Lightening phenomenon

Subject: Science and tech

Context:

In UP, five people were killed and one injured after being struck by lightning in the state.

Concept:

• Lightning is an electrostatic discharge that releases tremendous amount of energy, with the rapid movement of electrons converting air to super heated plasma.
• There are three categories of lightning
• intracloud (IC), which is flashes within a cloud
• cloud to cloud (CC), where lightning jumps from one cloud to another
• cloud to ground (CG), where lightning strikes from the ground.

Mechanism

• A fast, upward movement of air during a thunderstorm, called an updraft, carries with it warm humid air.
• As it moves upward in the cloud, the falling temperature causes it to condense. Heat is generated in the process, which pushes the molecules of water further up.
• As they move to temperatures below zero degrees celsius, the water droplets change into small ice crystals. They continue to move up, gathering mass — until they are so heavy that they start to fall to Earth.
• This leads to a system in which, simultaneously, smaller ice crystals are moving up and bigger crystals are coming down.
• Collisions follow, and trigger the release of electrons , a process that is very similar to the generation of sparks of electricity. As the moving free electrons cause more collisions and more electrons, a chain reaction ensues.
• This process results in a situation in which the top layer of the cloud gets positively charged, while the middle layer is negatively charged.
• The electrical potential difference between the two layers is huge of the order of a billion to 10 billion volts. In very little time, a massive current, of the order of 100,000 to a million amperes, starts to flow between the layers.

• An enormous amount of heat is produced, and this leads to the heating of the air column between the two layers of the cloud. This heat gives the air column a reddish appearance during lightning. As the heated air column expands, it produces shock waves that result in thunder.
• While the Earth is a good conductor of electricity, it is electrically neutral.
• However, in comparison to the middle layer of the cloud, it becomes positively charged. As a result, about 15%-20% of the current gets directed towards the Earth as well. It is this flow of current that results in damage to life and property on Earth.
• There is a greater probability of lightning striking tall objects such as trees, towers or buildings. Once it is about 80-100 m from the surface, lightning tends to change course towards these taller objects.
• This happens because air is a poor conductor of electricity, and electrons that are travelling through air seek both a better conductor and the shortest route to the relatively positively charged Earth’s surface.

The world’s most electric place

• The most lightning activity on Earth is seen on the shore of Lake Maracaibo in Venezuela
• At the place where the Catatumbo river falls into Lake Maracaibo, an average 260 storm days occur every year, and October sees 28 lightning flashes every minute — a phenomenon referred to as the Beacon of Maracaibo or the Everlasting Storm.