Auroral Audibility

Abstract

A comprehensive compilation of reports on auroral sounds ranging from the 16th century to the present have been made. The reports have been evaluated for their accuracy and catalogued according to their locations which range from 55° to 70° geomagnetic latitude. A detailed study showed that significant correlation exists between sunspot cycles, magnetic character figures, and the reports of auroral sound. The duration, quality, and possibly accompanying effects such as odor have been carefully examined. In determining a theoretical explanation, we have considered the psychological effect, tinnitus, meteorological effect, direct transmission, infrasonic waves, emission of radio waves in the audio region, direct perception of electromagnetic radiation, and electric field pressure effect. In considering the direct conversion of electrical energy to sound energy through electrostriction we considered two models, an isothermal and an adiabatic model. Calculations from these models showed that the electric fields are insufficient for producing audible sounds. Our final conclusion is that a fraction of the most intense auroras have associated electric fields which produce induced fields at ground level and that these induced fields in dry, calm weather lead to brush discharges which are audible.