by The Arctic Circle(opens in new tab) clouds, known as polar stratospheric clouds (PSC), only form when the lower stratosphere reaches temperatures below minus 114 degrees Fahrenheit (minus 81 degrees Celsius).
This means PSCs can form much higher up than normal clouds, between 9.3 and 15.5 miles (15 to 25 kilometers) above the ground.
As sunlight shines through these crystal clouds, it gets scattered, creating multiple different wavelengths of light, which has inspired the PSCs nickname, "rainbow clouds."
Due to the extreme altitude of the clouds sunlight can hit the crystals and scatter above an observer even if the sun is beyond the horizon, which is when these clouds appear brightest.
Source
This means PSCs can form much higher up than normal clouds, between 9.3 and 15.5 miles (15 to 25 kilometers) above the ground.
As sunlight shines through these crystal clouds, it gets scattered, creating multiple different wavelengths of light, which has inspired the PSCs nickname, "rainbow clouds."
Due to the extreme altitude of the clouds sunlight can hit the crystals and scatter above an observer even if the sun is beyond the horizon, which is when these clouds appear brightest.
Source
