A town in southern China witnessed a once-in-a-lifetime sight earlier this week when a vibrant rainbow-coloured scarf cloud danced above a towering thunderstorm.
The stunning cloud formed above Haikou, a city of two million in far southern China. A billowing cumulus cloud sprouted in the tropical air over Haikou around sunset. It wasn’t the cumulus that drew all the attention—it was the incredible formation that rose above it, called a pileus cloud.
Pileus, sometimes called cap clouds or scarf clouds, are smooth clouds that form atop a growing cumulus or cumulonimbus cloud.
A typical pileus cloud above a growing thunderstorm. (Dennis Mersereau)
The rapidly rising air in the updraft of a towering cumulus pushes against the cooler air above it, condensing the moisture right along the top of the updraft. The end result is a graceful pileus donning its neighbouring cloud like a cap.
This was no ordinary pileus, though.
The spectacular rainbow hue that painted the pileus is the wonder over Haikou that stole the show. Cloud iridescence isn’t unusual at all. Sunlight diffracts through water droplets and ice crystals in the clouds, scattering the light into its individual wavelengths.
We usually only see a few colours at a time. But the low angle of the sun and the size of the pileus led to a fantastic and rare splash of a vivid rainbow dancing above the city as the day drew to a close.
Editor's Note: An earlier version of the video for this story included footage that may not have represented the event in question.
Thumbnail courtesy of Newsflare via Reuters Connect