Abstract
The disturbance of the atmospheric electric field caused by the smoke-cloud of the Volcano Asama-yama was observed at Karuisawa Weather Station (about 9 km from the crater), Maebashi Weather Station (about 50 km from the crater) and several other temporary stations around Maebashi. At Karuisawa the disturbance of the electric field is composed, earlier, of a small positive and, later, of a large negative one, but at Maebashi the disturbance is mainly in a negative field.
In the smoke-cloud the screening of ash grains with respect to height is performed by the action of gravity. Smaller ash granules have a positive electric charge and exist in the upper part of the smoke-cloud and larger ash grains have a negative electric charge and exist in the lower part of the cloud. Laboratory experiments on the electrification of volcanic ashes were made and it was confirmed that larger ash grains obtain a negative electric charge and smaller ash granules obtain a positive charge after mutual collision.
Two hypotheses were proposed to explain the fact that near the crater the effect of both positive and negative charges is observed but far from it only the effect of the negative charge is observable.
