The Arctic skies are shining with ethereal, multi-colored light, but this stunning spectacle is not caused by auroras. The iridescent rainbows are a result of polar stratospheric clouds (PSCs), made of tiny ice crystals floating higher in the atmosphere than is normally possible.
These clouds only form when the lower stratosphere reaches extremely low temperatures below minus 114 degrees Fahrenheit. The extreme altitude of the clouds allows sunlight to hit the crystals and scatter above an observer even if the sun is beyond the horizon, creating multiple different wavelengths of light and producing vivid colors.
There are two types of PSCs, Type I and Type II. Type I clouds are a mix of ice crystals and nitric acid and may be linked to the formation of ozone holes. Type II clouds, also known as nacreous clouds, are composed of pure ice crystals and produce more vivid colors, sometimes resembling mother of pearl. These clouds typically occur two to three times a year in the Arctic, but experts believe that both types could occur more often in the future due to climate change and its impact on the ozone layer.
Nacreous clouds are often confused with the northern lights, but these occur when highly energetic particles emitted by the sun travel down the magnetic field lines of Earth’s magnetosphere. Recently, a rare outbreak of Type II PSCs was captured in photos by amateur photographers Jónína Guðrún Óskarsdóttir and Fredrik Broms (https://www.northernlightsphotography.no/) in Iceland and Norway.