What is Lightning and How is it Formed?
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Lightning is a powerful force of nature. How is it formed and what are the different types?
Cumulonimbus clouds contain both water and ice. Warm currents and gravity move the ice and water around inside the cloud. The ice particles rub together as they move to create static electricity, which charges the ions in the cloud.
The positively charged ions travel to the top of the cloud and the negatively charged ions to the bottom. When the negative ions have accumulated and become too crowded they jump to another part of the cloud, another cloud or the ground discharging its energy and creating lightning.
Sometimes an invisible path of negatively ionized air descends from the bottom of the cloud. This is called a leader stroke or a stepped leader stroke. The earth’s surface is usually negatively charged, but when a charged storm cloud travels over the ground the positively charged ions start to build up on ground.
When the stepped leader stroke extends close to the ground the positive charge jumps from the earth’s surface and travels back to the cloud.
This forms a path of low electrical resistance, meaning that more charge from the ground travels to the cloud. This is called the return stroke and is the visible part of lightning and lasts for about a quarter of a second.
Different Types of Lightning
Cloud to Ground Lightning
The electrical discharge or lightning strike reaches from the cloud to the ground. This type of lightning poses a risk to humans.
Bead Lightning is one of the rarest forms of lightning. The lightning stroke is broken into evenly space segments. The lightning flash lasts longer than normal (a couple of seconds). As if fades the lightning stroke looks like a string of beads.
Ribbon Lightning can happen during lightning storms with a high crosswind. The return strokes are blown sideways giving the appearance of parallel identical strokes.
Staccato Lightning is a single stroke of lightning with lots of branching. It has a short duration and has a single bright flash.
Forked Lightning is a form of staccato lightning that forms two branches simultaneously.
Anvil Lightning is a common type of cloud to ground lightning. The lightning is positively charged and starts from the top of the cloud. It travels horizontally before it changes direction and travels to the ground.
Cloud to Cloud Lightning
The negatively charged ions at the bottom of the cloud can jump to the positively charged ions at the top forming lightning. This is called intra-cloud lightning and is the most common form of lightning. Less often, the positively charged ions in one cloud can jump to the negatively charged ions in another cloud. This is called inter-cloud lightning. Cloud to cloud lightning does not pose much risk to humans as it happens high in the atmosphere.
Sheet Lightning happens within a cloud and the light emitted by the lightning lights up the whole cloud giving the effect of a sheet of light.
Anvil Crawler or Spider Lightning happens within a cloud. The lightning forms many branches that look like spiders legs, which travel up the sides of the cloud and spreads out at the top.
Interesting Lightning Facts
- Lightning can be up to 20,000 degrees centigrade, hotter than the surface of the sun.
- The air around the lightning heats very quickly causing a shock wave to form, which makes the rumbling noise known as thunder.
- There are approximately 2,000 thunder and lightning storms at any one time on the Earth. They produce 100 strikes a second, which works out to over 8 million lightning strikes a day.
- Each lightning stroke can be 3 miles long and approximately 1cm wide.
- A strike can discharge 1-10 billion joules and 300,000 amps (electrical wires in a house carry 20-30 amps).
- Each strike is made up of 3-12 individual small lightning strikes called “strokes”.
- Lightning can often strike in the same place. The Empire States Building is struck on average twenty thee times a year.
- Lightning can travel as fast as 62,000 miles per second.
- Roy Sullivan of Virginia, USA is in the Guinness Book of Records for being struck by lightning the most, seven times.
Lightning has been observed on other planets in the solar system. Lightning on Jupiter is thought to be 100 times stronger than that on Earth, but it is a much rarer event.
Also an electrical discharge between Jupiter and Io, one of its moons, has often been observed.
Lightning also occurs on Venus and happens very frequently.