Thunder's a wonder, but lightning is frightening. Meteorologist Al Peterlin answers students' questions about stormy weather phenomena.


Why is there lightning and thunder?

Al Peterlin: Lightning is electricity. In effect, positive charges and negative charges collect in different parts of a cloud — no one really knows exactly how. When enough charges collect, there is a bolt of lightning as the electricity travels between areas of opposite charge. Lightning can flow between clouds or from the cloud to the ground. The lightning jumps through the air, heating the air and making it expand. The air then quickly contracts again as it cools. This movement of air makes the sound wave called thunder. 


How powerful is a bolt of lightning?

Al Peterlin: How's this for an answer you'll have to research? Peak current intensity is of the order 10 to 100 million volts of electricity; the average about 30,000 amps. Energy goes into light and heat with temperatures about 54,000 degrees Farenheit, six times hotter than the sun. 


Does lightning come up from the ground or down from the sky?

Al Peterlin: Both. Lightning streaks inside a cloud, between clouds, and from clouds to the ground. Lightning is a flow of electrons (a negative charge) that zigzags downward in a forked shaped pattern (scientists call this a step leader). As it nears the earth, a stream of positive charges moves up to the charge of electrons (negative charge). When they meet, the power flows. We can't see this because it moves too fast (first stroke). The return flow (positive charge) moves upward more slowly. This is what we see and call lightning (return stroke). If there is a flicker, the upward stroke is repeating the process. 


How many forms of lightning are there?

Al Peterlin: Lightning is, generally, any and all forms of visible electrical discharge produced by thundershowers. There are many names. Directly from the Glossary of Meteorology, different forms include: streak lightning, forked, sheet, heat lightning, and ball lightning. 


What happens to something as lightning strikes it?

Al Peterlin: Lightning is electricity and it flows through the objects it comes in contact with as it moves to the ground. 


What color is lightning and why?

Al Peterlin: Lightning seems to be clear or a white-yellow color, but depending on the background it can appear to be other colors. 


Is it true there are lightning strikes in space?

Al Peterlin: I really don't know. Space could be defined as "at or close to a vacuum" with little to trigger an electrical discharge. Wherever in space there is an atmosphere and convection (tumbling energy), such as on other planets, there probably could be lightning.