PHA 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.
Why doesn't this happen more often?
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.
excerpt from Scijinks
. 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.
Why doesn't this happen more often?
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.
excerpt from Scijinks
