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Source: BBC

Context

Rare noctilucent clouds, which form in the summer high up in the Earth's atmosphere, have lately been observed in regions of Scotland.

What are noctilucent clouds?

• Noctilucent clouds (NLCs), sometimes known as night sparkling clouds, are a thin cloud-like phenomenon in the high atmosphere. When viewed from space, they are known as polar mesospheric clouds (PMCs), which appear as a diffuse scattering layer of water ice crystals near the summer polar mesopause. 
• They are made of ice crystals and are only visible from the ground at astronomical twilight. Noctilucent approximately translates to "night shining" in Latin. During the summer months, they are typically seen at latitudes ranging from ±50° to ±70°.
• In the Southern Hemisphere, noctilucent clouds are far less common, yet they can be seen from the end of November to the beginning of February, with the most possible sightings in December and January.
• During these months and at the appropriate latitudes, the Sun just briefly sets below the horizon at night.
• That means that even while the rest of the surface is dark, these very high clouds can still be illuminated by intense sunlight from below, giving the clouds the appearance of glowing.
• The Sun sets lower below the horizon as you move north, therefore noctilucent clouds will last longer at night.

Noctilucent Clouds Formation

• Noctilucent clouds occur in the third layer of Earth's atmosphere, the mesosphere, between 47 and 53 miles (76 to 85 kilometers) above the surface, making them the highest clouds on the planet. 
• Noctilucent clouds require water vapor, dust, and extremely low temperatures (as do most clouds). 
• Noctilucent clouds appear during the summer months, when the mesosphere is coolest near the poles. When temperatures are low enough, water vapor freezes on dust particles, generating ice crystals.
• When the sun shines on them from below, the ice crystals reflect the light and seem like electric blue wisps in the night sky, reaching out to the edge of space. 
• Mesospheric dust can arrive from space in the form of tiny meteorites or from Earth as a result of volcanic eruptions or pollutants. According to ESA, these peculiar clouds were first reported in 1885, two years after Krakatoa's volcanic outburst.

FAQs

Q1. What are Noctilucent Clouds and where do they form?
Ans: Noctilucent Clouds are bright, night-shining clouds that form in the mesosphere, about 76–85 km above Earth’s surface. They are the highest clouds in the atmosphere.

Q2. Why are Noctilucent Clouds important for climate studies?
Ans: These clouds act as indicators of climate change and upper atmospheric conditions, helping scientists track changes in temperature and water vapor in the mesosphere.

Source: BBC.com