different thunder – clap vs roll

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Why is some thunder a sudden loud bang (with minor echos), while other times it’s a long drawn-out roll that goes on & on? Is it simply how close I am to the lightning, or is there more to it?

In: Physics

This is multipath interference.

If you are close to the lightning, you hear a sharp clap, because there aren’t many ways to cover a short distance. You hear echos when the shortest path to you is supplemented with a reflection from some distant reflector (building, canyon, …).

If you are farther from the lightning, the shortest path is still the first sound you hear, but lots of shallow reflections of buildings that are mostly “on the way” from the lightning to you are only slightly delayed. Sometimes this causes interference, particularly the higher the frequency. The remaining low frequencies give the long low rumble.

Could also be the orientation of the lightning with respect to you…consider if it is 10 miles away and the lightning is cloud-to-ground (vertical) say 2 miles high….the sound from it pretty much arrives where you are all at once.
Now consider it is horizontal intracloud lightning, and one end is 2 miles from you, and the other end is 20 miles from you. The delay from the far end is a lot longer than the delay from the near end.

Lightning generate sounds along a whole arc it travel almost at the same time. And the length of this path can be pretty long. This means you’re receiving sounds from different point sources. If every point on the arc are mostly has roughly the same distance to you, the sound is sharp; if it’s not, it’s a drawn out rumbling.