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Translations of Encyclopedia about Geology

 

Thunderstorm

A thunderstorm is a meteorological phenomenon, where the air electricity discharges between the clouds or into the ground. This occurs in the form of lightning and thunder, often accompanied by heavy precipitation and high winds.

When the thunderstorm forms due to high heat in the air layers near the earth's surface in combination with high humidity, we classify it as a heat storm. This type of thunderstorms occurs mainly in summertime in the afternoon. Frontal thunderstorms occur due to the transition between two different air masses, for example, when upper air layers cool down on one front due to the penetration of cold air masses. When a thunderstorm is far away, we see only lightning, a lightning storm, but hear no thunder.

Thunderstorms are an everyday occurrence. At any moment somewhere in the world there is lightning and thunder. The sunlight heats the ground. Rising warm air forms cumulus clouds, which may change into cumulonimbus clouds. Formation of thunderstorm clouds is increased by high air humidity, which we feel as sultry air.

The upper parts of a thunderstorm cloud generally carry the positive electric charge, while the lower parts carry the negative charge. This is because rising current transports light ice crystals containing the positive charge, while the heavier, negatively charged drops descend. This tension is neutralised by lightning.

The majority of lightning strikes, approximately 70 percent, never hit the ground, they are spent as cloud-to-cloud lighting. When a lightning strikes the ground, there is first a primary discharge, which creates an electrically conductive path, called stepped leader. The lightning draws a zigzag line from the cloud to the ground. However, the lightning conductor does not hit the ground directly. It is met by the so-called streamer.

When the gap between the stepped leader and the streamer closes and a lightning channel is formed, then the main lighting bolt follows. It starts on the ground and goes upwards. This is the lightning that we see. Its average length is between 1000 to 2000 metres. The intensity of the current may reach up to 2000 amps.

Another form of lightning, about which we know very little, is the ball lightning. Eyewitnesses describe the ball lightning to be the size of a billiard ball, sometimes larger. It is believed to be a mixture of hot gases which forms when, following a lightning discharge, the thunderstorm cloud releases electromagnetic waves.

The fact that during a thunderstorm we notice more the lightning than the thunder is given by the speed of light, which is higher than the speed of sound. The extremely high temperature of the lightning bolt (5.000 to 10.000 degrees Celsius) causes an explosive expansion of the air. This creates a crashing sound we call thunder. If the thunderstorm is far away, we hear the thunder as a deep rolling sound. It is caused by artificial or natural protuberances and clouds deflecting the sound.

Lightning poses a danger that should not be underestimated. In the past, lightning often caused fires, destroying entire cities. By means of a lightning rod, which was invented in the mid-18th century by Benjamin Franklin, this danger has been largely eliminated. Today, the number of people killed by lightning is also substantially lower, because nowadays we are more protected inside the cars than people used to be in the open fields.

In view of the fact, that we are heavily surrounded by electronics, the biggest potential danger is found precisely there. Lightning can destroy computers by passing through the power supply devices directly into the computer. Unfortunately, lightning can also paralyse electronic components of airplanes, which in 1988 in Dusseldorf resulted in a crash of an airplane. Insurance companies draw the attention to the fact, that every year damages to electronic devices caused by lighting cost billions of DM.

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