Porpoises
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We humans tend to think of snow as a peaceful, quiet thing. But, if you were a porpoise swimming around below a snowstorm, you might be thinking 'what's with all the racket?' Hi, I'm Dave Thurlow and this is the Weather Notebook. When snow hits water it makes a high-pitched sound at around 50 - 200 KHZ. Now that's too high for us to hear but it's not too high for a porpoise's hearing.In fact, the noise underwater can increase up to a thousand times during a heavy snowfall.

Harbour porpoise Porpoise Science and Conservation

A team of scientists has figured out why this is. By putting sensitive microphones underwater they've measured the sound from different kinds of precipitation. As you might expect, rain and hail are much louder than snow.

But the noise from rain and hail is concentrated closer to our hearing range. It sounds like this. (soundbite) But snowfall isn't audible. For years scientists puzzled over why snow falling on water should cause a high frequency noise.

The answer turns out to be not just the snowflake itself but the air trapped inside it. A typical snowflake is only 10% water and 90% air. When snowflakes hit the ocean and melt tiny air bubbles are released. It's the oscillation of these bubbles near the surface that causes the distinctive high-pitched sound. Scientists from Johns Hopkins, Washington, Edinborough and Boston Universities worked together to figure this out. They say that the study could help people correct for underwater noise when they use sonar to track fish or detect other sounds.

So you have to wonder; is there a grateful porpoise out there thinking "I told you so?'.

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