Initiation of cloud-to-ground lightning strokes

Using a computer and postulating highly idealized thundercloud conditions, we have modeled the interaction between a population of raindrops and a region of high electric field. Under favorable circumstances, the interaction produced a downward-moving wave of potential gradient that intensified the preexisting field without apparent limit. The two major parameters that determined the intensification were the raindrop concentration and the amount of immobile negative charge produced by a stressed raindrop. Field intensification seems to depend critically on the peculiar characteristics of a water-drop discharge at the altitude considered, namely the production of large numbers of highly charged negative droplets. Charged raindrops alone could not produce the required effect. It is suggested that the mechanism modeled here could be responsible for the initiation of cloud-to-ground lightning strokes. The mechanism should strongly favor a downward-moving negative discharge.