Noctilucent clouds blue

Blue noctilucent clouds are rare atmospheric phenomena visible at twilight in high latitudes, formed by ice crystals in the mesosphere.

About this subject

Noctilucent clouds are the highest clouds in Earth's atmosphere, forming at around 80 km altitude in the mesosphere. They are visible only during twilight, when the Sun illuminates these layers while the surface is already dark. Their blue coloration results from the scattering of sunlight by very small ice particles.

Where and when do they occur? They are typical of latitudes between 50° and 70° north and south, during summer months (May to August in the Northern Hemisphere, November to February in the Southern). They are most frequently observed in Scandinavia, Russia, Canada, and Alaska. In the Southern Hemisphere, they appear over Antarctica and southern oceans.

Scientific importance and curiosities: Studies indicate that the increasing frequency of noctilucent clouds may be related to climate change and the presence of methane in the atmosphere. They are also an indicator of mesospheric dynamics and water vapor transport. Despite their name (from Latin for night and shine), they do not emit light; they reflect sunlight.

Frequently Asked Questions

What causes the blue color of noctilucent clouds?

The blue color is caused by Rayleigh scattering of sunlight by very small ice particles (less than 0.1 micrometer), which preferentially scatter shorter wavelengths (blue).

Can noctilucent clouds be seen in Brazil?

No, because Brazil is at tropical and equatorial latitudes, far from the polar regions where these clouds occur. They are only observable at high latitudes, above 50°.

Are noctilucent clouds becoming more common?

Yes, evidence suggests that the frequency of these clouds has increased in recent decades, possibly due to increased methane emissions and cooling of the mesosphere caused by climate change.