Snowflakes create «problems»
Imagine walking down the street, hearing only the crunch beneath your feet and your own breathing as snow falls quietly around you. In fact, snowflakes absorb sound, creating the sensation of the distinct silence of a snowfall. But while snowflakes often evoke a feeling of calm and peace in people – falling snow affects aquatic creatures in a completely different way.
When a team of American researchers from four universities analyzed recordings made underwater during winter storms, they encountered rather blurred sonar readings – sonar also being known as a hydrolocator (a means of detecting underwater objects by sound using acoustic emission). The specialists attributed the noise that caused the interference to oscillating air bubbles, too small and short-lived to be seen with the naked eye.
It turned out that this was indeed the case. Later the scientists concluded that when a snowflake falls onto water, it leaves a small amount of air just beneath its surface. However, the sound it makes not only interferes with electronic equipment but also significantly disturbs aquatic animals.
The scientists' research
Lawrence Crum, the lead author of the study, launched a project in which, using sensitive sonar and underwater microphones, he analyzed the acoustic «fingerprints» of the sounds of falling snowflakes and air bubbles and concluded that they were identical. Later, Prosperetti, a world-renowned scientist in the field of physics, was asked to join the research, given that in the past he had studied the underwater noise produced by raindrops. It was he who developed the theoretical framework explaining how the tiny bubbles formed when snow falls can produce the sounds previously recorded by Crum and his colleagues.
The cause lies in the air
When a snowflake lands on the surface of water, two different sounds are produced: the first resembles a «click», and the second a piercing «squeal». The «click» occurs at the moment when some air bubbles escape as the snowflake hits the surface. The «squeal» is heard as soon as the snowflake begins to melt, releasing the tiny air bubbles trapped in its crystals.
The latter sound, as meteorologist Keith Heidorn put it, sounds like a «snowy cry of death agony». This «squeal», reaching a frequency of 200 kilohertz, lies far beyond human hearing, but can even be heard by porpoises or dolphins. And heavy snowfall combined can add up to 30 decibels of noise to the surrounding high-frequency sounds.
«Snow is incredibly complex, – notes Prosperetti. – The shape and size of a snowflake depend heavily on the temperature it has been exposed to: not only the temperature at the Earth's surface, but also the temperature of the cloud in which it formed. Scientists know that snowflakes are formed from many ice crystals arranged in such a way that a great deal of space for air remains between them. It turns out that nine-tenths of a snowflake is air. When a snowflake melts, it releases that air, and when the air oscillates – it makes noise».
Mysterious and strange things that can happen only in severe frosts
