Vertical electric currents below thunderstorms and showers

Abstract

Listen

Translate article

In a previous paper an account has been given of apparatus which was found to be suitable for studying the discharge of electricity from a raised metal point in the strong electric fields which occur at the surface of the ground during thunderstorms and showers. The two methods of observation which were employed consisted, first, in measuring the quantity of electricity of each sign which was discharged from the point in a definite period of time, usually the duration of a storm; and secondly, in obtaining a continuous record of the current from the point throughout a storm. Observations on a number of thunderstorms and showers over a period of several months, by the first method, showed that there was a considerable preponderance of upward discharges of positive electricity, indicating that negative gradients of potential predominated at the surface of the ground in such disturbed weather conditions. Some examples of records obtained by the second method were also given. In the present paper, results obtained by the first method over a period of two years are discussed, the observations including all occasions, during that time, on which intense electric fields existed at the observing station for a sufficiently long time to cause a measurable quantity of electricity to be discharged from the point. (The smallest quantity which would be detected by the integrating device is about 0·1 milli-coulomb.) The preponderance of negative potential gradients during periods of intense electric field has been confirmed over the longer period of time. Records obtained by the second method are also described, and their bearing on the question of the polarity of the clouds is discussed. For this purpose, the method of observation is simply a convenient way of obtaining an unambiguous continuous record of the sign of the potential gradient, and a rough estimate of its magnitude, throughout periods of heavy rain. Finally, the problem of the total interchange of electricity between the earth and the atmosphere from known causes is re-discussed, utilising the results already given.