Published: 2007-06-20 09:16:44
Updated: 2007-06-20 09:16:44
Posted June 20, 2007 9:16 a.m. EDT
By STEVEN BLAIR
MIKE MOSS SAYS: Steven, In a way, lightning actually goes in both directions. The most common cloud-to-ground strikes that we are concerned about being hit by originate in the clouds with an ionized channel, usually invisible to us, called a stepped leader. This leader zigs and zags its way toward the surface in a series of split-second starts and stops. When it gets close enough to the surface, a second, much shorter ionized channel, called a streamer, reaches up from the surface and joins up with the stepped leader. At that instant, the path between charge center in the cloud and the ground is completed and the brilliant flash of lightning that we see (called a return stroke) then rushes back up toward the cloud almost instantaneously, and the main body of electrical charges is transferred between the cloud and ground.
The reason we are advised not to be the "tallest object" is that a given stepped leader may induce streamers from several objects below it, and the streamer which ends up connecting to the stepped leader, and thus conducting the main lightning strike, is often the one that emanates from the highest point in the vicinity of the downward moving leader. You would much rather that point be some other object than yourself. Also, note that most lightning safety experts do not suggest lying flat on the ground, but rather crouching as low as possible with only your feet touching the ground. This minimizes the surface area of your body in contact with the ground, which could be helpful if there is a strike nearby and current runs along the ground beneath you.
Finally, regarding you last question, lightning can strike many times in the same place. This is especially true in regards to tall buildings, trees that reach higher than their surroundings and towers of various kinds.