Reflection of sunlight from smooth water surfaces (such as lakes, or occasionally a calm sea or calm coastal waters) sends reflected sunlight upwards. The reflected sunlight can act as a light source for both primary and secondary “reflection rainbows”.
Rainbow - Cloud Appreciation Society
Rainbow - Cloud Appreciation Society
Cloud Atlas (film), Warner Bros. Entertainment Wiki
Rainbow - Cloud Appreciation Society
A New Edition of the International Cloud Atlas
Stunning 'new' cloud formations captured in updated atlas – in
Extremely rare 'rainbow clouds' light up Arctic skies for 3 days
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Cloud Atlas
How To Recognise Clouds – The International Cloud Atlas, 1896