Viral Video: Rare Rainbow Cloud Stuns People In China

A spectacular and vanishingly rare ‘rainbow scarf cloud’ dazzled residents in China during sunset. It was later understood to be a natural phenomenon.
The brightly-colored cloud reportedly left locals baffled by its surreal appearance after it was spotted hanging low in the sky. 
The unique phenomenon was captured over the Chinese city of Haikou on the southern island of Hainan on August 21.
A video on Twitter showed a dark, bulbous cloud topped by a cyan rainbow crown with fiery oranges, yellows, and greens on the rims. The nine-second video has since gone viral, garnering over 28 million views and over 15,000 likes. It also received over 4,000 re-tweets.

‘These are certainly some very striking images,’ MailOnline’s Senior Operational Meteorologist Matthew Box said.

‘The footage shows a pileus (or scarf) cloud encircling a darker colored cumulus cloud,’ he said, adding that ‘one might expect to see some optical phenomena as you have ice crystals aloft (the pileus cloud) and the sun almost on the horizon.’

Viral Video: Rare Rainbow Cloud Stuns People In China
Viral Video: Rare Rainbow Cloud Stuns People In China

‘Pileus clouds are accessory clouds that commonly form in association with cumulus or cumulonimbus clouds (where there are strong updrafts) and, because pileus clouds form high up in the atmosphere, they are made of ice crystals. 

‘The low sun appears to be catching these ice crystals and being refracted by them which is why the observer at ground level can see an array of rainbow colors.’ 

However, he sounded a note of caution, warning that the pileus cloud almost seemed ‘too bright’ and that the footage might have been ‘tampered with.’

The phenomenon was the result of the pileus cloud – sometimes known as a ‘cap cloud’ or ‘scarf cloud’ – forming just at the right time of the evening to produce ‘cloud iridescence’ – or a rainbow cloud. 

The quickly rising hot air of a cumulus cloud pushes against cold air above it, creating a smooth ‘scarf’ effect as moisture condenses exactly along the top of the updraft.

The ice crystals and droplets in the cloud’s scarf then refract the sun’s light when it strikes at just the right angle, creating the incredible rainbow effect.

Viral Video: Rare Rainbow Cloud Stuns People In China

The clouds must be very thin and composed of uniformly sized ice crystals or water droplets.

Pileus clouds are typically short-lived and are absorbed by the growing cloud beneath through the process of convection.

Pileus clouds aren’t always as colorful as the one in the video, but Haikou residents were treated to a stunning example hanging low in the sky.
They are thought to be precursors to severe weather, but they can also form above mountains, as flammagenitus clouds during volcanic eruptions, and as other types of ash clouds.

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