physics question #3153



Ian Gordon, a 50 year old male from Exeter UK asks on December 29, 2005,

Q:

Why are sounds so much louder downwind, even when the wind is light?

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the answer

Barry Shell answered on January 2, 2006, A:

Sound waves are pressure waves. They are relatively tiny variations in air pressure, too small to be felt as wind, but they are carried through the air around us. Sounds are louder downwind due to something called downward refraction which happens because air on the ground moves slower than air higher up. There is a steady increase in wind speed as you get higher off the ground. This acts on sound in the same way a prism acts on light. It tends to bend sound downward. The sounds hit the ground and bounce off, so you end up with multiple copies of the same sound and it sounds louder to your ears.

A diagram of how this works by Dietrich Heimann in Germany, and a very comprehensive explanation how sound works, and how the wind can amplify it by Erik Salomons in Netherlands.

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