Rhythm of snow even more deafening

Underwater may be the one place that snow is louder than rain - again because of bubbles.

In fact, to water animals with keener hearing than humans, the racket of snow falling on water can be deafening, according to Larry Crum, a principal physicist with the Applied Physics Laboratory and lead author on the subject in a recent issue of the Journal of the Acoustical Society of America. Snowflakes also pose problems for electronic devices used underwater by blurring sensitive sonar readings.

Crum and colleagues from Johns Hopkins University, University of Edinburgh and Boston University say that nine-tenths of the volume of a snowflake is air. When a snowflake hits water, it starts to melt and the air inside is freed up as a bubble. Trapped underwater, the bubbles oscillate as they are released from the snowflakes and produce very loud, high-frequency noise.

Ranging from 50 to 200 kilohertz - too high pitched to be heard by human ears, which generally pick up nothing higher than 20 kilohertz - the noise might be quite annoying to porpoises and other aquatic animals that detect the higher frequencies. It would be like the difference between quiet conversation and a rock band performance, Crum says.

For users of sonar devices, which employ sound waves to outline forms underwater, snowstorms can produce a tremendous amount of clutter.

The journal article is based in part on readings taken from the swimming pool at a hotel in Virginia. At that time Crum was working at the University of Mississippi, a place with little snow. During a trip north he heard snow was in the forecast so he and a colleague borrowed a van and hydrophones and headed out. They ended up in the wee hours of the morning renting a hotel room and running wires from their room out to the pool to take their measurements. ¶