Thunder is the sound of air expanding around lightning.
Thunder is caused by the sudden expansion of air around the path of lightning. The deep rumble and sharp cracks of thunder are produced as the air around the lightning is superheated – up to about 54,000° Fahrenheit (about 33,000° Celsius) – and expands rapidly. This rapid expansion creates an acoustic shock wave that manifests as thunder. The closer the lightning is, the louder the rumble of thunder will seem.
Hail can accompany storms.
Lightning is a discharge of electricity into the atmosphere. Lightning takes just a few milliseconds to travel from clouds to ground or to an object that is lifted off the ground and then back to clouds along the same path. Electrostatic discharge raises the air around this pathway to a temperature that is about five times hotter than the surface of the sun. This happens so quickly that the heated air does not have enough time to expand and is compressed to many times normal atmospheric pressure. As the compressed air expands outward, it creates an acoustic shock wave that is heard like thunder.
what affects the sound
Air rapidly expands around the path of lightning, creating an acoustic shock wave that is heard like thunder.
The location and shape of lightning will affect how the thunder will sound to the listener, as will the ambient air temperature. Lightning nearby will sound like a loud crack or pop, and lightning that is far away will sound more like a long bang as shockwaves bounce off clouds and hills. A forked lightning bolt can also sound like a bang when sound waves bounce off each other.
Also, thunder will sound louder when the air near the ground is cooler and the air higher in the atmosphere is warmer. This is because acoustic shock waves get “trapped” in the cold air. This temperature difference, called an inversion, tends to happen at night, which is why thunder often sounds louder at night.
Before the 20th century, science could not explain the sounds of thunder, so the cause was a matter of much dispute. The early Greeks believed it was caused by the collision of clouds. Other theories included vacuums, explosive gases, and steam. Thor, a god in Norse mythology whose name derives from the Old Norse word for thunder, is usually portrayed as wielding a thunder hammer.