Introduction

This chapter is concerned primarily with the artificial initiation (triggering) of lightning discharges from natural thunderclouds by means of the “rocket-and-wire” technique. This technique involves the launching of a small rocket that extends a thin wire (either grounded or ungrounded) into the gap between the ground and a charged cloud overhead. Additionally, other types of ground-based activity used to trigger lightning will be briefly reviewed. We limit the use of the term “triggered lightning” to those discharges intentionally stimulated to occur by ground-based activity, the energy source being a naturally electrified cloud. Laboratory discharges between metallic electrodes, which are often used to simulate lightning effects and whose length can reach some tens and even hundreds of meters (e.g., Anisimov et al. 1988; Mrazek 1998) and discharges of up to 3 m length produced using artificially charged aerosol clouds (e.g., Vereshchagin et al. 1989, 1996; Antsupov et al. 1990, 1991) draw their energy from man-made sources and therefore are not considered here. Upward lightning discharges between a stationary, ground-based object (usually of large height) and a naturally electrified cloud, which are sometimes (e.g., Pierce 1974) referred to as triggered lightning, are considered in Chapter 6.