Experimental analysis of the electromagnetic characteristics of cloud discharges in the 200 Hz-20 MHz band

Equipment employed for measuring electromagnetic (EM) signatures of lightning and the EM characteristics of the accompanying fields are reviewed, together with data on tropical lightning monitored during the COPT experiment. The signatures were tracked in the 150-20 MHz range with magnetometers featuring 20 nsec sensitivity. The signals were displayed on oscilloscopes whose images were recorded. The traces were analyzed in terms of the current at the base of the stroke, distance of the discharge from the point of observations, and the wave form and amplitude of the EM field at varying distances from the antenna. The type of EMP varied during a strike, displaying, e.g., constant or changing polarity, relatively larger or shorter rise times, and nonrepetitive peak durations. Cloud-cloud lightning generated significantly smaller magnetic fields than cloud-ground lightning.