Variations in the earth's electric field

Abstract

The nature and causes of variations in the atmospheric electric field as measured at the earth's surface at Durham are investigated. Determinations of the horizontal velocity of travel of variations of periods less than one hour, are made from simultaneous field measurements, using two rotating electrostatic fluxmetera, at two points approximately 100m apart. In fair weather the horizontal speed of the variations is about 1.2 times that of the wind at 10m, suggesting that they are due primarily to the motion of windborne space charges contained in the first 100m of atmosphere. In general the magnitude of the field variations appears to be dependent on the vertical stability of the lower atmosphere. Certain distinctive variations are believed to originate from charged locomotive steam while others appear related to atmospheric convective motion. Measurements in mist and fog support the view that the undulatory nature of the field is due to the horizontal drift of fog of varying thickness or density. Frequently fields below layer clouds show wave-like variations, these are shown to be due to the horizontal motion of cloud layers which contain a periodic spatial distribution of charges. This charge distribution appears to be closely related to visible structural variations in cloud thickness or density. Reasons are given for suggesting that, in stratus cloud, charge is separated by the Wilson process. It is shown that the field disturbances below shower clouds are due mainly to the horizontal drift of the charge system associated with the cloud. Such systems may be complex for appreciable charges appear to exist outside the cloud bounderies. Examples are given of the modification of surface fields by space charges liberated by point discharge processes and it is shown that surface measurements may be critically dependent on the location of the measuring instruments relative to discharging points.