APOD: Storm Cloud Over Texas (2024 Aug 06)

[APOD Robot]

Storm Cloud Over Texas

Explanation: What makes this storm cloud so colorful? First, the cloud itself is composed of millions of tiny droplets of water and ice. Its bottom is almost completely flat -- but this isn't unusual. Bottom flatness in clouds is generally caused by air temperature dropping as you go up, and that above a specific height, water-saturated air condenses out water droplets. The shape of the cloud middle is caused by a water-droplet-laden column of air being blown upward. Most unusual, though, are the orange and yellow colors. Both colors are caused by the cloud's water drops reflecting sunlight. The orange color in the cloud's middle and bottom sections are reflections of a nearly red sunset. In contrast, the yellow color of the cloud's top results from reflection of light from a not-yet-setting Sun, where some -- but less -- blue light is being scattered away. Appearing to float above the plains in Texas, the featured impressive image of a dynamic cumulonimbus cloud was captured in 2021 while investigating a tornado.

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[Eclectic Man]

What a wonderful photograph. Interesting and informative explanation. However, one minor quibble,

the cloud itself is composed of millions of tiny droplets of water and ice

Well, yes, but clouds are tenuous things and contain approximately 1000 droplets per cubic centimetre. So a cubic kilometre of cloud (not unusual) would contain approximately 10¹⁸ water droplets, rather than mere 'millions'.

(https://www.wtamu.edu/~cbaird/sq/2014/0 ... y%20spaced. )

[bls0326]

I live in this area. We do get some spectacular weather (sunsets, thunderstorms, tornados) but this picture is most impressive. Great shot!!

[johnnydeep]

In contrast, the yellow color of the cloud's top results from reflection of light from a not-yet-setting Sun, where some -- but less -- blue light is being scattered away.

Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?

[Ann]

In contrast, the yellow color of the cloud's top results from reflection of light from a not-yet-setting Sun, where some -- but less -- blue light is being scattered away.

Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?

Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.

Click to view full size image

Click to view full size image

Ann

[johnnydeep]

In contrast, the yellow color of the cloud's top results from reflection of light from a not-yet-setting Sun, where some -- but less -- blue light is being scattered away.

Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?

Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.

Click to view full size image

Click to view full size image

Ann

Maybe it's a density thing? Denser air will reflect more blue light simply because there are more molecules to do the deflecting?

[Ann]

Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?

Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.

Click to view full size image

Click to view full size image

Ann

Maybe it's a density thing? Denser air will reflect more blue light simply because there are more molecules to do the deflecting?

I think that is just right, Johny!

Ann

[Chris Peterson]

In contrast, the yellow color of the cloud's top results from reflection of light from a not-yet-setting Sun, where some -- but less -- blue light is being scattered away.

Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?

Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.

Click to view full size image

Click to view full size image

Ann

We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.

[johnnydeep]

Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?

Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.

Click to view full size image

Click to view full size image

Ann

We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.

And there's no air density factor affecting how much blue light it scattered?

[Chris Peterson]

Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.

Click to view full size image

Click to view full size image

Ann

We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.

And there's no air density factor affecting how much blue light it scattered?

Obviously, lower density air scatters less light. But in what way would that impact these images? There isn't much variation in density between the bottom and top of the clouds. And what we see in the air itself is a product not of density variation, but of path length.

[johnnydeep]

We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.

And there's no air density factor affecting how much blue light it scattered?

Obviously, lower density air scatters less light. But in what way would that impact these images? There isn't much variation in density between the bottom and top of the clouds. And what we see in the air itself is a product not of density variation, but of path length.

Ok, thanks.

[Ann]

Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?

Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.

Click to view full size image

Click to view full size image

Ann

We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.

I can' figure out why the colors are so well separated. The orange part of the cloud appears to be the same shade of peach, although admittedly the very bottom part appears to be a tad redder. And the yellow part of the cloud is almost the same shade of lemon overall.

---

A storm cloud made of lemons and peaches (and water)? Though I guess there is no sugar or vanilla extract in it. Credit: Lyuba Brooke,

---

Ann

[Chris Peterson]

I can' figure out why the colors are so well separated. The orange part of the cloud appears to be the same shade of peach, although admittedly the very bottom part appears to be a tad redder. And the yellow part of the cloud is almost the same shade of lemon overall.

---

A storm cloud made of lemons and peaches (and water)? Though I guess there is no sugar or vanilla extract in it. Credit: Lyuba Brooke,

---

Ann

Well... I'll note that the image was taken with a phone, and the sad reality in this Instagram obsessed world is that the default camera settings on most phones (or even the deliberately chosen ones) are frequently "vivid" or a similar one that boosts clarity and saturation. The colors here look to me like they've been pushed beyond the actual visual appearance of the phenomenon somewhat. So I wouldn't look too deeply into the exact colors, just the color range and general transition trends.