An upward advancing column of high ionization (a streamer or arc) that typically ascends from a point on the earth's surface toward a descending stepped leader. The ground streamer usually joins the stepped leader about 50 m above the ground, after which the upward propagating light and current of the return stroke begin. Ground streamers occur because of the very high electric field intensities that build up directly below the descending, charged stepped leader. Often, more than one ground streamer starts up from the general area under a descending leader, but usually only one makes contact with the leader.