The Electrical Charge on Precipitation at Various Altitudes and Its Relation to Thunderstorms

Abstract

The free electrical charges on individual precipitation particles were measured at various altitudes up to 26,000 feet by an induction method that avoided touching them. In a weak cold front exhibiting no thunderstorm activity, and having the freezing level at 11,000 feet, positive charges averaging 0.033 e.s.u. were observed from 10,000 to 26,000 feet. Negative charges averaging 0.04 e.s.u. were measured from the surface up to 20,000 feet. Positive charges were not observed below 10,000 feet and negative ones were not detected above 20,000 feet. Between these levels a mixture existed. The free charge on a large number of the particles was so great that the electric field at their surface was an appreciable fraction of the breakdown field for air, showing that powerful electrifying agencies exist even under rather quiet frontal conditions. Electric field measurements on the airplane showed that the particle charges were largely neutralized by nearby charges, presumably on the air or on the tiny cloud droplets. It is shown that the removal of this neutralizing charge will immediately produce thunderstorm electric fields and potentials. A time plot of the electric field on the surface of a flying airplane during the interval of a lightning strike is given.