Weather Blog

How fog can play tricks on your ears

How fog can play tricks on your ears
Have they started ferry service in Bothell? Not exactly, but you could be forgiven if that thought popped in your head on Sunday.

I had a viewer who lives in Bothell write in that he could hear the fog horns from the Edmonds ferry on Sunday, and wondered how it was possible, what with the ferry roughly 11 miles away.

Turns out, Sunday was a great day, atmospherically speaking, to listen in on distant events.

There were two factors in play -- one, a fog layer hugging the Puget Sound shoreline, and second, a temperature inversion over the area. Sound travels better in a dense medium -- that's how you can hear a watch beeping much better under water, and why you can hear banging on a metal pipe much louder than if that same sound were made in air.

[In fact, that's a good experiment next time you're at a swimming pool with a friend.  Have each of you be on the opposite ends of the pool and have a watch that's water resistant. Have the alarm go off under water, and note how if you stick your ear in the water, you'll hear the alarm beeping as if the watch is right next to your ear, even if the watch is on the other side of the pool.]

Fog occurs when the air is saturated and near 100% humidity. The tiny water droplets are much better conductors of sound than just regular air. Bottom line, sound can travel greater distances in a fog than in just plain old regular-humidity air.

Secondarily, we had a temperature inversion where cold air was pooled at the surface (helping to create the fog), and warmer air was sitting aloft. This boundary between the cold air and warm air can actually reflect sound waves back toward the ground, allowing sound that would normally radiate out into the hinterlands of the higher atmosphere to bounce back and travel near the surface. (Ask anyone who has served on a submarine, and they can tell you about the importance of those temperature boundary layers in the water and how they can affect sound transmissions when tracking via sonar.)

Bottom line -- it can make sounds travel farther than they would under normal atmospheric conditions.  So when it's foggy outside, and/or there's a temperature inversion, better not to be discussing state secrets or anything :)