INSTANT EXPERT: THUNDER AND LIGHTNING

Thunder and lightning cause both surprise and fascination, but scientists still do completely understand the weather phenomenon in every detail. At any given time there are some 1,800 thunderstorms taking place, with our planet struck by up to 6,000 light

Earth receives 6,000 lightning bolts every minute. Here’s how it happens, and where best to avoid them...

Lightning is assumed to have been an important element in the origin of life, and early humans probably got fire from lightning strikes. They must have considered lightning a blessing from the gods, but now we know that behind thunder and lightning there are natural processes that scientists still do not yet completely understand.

Thunderstorms have to do with the formation of major shower clouds in unstable air. The instability typically involves heating from Earth’s surface in a situation where there is cold air at higher altitudes of the atmosphere. Bubbles of air that become warmer than the surrounding air will rise to form clouds, intensifying upward flow even more. The process is known as convection and is very common – particularly near the Equator and above very large land masses.

Convection is first observed as white, domeshaped cumulus clouds. As the process intensifies, the cloud grows upwards, At some point, the cumulus cloud turns into a shower cloud, which could develop into a thundercloud with a characteristic fan of ice crystals at the top – a cumulonimbus or Cb. But whether a cumulonimbus will cause a thunderstorm or not is difficult to say. Only a few hundred metres of

growth at the top of the cloud might make the difference. Lightning bolts are brief, very violent electric discharges in and between clouds and the surroundings. Lightning bolts can be sparked in the cloud, travel from cloud to cloud, from cloud to air, or end up as lightning strikes between clouds and Earth’s surface. The voltage difference can be hundreds of millions of volts and the amperage some 200,000 amps.

The total energy transmitted in the microseconds during which lightning strikes differs, but the energy corresponds to about five 100W light bulbs turned on for a month. Only a slight fraction of the energy is left where lightning strikes, depending on the electrical resistance of the object struck. The majority of the energy is left in the lightning channel between the cloud and the ground. The temperature of the lightning is 15,000-30,000°C – up to around five times hotter than the Sun’s surface.

The immediate and intense heating of the air around a lightning bolt causes shock waves of sound: thunderclaps. The rumbling is due to the time gap between shock waves from different places in the lightning channel, and to sound waves reflected between clouds and ground.