ELECTRIC-FIELD REGENERATION IN THUNDERSTORMS

Abstract

A season's.record of the electric-field intensity measured on the earth during active thunderstorms is evaluated. The records show that two basic types of storms exist. The most common, or positive, type of active storm systematically induces positive electricity on the earth. The normal systematic increase in electric field is interrupted and partly neutralized or over-neutralized by two types of lightning discontinuity. The most frequent electrical discharges reduce the field only by a small fraction. After four to ten fractional decreases in field, a large change is observed that frequently reverses the field. Negative storms that systematically induce negative charge on the earth occurred infrequently, as did storms of the mixed type. The fundamental cloud-charging mechanism is formulated in quantitative terms. The analysis suggests that two basic time intervals related to the observed field discontinuities are associated with thunderstorm electricity. The first is the regeneration time necessary for the falling rain to raise the electric field to the critical breakdown field for air. The second is the relaxation time required to distribute free electrical charge through the thundercloud by conduction. The regeneration time in active storms is always a fraction of the relaxation time. The quantitative formulation is compared with observed measurements made inside an active thunder-storm, and it is concluded that electrified falling rain is just adequate to describe the observed phenomena.