Knowing about Lightning

Dr. S. S. VERMA; Department of Physics, S.L.I.E.T., Longowal; Distt.-Sangrur (Punjab)-148 106

2020-06-29 05:19:01



Coming of rainy season mostly brings happiness and prosperity to people but along with some unwanted repercussions due to heavy rains like floods, storms, typhoons, land sliding and lightning leading to a great loss of organism, human lives and property. Few other natural calamities have inspired as much fear, reverence, or fascination - not to mention legends, mythos, and religious representations than lightning. All regions of the world often have lightning fatalities each year during  the rainy season.

Lightning is always taken as a serious natural calamity for the well being of mankind. According to reports from the National Crime Records Bureau (NCRB), more than 2,500 people die due to lightning strikes in India every year. Recently, in Bihar and UP there was a great loss of about 100 human lives due to lightening. Most of these farmers were busy in paddy sowing activities in their fields.

The first systematic and scientific study of lightning was performed by Benjamin Franklin during the second half of the 18th century.  According to scientific understanding, during rain, lighter, positively charged particles form at the top of the cloud and heavier, negatively charged particles sink to the bottom of the cloud. When the positive and negative charges within the cloud grow large enough, a giant spark (lightning) occurs between the two charges within the cloud.  All the collisions between clouds cause a buildup of electrical charge and thus producing lightning is an electric current. As negative charges fly down the channel towards earth, the electrical current flows and a visible flash of lightning streaks upward transferring electricity as lightning in the process at a speed of about 3x108kph (8.33x107m/s) (speed of light in vacuum is 3x108m/s). Most lightning happens inside a cloud, but sometimes with more favorable environmental conditions for electric current generation and propagation it (lightning) happens between the cloud and the ground. A build up of positive charge on the ground beneath the cloud gets attracted to the negative charge in the bottom of the cloud.

The ground's positive charge concentrates around anything that sticks up electricity conducting structures like trees, telephone poles, wire fences, water bodies, metal bodies, houses and even people. The ground at a positive charge in comparison to negative charge on the cloud connects with the negatively charged clouds and a spark of lightning strikes and before the electrical discharge is complete, we may see several lightning strokes using the same path, giving the lightning bolt a flickering appearance. In a fraction of a second, lightning heats the air around it to incredible temperatures, as hot as 30,000 °C which is five times hotter than the surface of the Sun. Explosive expansion of heated air as the surrounding air is rapidly compressed creates a shockwave. The air then contracts rapidly as it cools which creates an initial crack sound followed by rumbles as the column of air continues to vibrate.

Lightning is seen before hearing the thunder sound because light travels much faster than sound waves. The distance of lightning place can be estimated by counting how many seconds it takes to hear the thunder.  If the thunder follows the lightning almost instantly that means the lightning is too close. In general, lightning has a disastrous effect on the surrounding environment. The direct effect of a lightning strike is the structural damage or even physical harm. Buildings or tall structures hit by lightning may be damaged as the lightning seeks unintended paths to ground and can harm humans or animals nearby. People of all strata are no doubt self aware of conditions for the happening of lightning and its consequences and possible precautions to be taken.  However, there is a great need not only to run awareness programmes but also give people protection and options so that they become less vulnerable to menace of lightning.  This article is an effort only to bring out some important facts, safety precautions and some myths associated with this unstoppable natural phenomenon. In case of such incidents, it is right to say that “be aware be safe”.

Some important facts

>With heavy rainfall, the change in moisture level results in thundering and lightning.

>Lightning occurs mostly in open space and rarely in urban areas and the reason is that there is more moisture on the surface in open spaces and due to moisture, positive and negative currents are formed due to which there is greater possibility of lightning.

>Lightning can cause destruction anywhere & anytime during rain but the deaths in India often occur among farmers, who head outside to prepare their fields just as the monsoon rains arrive as they want to cut or seed it as close as possible to the start of the rains as well as during rain due to the non-availability of irrigation facilities.

>Lightning occurs on too large scale to be influenced by small metallic objects on the ground as well as on human body.

>The overhead location of the thunderstorm alone determines where lightning will hit the ground.

>Lightning generally strikes about 10 miles away from the storms and heavy rainfall.

>Lightning often strikes repeatedly at the same place.

>Rule 30-30 is an easy way to determine the threat of lightning in the area. It means 30 seconds (count the seconds between seeing lightning and hearing thunder) and if this time is less than 30 seconds, lightning is a threat and indication for seeking immediately protection.

>Lightning was the main electromagnetic presence in the Earth's atmosphere and these electromagnetic fields are weak and difficult to detect. Scientists never suspected that they had any tangible impact on life on Earth but a new study finds that these fields may have protective properties for organisms living under stress conditions.

Safety precautions

>Avoid being in or near water during a thunderstorm as lightning can travel through plumbing.

>Stay off corded phones, computers and other electrical equipment that put you in direct contact with electricity as lightning can travel through electrical systems and radio and television reception systems.

>Avoid concrete floors and walls.

>During heavy rains with storms, it is always safe to stay away from windows, doors and porches.

>It is safe to keep away from open fields, hilltops, forests, swimming pools, and open water bodies during storms.

>Don't stand near trees, tall isolated objects, or metal objects that could attract lightning strikes.

>It is perfectly safe not to use data cards, mobile phones or any other antenna based devices in a thunderstorm.

>When a thunderstorm threatens it is always safe to get inside a home or large building, or inside an all-metal (not convertible) vehicle.

>When outside with no time to reach a safe building or an automobile, do not stand underneath a natural lighting rod such as a tall & isolated tree.

>Get away from tractors and other metal farm equipment as well as motorcycles, scooters, golf carts and bicycles.

>Stay some distance away from wire fences, metal pipes, rail lines and other metallic paths which could carry lightning.

>It is not safe to stand in small isolated sheds or other small structures in open areas.

>In a forest, it safe to seek shelter in a low area under a thick growth of small trees.

Lightning myths

>Lightning never strikes repeatedly in the same place.

>Lightning only strikes the tallest objects.

>During a thunderstorm, being under a tree is better than with no shelter at all.

>To think that if we don't see rain or clouds, we're safe. Lightning often strikes more than three miles from the place of thunderstorm which is far outside the rain or even the thunderstorm cloud.

>The human body doesn’t store electricity so it is perfectly safe to touch a lightning victim to give them first aid.

>The presence of small metal objects like pins, rings and bracelets makes very little difference in determining where lightning will strike, whereas, high, pointy shape and isolated metallic objects are the dominant factors influencing the lightning strike.

>Installment of surge arresters and suppressors in the building as components of a complete lightning protection system is important but cannot do much to protect a structure against a direct lightning strike.