Abstract

A simulation of tornadoes translating over the ground was carried out in a modified Ward simulator. The purpose was to investigate the effects of translation on tornado dynamics. The results are as follows:

• Secondary vortexes were found to be generated by the relative motion between the main vortex and rough “ground.” The secondary vortexes trail the primary vortex. Apparently they feed off the energy of the primary vortex, and achieve a momentary transition state from a single vortex to multiple vortexes.

• The core radius increases with swirl ratio and decreases with surface roughness. Translation causes a local increase in swirl ratio, increasing the core size over that of a stationary vortex.

• The central pressure drop increases with swirl ratio during translation. Translation also causes a steeper pressure gradient on the trailing side of the vortex core. A similar characteristic tilt on the trailing side of the pressure profile has been noted on barograms for real tornadoes.

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