HOW LIGHTNING FORMS
1. Ice crystals and raindrops move violently in storm clouds.
2. Because of the motion, electric charges build up at the bottom of a cloud. An opposite electric charge builds up in the ground just under the cloud.
3. Small streamers of sparks called stepped leaders begin to shoot downward in 50-yard leaps, starting in the cloud.
4. As the leaders approach the ground, they meet upward leaders from the ground. The upward leaders most likely come from high places like treetops and tall buildings.
5. When the two streamers meet, their paths form a channel and a lightning bolt is born.
Even though this kind of lightning seems to shoot down from the clouds, what we actually see is the return stroke of electricity flashing upward from the ground.
FULGURITES
Lightning somethimes strikes the ground and tunnels downward into the ground. The intense heat of the electricity causes the sand particles to come togehter of the shape of the bolt's path. The resulting tubular crust is called a fulgurite, after the Latin word for lightning. Some fulgurites are longer than ten feet.
TUCSON, ARIZONA
Spectacular lightning is common in Tucson, Arizona. During the summer's rainy season, thunderstroms can generate more than 10,000 strokes of lightning per night. The summer thunderstorms start when moist air flows in from the Gulf of California and is forced upward by nearby mountains. The rising moisture condenses into thunderhead clouds that tower into the shape of a mushroom, reaching 60,000 feet above the ground. Because of these high clouds, lightning in Tucson is the most dramatic to be found in all of North America.
