Nature’s magic: Here’s how iridescent cloud beams over Garden Route occur

The appearance of a rainbow glowing through fluffy clouds sighted on Tuesday over Hoekwil on the Garden Route has been confirmed as an iridescent cloud. 

The SA Weather Service, confirming the pictures show an iridescent cloud, said on Wednesday iridescent clouds are quite often encountered at higher latitudes.

Chief forecaster Kevin Rae said iridescent clouds occur when rays of sunlight shine through a thin layer of cloud comprising ice crystals.

“Such clouds are, in meteorological terms, referred to as cirrus or cirrostratus clouds. The public would be very familiar with the common phenomenon of rainbows, when falling rain, drizzle or sometimes fog is ‘backlit’ by bright sunshine. The rainy region acts as a giant prism, splitting up the light into its component colours according to (longer/shorter) wavelengths,” he said.

Rae said in the case of an iridescent cloud, the process is exactly the same, only a thin layer of ice crystals is substituted to act as the prism.

“The result is that particular section of cloud will appear to shine or glow in rainbow colours,” Rae said.

He said the phenomenon of iridescent clouds is not rare.

“Iridescent clouds are encountered quite often at higher latitudes. It is a common phenomenon in the northern hemisphere, where many countries are positioned at higher latitudes, and in the southern ocean regions of the southern hemisphere.

“In SA I would suggest it is uncommon but by no means rare,” he said.

Rae said another meteorological phenomenon related to iridescent clouds  is the “halo” phenomenon.

“When a point source of celestial light (such as the sun or moon) shines through a thin cirrostratus ice cloud veil, resulting in a bright halo around the sun (or moon).

“In SA, the halo phenomenon is also fairly uncommon and usually restricted to the southern provinces in the winter months.” 

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