Ukrainian polar explorers of the 31st Antarctic Expedition observed a unique atmospheric phenomenon over Antarctica’s winter sky – pearly clouds. They form in the stratosphere at an altitude of 15–30 km, unlike ordinary clouds that arise in the troposphere.
“Several conditions are required for their formation. Most of the clouds that we observe in the sky “live” in the troposphere. This is the lower moist layer of the atmosphere, and it is the “kitchen” for most weather phenomena. But nacreous clouds form in the next layer – the stratosphere, at altitudes of 15–30 km. It is already mostly dry there. So, the first condition is that a flow of moist air must enter the stratosphere. It is “thrown” there by strong tropospheric cyclones or mountain waves – when the flow encounters a high mountain range, “goes” up, goes around it, and “falls” down. At this time, the top of the wave is in the stratosphere. The second condition: very low temperatures (-50°C and below), which quickly turn moisture into ice crystals or the smallest droplets of supercooled water. Strong winds also “help,” the scientists explained.
It is noted that the characteristic rainbow effects appear due to the scattering of sunlight by ice particles. This phenomenon is best seen during sunrise or sunset, when the sun is slightly below the horizon.
