Approaching the airport on my way to work today - winter is here
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… but typically for NS, it’s all change by the end of the week 
I think the only thing we won’t see this week is thunder and lightning 
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Something for everyone there 
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Nice for a bit of wild swimming on Wednesday 
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I’ll just check if the sea ice has melted first
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Anyone see this?
Not in fog, but I’ve seen it under other conditions. It’s The Tyndall Effect, I’m pretty sure.
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Also how optical smoke detectors work.
The light source is normally a gallium arsenide IR LED with a labyrinth between it and the photocell so it normally sees nothing. Combustion particles reflect and refract the light through the labyrinth as it is easier to measure from 0 to 1 than from 100 to 99.
It’ll be some kind of optical scattering for sure that gets the light round the labyrinth’s corners.
The Tyndall Effect is a very specific kind though - it sorts out the red light from the blue due to some close relationship between the wavelength of the light and the size of the scattering particles. Hence generating Stuart’s weird pink fog* when the water droplets are just the right size.
You probably wouldn’t want that colour dependence in a smoke detector a) as your IR LED only supplies light of one colour and b) as Tyndall scattering would only work for that colour with one size of smoke particle, whereas you’d want your alarm to work for all sorts of smoke.
*Pink fog is not to be confused with red mist. I’ve seen the latter come down once in a while too … 
.
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I am not a physicist but when I started work in the Fire Engineering world (late 70s) , optical smoke detectors were fairly new (as opposed to ionisation smoke detectors which had been around a while)
They were then known as ‘Tyndall effect optical smoke detectors’ which was a bit of a mouthful and got shortened. If you google that term you will get a lot of results.
Whether that is technically correct is another matter but it is how they were known
Ah, then you will know more than me. I am a physicist but all I know about the Tyndall Effect comes from an A-level chemistry project we did on colloids, and on what I can now find in Wiki. There does seem to be a deal of disagreement about how the term should be used, mostly among the experts who actually need to use it (no-one else cares sufficiently).
The Wiki article on it even has a section illustrating ways in which it’s possible to get mixed up. Ironically it includes this para
When the daytime sky is cloudless, the sky’s color is blue due to Rayleigh scattering instead of Tyndall scattering because the scattering particles are the air molecules, which are much smaller than the wavelengths of visible light.
It’s ironic because Rayleigh worked out the theory of the scattering named after him while he was busy also working out the explanation of Tyndall scattering (Tyndall was the first to record it, but he couldn’t explain it).
It’s easy to see how confusion arises !
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The forecast said that the snow would continue overnight. A Quick Look out of the back door, a minute ago, would seem to confirm that.
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Are you going to write your name in it ?
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Time for snow angels. You know you want to.
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Same view from the back door this morning
and from my bedroom window
Drifts well over 3’ deep in places, roads impassable, other than quads & tractors. First walk with the girls is going to be a hoot.
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What’s the wind doing - sky still looks a bit ‘busy’…
F7/8 Northerly.
Whipping up the fallen snow a treat. Still snowing too.
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