What Causes Thunder?
Thunder is caused by lightning. During a thunderstorm, electrical charges build up in the clouds. When a charge becomes strong enough, there is a flash of lightning. As it flashes across the sky, the hot spark heats the air in its path.
The heated air expands violently, producing sound waves that we hear as thunder. The exploding noise of the hot expanding air happens at each segment of the zig-zaggy bolt, so you hear thunder as a series of rumbles. Sometimes it seems like a short clap. This happens when most of the noise reaches your ear all at once.
The cause of thunder has been the subject of centuries of speculation and scientific inquiry. The first recorded theory is attributed to the Greek philosopher Aristotle in the fourth century BC, and an early speculation was that it was caused by the collision of clouds.
Subsequently, numerous other theories were proposed.
By the mid-19th century, the accepted theory was that lightning produced a vacuum. In the 20th century a consensus evolved that thunder must begin with a shock wave in the air due to the sudden thermal expansion of the plasma in the lightning channel.
Experimental studies of simulated lightning have produced results largely consistent with this model, though there is continued debate about the precise physical mechanisms of the process.
Other causes have also been proposed, relying on electrodynamic effects of the massive current acting on the plasma in the bolt of lightning. The shockwave in thunder is sufficient to cause injury, such as internal contusion, to individuals nearby.
Inversion thunder results when lightning strikes between cloud and ground occur during a temperature inversion. In such an inversion, the air near the ground is cooler than the higher air. The sound energy is prevented from dispersing vertically as it would in a non-inversion and is thus concentrated in the near-ground layer.
Inversions often occur when warm moist air passes above a cold front; the resulting thunder sound is significantly louder than it would be if heard at the same distance in a non inversion condition.