A Refined Charge Distribution in a Stochastic Electrical Model of an Infinite Cloud

The stochastic electrical numerical model of cloud growth and precipitation development of Scott and Levin (1975) has been refined to include a distribution of charge within each size class. Each size class is separated into three subclasses containing negative, neutral and positive charge, respectively. The results indicate that the electric field reaches values of around 4 kV cm−1 within about 1000 s and that both positive and negative charges are carried on the particles. In agreement with the previous model, most precipitation size particles carry negative charges while most smaller cloud particles carry positive charges. However, the electrification shows an enhancement in precipitation in the early stages of cloud development. The effect reverses when the field approaches its maximum value. At that point the electrical forces affect the particle interactions through their fallspeed, and the precipitation rate falls below the corresponding rate in the unelectrified case.