INFRASONIC THUNDER: EXPLAINED

The existence of infrasonic pulses induced by lightning within thunderclouds is now firmly established from experimental observation. The observed waveform has a compressive pulse followed by a rarefactive pulse. This is of opposite polarity to that predicted by pre-existing theories. This thesis presents a version of a previous theory modified to explain the difference in polarity. It is shown that these infrasonic pulses are wholly electrostatic in origin and arise out of the interaction of the large space charges inside thunderclouds. The positive part of the pulse is due to the relaxation of the mutual attraction of the negative charge layer and the positive shielding layer beneath it during a lightning event. The negative portion of the pulse is due to the reduction in the mutual repulsion of the charged cloud particles in the negative charge storage layer. A series of calculations, done with spherical charges, is presented that describes the changes in the electrostatic potential energy in a simple thundercloud as the result of the partial neutralization of the stored charge by a lightning flash. These calculations are used to demonstrate that two competing theories, ohmic heating of the air within the charge storage region and rapid charge separation, cannot explain the amplitude of the initial positive excursion in the infrasonic waveform