Gabe Garfield
School of Meteorology
The University of Oklahoma, Norman, OK
05 November 2009, 11:30 AM
National Weather Center, Room 5820
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK
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Direct numerical simulations (DNS) and large-eddy simulations (LES) of tornadoes have revealed much regarding the structure and intensity of tornadoes. In particular, it has been shown that tornadoes regularly break the “thermodynamic speed limit” -- the top wind speed attainable by buoyancy supporting a hydrostatic pressure drop -- and might be capable of even higher velocities than currently reported. However, the potentially crucial role of turbulent transport in determining the maximum tornadic velocities is not well-understood.
Various turbulence closures are applied within a 2-dimensional, axisymmetric tornado model. Simulations are performed at very high Reynolds numbers, for varying Coriolis parameter, surface roughness lengths, and choice of closure scheme. Graphical and qualitative comparisons of the parameterizations are made. The results show that the inclusion of turbulence parameterization does not challenge previous predictions of maximum intensity--in fact, simulations indicate that turbulent transport may enhance tornadic velocities. More importantly, the predictions of maximum wind speed in large-eddy simulations are demonstrated to be strongly dependent on the sub-grid closure scheme, which has implications for simulations of tornadoes within numerical weather prediction models.
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