Dear Tom,
I’ve noticed that sounds carry better at night than during the day. Could you provide an explanation?
— Louise, Park Forest
Dear Louise,
Sounds do carry better and farther at night. Because it tends to be quieter then, individual sounds are easier to distinguish. By far the most important factor, however, is a difference in the temperature structure of the lower few hundred feet of the atmosphere between day and night.
Sound travels through cold, dense air more slowly than through warmer, less dense air. When air temperatures change on the path along which sound waves are traveling, the waves always bend toward the colder air.
By day, it’s warmer near the ground and colder above; sound bends up and away from the ground (and you). At night, it’s colder near the ground and warmer above; sound waves bend down.
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