1. 1 Return Stroke n One of the streamers will meet the stepped leader -- not necessarily the one from the tallest object! n When they meet a pulse of energy flows up toward the cloud (along the ionized path) and toward the ground. n This luminous pulse of electrical energy is called the return stroke. n Occurs very fast -- we see it as a flash!

2. 2 Dart Leader n Often a second series of stepped flow of electrons moves from the cloud toward the ground. n Since the ionized channel already exists, the stepped flow is much faster. n This stepped flow is called the dart leader.

3. 3 Return Stroke n When the dart leader connects with a streamer from the ground (usually along the same path) another return stroke moves toward the cloud and ground. n May get several sets of dart leader/return stroke pairs. n Appears as if the lightning “flashes.”

4. 4 Thunder n Lightning is very hot (~30 000  C). n Violently expanding air causes an audible shock wave. n Nearby Lightning – –Thunder sounds like a “crack” or a loud bang. n Distant Lightning – –Thunder sounds like a rumble. We are hearing the sound from different parts of the lightning channel.

5. 5 Thunder n How far is that lightning???? – –Light travels much faster than sound. – –Count the time between when you saw the flash and heard the thunder. » »5 seconds per mile » »3 seconds per km n No thunder? – –Could be too far away – –Sound could be “bent” by the atmosphere away from you.

6. 6 Thunder 2 km 2.8 km The man hears thunder from the bottom of the lightning channel in 6 seconds. He will continue to hear the thunder until sound from the top of the channel (2.8 km away) in 8.4 seconds. The short sound of thunder indicates a nearby strike.

7. 7 Thunder 2 km 2.8 km The man hears thunder from the bottom of the lightning channel in 8.4 seconds. He will continue to hear the thunder until sound from the top of the channel (4.8 km away) in 14.4 seconds. The long sound of thunder indicates a long strike, probably in-cloud.

8. 8 Lightning During the Day n Lightning is more common during the day. – –This is primarily due to the fact that more convection occurs during the day and at dusk. n Lightning also occurs at night over the oceans. Puzzling! – –The land cools much more than the oceans. Air over the warm oceans destabilizes resulting in nocturnal convection.

9. 9 Lightning Rods n Lightning rods act as locations where streamers can be launched toward descending stepped leaders. n It is better for the lightning rods to be struck, where the electrical energy can be safely transferred to ground, than the house. n The “cone of safety” is about 45 o under the lightning rod.