On the Disturbance of the Surface Electric Field Caused by Snow Fall

Abstract

Simultaneous observations of the surface electric fields, the charge on snow particles, and the intensity of snow fall were carried out from Mar. 1956 to Apr. 1960 at the Hokkaido University., Sapporo.Analyzing the data of these records, the following conclusions were reached.When the snowfall was weak or steady, positive field patterns of approximately from 200Volt/M to 1, 000Volt/M were observed. When strong steady snowfall or strong snow shower occurred, wave patterns of the surface electric field were observed. Both in the positive and wave pattern of field, roughly inverse relations were found, between the sign of field and of the charge on snow particles. But the time at which the field changed its sign did not exactly coincide with that of change in sign of the charges of snow particles, that is, the changes in the field preceded or followed the charges of the particles. It was observed that continuous fall of snow particles of the same sign changed suddenly to that of particles having the opposite sign. The time interval required for such a change was about 1030 sec. Furthermore, when a remarkable depression or convexity in the field pattern suddenly occurred with out changes in sign, the sign of charge on snow particles often changed.Thus Wilson's ion capture theory can not always be applied to explain the inverse relation mentioned above. The author considered that the snow particles were mainly electrified in the cloud and carried both positive and negative charges simultaneously down to the ground, consequently the cloud may be electrified to the sign opposite to the net charge which was carried down to the ground by the snow particles.When various form of snow particles alternately fell from Cb cloud, some relation between the form of snow particles and the sign of the charge on them were found.During blowing snow, surface electric field reached to about 10 times that of the fair weather value, and charges were observed larger than the largest ones which the author had observed during snowfall up to this time.Considering these results and many other facts which are described in this paper the author concluded that the electrification of snow particles may be caused mainly by friction of the snow particles with each other, and when this effect is weak as in the light snow or ordinary steady snowfall, Wilson's theory may become applicable.