Asked by: Anonymous
The most common type of lightning discharge begins with a negatively charged 'stepped leader,' which travels from the base of a cloud to the ground in a series of short steps, changing direction at each step. The physics that underlies the formation of these steps is still not fully understood, but the dominating factors that determine their direction and length are the extremely high electric field at the tip of the leader and the current at its core. The leader is almost invisible to the naked eye and seems to seek out the path of least resistance, which is not necessarily a straight line towards the ground (see www.bit.ly/3WyO14 for a video example). Eventually one branch gets sufficiently close to the ground to induce a rising 'return stroke' that joins up with the original stroke and follows its jiggling path back to the cloud with an awesome release of energy. It is this return stroke that you actually see.