1. Lightning phenomenology

1.1 Lightning physics

Lightning is an aerial electrical discharge that allows electrically-charged clouds to transfer some of their charge to the ground, thus compensating for the fair-weather current that is permanently distributed between the electrosphere and the Earth.

Vertical thunderclouds are called cumulonimbus clouds. In cumulonimbus clouds, various electrification mechanisms lead to the separation of electrical charges, thanks to the movement of warm air. Positive charges carried by ice crystals find their way to the top, while water droplets at the base of the cloud are negatively charged. An island of positive charges is also created at the bottom of the cloud, in a region of negative temperatures between – 10 and – 20 °C