Why does the thunder from close lightning produce a BOOM and then a slow fade off? Why does it fade off instead of just stop? Conversely, why is thunder from far away a slow fade-on instead of an instant but quieter boom?

Question

Why does the thunder from close lightning produce a BOOM and then a slow fade off? Why does it fade off instead of just stop? Conversely, why is thunder from far away a slow fade-on instead of an instant but quieter boom?

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Answer 1

The sound you hear is a combination of the sound following different paths to your ears.

Imagine if the entire world was made of mirror. You’d see thousands of reflections of the same object, coming from all directions and distances. Every blade of grass, another tiny reflection of the world.

That’s the world for sound. Every blade of grass, leaf, tree, building, and rock reflects a bit of sound. Normally you can’t hear that reflection, but with a loud BANG you hear all of those little reflections adding together. The more distant reflections are weaker and reach you later, so you hear the initial noise and then a fading stretched-out echo of it.