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I've noticed on multiple occasions, that after heavy rainfall, the sun appears a pure glistening white, even if it's already standing low in the sky. I can't discount psycho-visual effects as an explanation, such as cloud shadows from above affecting color perception. Yet considering the many warm cloudy sunrises/sets I've seen, I'd be surprised if that's all there is to it.

Is anyone familiar with what I'm describing and knows of a scientific description of the phenomenon?

Edit: I've gathered a few images which I think show what I'm seeing sometimes: https://i.stack.imgur.com/46Dwa.jpg

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    $\begingroup$ I don't know if this is a full explanation, but dust, particles, and pollution, can create a redder sunset. Rain tends to remove dust, tiny particles and water soluble pollutants from the air. Source: scientificamerican.com/article/… and news.mit.edu/2015/rain-drops-attract-aerosols-clean-air-0828 . . . putting as a comment cause it may be incomplete, but that would be my guess. $\endgroup$
    – userLTK
    Apr 29, 2016 at 4:34
  • $\begingroup$ As a footnote, the Sun is white. Viewed from space it's pure white. The sun appears yellow and the sky blue (and red at sunset) due to scattering. I know that wasn't your question, I just thought it's worth pointing out just in case. math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html $\endgroup$
    – userLTK
    Apr 29, 2016 at 4:40
  • $\begingroup$ @userLTK: Yes, thank you for those articles. I assumed that the cleanliness of the local air column has a negligible effect on sunlight coming from a shallow angle, but I think I might have been wrong on that. $\endgroup$
    – Adrian
    Apr 29, 2016 at 5:59

2 Answers 2

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When it rains the raindrops nucleate around aerosol particles of salt, dust, clay, soot, dimethyl sulphide, etc. In addition a falling raindrop may pick up any particulate matter that may be in its trajectory. The net result is that rain 'scrubs' the atmosphere clean. Without all these polluting particles to diffuse different wavelengths of the spectrum, the eye perceives the 'full spectrum', which the brain interprets as 'white light'.

In addition, you are quite correct that the eye's response to light, and to what constitutes 'white light' is very variable, depending upon light intensity, extent of blue sky vs. cloud, direction relative to the sun, reflections from buildings, the sea, etc. and other factors.

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    $\begingroup$ One remark: dimethyl sulphide forms sulfate (ultra-fine sulfate particles). These sulfate particles are cloud condensation nuclei. The dimethyl sulphide does not exist anymore when the sulfur is washed out. $\endgroup$ Apr 29, 2016 at 12:20
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    $\begingroup$ Perhaps Daniel is correct that more raindrops nucleate around oxidised derivatives of DMS, including sulphuric acid itself. Nevertheless, DMS has a residence time in the atmosphere of about a day, and may therefore, to some extent, may be a nucleating agent in its own right. $\endgroup$ Apr 30, 2016 at 8:03
  • $\begingroup$ "Nevertheless, DMS has a residence time in the atmosphere of about a day, and may therefore, to some extent, may be a nucleating agent in its own right." Could be. I am not sure. $\endgroup$ May 1, 2016 at 11:19
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    $\begingroup$ This answer seems to imply that a clear, clean sky would be white, which is not consistent with the standard explanations for why the sky is blue. A white sky occurs when more light is being scattered, not less. For example, clouds appear white because Mie and non-selective scattering from particles comparable to or larger than the wavelength of light have little wavelength dependence. $\endgroup$ Dec 24, 2022 at 15:44
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The sky appears white because immediately after the rain stops and the clouds have started to dissipate, there are often water aerosols (i.e. diffuse clouds) still lingering in the atmosphere. Unlike Rayleigh Scattering from sub-wavelength sized air molecules which makes the sky blue because of its strong wavelength dependence, Mie scattering and non-selective scattering from larger particles such as water aerosol droplets scatter all wavelengths relatively equally. This is why clouds are white when illuminated by sunlight.

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