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High-resolution simulations of the tornado core using the Fiedler-chamber configuration with turbulence parameterizations

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Monday, 3 November 2014
Capitol Ballroom AB (Madison Concourse Hotel)
David S. Nolan, Univ. of Miami/RSMAS, Miami, FL; and N. A. Dahl and G. H. Bryan

Historically, idealized simulations of the tornado core and its interaction with the earth's surface have been divided into two configurations. The first is a computational version of the Ward tornado vortex chamber, where by rotating fluid is forced into the sides and out the top of a cylindrical container. The second configuration, known as the "Fiedler chamber," uses a larger, closed domain, weak background rotation, and a fixed forcing function along the chamber axis which forces fluid to converge at the center. The Ward configuration is more computationally efficient and allows for more explicit control of the low-level inflow, while the Fiedler chamber allows a more straightforward comparison between peak wind speeds and the so-called "thermodynamic speed limit." However, most of the recent numerical studies using the Ward chamber have used turbulence parameterizations, while those using the Fielder chamber have used large eddy viscosities and no-slip lower boundary conditions. We will present the results of three-dimensional simulations using the Fiedler chamber configuration and a series of turbulence parameterizations of increasing complexity. In particular, we will assess whether the azimuthal-mean, quasi-steady tornado intensity can indeed exceed the thermodynamic speed limit.