The Weather Notebook: Listener Question: The Sound of Thunder

Listener Question: The Sound of Thunder
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It's listener question time again here on The Weather Notebook. Hi, I'm Dave Thurlow. Today's question comes from Richard Ashcraft from Fletcher, NC:

"Quite often during thunderstorms, you'll first hear some high pitched or relatively high pitched crackling sounds and then several seconds later you hear a much more forceful boom which is low frequency. Does the sound travel different speeds according to its frequency?"

In order to explain this, we'll need some thunder. Listen to the opening of the next thunderclap. There! Did you hear it? Let's listen again and pay attention to the pitch of the first crack. See how it starts close up and sharp. The crackling sounds come from what are called high frequency sound waves and the long lasting drawn out part of the thunder, comes from low frequency sound waves.

Now both kinds of sounds come from the explosion of lightning heating air at the same time, but the cracking sounds dissipate much faster than the rumbling sound. The longer slower, rumbling waves can travel from along the whole length of the lightning stroke channel and arrive at your ears over many seconds. But the crack comes only from the part of the lightning stroke closest to you, and dissipates right away. The rest of the lightning stroke and lightning strokes farther away, send out those wonderful low rumbling sounds that seem to go on into the night.

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