An experimental study of the atmospheric electric elements at a rural site in conditions of low air pollution

Abstract

Continuous measurements have been made of the air-earth current density, by the direct method, potential gradient, space charge density, by filtration, and the positive conductivity at Lanehead, situated in the N. Penninea, 440m above sea level. Wind speed, wind direction and rate of rainfall were also recorded, but the measurements used only qualitatively. The problems of making continuous measurements for long periods of time and under difficult weather conditions are discussed. The results can be divided into two types; fair weather and disturbed weather. Of the former, diurnal variations for the one-year period July 1967 to June 1968 were calculated. That of potential gradient shows a close similarity with the variation found on the Carnegie in the Pacific (TORRESON et al, 1946), contrary to expectations for a land station within the austausch region. The air-earth current, on the other hand, is found to depend on the variation in columnar resistance, and its variation is similar to that of the space charge density. The diurnal variation of columnar resistance is estimated, and the role of pollution in controlling this variation is discussed. For disturbed weather, a high positive correlation has been found between space charge density and potential gradient at the ground during steady precipitation. Both were mostly negative during the precipitation, i.e. of opposite sign to the precipitation current. Splashing and point discharge are ruled out as sources of the space charge, so that the results imply some charge separation process within a few tens of metres of the ground giving positive charge to the rain and negative to the air. For 42 periods of steady rain, with some of snow, relations of the form F = Ao + B were calculated and the frequency distributions of A and B are given. The importance of making continuous measurements of several electric parameters is stressed, together with the necessity of using statistical methods to eliminate the effects of unknown variables such as meteorological conditions. An atmospheric electric station has been set up at Lanehead, where air pollution is low, and an atmospheric electric climate for the station has been established.