Short-period fluctuations in the fair-weather electric field

Abstract

An electrometer was developed to measure the voltage on a copper screen used as a passive antenna 1 m above the ground. An array of three antennas, arranged first downwind and then crosswind, provided data concerning the time variation of the atmospheric potential gradient in the range of frequencies between 0.004 and 0.06 Hz. Results indicated that the fluctuations in the field are primarily associated with drifting clouds of space charge 135–425 m in diameter that are near the level of the antenna. The drift velocity is essentially equal to the wind velocity. The rate of variations in the electric field associated with processes effecting changes in the distribution of space charge density within the clouds is about one half the rate associated with the drifting clouds or about one third of the locally observed rate of change in the potential gradient. The time scale for the field fluctuations is about 62 s, and the spectral estimates are proportional to ƒ−2.2, where ƒ is the frequency.