AXISYMMETRICAL NUMERICAL STUDY OF CONVECTIVE CLOUD ELECTRIFICATION

An axisymmetric numerical model of convective electrification is prese nted. The model includes aerosols and small. ions, and it takes into a ccount the difference in mobilities between positive and negative smal l ions. The microphysics is represented by a bulk parameterization inc luding cloud ice, cloud water, hail and rain. Although the results obt ained with this model give the polarity structure most frequently obse rved in clouds, the characteristic times for charging appear to be lon ger than observed with electric fields too weak to produce lightning. The maximum electric held in a typical run reaches 8 kV/m in about 20 min. The charge conversion among particle categories arises as an impo rtant aspect previously overlooked in convective electrification. Base d on these results it appears unlikely that the convective mechanism c ould be considered as the primary charging mechanism. (C) 1998 Elsevie r Science Ltd. All rights reserved.