Measurements of space charge in the lower atmosphere using double field mills

Two double field mills (Smiddy and Chalmers 1958) have been used to study space charge in the lowest 5 m of the atmosphere. Results in fair weather show small values, often negative, which can be explained in terms of radioactivity of the ground. Comparison with results from filtration apparatus suggest that the latter may be in error when small ions are present in large numbers. Results in light or moderate rain show small space charges, but in heavy rain, negative space charges of the order of – 1,000 μμc m−3 are found, probably formed by splashing. In snowfall, there are charges of both signs of about ± 500 μμc m−3.