Abstract
Measurements of the electric potential gradient from a U-2 airplane flying over thunderstorms show that sustained gradients occurred only in the vicinity of convective cloud disturbances that rose above the stratiform anvil cloud. The potential gradient often reversed in polarity immediately after lightning occurred in the cloud. We interpret these effects as indicating the presence of a charged screening layer at the upper cloud boundary.
The observations further suggest to us that Wilson conduction currents flow from thunderstorms to the upper atmosphere for only as long as convection continues.
