Meteorology: Understanding the Atmosphere            Ackerman and Knox



Thunder and Lightning

We have all experienced the dark, threatening skies and sheets of rain that accompany thunderstorms. Flashes of lightning and blinding rain are cliché in horror films to signal some diabolical deed. In addition to monsters, severe thunderstorms can produce very destructive weather, including lightning, hail, tornadoes, downbursts, torrential rains, and flooding. In addition to threatening life, weather associated with thunderstorms may have a significant impact on the environment: flooding may result in severe soil erosion and lightning strikes may start large fires.

Thunder and lightning are viewed by many religions as the weapons of the gods. Expended to provide a warning or a punishment. Thor, the god of storms and combat in Norse mythology, uses his hammer to rule and in so doing generates thunder and lightning. In mid-evil times some people thought that ringing church bells could bring an end to a thunderstorm. We know today that such an action during a thunderstorm is not a good idea. Nor is it a good idea to stand under a tree during a thunderstorm. If you are in the woods it is better to remember the advice offered by the following weather lore:

Beware the oak,
It draws the stroke;
Avoid the ash,
It draws the flash;
But under the thorn
You'll come to no harm

This page discusses heat lightning and lightning safety.

Lightning occurs in all thunderstorms. Sometimes on a hot evening, lightning appears in the distance with clear sky above and no thunder. While the thunder cannot be heard, it is still exits. Thunder is a sound wave. Sounds traveling through the atmosphere are rapid variations in air pressure and are affected by air temperature. Sound waves travel faster in warm air and slower in cold air. As sound waves propagate through the atmosphere with varying temperatures, the sound waves can change direction, or refract. During summer, the air near the ground is normally warmer than the air above. This causes the sound waves to move away from the surface. The applet below demonstrates this. You can 'drag' the person with your mouse toward or away from the storm by clicking on the person. The sound waves generated by the cloud-to-ground lightning are represented by

Becareful! Each year in the United States lightning kills, on average, 93 people and injures approximately 300 people! Lightning causes several hundred million dollars of property damage each year. While your chances of being struck by lightning are small, about 1 in 600,000, it is important to understand the dangers of one of nature's fireworks and to know basic safety precautions.

To determine the rule of thumb that estimates how far away a thunderstorm is, do the following:

  1. Place the person (click and drag) at the one mile mark.
  2. Once you see a lightning bolt, begin counting (e.g. one-onethousand, two-onethousand,...) and watch the moving sound wave.
  3. Stop counting when the sound wave reaches the person and you hear the thunder.
  4. How many seconds was that?
  5. You should confirm you finding by putting the person at a different distance (say 3.5 miles) and repeat the experiment.

You can move the person around by 'dragging' with the mouse. How many seconds does it take the sound to travel (if you have an audio-enabled computer, you might be able to hear the thunder!)

Before lightning was studied in detail, it was identified by its appearance. Forked, streaked, ribbon, heat, and ball lightning are all lightning that have a different appearance. Forked lightning is commonly shown in photographs and is cloud-to-ground lightning discussed above. Heat lightning is lightning that we see but do not hear the associated thunder. The storm is far away so the thunder is not heard, though the lightning seen. Ribbon lightning is rarely seen. It is cloud-to-ground lightning that occurs when a strong wind is blowing. The wind blows the channel sideways and the return strokes are displaced from one another.

These applets were designed by Tom Whittaker and Steve Ackerman. Thanks also to the Why Files