The relationship between precipitation and lightning in tropical island convection: A C-band polarimetric radar study

[...]the presence of large precipitation-sized ice (i.e., D $ 1 mm) is largely inferred from the temporal evolution of reflectivity at a given environmental temperature and cannot be conclusively determined with conventional radar. [...]a few anecdotal observations of warm cloud lightning have been reported (e.g., Foster 1950; Pietrowski 1960; Lane-Smith 1971) and, in one case, investigated in detail with cloud photography and 3-cm radar (Moore et al. 1960). In merged systems, a new updraftmay rise through cloudy air that already contains high concentrations of ice crystals. Since the NIC mechanism is linearly proportional to ice crystal concentration, charging and hence lightning would be enhanced.