The favourability of one process over another has fluctuated over time due to the inadequate number of laboratory experiments and scarcity of useful field observations. One clear conclusion is that there is no unique mechanism to generate the required charge under all conditions. For example, the ice-ice process, presently the most favoured, does not explain warm cloud lightning, albeit a not too frequent event. As research develops, the most likely explanation will lie in a combination. The charge buildups in thunderclouds are unstable.
Charge is exchanged by a lightning flash.
Lightning can occur in four ways. Lightning can travel between points within a cloud, from a cloud to clear air, from a cloud to an adjacent cloud, and from a cloud to ground. Besides aviation, these three types of flashes have little impact on man. They exchange charge between the cloud and ground. These flashes affect man greatly, causing injury and death, disrupting power and communications, and igniting forest fires.