Why do tornadoes make a freight train sound?
There are a number of possible sources for the audible sounds accompanying tornadoes. A paper by Arnold et al. (Journal of the Acoustical Soc. America, Vol.60, pages 584-593) reviews measurements and some of the possibilities. Interactions with the ground will produce strong turbulent eddies which will create a continuous roar. Also, the strong winds interacting with obstacles can produce aeolian tones over a range of frequencies. Even funnels above the ground can produce sound, mainly associated with windshear; but probably also from smaller, imbedded vortices. We have also studied sound from aircraft wake vortices, observing a number of distinct sound generation processes. In other words the sound from a tornado can result from an ensemble of different mechanisms.
