Measurements of precipitation electricity

Abstract

Early workers in Atmospheric Electricity, found that in steady continuous rain, when fields were in the range ±400 V/m, the Potential Gradients at the top and bottom, of a high mast were positive and negative, respectively, giving a charge at top and bottom of negative and positive. This indicates the presence of negative space charge in the layers of air between the ground and the top of the mast. As yet this phenomena has received no satisfactory explanation and the problem in hand was to investigate the origin of this negative space charge. The proposed idea was to measure precipitation currents at the ground and at various heights above the ground, using a 30 metre mast, situated in a field adjoining Durham Observatory. Simultaneous measurements of Potential Gradient would serve to show the height to which the space charge extended. Shielded rain collectors were situated at ground level and at 30 metres above the ground together with Field Mills for Potential Gradient measurements. Precipitation currents and Field changes were recorded photographically by connecting the respective outputs to four mirror galvanometers. The Field Mill amplifiers and a monitoring panel were situated in a separate room at the observatory. Unfortunately, once all the apparatus was in working order, only two periods of suitable conditions arose, The results so obtained could not possibly give any conclusive evidence in view of the small number of readings taken. A large difference in value of the Precipitation Currents at the two levels was observed, and is discussed in Chapter IV. Potential Gradient signs and values were much as expected from previous workers' results.