14th August 2022 – (Hong Kong) Many Hong Kong people captured the so-called “rainbow cloud,” which looks like a bright prism of color behind soft clouds above the International Finance Centre at the Victoria Harbour in East Tsim Sha Tsui on 12th August.
Hong Kong Observatory explained the mystery behind the rainbow cloud today. Cloud iridescence forms when the water droplets or ice crystals in the cloud diffract the light around the outside of the droplet, as opposed to bending the light through it. A rainbow cloud can occur because of something called cloud iridescence. It usually happens in altocumulus, cirrocumulus, lenticular and cirrus clouds. Iridescent clouds happen because of diffraction – a phenomenon that occurs when small water droplets or small ice crystals scatter the sun’s light.
Cloud iridescence is relatively rare. The cloud must be thin and have lots of water droplets or ice crystals of about the same size. When that happens, the sun’s rays encounter just a few droplets at at time. For this reason, semi-transparent clouds or clouds that are just forming are the ones most likely to have iridescence.