Parameterisation of non-inductive charging in thunderstorm regions free of cloud droplets

The study examines the effect of the weak charges transferred during non-inductive interactions between graupel and ice crystals in the absence of cloud droplets on the charge density in the updraughts of vigorous thunderstorms. Two types of parameterisation based on laboratory experiments and on existing published hypotheses for the sign of charge transfer were incorporated into a numerical model of a thunderstorm. The model is with parameterised microphysics and employs the concept of successive thermals rising through the same volume with two regions identified: an updraught simulated by successive ascending thermals and a non-active cloud mass formed from the debris of previously risen and stopped thermals. The charge distribution in two simulated thunderstorms with the new parameterisations are compared and contrasted with the case for zero charge transfer in regions with no liquid water present, LWC = 0. The study shows that the small charges separated in the absence of cloud droplets have a certain influence on the charge density in the upper part (above the - 40 °C level) of the updraughts of vigorous thunderstorms. © 2006 Elsevier B.V. All rights reserved.