Interpretation of Thunderstorm Charging by the Polarization–Induction Mechanism

Abstract

The numerical calculations of the combined stochastic growth and induction charging due to drop interactions by Scott and Levin (1975) are analyzed in terms of a phenomenological model. The assumed initial drop size distribution which is concentrated around 20 μm radius evolves at one point in time to a two–peaked distribution at 20 and 150–200 μm, respectively. We show that when this two–peaked distribution occurs, the charging by the polarizationndash;induction mechanism is powerful enough to overcome the several charge reduction mechanisms and to make the actual charge a significant fraction (>1/3) of the saturated charge for a wide range of parameters. The saturation charge is defined as the charge carried on the particle so that no charge will be separated on the average in subsequent interactions as long as the field remains the same. Also, using the actual charge, one predicts in agreement with the numerical calculations what range of parameters permits a full 7–8 e–folds (e⁷–e⁸) of electric field growth to take place before the small droplets are depleted.