Learning to tackle lightning and thunderstorms
Learning to live with the powerful and destructive natural phenomena such as lightning, thunderstorm, volcano, earthquake, flood, cyclone, hurricane etc. has been a great challenge for mankind. Inquests have been continuing to recognise and understand these freaks of nature since time immemorial. Acquiring appropriate knowledge is the most powerful tool to mitigate the risks of these natural calamities. Along with the many parts of the world Bangladesh has been frequently experiencing the devastating effects of lightning and thunderstorms in recent years.
According to the Ministry of Disaster Management and Relief lightning strikes killed 2,164 people during 2011 to 2020. The data from 'Save the Society and Thunderstorm Awareness Forum (SSTAF)' showed at least 177 people were killed in between March 31 and June 07 in 2021. And from July to 09 Sept/21, 32 people were killed by lightning strikes according to the media reports. Grave concerns have been growing with the continuous destructive effects of lightning strikes.
Recently I have come across a number of articles published in our national dailies, in online portals, and two academic theses where many writers, academics, meteorologists, researchers and scientists expressed their valuable observations, comments, safety measures and recommendations. It gives us huge information and knowledge to understand the peculiar natural phenomena and develop strategic techniques and skills to save our lives, properties and resources.
What is lightning?
Lightning is a natural phenomenon which develops when the upper atmosphere becomes unstable due to the convergence of a warm, solar heated, vertical air column on the cooler upper air mass. It is a huge electrical spark (discharge) that flows from a cloud (called a cumulonimbus or thunderstorm) to the ground, or within and between clouds, or from the cloud to air. This same updraft gives rise to an electric charge separation which ultimately leads to the lightning flash. Lightning may be of different types such as Cloud-to-Ground (CG), Negative Cloud-to-Ground (-CG), Positive Cloud-to-Ground (+CG), Cloud-to-Air (CA), Ground-to-Cloud (GC) and Intra-cloud (IC).According to the form or appearances lightings have been classified as: 1) Ball lightning, 2) Rocket lightning, 3) Pearl-necklace lightning, 4) Ribbon lightning, 5) Forked lightning, 6) Sheet lightning and 7) Streak lightning
How does lightning form?
'As tiny water droplets form inside a storm cloud, they are propelled towards the top of the cloud by strong internal winds (up draughts) where they turn to ice. Some of the pieces of ice grow into hail, but others remain very small. Some of the hail that forms becomes too heavy to be propelled by the up draughts and so begin to fall back through the cloud, bumping into smaller ice particles as they do so. During these collisions, electrons are transferred to the hail giving the hail a negative charge, while the ice particles that have lost electrons gain a positive charge.
The up draughts continue to carry the ice particles upwards, giving the top of the cloud a positive charge. The hail continues to fall through in the lower part of the cloud, giving it a negative charge. As well as being attracted to the positive charge in the top of the cloud, the surplus of electrons in the cloud base are attracted to positive charge in other clouds and on the ground. If the attraction is strong enough, the electrons will rapidly move towards the positive atoms. The path they make in doing so forms the channel we see during a flash of lightning.As negative charge builds at the base of the cloud, the electrons near the ground's surface are repelled. This leaves the ground and the objects on it with a positive charge. As the attraction between the cloud and the ground grows stronger, electrons shoot down from the cloud cutting through the air at around 270,000 miles per hour.'
What is Thunder?
'Thunder is the sound produced by the rapid heating of the air by a lightning flash. The air expands explosively and contracts rapidly, producing sound waves.When lightning strikes, the narrow channel of air through which it travels reaches temperatures of up to 30,000 �C almost instantly. This intense heating causes the air to rapidly expand outward into the cooler air surrounding it creating a rippling shockwave which we hear as a rumbling thunder clap, which can be heard as either a sudden, loud crack or a low, long rumble. The lightning and thunder clap are generated simultaneously but with the speed of light at 299,792,458 m/s and the speed of sound at 340.29 m/s, the thunder is always heard after the lightning is seen.'
Safety measures for lightning and thunderstorms
There are some safety measures that we must know and practice them properly at the individual and community level as follows:
a) Individual or personal level: It is very tough to recall the tips of taking effective measures at the time of a lightning strike, so we need to drill ourselves to get familiar with them as follows:
1. Stay alert: As thunder or lightning approaches:
l Monitor local weather conditions with an AM/FM or dedicated weather radio, TV, internet etc.
l Recognize the signs of an oncoming thunder and lightning storm: towering clouds with a cauliflower shape, dark skies and distant rumbles of thunder or flashes of lightning.
l Do not wait for lightning to strike nearby before taking cover. Lightning can strike as far as 10 miles from the area where it is raining. That's about the distance you can hear thunder. When you see lightning, count the time until you hear thunder. If that time is 30 seconds or less, then it's dangerous!
l Recall the 30-30 lightning safety rule that every 3 seconds of delay between a flash to thunder, equates to a distance of 01 km, so where 30 sec flash-to-thunder time interval, the lightning activity is about 10km away. Now is the time to take shelter: quickly! Get inside a house, if possible, into an all-metal vehicle, or move to a low-lying area. Stay put. Once you've heard the last peal of thunder, wait for 30 minutes before leaving your shelter.
2. Seek shelter
l Look for a large, enclosed building. That's the best choice.
l If you are in a car and it has a hard top, stay inside and keep the windows rolled up.
l If you are swimming, fishing or boating and there are clouds, dark skies and distant rumbles of thunder or flashes of lightning, get to shore immediately and seek shelter.
l Avoid small sheds and lean-tos or partial shelters, like pavilions.
l Stay at least a few feet away from open windows, sinks, toilets, tubs, showers, electric boxes and outlets, and appliances. Lightning can flow through them and "jump" to a person.
l Do not shower or take a bath during a thunder or lightning storm.
l Avoid using regular, land-line telephones, except in an emergency. If lightning hits the telephone lines, it could flow to the phone. Because they are not connected directly to the building's wiring, cell or cordless phones are safe to use.
l In so far as possible, unplug appliances and electronic equipment, including antenna connections.
(To be continued)
The writer is former editor, Journal of the Institution of Engineers, Bangladesh and writes from England