A dominant 200-hertz peak in the acoustic spectrum of thunder

Abstract

The dominant peak in the acoustic spectrum of thunder was determined from two independent studies in which two separate techniques were used. The dominant frequency determined by counting zero crossings in a unit time interval on a pressure versus time record peaked in the range 180 to 260 hz. An average power spectrum of twenty-three thunder records showed a broad maximum near 200 hz. In neither study was there any evidence of a dominant infrasonic component (<20 hz), although the equipment used was capable of measuring frequencies as low as 0.1 hz. A theoretical analysis is presented to show that the observed peak occurs in a frequency range expected to be radiated from a cylindrical source with an energy input per unit length equal to that produced by a lightning flash.