Why does Lightning Strike?

Every time a storm begins rumbling in the sky, we on Earth are quite lucky to look up and see a sky full of lightning. Sometimes, you will see bolts of lightning even when it’s not raining. The sharp branches of lightning strikes look like an arsenal of sharp weapons stabbing the sky, all at the same time. For some, the image is majestic, while for others, it is utterly terrifying. No wonder people sometimes shudder when they hear a thunderclap!

What is the cause and mechanism associated with lightning strikes? Why we see lightning before we hear thunder ? For that first we need to have a little knowledge about Lightening. 


What is Lightning?
Lightning is basically an electric current. Yes, just like those we have in our houses, except same thing happens when lightening occured, but on a much bigger scale. The temperature of lightning is around 27,000 degrees Celsius, which is nearly 5 times hotter than the surface of the Sun. Lightning is a type of electric current that, most of the time, forms in the clouds, but occasionally forms between the cloud and the ground, resulting in a lancing line of lightning that we can see.

Within a thundercloud way up in the sky, many small bits of ice (frozen raindrops) bump into each other as they move around in the air. All of those collisions create an electric charge. After a while, the whole cloud fills up with electrical charges. The positive charges or protons form at the top of the cloud and the negative charges or electrons form at the bottom of the cloud. A build up of positive charge builds up on the ground beneath the cloud, attracted to the negative charge in the bottom of the cloud.

The ground's positive charge concentrates around anything that sticks up - trees, lightning conductors, even people, as you all know that Electricity finds it hard to travel though air (it has low conductivity). So, the positive charge from the ground connects with the negative charge from the clouds and a spark of lightning strikes.

The Mechanics of a Lightning Strike
As the static charge buildup in a storm cloud increases, the electric field surrounding the cloud becomes stronger. Normally, the air surrounding a cloud would be a good enough insulator to prevent a discharge of electrons to Earth. Yet, the strong electric fields surrounding a cloud are capable of ionizing the surrounding air and making it more conductive. The ionization involves the shredding of electrons from the outer shells of gas molecules. The gas molecules that compose air are thus turned into a soup of positive ions and free electrons. The insulating air is transformed into a conductive plasma. The ability of a storm cloud's electric fields to transform air into a conductor makes charge transfer (in the form of a lightning bolt) from the cloud to the ground (or even to other clouds) possible.

Why does thunder occur?

Thunder and lightning occur at roughly the same time, although you see the flash of lightning before you hear the thunder. Thunder is the sound caused by lightning. When a lightning bolt travels from the cloud to the ground it actually opens up a little hole in the air, called a channel or a pathway. The enormous and rapid flow of charge along this pathway between the cloud and Earth heats the surrounding air, causing it to expand violently. The expansion of the air and after the light is gone, the air collapses back in, which creates a shock-wave that we observe as thunder.