Pink Clouds at High Sun

Last updated on September 16, 2023

Pink Clouds at High Sun: A Phenomenon Explained

Have you ever looked up at the sky and noticed pink clouds during the middle of the day when the sun is high? This intriguing atmospheric optics phenomenon occurs when certain conditions align, resulting in a stunning display of pink hues against the backdrop of the blue sky. In this article, we will delve deeper into the science behind these pink clouds and explore the factors that contribute to their formation.

The Nature of Thunderclouds and Cloud Colors

Thunderclouds, known for their dense and towering formations, do not possess any intrinsic color. The appearance of color in clouds is a result of how light interacts with the cloud particles and the atmosphere. When light rays encounter water droplets within the cloud, they undergo multiple scattering, causing the wavelength-dependent angular scattering to average out. As a result, iridescence and the colors of coronae, which are commonly observed in thin clouds, are not prominent in thunderclouds.

The Role of Sunlight Scattering

The pink coloration of these clouds can be attributed to two main factors. Firstly, sunlight scattered by the cloud towards our eyes is further scattered by air molecules in the atmosphere. This scattering process affects different wavelengths of light differently. Shorter wavelength blues and greens are scattered out of the direct line of sight more than red, leading to a reddening effect on the cloud's light. This reddening phenomenon is also observed during sunset when the sun appears more red due to the scattering of shorter wavelengths.

The Influence of Airlight

The second factor contributing to the pink appearance of these clouds is known as "airlight." Airlight refers to the preferential scattering of blue light towards our line of sight by the air molecules in the atmosphere. This scattering phenomenon is responsible for the blue color of the sky and partially contributes to the blue hue observed in distant mountains. Airlight is polarized and its intensity can be influenced by the setting of a camera polarizing filter.

The Synergy of Scattering Effects

When sunlight scattering and airlight scattering act together, they produce the mesmerizing pink clouds that capture our attention. The reddening effect caused by the scattering of shorter wavelengths and the preferential scattering of blue light towards us combine to create the distinctive pink hues observed in these clouds. The intensity and appearance of the pink color can vary depending on the specific atmospheric conditions and the angle at which the clouds are viewed.

Observations and Experiences

One interesting observation made by a photographer, Doug Zubenel, provides a valuable insight into the role of polarization in enhancing the reddening effect of the clouds. Zubenel noticed that when he used polarized sunglasses to view the distant thunderstorm and nearby Cumulus humilis clouds, the atmospheric reddening appeared more pronounced compared to when he viewed them without polarization. This observation highlights the impact of polarization on our perception of color in the atmosphere.

Conclusion

Pink clouds at high sun are a captivating atmospheric optics phenomenon that results from a combination of sunlight scattering and airlight scattering. The reddening effect caused by the scattering of shorter wavelengths and the preferential scattering of blue light towards us interact to produce the beautiful pink hues observed in these clouds. By understanding the science behind these phenomena, we can appreciate the wonders of our atmosphere and the intricate interplay of light and particles that create stunning visual displays in the sky. So, next time you find yourself gazing at the heavens, keep an eye out for those enchanting pink clouds and marvel at the intricate beauty of our atmosphere.

Pink Cloud at Noon imaged through a polarizing filter by Doug Zubenel in Kansas.

"We had a big squall line blast through here night before last, and yesterday the atmosphere was very, very clean. With the sun nearly overhead, my polarized sunglasses hightened the atmospheric reddening seen in the distant thunderstorm compard to the Cumulus humilis clouds only a mile or two away. Without the polarization, the difference was not as pronounced." Image ©Doug Zubenel, shown with permission.

Why pink? Thunder clouds are very dense and dense clouds have no intrinsic colour. Light rays are multiply scattered by their water droplets and so the wavelength dependence of angular scattering that, in very thin clouds, gives rise to iridescence or the colours of coronae is averaged out. Thick cloud colours result only from those of the light incident upon them be it the reds of sunset, the blues of the summer sky or the greens and earths reflected from the ground.

Two effects produced this cloud's pinks. Firstly, sunlight scattered by the cloud towards our eyes is scattered again by air molecules. Shorter wavelength blues and greens are scattered out of the direct line of sight more than red, causing the cloud's light to be reddened. The reddening of the sun at sunset is the same effect. The second effect is that the air also preferentially scatters blue light towards us, this is called 'airlight'. It is responsible for the blue sky and partly for the blue colour of distant mountains. Airlight is polarized and so its intensity depends on the setting of a camera polarising filter. The two effects acting together produced the pink.

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Reference Atmospheric Optics

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