Suction Vortices, Spiral Breakdown and Multiple Vortices in Tornadoes

Three-dimensional simulations of idealized, laminar, tornadic vortices under a perpetual buoyancy updraft were presented Fiedler (1998). These simulations are being updated with modern computing power. Simulations at merely twice the resolution used in 1998 now reveal intense suction vortices capped by a helical vortex breakdown. Though the helical breakdown has commonly been studied in an engineering context, those studies have not been focused on its role in maintaining, or limiting, the strong winds at the base of a tornado. That role is the focus in the current study. As these simulations move to higher Reynolds number the 1998 conclusion is still valid: "These results are exactly in line with the deduction of Fujita (1971), who estimated that a suction vortex would have a wind speed twice that of the parent vortex." Plans for studies at still higher Reynolds number, and preliminary results from those simulations, are also presented.

Fiedler, B. H., 1998: Wind-speed limits in numerically simulated tornadoes with suction vortices. Q. J. R. Meteorol. Soc. 124, 2377-2392.

Fujita, T. T., 1971: Proposed mechanism of suction spots accompanied by tornadoes. Preprints of the seventh conference on severe local storms, 208-213.