[James]

James asked the Naked Scientists:
   
Hi Chris,
 
One of your listeners earlier noticed that sounds seemed to be dampened down when it's foggy.  
 
I've noticed the opposite effect when the weather is stormy, ie just before a thunderstorm, that sounds actually appear to get louder & travel further!  Is this true, or is it just my imagination?  
 
Regards,
 
 
James in Cambridge.

What do you think?

[paul.fr]

I can't say I've noticed this, and I wonder if it has anything to do with "calm before a storm"?

More often than not, before thunderstorms we experience high humidity. As sound travels faster in humid air I wonder if the sound is not louder, but reaching you sooner and therefore appearing louder?

Maybe a passing physicist can answer this better.

[WylieE]

I used to live close (too close) to a train track and there was a big change in the sound of the train whistle depending on how humid it was.  I can't say if it was louder or not, but very distinct, less "tinny" and more fluid sounding on a humid day than a cold, dry day  (the only time it was not humid was when it was cold). 

There was also a change between winter (in Michigan, so below freezing) and summer.  I love the above freezing train sound because it means summer is coming.

Of course it was always louder in summer, I had my windows open  []

[RD]

Could be refraction ... http://www.school-for-champions.com/science/sound_over_water.htm

[Make it Lady]

Would the higher pressure have anything to do with it? I'm not a physicist either but I'm sure if one were passing they would give a doppler effect!

[RD]

A local change in atmospheric pressure would alter the refractive index and redirect the sound...

The sound of thunder created by lightning may be refracted upward so strongly that a shadow region is created in which the lightning can be seen but the thunder cannot be heard. This typically occurs at a horizontal distance of about 22.5 kilometres (14 miles) from a lightning bolt about 4 kilometres high.

http://www.britannica.com/EBchecked/topic/555255/sound/63980/Refraction

[James 1]

The humidity idea sounds plausible, although it seems to conflict with the original question, about sounds being muffled in foggy conditions.  Having said that, I suppose fog particles being tiny droplets of water, rather than water vapour, would have a different effect on sound. 

[Make it Lady]

I love this question. It was really high pressure last night and I could hear the distant main road last night. No wind so it wasn't that. It has really made me listen and think. Thanks James. You I like.