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Back to the Thunderstorms Index Page
Lightning and Thunder
Lightning
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During thunderstorm conditions the turbulence in the cloud causes the charges to separate in such a way that the negative charges concentrate in the
base of the cloud. Since like charges repel, some of the negative charges on the ground are pushed down away from the surface, leaving a net positive
charge on the surface. With other words: It's all about static electricity! So the lightning happens when the negative charges in the bottom of
the cloud are attracted to the positive charges (protons) in the ground.
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Opposite charges attract, so the positive and negative charges are pulled toward each other. since the negative charges (electrons) are many thousands
of times smaller than the positive charges (ions--charged atoms) they move much more easily and cover most of the distance. This first, invisible stroke
is called a stepped leader. The accumulation of electric charges has to be great enough to overcome the insulating properties of air.
When this happens, a stream of negative charges pours down towards a high point where positive charges have clustered due to the
pull of the thunderhead.
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As soon as the stepped leader connect there is a conductive path from the cloud to the ground and the negative charges rush
down it causing the visible stroke. The channel created by the stepped leader is full of relatively static charge, like a line of cars at a red light. When the two
parts join, it is like that light turning green, and just as the cars near the light start moving first, so do the charges near the join. Since it is the fast-moving charges
that create the light, the visible stroke actually travels upwards, even though the charges are moving downward! The connection is made and the protons
rush up to meet the electrons. It is at that point that we see lightning and hear thunder.
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Thunder
The temperature of lightning is over 22,204 degrees Celsius (40,000 degrees Fahrenheit), so a bolt of lightning heats the air along its path causing it to expand
rapidly. Thunder is the sound caused by the rapidly expanding gases. Light is moving faster then sound, so thats the reason you see first the lightning and later the thunder.
If the lightning and the thunder are at the seme time, be aware! The thunder is right above you.
You can easily calculate the approximate distance between you and the thunder. Sound travels with a speed of approx. 330 meter per second. So the only thing to do is
count the seconds between the ligthning and the thunder. The best thing to do this is with a stopwatch.
This is how it goes: You see the lightning, start to count immediately: 1...2...3...Booooom! Three seconds means: 3x 330 meter.
The thunder is about 1 Km away from you.
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The images on this page and a part of the explanaition are provided by the National Center of Atmospheric Research and
Windows to the Universe.
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