Weird Science | The science of lightning
While the exact mechanism of how lightning is created is still a subject of research, one thing's for certain. It can get deadly
Over the last couple of days, Lucknow has witnessed severe bursts of lightning, with one bolt even damaging an elephant statue. Earlier this month, lightning killed 10 people in Odisha, and in July, 21 people were killed in parts of Uttar Pradesh beyond Lucknow.
Lightning kills an estimated 2,500 people in India every year, according to the India Meteorological Department (IMD), quoting data from the National Crime Records Bureau. And, according to the latest Annual Lightning Report by the Climate Resilient Observing-Systems Promotion Council, lightning events in India have increased by 34% between 2021-22 and 2022-23. The ones that cause real damage — the cloud-to-ground strikes — increased by 23%.
What makes lightning so deadly? To understand that, we first need to understand what a bolt of lightning really is.
Simply put, lightning is a spark of electricity that is generated as a result of thundercloud formation. When warm air rises and cools in the atmosphere, the water vapour in it condenses into droplets that accumulate into a cloud. The droplets combine to form larger ones, some of which freeze into ice crystals as the air pushes them higher up. The droplets and crystals eventually become too heavy and fall downwards as hail.
On the way down, they collide against lighter droplets and crystals. This collision causes electrical polarisation in the cloud, with the top acquiring a positive charge and the bottom becoming negatively charged. The exact mechanism behind this remains a subject of continuing research.
One widely accepted theory suggests that the collisions between droplets and crystals knock out electrons (negatively charged particles) from some of them. These droplets and crystals, now positively charged, are pushed ever upward by the air. The released electrons, meanwhile, cluster on the surfaces of other crystals and droplets, not only giving them a negative charge but also making them heavier and carrying them to the bottom of the cloud. This causes the electrical polarisation between the top and the bottom of the cloud, eventually leading to lightning.
The lightning flash can move within the same cloud, between one cloud and another, or to the ground. The last is a lightning strike.
For the lightning to move, the ground has to attract the electric charge. This happens when the bottom of the cloud acquires a negative charge that is high enough to repel the electrons on the earth’s surface thus giving the surface a positive charge. The attraction causes the positive charges from the earth to move up into tall structures like buildings and houses, while the negative charges from the cloud descend towards them. Once they are close enough, a positive charge moves into the air and meets the negative charge, resulting in a lightning flash or a series of flashes.
When does this turn fatal?
Whether you look at the electric potential driving the current (which can be several hundred million volts) or the current itself (an estimated 30,000 amperes), a single lightning flash can kill or injure any person, animal or tree it strikes. However, not all deaths and injuries are through direct strikes by a bolt of lightning.
Other ways lightning can cause harm include the side flash (when lightning strikes a tall object and a flash deflects towards the victim), conduction (when the victim touches an object conducting the current from lighting), and ground current (something to which four-legged animals are particularly vulnerable).
To understand how these indirect strikes can happen, let us look back at a much-publicised lightning strike in 2021, when 18 elephants were killed in Nagaon of Assam. The question many asked then was whether it was even possible for a single bolt of lightning to kill so many elephants. Existing research and previous such instances elsewhere around the world, however, make it clear that it was indeed possible.
Different types of indirect strikes
Side flash: A bolt of lightning might have struck a tall tree, for example, and generated side flashes that could have struck the elephants. Although theoretically possible, this was probably not the case, because there were not too many large trees in the vicinity. In any case, this is something that can happen to people, especially if they take shelter under a large tree during a storm marked by lightning.
Conduction: Did the elephants reach out with their trunks to touch trees that had been struck by lightning, leading to electrocution? The absence of too many large trees may rule this out too. Where humans are concerned, however, conduction can be a real threat. A wire or a metal surface struck by lightning can conduct the electricity, and carry it indoors. Something plugged into an electrical outlet, or even a metal door, can be risky to touch.
Ground current: This was possibly the most likely cause of the elephants' deaths. When an animal’s front and hind feet are far apart (which is true of elephants), there can be a large difference in electric potential between those two spots. If electricity from a lightning flash has been routed into the ground, the potential difference between the two spots can cause a partial current to pass through the four-legged animal’s body. In fact, ground current is said to cause the most injuries and deaths in humans too, besides large farm animals.
How to stay safe
The effects of a lightning strike can be deadly but are usually short-lived. Once a bolt of lightning carrying a negative charge reaches the ground, it neutralises the positive charge that the surface has acquired. The electrical charge travels for some time and distance, depending on the intensity, before it is dissipated (along with the associated energy) into the ground and the atmosphere.
The best way to avoid being struck is to stay indoors during lightning, with obvious precautions such as not touching objects that conduct electricity until the thunderstorm has passed. For those who plan to go outdoors, there is an early warning system, part of the Lightning Resilient India Campaign, a collaboration between the Climate Resilient Observing Systems Promotion Council (CROPC) and the IMD. According to the CROPC annual report, the number of fatalities has fallen in several states as a result of the campaign.
The IMD lists various dos and don'ts to observe if you are outdoors when lightning is in the air. Stay away from high places such as hilltops, tall structures such as buildings or trees, and even water bodies. Avoid touching metallic objects and electric wires. If you cannot find safe shelter, get into the “lightning crouch”: A ball-like position with your head tucked and hands over your ears so that you are down low with minimal contact with the ground.
Kabir Firaque is the puzzles editor of Hindustan Times. His column, Weird Science, tackles a range of subjects from the history of inventions and discoveries to science that sounds fictional, but it isn't