Deanna wondered: “In a recent column, you said there is never lightning without thunder, even if it is inaudible from being too far away. OK, I can live with that. My question is: Can there be thunder without lightning?”
Thunder by definition is the sound that lightning makes, so no, you can’t have thunder without lightning somewhere. In all likelihood, the bolt of lightning that Deanna heard (but didn’t see) was either behind a cloud or perhaps behind the mountains.
Fair enough, but she had a follow-up question: “What are the mechanics of thunder? (I suspect it isn’t some old codger who likes to bowl among the clouds.)”
No… no old codgers. Thunder is caused by the rapid expansion of superheated air. An average lightning bolt has a temperature of about 50,000 degrees F. This causes a rapid expansion of the column of air around the bolt, creating a sonic shockwave that goes outward from the bolt, and then sucks back in as the air rapidly cools. Think of a giant woofer on a stereo speaker, and you can get a general idea.
Thunder can usually be heard at least 10 miles away from its lightning source, and if the conditions are just right, it’s possible to hear thunder more than 20 miles away.