontal near-ground vorticity that has been produced via surface drag and baroclinicity. • In cases where there is ambient storm-relative crosswise vorticity at the origin height of the relevant parcels, the barotropic vorticity weakens the horizontal near-ground vorticity that has been produced via surface drag and baroclinicity. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.