Some clouds sometimes display the colors of the rainbow, which give them a magical and supernatural appearance. These are iridescent clouds, also called “rainbow clouds”.
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This phenomenon, rarely observed in France, is more often observed in the regions in the tropical climate ; it is related to the internal composition of the cloud. The spacing and size of the droplets, or ice crystals, that make up the cloudcan allow the light from Sun or the Moon, to make the cloud iridescent. It’s here diffraction light, at the right angle (10 to 40° with respect to the Sun), which causes the appearance of colors : when encountering fairly fine drops of water or ice of similar sizes, the light scatters and gives rise to theiridescence.
Where can iridescent clouds be seen?
Iridescence occurs especially in clouds fine, cirrus-like, cirro-stratuscirrocumulus, as well as on the altocumulus and lenticular. But this multicolored appearance can sometimes be observed at the top of the cumulonimbus on an additional cloud, the pileuswhich “caps” the storm cloud.
These multicolored clouds are more common at high altitudes and in very humid regions. The most spectacular iridescent clouds occur after a downpour or thunderstorm, in the late afternoon or early evening, at the end of a hot day.
Thundercloud capped by an appendix and iridescent cloud in Thailand in June 2021. © ab Khan Insights
The most beautiful photos of the phenomenon are often taken in hot and humid areas, such as India, the Philippines, Sri Lanka, Thailand, Brazil or Florida.
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