Naked Science Forum
Life Sciences => The Environment => Topic started by: James on 23/06/2009 11:30:02
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James asked the Naked Scientists:
Hi Chris,
One of your listeners earlier noticed that sounds seemed to be dampened down when it's foggy (http://www.thenakedscientists.com/HTML/content/questions/question/2327/).
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?
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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.
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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 [:-\]
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Could be refraction ... http://www.school-for-champions.com/science/sound_over_water.htm
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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!
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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
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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.
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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.