Variation with Temperature of the Electrification Produced in Air by the Disruption of Water Drops and Its Bearing on the Prevalence of Lightning

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Abstract
The total charge carried by the negative ions which are produced in the air when a water drop is disrupted by falling through a horizontal stream of air was measured for different stream velocities at temperatures between 1°C and 63°C. The dependence of this charge upon the size of the drop was found from observations made with drops differing in volume between 0.076 cc and 0.092 cc. For blasts exceeding that necessary just to disrupt the drops, the charge obtained per drop disrupted increases rapidly both with the velocity of the blast and with increase of temperature. The rate at which the charge changes with increase of temperature of the drop depends upon the magnitude of the air stream employed for producing the disruption. For drops of 5.8 mm diameter falling from a height of 2 cm through a horizontal cylindrical stream of 1 cm diameter and having an average velocity of 20 m/sec., the relation between the numbers of negative ions produced per drop disrupted at the temperatures 1.3°C, 24.2°C, 42.1°C and 62.5°C, respectively, was found to be 1: 3: 6.4: 11. In the range of temperatures found in the atmosphere at different times the amount of electrification produced in the air when raindrops are disrupted by air currents of a given magnitude may be at least three times as large when the rain-water is warm as when it is cold. Rain temperature is therefore an important factor in determining the frequency and the intensity of lightning discharges.

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