Thunderstorm
- What are thunderstorms?
- What causes lightning?
- What causes thunder?
- Storm survival
- Thunderstorm protection

Thunderstorms usually happen when the air is warm and humid. Huge cumulonimbus clouds form in the sky and gusty winds begin to blow. Thunderstorms always include lightning followed by its noisy companion- thunder. A thunderstorm often lasts for less then an hour but it produces the most dramatic type of weather.

Lightning

Lightning occurs when thunderstorms concentrate positive electrical charges in the upper part of cumulonimbus clouds and negative charges in the lower part. When the difference in the charge between the top and bottom of the storm clouds become great enough to overcome air resistance, a sudden and violent electrical discharge occurs in the form of a lightning strike or stroke. Although this lasts for only millionths of a second, the temperature of the stroke rises to 28, 000 degrees Celsius, which causes the flash and the thunderclap.

>> The formation of lightning.

Lightning strokes can have four main effects:
1. People and animals can be electrocuted
2. Material in the path of the lightning strike can be burnt up.
3. The high temperatures of the lightning strike can cause fires
4. Sudden power surges can damage electrical equipment.

Thunder

Lightning can heat the air in its path to 30, 000 degrees Celsius which is 5 times hotter than the Sun's surface. This air expands at great speed and causes the booming noise we call thunder. Thunder can be heard at least 16km away. Lightning and thunder happen at exactly the same time, but you see the lightning before you hear the thunder because light travels faster than sound.

You can work out how far away the thunderstorm is like this: As soon as you see the lightning, start counting the seconds. Stop when you hear the thunder, and divide the number you have counted by three. The answer you get tells you roughly how far you are, in kilometres, from the thunderstorm.

Did You Know?
There are about 16 million thunderstorms a year throughout the world. About 1, 800 storms rage at any moment day or night.

Storm Survival

Lightning always takes the quickest path to the ground. Tall trees and buildings are most at risk. Very few people are struck by lightning but it is dangerous to stand near a tree in a storm. It is safest to be in a car as the lightning will go into the ground through the rubber tyres.

Thunderstorm protection

Towns and cities can be badly damaged by storms. Strong winds can lift the roofs off houses, or destroy buildings completely. Therefore, in order to reduce the damage caused, tall buildings are fitted with lightning conductors to carry lightning safely to the ground. They are also often fitted with anemometers to record the wind speed at roof level. This information is useful to designers when they plan new buildings in a city.

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