THUNDER AND LIGHTING
VERY VERY FRIGHTNING ME
From the News Desk of Jeanne Hambleton
Having been awakened by one of the loudest thunderstorm I can ever remember, I am curious to know more about it. I heard my thunderstorm rhapsody about 12.45am this morning on the South Coast.
If you have not already had some storms the chances are you will. As a child my mother always told me thunder was Johnny’s gun. Not sure where that might have come from but I did not worry about the noise after that. But last night was something different and Johnny had certainly upgraded his guns. It sounded like some faraway war.
What causes the sound of thunder – it sounded different last night to anything I had heard before.
According to Everyday Mysteries from Science Reference Services of the USA Library of Congress, thunder is caused by the rapid expansion of the air surrounding the path of a lightning bolt. From the clouds to a nearby tree or roof, a lightning bolt takes only a few thousandths of a second to split through the air.
The loud thunder that follows the lightning bolt is commonly said to come from the bolt itself. However, the grumbles and growls we hear in thunderstorms actually come from the rapid expansion of the air surrounding the lightning bolt.
As lightning connects to the ground from the clouds, a second stroke of lightning will return from the ground to the clouds, following the same channel as the first strike. The heat from the electricity of this return stroke raises the temperature of the surrounding air to around 27,000 C° (48,632 F°).
Since the lightning takes so little time to go from point A to point B, the heated air has no time to expand. The heated air is compressed, raising the air from 10 to 100 times the normal atmospheric pressure.
The compressed air explodes outward from the channel, forming a shock wave of compressed particles in every direction. Like an explosion, the rapidly expanding waves of compressed air create a loud, booming burst of noise.
Because electricity follows the shortest route, most lightning bolts are close to vertical. The shock waves nearer to the ground reach your ear first, followed by the crashing of the shock waves from higher up. Vertical lightning is often heard in one long rumble.
However, if a lightning bolt is forked, the sounds change. The shock waves from the different forks of lightning bounce off each other, the low hanging clouds, and nearby hills to create a series of lower, continuous grumbles of thunder.
Thunder Fun Facts:
To judge how close lightning is, count the seconds between the flash and the thunderclap. Each second represents about 300m (984.25ft).
Thunder is not only heard during thunderstorms. It is uncommon, but not rare, to hear thunder when it is snowing.
Lightning does not always create thunder. In April 1885, five lightning bolts struck the Washington Monument during a thunderstorm, yet no thunder was heard.
A government site called Ready.gov/thunderstorms-lightning, warns all these storms are dangerous and lightning remains to be one of the top three storm killers. Thunderstorms injured hundreds and have killed 51 folk in the USA.
This site warns you to unplug electrical equipment including your computer or electric blanket if you are snug in bed. Have an emergency kit – torches, blankets, enough food and water – whatever you think you might need. Get prepared if you think storms are coming.
If you know there is a risk of thunderstorms be sure to secure anything lose outside the house or likely to blow away and cause damaged. Dispose safely of loose rotting trees and dead branches.
If you are out take cover. They say you would be safer in a thickly densed wood rather than wandering about in the storm. If you are on the water get to dry land.
About 10 per cent of all thunderstorms are classified as severe. Lightning is not always associated with heavy rain and can strike as far as 10 miles away before any rainfall.
In the States your chances of being struck by lightning are estimated to be 1 in 600,000 but this could be reduced even further by following any safety precautions.
On the Naked Scientists forum one man said some of the thunder sounds like one loud bang or clap and other thunder sounds like a long rolling sound similar to a bowling ball going down an alley. What causes the difference?
Different sounds of thunder
The difference is due to the way in which the lightning jumps from one spot to another. A vertical lightning strike from cloud to earth arrives at the ear as a bang. A cloud-to-cloud strike can sound like rolling thunder because the bang you hear comes along the length of the bolt.
Sound moves at about 300 meters a second or about 1000 feet a second. That is fairly rough, but gives you an idea of the speed. If a lightning bolt is quite long across the clouds, say 1500 meters, then you hear the bang over 1500/300 = 5 seconds. That is the rumble you hear.
Why are there different kinds of thunder?
The reason thunder rumbles is due in part to two things. The first being a lightning bolt is very rarely a straight line and is never equally distant from you at all points.
A lightning bolt on average is 4 miles long, it zigzags all over the place, and can have many limbs that branch out in many different directions separated by many miles.
As a result, the compression waves created by each part of the lightning bolt reach you at different times. The sound wave that has travelled a greater distance will be softer and arrive later than a compression wave created by a part of the lightning bolt that was closer to you.
The second thing is the compression waves (or the thunder) will bounce around and off the clouds, the ground, and other objects nearby.
Much like your voice echoes in a canyon or large auditorium, so do the compression waves generated by lightning. These two things will cause some compressions waves to arrive at the same time which is why the thunder might get loud, then soften a bit, then get loud again (the rumbling we hear).
If you have had a lightning bolt crash down really close to you, the thunder does not rumble as much and sounds more like an explosion. That is because the compression waves did not have a chance to bounce off many things before you heard it. Whereas if you were further away, you would of heard the rumbling.
For questions and more information try
I am glad I know that but I still will not sleep soundly when lightning strikes near my house and thunderclaps keep me awake. I cannot say I feel reassured and feel safe in thunderstorms. I will just get further under the blankets and pretend it is not happening. Maybe I will think about Johnny and his gun for reassurance.
See you soon. Jeanne