Introduction

The term cloud discharges is used to denote three types of lightning: (i) intracloud discharges, those occurring within the confines of a thundercloud, (ii) intercloud discharges, those occurring between thunderclouds, and (iii) air discharges, those occurring between a thundercloud and clear air. It is thought that the majority of cloud discharges are of the intracloud type, although no reliable statistical data are found in the literature to confirm that this is the case. Often the abbreviation IC (for intracloud flash) is used to refer to all cloud flashes. Ogawa and Brook (1964) reported that intracloud and cloud-to-air lightning discharges produced similar overall electric field changes. As discussed in Section 2.7, approximately three-quarters of lightning discharges do not contact ground, although this fraction depends on storm type, the stage of storm development, and possibly other factors. The early stages of thunderstorm development tend to be dominated by cloud discharges. According to Williams et al. (1989), 10 or more cloud flashes may occur before the first cloud-to-ground flash.