Going outside after a snowfall can be magical, with the spectacle of a winter wonderland underlined by the change in the soundscape. Suddenly, all is quiet.
The peculiar hush is partly due to the reduction in human activity. There are fewer people and less traffic about, often fewer planes and trains. Building sites, road mending and other sources of noise fall silent. Birdsong is equally subdued.
But it is also due to the fact that snow has an acoustic damping effect, muffling the echoes that resound from the ground and other surfaces. Snow is formed of ice crystals, which would not normally be good soundproofing, but in this case they are packed together loosely with a lot of air. The resulting porous material is a good sound insulator. A 2008 study in Alaska found that a blank pistol shot was dampened by 30 decibels across a snow-covered surface, the difference between talking and whispering.
Sound refraction also plays a part. During snowfall there tends to be warmer air near the ground with colder air above. This combination causes sound to refract, curving it upwards, further reducing the volume that is transmitted at ground level
However, if snow partially melts and freezes, sounds may be reflected better than in normal conditions. The eerie hush after snowfall is often a brief quiet interlude before service is noisily resumed.
