Atmospheric Electrical Mechanical Transfer Currents to Plate Antennas

Abstract

As measured in fair weather by the direct method the air-earth current appeared to depend on the antenna as if convection was affecting the result. A circular plate of 1 m² area, the “open antenna”, was set horizontal and 0.5 m above the ground. A similar but “shielded antenna” was inside an earthed wire cage which reduced the potential gradient by 90 per cent. On 10 summer days the ratio of open antenna average current to shielded antenna average current ranged from 1.1 to 26.0. With conduction alone this ratio should remain near 10. In a wind tunnel two horizontal plates were set one above the other. With the upper at some positive potential V the positive current to the lower was measured when air carrying positive space charge flowed between them at speeds u between 5 and 10ms^–1. The current depended little on V but increased rapidly with u. Both the field and laboratory experiments suggest that current to conventional antennas is due considerably to wind-borne space charge. This “mechanical transfer current” probably contributes nothing to the overall vertical flow of charge and its sign is opposite to that of the conventional eddy diffusion current. It may result in wrong estimates of the air-earth current.