Rare types of winter clouds: what do "pearl" and "mother-of-pearl" clouds look like?

The winter sky sometimes presents phenomena that seem almost unreal. Pearlescent, or nacreous, clouds are rare guests in our latitudes, but when they appear, the cold landscape transforms into a radiant fairytale. These clouds shimmer with pink, blue, green, and purple hues, as if glowing from within or reflecting the light of another world. We explain how they form and why they are so rare to see.

Pearl clouds (also known as polar stratospheric clouds) form very high in the stratosphere, at altitudes of 15–30 kilometers. Their structure resembles thin cirrus or cirrocumulus clouds, but their main distinguishing feature is their bright, iridescent glow. Their surface can shimmer with all the colors of the spectrum: from red and gold to green, blue, and purple.

They are best seen during the brief window immediately after sunset or shortly before sunrise, when the sun is just below the horizon. It is at this moment that the rays, passing through the lower layers of the atmosphere, illuminate the clouds from the sides, creating a fantastic play of color that is often mistaken for the northern lights.

The rainbow effect is caused by the refraction, scattering, and diffraction of sunlight by tiny ice crystals and supercooled droplets of sulfuric and nitric acid, which remain liquid even at -80°C and below.

These particles are lifted into the stratosphere by powerful updrafts, orographic waves (when air "rolls" over mountains), and general atmospheric turbulence. In mid-latitudes, such conditions occur extremely rarely and only in winter, when the stratosphere above the poles cools significantly.

Residents of high latitudes have the best chance. In Iceland, Norway, Alaska, northern Canada, and northern Scandinavia, mother-of-pearl clouds can be seen almost every winter, sometimes even several times a season. In Russia, they are most often photographed in Karelia, the Kola Peninsula, the Northern and Subpolar Urals, Taimyr, and Yakutia. But during particularly cold winters, when the polar vortex descends far south, residents of the central part of the country can also get lucky—they have even been observed over Moscow and the Moscow region.

Mother-of-pearl clouds are one of the most beautiful and rare atmospheric phenomena. If you're ever lucky enough to see one, it's a sight you'll remember forever. Have you ever seen mother-of-pearl clouds with your own eyes? Tell us in the comments where you saw them and what emotions they evoked!