Technically they are known as circumhorizontal arc.
It’s happened in Singapore on 18 August 2016 during the Sunset around 6pm Singpaore time.
The fire rainbow clouds are created when sunlight passes through tiny ice crystals that form tens of thousands of feet in the air.
A circumhorizontal arc is an optical phenomenon – an ice-halo formed by the refraction of sun- or moonlight in plate-shaped ice crystals suspended in the atmosphere, typically in cirrus or cirrostratus clouds. In its full form, the arc has the appearance of a large, brightly spectrum-coloured band running parallel to the horizon, located below the Sun or Moon. (Source: https://en.wikipedia.org/wiki/Circumhorizontal_arc )
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