What is a Lightning Strike?
It is a very rapid and massive discharge of electricity in the atmosphere, some of which is directed towards the Earth’s surface. These discharges are generated in giant moisture-bearing clouds that are 10-12 km tall.
How does it strike?
- The base of these clouds typically lies within 1-2 km of the Earth’s surface, while their top is 12-13 km away. Temperatures towards the top of these clouds are in the range of minus 35 to minus 45 degrees Celsius.
- As water vapor 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.
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 traveling through air seek both a better conductor and the shortest route to the relatively positively charged Earth’s surface.
Highlights of Lightning Strike
- Brazil recorded a lightning strike that traveled a distance of 709 kilometers in 2018.
- The previous record for the longest detected distance for a single lightning flash was 321 km on June 20, 2007, across the US state of Oklahoma.
- Brazil has the highest incidence of lightning in the world — an average of 77.8 million strikes per year.
- Argentina recorded a strike that lasted for 16.73 seconds in 2019.
- The previous record was a single lightning flash that lasted continuously for 7.74 seconds on August 30, 2012, over Provence-Alpes-Côte d'Azur, France.
- The lightning flashes that have now entered the record books are known as ‘Megaflashes’ in scientific parlance.
Lightning Strikes in India
- Bihar is second after Uttar Pradesh with the maximum number of deaths due to lightning.
- At least 170 people died in Bihar due to lightning in 2019 between April 1 and July 31.
- The number of lightning days across India has been increasing significantly every month.
- Lightning strikes kill more people in India than any other extreme weather event.