What Causes Lightning and Thunder?

Lightning, is not just a magnificent phenomena of nature, depicting its beauty, but also a dangerous process, known to man. Scientists have been trying to crack the process of lighting, and done their part, excluding the process of cloud charging, which is elusive even to the today’s world.



What causes Lightning and Thunder? (Image source: sxc.hu)

Lightning, significantly is a flash of light, created by electro static discharge, between the charged regions of the clouds or between the Earth and the electrically charged regions of the clouds. The lightning flash composes of a series of strokes, with an average of about four. The length and duration may vary, but on an average accounts to about 30 micro seconds.


Types of Lightning:

Primarily, there are three basic types of lightning, namely


1. Intra cloud (IC) Lightning: This is the most common type of lightning. This process takes place within the cloud and occurs between oppositely charged centers, within the cloud. This is visible from many miles, as a bright flickering.


2. Inter cloud Lightning: This happens in between two charged centers in different clouds, bridging the air gap between them through the process of discharging.


3. Cloud to Ground Lightning:  This form of lightning is the most damaging and dangerous form of lightning. This lightning, is basically the discharge between a thunder cloud and the ground. It is usually negative in polarity.

Types of Lightening

Types of Lightning


How charge gets accumulated on the cloud?

Just like rubbing a balloon can create static electric charge, the particles in the cloud acquire charge, by the movement of water and ice particles. The ice and water particles are forced upwards by the warm air currents and forced downwards by gravity. Hence charge gets separated in the cloud, positive charge moving up and negative charge, accumulating in the lower parts of the cloud.


After a significant charge build up, both positive and negative charge seeks to neutralize each other. ‘Streamers’ reach to the ground, to form a path way and along the process, a spark is generated, while neutralization takes place.


How lightning ‘discharges’:

The streamer moves in discrete steps of 50m and hence known as ‘stepped leader’. Along the process of the movement, it creates an ionized path, depositing the charge along the channel and when reaches the ground surface, a large potential difference is created between its end and the ground surface and once a connecting path is achieved, a return stroke flies up the ionized path, releasing huge energy, bright light and rumbling thunder with the speed of light.


This ground to cloud flash, generally transfers a net positive charge to the Earth’s surface.


Similar process occurs in intra cloud lightning, except that the discharge occurs between the oppositely charged regions of the cloud. More ever, a return stroke is also not produced, but characterized by slower propagating, ‘recoil streamers’ and ‘K’ changes.


How does Lightning know, where to ‘strike’?

The electric field looks for the closest and easiest path to release it’s charge. In the process of cloud to ground lightning, as the storm descends to the ground, the strong negative charge, accumulated at the bottom of the cloud, attracts positive charges on the ground and these positive charges move up into the trees, buildings, houses or even humans.


The ‘stepped leader’, of negative charge, descends from the cloud, seeking the shortest and easiest path, towards the ground and simultaneously, a positive charge from ground called, ‘streamer’, reaches up to meet the negative charge to complete the process of lightning. Several strokes can be seen, resulting a flickering appearance, during the process of discharge.


Formation of the step leader and the return stroke

Formation of the step leader and the return stroke

Striking facts about Lightning:
  • The average temperature of lightning is around 20,000 degrees.
  • A single bolt of lightning is five times hotter than the surface of the sun.
  • There exists two types of lightning, negative and positive strikes and positive strikes are five times more powerful than negative strikes.
  • A flash of lightning is brighter than 10,000,000 100-watt light bulbs.
  • Each second, there are 50 to 100, cloud to ground lightning strikes to the earth worldwide.
  • During a cloud to ground lightning strike, it chooses the shortest path to the ground, which can be a tree, or a building or a man.
  • Most lightning strikes occur on land rather than on oceans, occuring around 70% in tropics.
  • Lightning is usually produced by Cumulonimbus clouds, which are tall and dense.
  • The science of lightning is called fulminology.
  • The fear of lightning is called Astraphobia.
  • Florida is the lightning capital of the United States.
  • A ‘fulgerite’ is formed, when a powerful lightning bolt, melts the soil into a glass like state. Such fossilized lightning specimen was found several years ago in Michigan.


