The rainbow rain cloud: Incredible occurrence looms over Chinese city like a multi-coloured halo 

A spectacular and vanishingly rare ‘rainbow scarf cloud’ dazzled residents in China when it briefly appeared on the horizon during sunset.

The brightly-coloured 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 posted to Twitter showed a dark, bulbous cloud topped by a scarcely believable rainbow crown of cyan, with fiery oranges, yellows and greens on the rims. 

The nine-second clip has since gone viral with over 28 million views and more than 15,000 likes. It also received over 4,000 re-tweets.

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

‘The footage shows a pileus (or scarf) cloud encircling a darker coloured 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.’

‘Pileus clouds are an accessory cloud 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 and array of rainbow colours.’ 

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 unique phenomenon was captured over the Chinese city of Haikou on the southern island of Hainan on August 21

A video posted to Twitter showed a dark, bulbous cloud topped by a scarcely believable rainbow crown of turquoise blue and fiery oranges, yellows and greens on the rims

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 scarf part of the cloud then refract the sun’s light when it hits just the right angle and creates the incredible rainbow effect.  

The clouds must be very thin and made of ice crystals or water droplets of uniform size. 

Pileus clouds are usually short-lived and end up being absorbed by the growing cloud underneath by the process of convection. 

Pileus clouds do not always boast bright colours like the one in the video, and Haikou residents were treated to an eye-catching example hanging low in the sky. 

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 scarf part of the cloud then refract the sun’s light when it hits just the right angle and creates the incredible rainbow effect

They are considered indicators of upcoming severe weather but can also form above mountains, flammagenitus clouds during volcanic eruptions, and other types of ash clouds. 

The beautiful sight could therefore be a bad omen for the island of Hainan as mainland has been experiencing its worst heatwave and drought since records began in 1961.

China has recently been undergoing an unprecedented heat wave and drought that has caused parts of the Yangtze River to dry up and weeks-long 40C temperatures to the west of the country.

The heatwave broke at the start of the week and now days of torrential rain have followed in the sprawling manufacturing hub of Chongqing and nearby areas of Sichuan province.