[Michael McCracken]

Michael McCracken asked the Naked Scientists:

Hello there Drs, I have a question about how snow might affect sound.

I live in a dry, arid climate set at about 1.6km above sea level (Denver, Colorado, USA). I've often noticed that when it snows a couple of inches or more, everything gets so very quiet. I'm wondering if snow has any sound dampening effects?

Thanks, love the show!

What do you think?

[lightarrow]

I'm wondering if snow has any sound
dampening effects?

Exactly.

[lyner]

If you've ever been in a UK classroom when it starts to snow, you might reconsider your question. It's total bedlam.
I guess that, near Denver, snow is not a novelty.

[chris]

I've noticed the sound-reducing effect of snow. I think there are several aspects to this; first the snow surface is not hard, rigid and reflective like a mirror or solid wall. Consequently sound reflection from a non-compacted snow layer is greatly reduced.

Secondly, when it snows heavily then other sources of noise - traffic, industry and human activities are reduced, cutting noise production.

Chris

[lightarrow]

I like snow very much, for two reasons: the first is that it reminds me Christmas and the second is the question of this thread.

[lyner]

I wonder whether there is any sound absorption as it travels through falling snow or is it all absorption when hitting snowy surfaces.

[JP]

I wonder whether there is any sound absorption as it travels through falling snow or is it all absorption when hitting snowy surfaces.

I've wondered that myself.  I just did some checking, and the wavelength of sounds audible to humans range from centimeters to meters, which seems way too big to interact strongly with snowflakes.

[dentstudent]

I wonder whether there is any sound absorption as it travels through falling snow or is it all absorption when hitting snowy surfaces.

I've wondered that myself.  I just did some checking, and the wavelength of sounds audible to humans range from centimeters to meters, which seems way too big to interact strongly with snowflakes.

Perhaps the question should be "when it has snowed". I think that Chris is on the right track, and that much of the effect is firstly down to a reduced number of people using cars etc so there is actually less noise (correlation effect) and that the snow deadens the noise in the same way that egg cartons on your walls do (you know what I mean.....), since the reflected sound is diminished as the snow surface is more rough (causation effect).

[Bikerman]

The simple answer is that pores (air gaps) in snow are responsible for much sound deadening.

When a pressure wave travels along the surface, some of the air is forced into the pores in the snow. Friction and thermodynamics mean that the pressure level is much reduced when the air emerges again. This gives a significant sound 'deadening' effect.

Here's an article from the US military on the basics...
http://snow.usace.army.mil/Snow_acoustics/

[lyner]

I agree about the pores as a reason. There can be very long air channels under the surface - plenty of drag and loss.
 As for absorption by falling snowflakes - if they are light enough (and they are smaller than most audible wavelengths) they could either be vibrated or obstruct the vibrations of the air. They are very flimsy so they could well flex and dissipate some energy that way.


I bet it's been measured by someone - Bell Labs in 1937, no doubt.

PS A coincidence. Just found this reference - not the paper though:
Kaye, G. W. C., and E. J. Evans, 1939: Sound absorption by snow. Nature, 143, 80.

[Michael Mc]

In researching my question a bit more, I believe that not only do the properties of snow in general contribute - but also the climate which produces the snow. For instance, because I live in a high-elevation, arid environment - we get a lot of 'dry' snow.

By dry/wet snow - I'm referring to the snow to water ratio, whereby as you melt snow how much water can be reclaimed. Average snow has a 10:1 ratio - or if ten inches of snow accumulate then melts, one inch of liquid precipitate will be produced. Wet snow will have a ratio lower than 10:1, while dry snow will have a ratio higher than 10:1 (sometimes much higher, perhaps 30:1).

I believe that some key points are that dry snow has a lower density, resulting in more space between snow crystals. Dry snow is also less sticky, prone to blowing around, and is therefore composed of a larger number of smaller flakes. This might allow dry snow to dampen sound more effectively than normal or wet snow, while covering a wider surface area.

Thanks,

Michael Mc


found much of the above information here: newbielink:http://www.theweatherprediction.com/habyhints/346 [nonactive]