Climate change makes Noctilucent clouds more visible

by Khushi Mehra

Cloud watchers have recently been given record-breaking glimpses of the rarest clouds in the skies. Stunning rippled blue clouds have been forming in the highest reaches of the atmosphere over Europe and the United States. These clouds are normally only seen around the poles. They have already been seen at the lowest latitudes ever recorded.

A tenuous cloud-like phenomenon, which consists of ice crystal majorly known as “night-shining” clouds. These clouds used to be a rare sight for humans of the past to observe. It was first recorded only after the 1883 Eruption of Krakatao that emitted an unconvincing amount of dust into the atmosphere. Since then they have become a more common sight.

Every year from May to August in the Northern Hemisphere, and from November to February in the Southern Hemisphere, people residing at high latitudes report seeing noctilucent clouds. “These beautiful clouds have now subsided to their lowest latitude of the 2020 season so far,” said

The water in these clouds is either transported up into the mesosphere from the lower atmosphere or forms when the methane in the mesosphere breaks down by absorbing the sun rays. However, other particles are needed for the formation of a cloud, so that the water can get condense on to.

In the lower atmosphere, these are normally aerosol particles from dust, sand, and salt. However, in the mesosphere, the main source of the particles is meteors. As these lumps of space lumber burn up in the higher layers of the atmosphere, they can leave behind a chain of meteor dust. At lower temperatures, the water in the mesosphere gets condensed on this dust and grow into clouds.

As for these noctilucent clouds, they are visible from Earth and space as well. European Space Agency (ESA) astronauts, Astronaut Luca Parmitano and Astronaut Tim Peake also took pictures of the clouds during their missions onboard the International Space Station.

Image Credits:- Vaonis

The lowest latitude, at which noctilucent clouds are seen each year, is moving slowly towards the south ever since 2002. In June 2019, the record for the lowest point we have ever seen these clouds were broken when they appeared not far from Los Angeles. This was because the mesosphere was strangely wet, containing much more water than it usually does. “This could be because an enormous planetary wave was transporting cold air and moisture into the North Pole,” states Jon Perrett in his article on TheConversation who is a PhD Candidate in Atmospheric Dynamics, University of Bath.

Lately, we are also in a deep solar minimum, the period of the sun’s 11-year cycle when it is least active. That means the ultraviolet radiation from the sun that sometimes destroys the water modules that form these clouds is a smaller amount intense, so more of them can form. 

Human emissions could also be a factor. Over the past 130 years, we have released abundant methane into the atmosphere, which means more water modules will form in the mesosphere.

So next time you’re out after dark, look up. You might just see the rarest clouds in the sky.

Image Credits:- SciTech Daily

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