From UPSC perspective, the following things are important :
Prelims level : About the report
Mains level : Lightening mapping and its benefit
- For the first time, a report has mapped lightning strikes across the country, and the lives they have claimed.
About the report
- It has been prepared by Climate Resilient Observing Systems Promotion Council (CROPC), a non-profit organisation that works closely with India Meteorological Department (IMD).
What has the report found?
- Lightning strikes have caused at least 1,311 deaths in the four-month period between April and July this year, according to a first-of-its-kind report on lightning incidents in India.
- UP accounted for 224 of these deaths, followed by Bihar (170), Odisha (129) and Jharkhand (118).
- It counted 65.55 lakh lightning strikes in India during this four-month period, of which 23.53 lakh (36 per cent) happened to be cloud-to-ground lightning, the kind that reaches the Earth.
- The other 41.04 lakh (64 per cent) were in-cloud lightning, which remains confined to the clouds in which it was formed.
- Odisha recorded over 9 lakh incidents of lightning (both kinds), the maximum for any state but fewer deaths than Uttar Pradesh, which had 3.2 lakh incidents.
Why are these findings important?
- The report is part of an effort to create a database that can help develop an early warning system for lightning, spread awareness, and prevent deaths.
- Between 2,000 and 2,500 people are estimated as killed every year in lightning strikes in the country.
- It is possible to predict, 30-40 minutes in advance, when a lightning strike heads towards Earth.
- The prediction is made possible through study and monitoring of the in-cloud lightning strikes.
- Timely dissemination of this information can save several lives.
- After carrying out a pilot project in 16 states, the IMD has begun providing lightning forecasts and warnings through mobile text messages from this year.
- However, this is not yet available in all regions, and there isn’t enough awareness as yet on the kinds of action that need to be taken after an alert.
- Lightning is a very rapid and massive discharge of electricity in the atmosphere. Some of it is directed towards the Earth.
- 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.
Mechanism of formation
- 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; a chain reaction is formed.
- The 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 billions of volts. 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 Earth?
- The Earth is a good conductor of electricity. While electrically neutral, it is relatively positively charged compared to the middle layer of the cloud.
- As a result, an estimated 20-25 per cent of the current flow gets directed towards the Earth. It is this current flow that results in damage to life and property.
- Lightning has a greater probability of striking raised objects on the ground, such as trees or buildings.
- Once they are sufficiently near the ground, about 80-100 m from the surface, they even tend to redirect their course to hit the taller objects.
- This is because travelling through air, which is a bad conductor of electricity, the electrons try to find a better conductor and also the shortest route to the relatively positively charged Earth’s surface.
- Thousands of thunderstorms occur over India every year. One thunderstorm can involve more than 100 lightning strikes.