Effect of ice crystal size and graupel velocity on thundercloud electrification

Abstract

A one-dimensional time dependent model for cloud electrification, which includes collision between ice crystal and graupel in the presence of cloud liquid water, has been developed in order to test the importance of various charge transfer parameters. The laboratory measurements .showed that the charge transfer depends on ice crystal size and impact velocity. The generated electric fields have been calculated for various values of size dependency (<i>a</i>), velocity dependency (<i>b</i>), precipitation intensity (<i>p</i>₀), concentration of ice crystals (<i>n</i>) and event probability (<i>p</i>).lt is found that the estimated electric field (4 x 10⁵ Vm^-1), within a time interval of about 1500 s, can be achieved for <i>p</i>₀≥ 30 mmh^-1. The maximum electric field (<i>E</i>_max) is not sensitive to the values of <i>a</i> and <i>b</i>, but its rate of growth is faster if <i>a</i> and <i>b</i> are larger. The obtained results have been discussed in the light of various experimental observations and it has been found that charging rates may be affected by the specified size and velocity dependencies.