How does lightning occur? | The physics of Lightning and Thunders

How does lightning occur? | The physics of Lightning and Thunders

The lightning we see during rains or storms are so fascinating in nature! A really huge spark of electrostatic discharge from clouds to the ground or sometimes within clouds itself. And after that bright flash follows a really loud bang which is called thunder. So what is it that really happens up above in the clouds that creates this huge electric discharge and a loud bang?

Branching of lightning bolt in slow motion.
Image credits: NOAA SciJinks

First we will understand how lightning works and then how thunder is generated.

Formation of Lightning

Lightning is the sudden discharge of electricity. Initially the charges get separated in the cloud formation itself. The primary source of lightning is the cloud type termed cumulonimbus, commonly referred to as the thundercloud. Due to the air currents inside the clouds and other factors the positive charges gets accumulated in the top region of clouds and negative charge is accumulated at the bottom region. Unfortunately we don’t know exactly why or how this charge separations occurs in the first place. One widely held theory is that the thunderstorm clouds have supercooled ice crystals and graupel (soft hail) and due to strong updraft they are pushed in the upper region of clouds and become positively charged.The heavier ice crystals which are negatively charged fall to the lower regions.

Now the lower region is accumulated with negative charge. As like charges repel, the negative charge on the ground is repelled and positive charge accumulates on the ground. Now unlike charges attract! When enough negative charge in clouds and positive charge on ground is accumulated, sudden discharge takes place which we see as a lightning strike. The negative charge starts flowing towards ground and the positive charge on ground starts travelling up towards the clouds. The point when these two flows meet is the point when we see a huge lightning bolt from cloud to the ground!

Negative charges from cloud (blue) and positive charges from ground (red) start moving towards each other eventually discharging suddenly creating a lightning. Image Credits: NOAA SciJinks

Its the same static discharge/zap we feel sometimes when we touch car doors or even other people, its just much larger in magnitude (and much lethal obviously).

Now the types of lightning:

  • Intra cloud: This type of lightning happens completely within clouds. It happens due to discharge between different charge regions within the clouds.

    Intra-cloud lightning.
    Image credits: NSSL, NOAA
  • Cloud to Cloud: This type of lightning strikes happen between two or more surrounding clouds.

    Cloud to cloud lightning.
    Image Credits: Wikimedia
  • Cloud to Ground: This is what we should be worried about! This is the type of lightning that strikes the ground.
    Cloud to Ground lightning strike.

    The branching can be clearly seen as the charges try to find the shortest possible path. This is the reason why tall buildings and trees are striked by lightning more often.

  • Cloud to air: This type of lightning occurs when there’s a discharge between clouds and oppositely charged air surrounding the clouds. The distribution of charges varies and depends on many factors so this type of discharge happens.

    Cloud to Air Lightning.
    Image Credits: NSSL NOAA

What causes Thunder?

Thunder is that very familiar loud rumbling sound we hear a few seconds after a lightning strike. We can actually determine how far away the lightning strike took place by counting the interval between flash and rumbling sound.

The average lightning bolt striking from cloud to ground contains roughly 1 Billion Joules of energy!! Now that’s just lot of energy and lightning strikes last for such a short duration. This immense energy superheats the air surrounding the lightning channel to plasma temperatures in a very short duration. Temperatures can go upto 30,000 Kelvins (53,540 degrees Fahrenheit). This creates a shockwave in the air rapidly and rumbling sound is generated. High frequency sound gets quickly absorbed by landscape so thunders due to distant lightnings sounds like low rumble.

How to survive a lightning strike?

If unfortunately you are in flat lands during a thunderstorm remember that you are one of the shortest possible routes for charges to discharge. Laying flat on ground won’t work as lightning can hit the ground and first and then your body. Avoid standing under trees, poles, any sort of tall conducting pointy things. It’s just safe to be indoors during a thunderstorm.

Staying inside a car or bus also might help as the frame or surface of vehicles act as a Faraday cage and lightning will flow on the surface and not through your body.

These are some tips just incase you are in the open during a thunderstorm.

  1. Crouch down low like a baseball catcher. Get as low as you can. The nearer you are to the ground, the less likely you are to be struck by lightning. But never lie down!
  2. If your hair begins to stand on end or your skin starts to tingle, a lightning strike is imminent. (You literally have a few seconds before you get hit). Immediately get into the crouching position. Lightning may strike without this warning, however.
  3. Place hands over ears to minimize hearing loss from the loud clap of thunder that will boom very close to you.
  4. The only thing touching the ground should be the front portion of your feet. Lightning can hit the ground first, and then enter your body. The more you minimize your contact with the ground, the less chance of electricity entering your body.
  5. Touch the heels of your feet together. If electricity from a ground strike enters through your feet, this increases the chances of the electricity going in one foot and out the other, rather than into the rest of your body.
  6. Don’t touch any possible conductors.

    How to survive a Lightning Strike?
    Image credits:


I hope you never get into such situation but knowing stuff is always good, ain’t it?


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