Home

Thunder and Lightning

Thunderstorm
© Clint Spencer

Thunder and Lightning happen in Thunderstorms. Are you frightened by thunderstorms? I am, but I also think thunderstorms are very fascinating. It is true people may be struck by lightning, but it doesn't happen very often and you can take precautions against it. Generally it is very safe to watch a thunderstorm from home.

How a thunderstorm starts

So what happens in a thunderstorm? Thunderstorms mostly happen in summer when it is very warm and muggy. If the sun shines a lot a lot of water from the ground evaporates and rises into the sky, where it gets cooled down a bit. Clouds start to form from the water steam. Clouds that form under these circumstances sometimes look like a huge cauliflower!
If warm water steam continues to rise up from the air this cloud gets bigger and most of all much higher. The top of the sky may be up to 8 miles high in the sky. Up there it is very windy and the clouds is pulles apart by the wind. If this happens, the cloud looks like a huge anvil in the sky. (What is an anvil? Find out on Wikipedia.) This top of the storm cloud is also called a "thunderhead". The thunderstorm starts within this cloud. There is a lot going on in that storm cloud now!

The thunderstorm cloud

In the upper half of the huge cloud it is very cold and the water forms to little ice crystals. In the lower half the water is still liquid and forms to little drops. There are very heavy winds within the clouds that swirl the ice crystals and water drops up and down all the time. The ice crystals melt when they fall and the water drops freeze as they rise, and this happens again and again. The water drops and ice crystals grow all the time because they join together with other drops and crystals on their way up and down. After a while the water has formed very heavy and big drops and the ice crystals have turned into big ice drops: hail.
They are so heavy now that the hail or water falls out of the sky: It begins to rain or hail heavily and people on the ground open up their umbrealls and run into their houses or some other shelter.

Friction within the thunderstorm cloud causes the lightning

But this is just the beginning. Through all that up and down of the ice and water drops in the huge cloud a lot of energy has built up within the cloud. This energy has developed through "friction". Friction means that the water and ice drops have rubbed against each other a lot.

How friction develops

You may have experienced this sort of tension yourself: Sometimes when you walk with your trainers over carpet a lot and touch a metal hand railing afterwards, you get a small electrical shock. This is because the plastic of your shoes and the plastic of the carpet have rubbed on each other a lot and tension has build up withing your body. The tension itself doesn't hurt you at all! It simply means that you have a few to many of particles in you that are charged with negative or positive electrical energy. Usually you have the same amountof positive and negative particles in you because the negative particles always look for positive particles to go with and the other way round. The superfluous particles constantly try to go to other particles so that there is a balance. This is why the tensions within you takes the next opportunity to jump from you onto something else that has enough other particles to create a balance again. This is called "discharging". This can be the metal hand railing or another person. This jump from you onto someting else happens very quickly and gives you a small shock that hurts just a tiny little bit. The tension is gone from you and has spread in the hand railing. If you touch the hand railing again the tension will not jump back onto you because it has already contacted opposite particles and there is a balance again.

So there is a lot of energy in the cloud that wants to get discharged. It looks for the next best thing that is charged in the opposite way. This can be a neighbouring cloud or the ground or a very high building or a tree - whatever is nearest (this energy is very impatient and always takes the shortest route). The discharge of the energy from the cloud to the neighbouring cloud or to the ground or the building or the tree is what we call the "lightning". A lightning is a very huge discharge of energy, similar to the little shock you had at the hand railing but millions of times bigger. It happens very quickly but is extremely loud and and light.
Big thunderstorms contain enough energy to power a whole country for a year - in theory. But no one has so far found a way to "catch" the energy that is contained in lightning.

Thunder

The lightning also produces a very loud sound, the thunder. This is because the air around the lightning gets heated up very quickly and moves away from the lightning in a sort of explosion. And this explosion is very loud.
If the thunderstorm is close to you you will see and hear that thunder and lightning happen at the same time. But thunderstorms move and can be seen approaching from far away. If the thunderstorm still is far away you will see the lightning before you can hear the thunder. This is because light travels faster than sound. The sound of the thunder takes longer to be heard by your ear than the light.

Measure how far a thunderstorm is away

The fact that you can see the lightning before the thunder gives you the opportunity to measure how far the thunderstorm is away from you. Measure the seconds between the lightning and the thunder. Then divide this number by three and the result tells how many kilometers the thunderstorm is away. For example if your see the lightning and hear the thunder 9 seconds later, then the thunderstorm is 9:3 = 3 km away from you.

What to do in a thunderstorm

You don't have to ba afraid in thunderstorms.
While there is a thunderstorm on,

  • don't swim
  • don't ride your bike
  • don't walk across an open field
  • don't stand under a tree

If your extra careful

  • don't use the shower
  • don't use the telephone
  • unplug electrical appliances like your TV or a computer (also remove any antenna cable)

You're safe

  • within a car or airplane because they are like a metal cage - the lightning will not go through there
  • in a building (most of them have a lightning rod to deduct the energy of lightning).

If you're ever caught by a thunderstorm whilst you are in the middle of nowhere, do not lie down on the ground but squat down with your legs close together. It is unlikely that anything will happen.

Check up-to-date weather information for London