The Lighting and Thunder, as We Can See It as We Know It

An incredible creation of nature is the planet earth, our home. We the Homo sapiens called as the social beings on this incredibly beautiful planet, watch many natural events occurring around us in. One of such is the bolt of light occurring in our atmosphere followed by a very loud sound wave. We have termed it as ‘Lightning’. As a host of a very complicated and intelligent nervous system, we always have the curiosity to know the hidden science behind the natural events. So let’s ask us that, what is the physical phenomena behind lighting?

Lighting is the big brother of the electrical spark that we often see in the electrical appliances. Let me set an example, we twist a rope, it gets stressed, if we release the rope it would automatically untwine and release the stress imposed on it. Similar to the mechanical stress, lighting is also a kind of stress release but here the kind of the stress is the electrical stress imposed on the atmosphere. The radioactive material of the earth’s surface emits highly energized particle which ionizes the variant components of atmospheric gasses. Particles of extremely high energy come from the sun and outer space, they enter the earth’s atmosphere and creates ions in the atmosphere. These electrically charged ions get attached to the suspending dust, the cloud, and the raindrops in the atmosphere. In a favorable condition like the thunderstorm, these charged particle gets accumulated in different parts of clouds because of different physical activities inside the cloud. The atmosphere doesn’t allow these charge to flow readily and thus more and more charges get accumulated in the regions. These accumulating charges create electrical stress in the atmosphere, in some cases between the regions of cloud itself or else between a region of cloud and the ground. As soon as the electrical stress (earth’s atmosphere can sustain a maximum of  3 million Volt/meter of electrical stress) exceeds this maximum value, the atmosphere no longer can resist the flow of charges. So to release the stress the accumulated charge begins to flow towards the earth surface and in some cases to the other regions of the cloud.When the charge flows down in a channel, the gas atoms in the channel emits light (due to ionization) and that’s the reason we see a sudden light coming down to the ground and is called as the cloud to ground (CG) lightning and if it occurs between the cloud, it is called the intracloud lightning (IC).
As the electric charges take the least resistance paths to flow in the atmosphere, sometimes we see many branches of an illuminated channel. The electric discharge process heats the discharge channel up to 24,000 K (room temperature ∼ 298 K) and creates a very high pressure (1 million Pascal) in the channel. This immense energy results a shock wave which moves very fast from the discharge channel, this shock wave as called as thunder.

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Lighting is one of the major meteorological hazards for the mankind. Over 44 lightning discharges take place in the atmosphere every second. The global estimate shows that over 24,000 people get killed by lightning strike every year around the world (Wikipedia).Lightning can cause electric power outages, forest fire, damage to the electrical equipment. Despite these adverse effects of lightning discharges on the biosphere of the earth, lightning is also known to have positive impacts on the living community. Lightning is known to cause nitrogen fixation in the atmosphere. The fixed nitrogen comes down to earth with rain and thereby increasing the fertility of the soil. Lighting activity in the earth’s atmosphere is believed to play a crucial role in the origin of life on this planet (as referred from Miller and Urey experiment).
As lightning can be hazardous, lightning protection is considered to be a very important area of scientific research. Use of ‘lightning rod’ is a standard procedure to divert the lightning current to the ground in residential or commercial buildings, popularly known a grounding. As sharp metallic objects, antennas, tall trees can produce a corona discharge in the intense electric field produced during the thunderstorm and thereby creates a less resistant path for the charges to come down from the cloud, and so it is recommended not to take shelter near these objects during a thunderstorm.

The author is engaged in extensive research about lightning and related atmospheric events at Indian Institute for Tropical Meteorology (IITM), Pune, India.


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