Acoustic spectral analysis of three tornadoes

Abstract

Three sound recordings of tornadoes have been analyzed over the frequency interval between 100 and 2000 Hz. The low-frequency analysis was limited by the spectral response of the microphones, and the upper limit was imposed both by the microphone response and the low signal level. Although the recordings are of low quality and the audio information required major spectral corrections, the data do indicate that the recorded audio emissions from the tornadoes decrease in intensity as a function of increasing frequency. An attempt has been made to correlate the spectra with real (and conjecture) physical properties of the tornadoes. It is clear to us from our objective analysis (and the more difficult subjective evaluation of the recordings) that audible identification of tornadoes is possible, and a study of tornadic sounds might provide a new tool for gaining insight into electrical and mechanical disturbances within a tornado's funnel system. Study of the change in intensity of the sounds emitted by the approaching Guin storm at both high and low frequencies suggests that noises generated by the high speed winds of the tornado cyclone as it scours the ground can be discerned from noises associated with the winds and/or electrical discharges aloft.