A numerical study of thundercloud electrification by graupel-crystal collisions

Abstract

A three-dimensional numerical study to evaluate the electrification caused by only the ice crystal-graupel collisions mechanism is presented. The electrification model includes the dependencies of the magnitude of the separated charge with the crystal size and the relative velocity. In addition, the dependence of the reversal temperature (Tr) with the liquid water content is taken into account following two different experimental data sets: Takahashi [1978] and Saunders et al. [1991]. The particle spectrum is discrete with eight categories. The results show that using the first data set, the tripolar structure is obtained producing magnitudes of the charge densities in accordance with in situ measurements, whereas using the second data set, an inverted dipole (negative on positive) is obtained. Possible causes for these discrepancies are discussed. Also, the charge on individual particles is discussed in the frame of experimental data reported by airborne in situ measurements. Copyright 1997 by the American Geophysical Union.