Posted on by Insights Editor
Print Friendly, PDF & Email

WMO findings on lightning strikes

Topics Covered: Important Geophysical phenomena.

WMO findings on lightning strikes

Highlights:

  1. Brazil recorded a lightning strike that travelled a distance of 709 kilometres in 2018.
  2. The previous record for the longest detected distance for a single lightning flash was for 321 km on June 20, 2007, across the US state of Oklahoma.
  3. Brazil has the highest incidence of lightning in the world — an average of 77.8 million strikes per year.
  4. Argentina recorded a strike that lasted for 16.73 seconds in 2019.
  5. 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.
  6. The lightning flashes that have now entered the record books are known as ‘Megaflashes’ in scientific parlance.

Lightning strikes in India:

  1. Bihar is second after Uttar Pradesh with the maximum number of deaths due to lightning.
  2. At least 170 people died in Bihar due to lightning in 2019 between April 1 and July 31.
  3. The number of lightning days across India have been increasing significantly every month.
  4. Lightning strikes kill morepeople in India than any other extreme weather event.

What is lightning?

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.

lighting

How does it strike?

  1. 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.
  2. 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.
  3. 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.
  4. This leads to a system in which, simultaneously, smaller ice crystals are moving up and bigger crystals are coming down.
  5. 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.
  6. 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.
  7. 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?

  1. 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.
  2. There is a greater probability of lightning striking tall objectssuch 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.

InstaLinks:

Prelims Link:

  1. How lightning strikes?
  2. What are megaflashes?
  3. Is earth a good conductor of electricity?
  4. Types of clouds.
  5. Lightning strikes in India.

Mains Link:

Write a note on how lightning phenomenon.

Sources: down to earth.