Preliminary results of an experiment to determine initial precedence of organized electrification and precipitation in thunderstorms

Observations of summer thunderstorms developing over Mt. Withington, New Mexico, show that electrification begins early in the cloud's development. Measurements within the cloud and above it show that electric charge accumulations similar in polarity to those of the mature storm begin to form before any echo can be seen with an x-band radar and before any electrical perturbations can be detected on the mountain summit beneath the cloud. Measurements of potential gradient were made within the cloud with radiosondes supported on tethered balloons. It was found that the gradient within the cloud was far larger than that outside the cloud and that it reached values as high as 20 v cm−1 before the appearance of the radar echo. Measurements made from an airplane flying over the top of the growing cloud showed that here the fair weather potential gradient reversed before any radar echo could be seen. The development of the initial electrical activity appeared to be closely related to convective activity as indicated by tension on the line holding the tethered balloon and by the rapid rise of the cloud tops. The initial radar precipitation echo within the cloud was frequently in the form of a hollow inverted cup that usually filled in and became solid in a few minutes.