If you ever went outside on a
winter day, during or after a
snow
storm you may have noticed the relative
silence of your surroundings.
Not only does everything
look as if it is covered with a big white
blanket, it also
sounds as such. The surroundings are
beautifully quiet.
The typical acoustics encountered after a snow storm are generally
not caused through dampening of the sound by falling snowflakes, since this phenomenon is also observed some time after
a snow fall. In fact, during the winter there is also often a
temperature inversion: a layer of cold air directly below a layer of
warmer air, that will actually increase the propagation of sound
through the cold air.
Then, what causes the typical snow acoustics? First of all, there may
actually be fewer sources of noise outside, since more people tend to
stay home after heavy snow fall. Secondly, the generation of sound
from each source may be significantly changed by a layer of snow on the
soil, causing a dampening of the sound generation. Finally, a layer of
fallen snow can absorb sound quite efficiently; a snow coverage of
approximately 2.5 cm will only transmit 25% of the sound1.
Thus, a significant part of the sound that would otherwise be
reflected by the street or soil will be absorbed by the snow
blanket.
As described in:
Prof. Dr.
Marcel G. J. Minnaert,
de Natuurkunde van het Vrije Veld,
1939.
1:
Nature,
143, 80, 1939