The local variation of the Earth's electric field

Abstract

Assuming that local diurnal‐variations are small over the oceans, and absent over the polar ice during the winter night, a curve has been adopted which represents the unitary diurnal‐variation for a mean ocean‐field of 129 volts per meter. The unitary variation at each land‐station has been found by multiplying the ocean‐variation by the ratio of the mean land‐gradient at each station to the mean ocean‐gradient. By subtracting these unitary variations from the observed mean curves the local diurnal‐variations have been obtained for 22 stations. Each local variation‐curve has been resolved into a 24‐hour component and a daytime depression‐component. The stations fall into groups according to latitude, and the mean latitude‐stations are of two types depending upon the amount of pollution. A theory is proposed which shows the significance of the components and accounts for the local diurnal‐variation by the cycle of turbulence, convection, and subsidence which is present at all land‐stations on all clear days.