Modelling and observations of thundercloud electrification and lightning

A two-dimensional lightning frequency model was applied to two case studies of thunderclouds: 9th July 1981, the CCOPE case, and 19th July 1991, the CaPE case. Factors influencing lightning activity were discussed. Although there was a strong link between updraft and lightning frequency, the relationship was not distinct; the initial environmental conditions, the updraft speed and more significantly the graupel number concentration were shown to have a large effect. The model computations suggested the importance of the 2-mm diameter graupel particles. No definite relationship between lightning frequency and cloud ice content could be established in this study. The results demonstrated the limitations of the current charge transfer parameterisation scheme used, with a more detailed structure being required. However, the model was capable of reproducing a realistic cloud structure and lightning activity using a relatively simple dynamical framework.