Lightning Incidents that shook the World:
  • In 1963, Pan Am Flight-214, crashed outside Elkton, Maryland, during an electrical storm, resulting a loss of 81 passengers and crew.
  • In 1665, lightning terminated on the main tower at the Osaka Castle, Japan, ignited a fire, resulted in the burning of the structure to its base.
  • In 1789, lightning struck the Church of St. Nazaire in Italy, igniting 90 tonnes of gun powder, in its vaults resulting in a huge explosion, killing 3000 people and destroying most part of the city.
  • In 1902, the top of the Eiffel tower has been struck by the lightning, which has been reconstructed later.
  • In 1994, an explosion of fuel tanks took place, as a result of lightning, in Dronko, Egypt resulting in around 500 fatalities.
  • In 2005, sixty eight dairy cows, all full of milk, died on a farm at Waterfall Way, New South Wales, when struck by a fierce lightning.


Misconceptions about Lightning and Thunder:

Lightning never strikes twice in the same place, is just a misconception, as the Empire State building in New York is a perfect example. The building in New York is struck 24 times a year and was once struck eight times in twenty four minutes.


According to the great Greek philosopher Aristotle, thunder was considered to be caused by the collision of clouds and most of the world believed it to be true, until later science unraveled the mystery.


What is Thunder?

Thunder is the sound produced during lightning. As, lightning is a phenomenon of electric discharge, while the electricity is passed through the surrounding air, the particles in the air gets vibrated. In addition to that, the air also gets heated due to the enormous heat produced during lightning and gets cooled in no time. As a result of sudden expansion and contraction of the air particles, result in the loud sound, popularly known as thunder. A balloon popping is an instance of such a phenomenon.

 What is Thunder

Thunderstorms need three things to form:

  • Moisture to form clouds and rain.
  • Lift, sea breezes and mountains are capable of lifting air to form thunderstorms.
  • Unstable air, warm air that rises rapidly.


Interesting facts about Thunder:
  • Light travels faster than sound and hence we see lightning before hearing thunder. (Also Read Is Time Travel Possible?)
  • The intense heat from lightning causes the surrounding air to expand and create a sonic wave, heard as thunder.
  • Thunderstorms typically produce heavy rain for a brief period, anywhere from 30 minutes to an hour.
  • Warm and humid conditions are highly favorable for thunderstorms.
  • To judge how close the lightning is, count the seconds between the flash and the thunder clap. Each second represents about 300 m.


Why Thunder rumbles:

Thunder bolt is not just heard as a loud ‘boom’, rather heard as a loud clap, followed by several moments of rumble. This can be explained from the fact that during the process of lightning, the surrounding air gets heated up to 20,000 degrees. The sudden heating, causes the air to expand and immediate cooling contracts the surrounding air again. Hence these expansion and contraction of air makes the air molecules to vibrate back and forth in no time, creating sound waves and hence the clapping is heard.


Often, the sounds from the thunder gets softer, louder, then softer and then louder and so on. This can be explained from the fact that when one hears the part of the lightning that is far from the observer, the sound is heard softer and the nearer part would be heard as a loud sound and  hence the rumble results.


Extra terrestrial Lightning:

Lightning is the phenomenon, not just limited to the planet earth, but can also be observed in the atmosphere of other planets like Venus, Jupiter and Saturn.


Lightning on Venus, is considered as a controversial subject, even after detailed study and research is being done to reveal the secrets of the atmospheres of other planets to explain the phenomenon of lightning there.


How to anticipate immense lightning strike on you?

If lightning is about to strike you or near you, the hair may stand or tingling may be felt on the skin. Light metal objects may vibrate and a crackling sound may be heard. Immediate measures are to be taken to prevent the loss of life.


How to treat a lightning victim?

Lightning often causes cardiac and respiratory arrests. Check the heart beat of the person, and if found not breathing, immediately start providing CPR and continue till rescue arrives. Besides cardiac arrest, lightning may also cause burns, shock, brain injuries, muscular and skeletal damage and some times, blunt trauma. Nervous system disruption may also be experienced.  Treat all these injuries until first aid arrives. Significantly, lightning victims die from cardiac arrest.


How to get protected from lightning strikes?
  • Look for protective shelters like buildings, equipped with lightning rods, electrical systems and groundings with plumbing.
  • Avoid standing under trees.
  • Keep watching at skies to spot cumulonimbus clouds, dark skies and rain to anticipate thunderstorms.
  • Stay inside at least 30 minutes, after the last strike.
  • When struck outdoors, move from higher to lower elevations, stay away from isolated objects like trees and light posts, and avoid open spaces.
  •  If absolute shelter is not found, squat on the ground, with feet close together.
  • Turn off all electronic appliances and avoid showers.
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