A computational study of the relationships linking lightning frequency and other thundercloud parameters

In an effort to optimize the value of global‐scale measurements obtained with the NASA/MSFC satelliteborne Lightning Imaging System (LIS), a simple computational model of thundercloud electrification has been developed, from which it is possible to derive crude relationships between lightning frequency f (which LIS will measure) and cloud parameters such as radar reflectivity Z, precipitation rate P, updraught speed w, cloud radius R, ice‐crystal concentration i and graupel‐pellet concentration Ng. Electric field‐growth is assumed to occur via the non‐inductive charging mechanism, for both Fletcher and Hallett‐Mossop types of glaciation mechanisms. A simple criterion is used to distinguish between cloud‐to‐ground and intracloud lightning discharges. f is found to be especially sensitive to w in situations where, as updraught speed increases, the temperature at balance level, Tbal, of the upper boundary of the charging zone falls. In these circumstances N1 and the sizes of the ice hydrometeors are significantly increased, with a corresponding enhancement of the effectiveness of charge transfer. Over a wide range of conditions, f is found to be roughly proportional to the first power of the parameters R1 Ni Ng and Z and (in some circumstances) to at least the sixth power of w. the relationship between f and P depends critically on whether or not w and Tbal are strongly linked. Hallett‐Mossop glaciation is capable of producing inverted‐polarity lightning from thunderclouds; Fletcher glaciation is not.