Measurement of space charge if the lower atmosphere

Abstract

A double field mill is described which, when, placed at a point above the earth's surface, is automatically brought to the potential of that point and registers the potential gradient. Two such instruments are employed to study space charge values in the first five metres, of the atmosphere •Comparison is made between results obtained using the double mills and an Obolensky-type air filter, which lead to the conclusion that the latter instrument gives incorrect readings in the presence of large small ion concentrations. Space charge studies in fair weather conditions, indicate the presence of a negative charge close to the ground of approximately -50µµC/m(^3)decreasing in the first two metres to aero and having an average value between one and three metres of +3 µµC/m(^3). The average height to which this charge extends is shown to be proportional to the potential gradient, and has it's origin in ionization produced by radioactive substances: in the earth, close to the surface. In disturbed conditions, heavy rain is found to generate a negative space charge of. the order of -1000 µµC/m(^3)arising from a splashing effect at the earth's surface. In snowfalls; charges of +500 µµC/m(^3) originate from the charge on the individual snowflakes and a positive charge left in the air due to rubbing or shattering of the snow as it. is falling. The fair weather results in the first metre show a good agreement with those of Norinder, but higher up show the usual positive charge found by Kahler, Daunderer, Scraae, Obolensky and Brown.