Evolution of the lightning stroke

  • once the stepped leader and the return stroke have connected, then electrons from the cloud can flow to the ground, and positive charges can flow from the ground to the cloud.
  • this flow of current from the cloud to the ground is visible at the return stroke.
    • the return stroke is several cm in diameter
  • after the first discharge, it is possible for another leader to propagate down the channel created by the first stepped leader.
  • This new leader is called a dart leader.
  • a subsequent return stroke propagates upward from the ground to the cloud.
  • this can happen 3-4 times in quick succession.

Other types of lightning (see pages 399-400 in the text for more details):

  • forked lightning
  • ribbon lightning
  • bead lightning
  • ball lightning
  • sheet lightning
  • heat lightning
  • St. Elmo's fire

This brief movie shows cloud-to-ground lightning, bolts of cloud-to-cloud lightning, and sheet lightning.

  • lightning produces about 10,000 fires each year

  • $50 million of timber is lost