Lightning
 

Cumulonimbus clouds usually generate lightning, and lightning emits a noise that we call thunder - hence the term ‘thunderstorm’. It is not known exactly how lightning is produced, but it is probably a manifestation of static electricity - a common phenomenon in our surroundings.

Many of us are familiar with the ‘crackle’ that is sometimes produced when combing our hair on dry days, or the mini electric shock we sometimes receive when touching a car that has just come to rest after a journey. This is static electricity, the result of friction between two different substances, such as plastic and hair in the case of the comb, and metal and air in the case of the car.

Meteorologists believe that friction is also important in thunderstorms, with colliding updrafts and downdrafts providing air-to-air friction and contact between ice crystals and water droplets providing another type of friction. As a result, [AQ: OK to add?] massive internal charge differences build up inside the cloud, reach critical levels and finally produce an electrical discharge as natural processes try to equalise these differences. This discharge takes the form of a gigantic electrical spark that we call lightning.

Lightning can discharge between cloud and ground, between cloud and cloud, or between two different areas within a single cloud. A lightning discharge can generate up to 1 billion volts of electricity and explosively heat up the surrounding air to nearly 10 000° C, or twice the temperature of the Sun’s surface.

The almost instantaneous heating of the air produces a shock wave in the air that travels outwards at the speed of sound. This is thunder. The sound of thunder can travel considerable distances, depending on the existing atmospheric conditions, but can often be heard up to 25 km away from the lightning discharge.

To estimate the distance at which a lightning bolt occurs, count in seconds from the moment you see the lightning. Stop counting when you hear thunder, and divide the resulting number of seconds by 3. This will tell you about how far away the lightning discharged. For example, suppose that 15 seconds elapse between the flash of the lightning and sound of the thunder. Divide 15 by 3 to obtain 5; we can therefore conclude that the lightning bolt was about 5 km away.

On average, ten Australians are killed each year by lightning, with several more surviving. However, perhaps the most celebrated lightning strike survivor was from the USA. In 1975, at the Western Open Championship in Illinois, professional golfer Lee Trevino was struck by lightning out on the course. He was later asked what he had learned by the experience and he famously replied, ‘When God wants to play through, you let him play through!’

The world champion lightning strike survivor was undoubtedly US park ranger Roy Sullivan (1912-83), who survived being struck by lightning on seven different occasions. He later killed himself after a failed romance.