'Fire rainbow' in Auckland's sky

The phenomenon is also known as a circumhorizontal arc or "ice halo". Photo / Supplied, Rachel Purcell

If you looked to the sky on Friday, you might have glimpsed a "fire rainbow".

Rachel Purcell sent this picture to the Herald after being lucky enough to see it while in the Viaduct on Auckland's waterfront.

"I was so pleased my camera captured the moment," she said.

MetService meteorologist Ciaran Doolin said the phenomenon was known as a circumhorizontal arc, or "ice halo".

He could not say how statistically frequent they were, but said the weather service occasionally got calls from the public about them.

Website IFL Science says the arc occurs when the sun has risen higher than 58 degrees in the sky, which is most common over summer.

"Aside from the position of the sun, the other ingredient to forming circumhorizontal arcs is cirrus clouds. Cirrus clouds are the thin, wispy clouds that occur at higher altitudes. Because the temperature is so low where these clouds exist, they are made of ice crystals."

The plate-like crystals then act like prisms and refract light to create the rainbow and so are sometimes called "fire rainbows".