Lightning discharges in the tropics: 1. Whole discharges

The Wilson sphere-electrometer method was used to study the net electrostatic field-changes produced by tropical lightning discharges. A linear equation connecting powers of distance and field-change was obtained for ground discharges to analyze the close discharge data. From more than 3000 discharges recorded in the 37 thunderstorms under observation, it was found that tropical thunderclouds are of positive polarity, and for simple ground discharges the average electric moment destroyed per discharge is about 260 coul km, the height of the charge, 4 km, and the charge transferred, 30 coulombs. For ground components of complex discharges, the average moment, as distinct from simple ground discharges, is about 80 coul km, and the charge transferred, 10 coulombs; both are about one-third the values of simple discharges, and the height of the charge is about 3.7 km. For all discharges reaching the ground, simple and complex, the average moment is about 210 coul km, the charge transferred, about 25 coulombs, and the height of the charge, about 4 km. The average moment of cloud discharges was found to be about 200 coul km, and the charge neutralized, probably about 15 coulombs. The over-all relative frequencies of occurrence of ground and cloud discharges were estimated to be about 1:5. A thundercloud cell was found to discharge in general at a rate of 1 per minute, with a total average charge transfer of about 50 to 200 coul to ground.