Investigation of correlations of precipitation electricity to different receivers

Abstract

Measurements were made of the precipitation currents to two identical shielded receivers, constructed according to the design first suggested by Scrase (1958), the earth's electric potential gradient by the Field Mill method, wind speed (using a cup-generator type anemometer), and wind direction (using a rotary potentiometer). The two rain receivers, situated on the flat roof of the Physics building of the Durham University, could be separated horizontally to 50 metres. Using an Elliott 803 digital computer, and by suitable programming, correlation coefficients between the two currents were calculated for various, tine lags between one current and the other, both when the receivers were placed side by side and when separated by 30 metres. The conclusion is reached that no significant difference could be obtained between the correlation coefficients calculated when the receivers were side by side and when they were at such a short distance apart, especially under continuous rainfall conditions. Comparisons were, therefore, made between the precipitation current measured at the Laboratory and that measured 900 metres away. Significant correlation was obtained for instantaneous measurements of the currents when there was no wind, but when the wind was blowing roughly in the direction of the receivers, a definite time lag was found between similar variations of the currents. By applying the same method of correlation-time lag analysis to the current, I, and the potential gradient, F, the author found on one occasion, for sleet and snow, that a significant negative correlation existed between the two parameters for a time lag-..of about 1+0 seconds of the current on the potential gradient, consistent with the idea that the time of fall of precipitation particles should be considered when fitting the functional relationship I = a(F + C): the discrepancy between the values of constants a and C for Summer and Winter results found by Ramsay (1959) could thus be resolved. Some of the records, especially those of rain showers, did show that the space charge on the falling precipitation (as pointed out by Magono and Orikasa (1960)) is an important factor in the "Mirror- Image" phenomenon in low potential gradients, The author's results indicate, also, that the melting process is a plausible mechanism of precipitation charging.