Unusual 'rainbow' clouds spotted in the south east
- Published
These striking rainbow coloured clouds, seen by BBC Weather Watchers, had us scratching our heads. We originally identified them as iridescent clouds but after more research we believe they are actually circumhorizon - or circumhorizontal - arcs. It's easy to confuse the two.
As the name may suggest, a circumhorizon arc sits parallel to the horizon. The sun must be higher than 50 degrees in a sky where there is also cirrus cloud. The ice crystals within the cirrus cloud must also be positioned in such a way that allows for the refraction of sunlight, leading to the rainbow colours that appear.
Circumhorizon arcs in the UK are quite unusual. The sun is only more than 50 degrees higher in the sky from May to July so there's a shorter window to observe them. Those who have been able to spot it are very lucky indeed!
