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Question

Why is it that on a cold day sky seems more blue? Is there a direct connection between temperature and the 'blueness' of the sky?
Asked by: Lynda Lau

Answer

I think there is few direct relationship between the color of the sky and the temperature. But there are three important factors that are indirectly related with temperature and that affects greatly sky appearance.

1) Altitude. As the altitude gets higher, the Rayleigh dispersion (which originates the blue color) gets smaller because atmosphere layer for dispersion gets thinner, making the blue more deep and dark. Eventually, when you get enough altitude the sky turns absolutely black. Temperature normally decreases with altitude.

2) Dust particles produces white dispersion that tends to shift blue color to the white. Dust presence is favoured by thermal convection. Anticyclonic conditions (often leading to cold days) kill thermal convection and so reduce atmospheric dust concentration.

3) Water condensation micro-drops. The effects are quite similar to the dust one. In cold anticyclonic days, the water condenses very close to ground, ( sometimes leading to fog), letting upper atmospheric layers very dry and clear.
Answered by: Lanjarote, Ph.D., Physicist, Spain
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