<p>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 <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html" rel="nofollow noreferrer">Rayleigh Scattering</a> from sub-wavelength sized air molecules which makes the sky blue because of its strong wavelength dependence, <a href="https://en.wikipedia.org/wiki/Mie_scattering" rel="nofollow noreferrer">Mie scattering</a> and <a href="https://www.mkrgeo-blog.com/light-scattering-in-the-earths-atmosphere-part-3-clouds-haze-and-surface/" rel="nofollow noreferrer">non-selective scattering</a> from larger particles such as water aerosol droplets scatter all wavelengths relatively equally.  This is <a href="https://www.mkrgeo-blog.com/light-scattering-in-the-earths-atmosphere-part-3-clouds-haze-and-surface/" rel="nofollow noreferrer">why clouds are white</a> when illuminated by sunlight.</p>

CC BY-SA 4.0
2022-12-24T15:58:19.220Z
2022-12-24T15:58:19.220Z
David Bailey
<p>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'.</p>

<p>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. </p>

CC BY-SA 3.0
2016-04-29T12:20:11.370Z
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.
daniel.heydebreck
CC BY-SA 3.0
2016-04-30T08:03:12.967Z
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.
Gordon Stanger
CC BY-SA 3.0
2016-05-01T11:19:00.873Z
"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.
daniel.heydebreck
CC BY-SA 4.0
2022-12-24T15:44:35.423Z
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](http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html). A white sky occurs when more light is being scattered, not less. For example, [clouds appear white](https://www.nrcan.gc.ca/maps-tools-publications/satellite-imagery-air-photos/remote-sensing-tutorials/introduction/interactions-atmosphere/14635) because Mie and non-selective scattering from particles comparable to or larger than the wavelength of light have little wavelength dependence.
David Bailey
CC BY-SA 3.0
2016-04-29T09:33:30.563Z
2016-04-30T03:25:58.307Z
2016-04-30T03:25:58.307Z
Gordon Stanger
<p>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.</p>

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

<p>Edit: I've gathered a few images which I think show what I'm seeing sometimes: <a href="https://i.sstatic.net/46Dwa.jpg" rel="noreferrer">https://i.sstatic.net/46Dwa.jpg</a></p>

CC BY-SA 3.0
2016-04-29T04:34:52.120Z
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:  http://www.scientificamerican.com/article/fact-or-fiction-smog-creates-beautiful-sunsets/  and http://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.
userLTK
CC BY-SA 3.0
2016-04-29T04:40:26.293Z
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.  http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html
userLTK
CC BY-SA 3.0
2016-04-29T05:59:48.757Z
@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.
Adrian
CC BY-SA 4.0
2024-03-30T01:43:58.857Z
Note that the imgur link (despite the `.jpg` ending) used to lead to a whole gallery with better images. It seems no tinkering with the URL can bring that back.
Adrian
<rainfall><sun>
The sun sometimes appears pure white after rainfall, how can this be explained?
Adrian
# The sun sometimes appears pure white after rainfall, how can this be explained?

(Asked by: username_0 on 2016-04-29)

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.sstatic.net/46Dwa.jpg>

**Tags:** rainfall, sun

> **Comments:**
> **username_1**: 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:  http://www.scientificamerican.com/article/fact-or-fiction-smog-creates-beautiful-sunsets/  and http://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.  
> **username_1**: 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.  http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html  
> **username_0**: @username_1: 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.  
> **username_0**: Note that the imgur link (despite the `.jpg` ending) used to lead to a whole gallery with better images. It seems no tinkering with the URL can bring that back.  

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## 2 answers

### Answer by username_3 on 2016-04-29. Score: 6 | Accepted answer

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.

> **Comments:**
> **username_4**: 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.  
> **username_3**: 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.  
> **username_4**: "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.  
> **username_2**: 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](http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html). A white sky occurs when more light is being scattered, not less. For example, [clouds appear white](https://www.nrcan.gc.ca/maps-tools-publications/satellite-imagery-air-photos/remote-sensing-tutorials/introduction/interactions-atmosphere/14635) because Mie and non-selective scattering from particles comparable to or larger than the wavelength of light have little wavelength dependence.  

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### Answer by username_2 on 2022-12-24. Score: 4

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](http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html) from sub-wavelength sized air molecules which makes the sky blue because of its strong wavelength dependence, [Mie scattering](https://en.wikipedia.org/wiki/Mie_scattering) and [non-selective scattering](https://www.mkrgeo-blog.com/light-scattering-in-the-earths-atmosphere-part-3-clouds-haze-and-surface/) from larger particles such as water aerosol droplets scatter all wavelengths relatively equally. This is [why clouds are white](https://www.mkrgeo-blog.com/light-scattering-in-the-earths-atmosphere-part-3-clouds-haze-and-surface/) when illuminated by sunlight.


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