LIGHTENING

Subject: Geography

Context: Gurugram: 1 dead, 3 injured after lightning strikes tree

Concept:

It is a very rapid and massive discharge of electricity in the atmosphere. It is the process of occurrence of a natural ‘electrical discharge of very short duration and high voltage between a cloud and the ground or within a cloud’, accompanied by a bright flash and sound, and sometimes thunderstorms.
Inter cloud or intra cloud (IC) lightning are visible and harmless.
It is cloud to ground (CG) lightning, which is harmful as the ‘high electric voltage and electric current’ leads to electrocution.

Process:

It is a result of the difference in electrical charge between the top and bottom of a cloud.
The lightning-generating clouds are typically about 10-12 km in height, with their base about 1-2 km from the Earth’s surface. The temperatures at the top range from -35°C to -45°C.
As water vapour moves upwards in the cloud, it condenses into water due to decreasing temperatures. A huge amount of heat is generated in the process, pushing the water molecules further up.
As they move to temperatures below zero, droplets change into small ice crystals. As they continue upwards, they gather mass, until they become so heavy that they start descending.
It leads to a system where smaller ice crystals move upwards while larger ones come down. The resulting collisions trigger release of electrons, in a process very similar to the generation of electric sparks. The moving free electrons cause more collisions and more electrons leading to a chain reaction.
The process results in a situation in which the top layer of the cloud gets positively charged while the middle layer is negatively charged.
In little time, a huge current, of the order of lakhs to millions of amperes, starts to flow between the layers.
It produces heat, leading to the heating of the air column between the two layers of cloud.
It is because of this heat that the air column looks red during lightning.
The heated air column expands and produces shock waves that result in thunder sounds.