Lightening and Thunderstorms "EMPOWER IAS"

In news:

• With the monsoon making a slow revival over several parts of India, except the northwest region, there is a rise in lightning-linked deaths.

 

Lightning

Meaning:

• 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.

 

How does it strike?

• As water vapour 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.

 

 

Making of the thunder

• 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.

 

How does this current reach the Earth from the cloud?

• 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.

 

What precautions should be taken against lightning?

• Lightning rarely hits people directly — but such strikes are almost always fatal.
• People are most commonly struck by what are called “ground currents”.
• The electrical energy, after hitting a large object (such as a tree) on Earth, spreads laterally on the ground for some distance, and people in this area receive electrical shocks.
• It becomes more dangerous if the ground is wet (which it frequently is because of the accompanying rain), or if there is metal or other conducting material on it.
• Water is a conductor, and many people are struck by lightning while standing in flooded paddy fields.
• For the reasons given above, taking shelter under a tree is dangerous. Lying flat on the ground too can increase risks.
• People should move indoors in a storm; however, even indoors, they should avoid touching electrical fittings, wires, metal, and water.