That's really fascinating. So as you say, in deserts at dusk the differential
between ground and air temperature will be huge, and any sound travelling
towards the listener will be refracted upwards, thus increasing the quietness
of the location. Its somewhat like a pool of light from a spotlight getting
smaller and smaller around the listener. And vice versa at dawn, when the air
starts to heat up. A long recording should reveal that effect?
--- In "Raimund" <> wrote:
>
> <But every now and then there's moments where the wind lies down and the
> flies stay away and it's silent. Not quiet. But silent. I'm sure that anyone
> who's ever driven into the Australian outback or desert know what I'm talking
> about. I can highly recommend it>
>
> Peter,
>
> I think I know what you are talking about. I experienced that stunning
> silence several times shortly after sunset while camping in the Sonoran
> Desert (Arizona).
>
> There is a simple explanation for that kind of silence: A strong temperature
> gradient in the air above the ground creates a sonic shadow region for each
> sound source (the ground is still hot, but the air is getting cooler at
> night). See http://www.acs.psu.edu/drussell/Demos/refract/refract.html. So, I
> think there is still some noise around, but it just cannot be heard due to
> these refraction effects.
>
> Regards,
> Raimund
>
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