Truth behind the clouds that ‘shimmer’ at night revealed

Rare noctilucent clouds over Whitley Bay Beach - PA

Rare noctilucent clouds over Whitley Bay Beach – PA

Morning rocket launches can cause clouds to glow at night above Britain in a rare phenomenon known as noctilucent, scientists have found.

Noctilucent clouds are the highest in the atmosphere, floating like iridescent wisps about 80 kilometers above the ground, 10 times higher than normal clouds, during dusk and dawn in summer.

They are so high up in the atmosphere that sunlight can still reach them even after the sun has gone down, giving them their ghostly, shimmering night glow.

Clouds usually form when water ice crystals condense into tiny particles of meteor debris in the mesosphere and are typically seen over the poles.

However, researchers at the US Naval Research Laboratory (NRL) in Washington have found that smoke from morning rocket launches can also trigger cloud formation at latitudes below 60 degrees, such as in Britain and northern Europe.

The team found a distinct correlation between the number of morning rocket launches in a year and the percentage of mid-latitude noctilucent clouds that were recorded.

Previous studies have shown that water vapor released into the atmosphere by space shuttle launches has increased noctilucent clouds near the poles, but it was not known if the launches were having an impact elsewhere.

“This study shows that space traffic, even after space shuttle launches have stopped, controls the year-to-year variability of mid-latitude noctilucent clouds,” said Michael Stevens, a researcher in the NRL’s Upper Atmospheric Physics Branch.

The Swedish sky lit up by 'bright' clouds

The Swedish sky lit up by ‘bright’ clouds

Noctilucent clouds over Tynemouth Priory and Castle in June 2022 - PA

Noctilucent clouds over Tynemouth Priory and Castle in June 2022 – PA

Britain experienced vibrant displays of noctilucent clouds earlier this month, with twilight skies lit up over Northumberland, North Yorkshire and even London. The increase coincided with several morning satellite launches that have taken place this year, including four by SpaceX’s Starlink program alone.

For the research, the team studied observations of noctilucent clouds obtained by the cloud and particle size imaging instrument on NASA’s ice aeronomy satellite on the mesosphere satellite, launched in 2007, and linked the data to rocket launches.

The analysis revealed a strong correlation between the number of launches that occurred between 11pm and 10am local time in a year and the frequency of mid-latitude noctilucent clouds observed between 56 and 60 degrees north latitude.

The more morning launches there were, the more mid-latitude noctilucent clouds appeared.

The researchers also analyzed the winds just above the noctilucent clouds and found that southerly winds were strongest during morning launches, suggesting that the winds may carry the exhaust gases from morning rocket launches at lower latitudes — such as Cape Canaveral, in Florida – to the north.

As they rise into the atmosphere, the rocket releases steam in ice crystals and descends to form clouds.

Scientists also analyzed the activity of the sun and found no correlation between solar production and the percentage of clouds.

John McCormack, NASA’s heliophysics program scientist who contributed to the study, said: “This research, relating changes in the frequency of mesospheric clouds to rocket launches, helps us better understand the observed long-term changes in the occurrence of these clouds. ”.

The research was published in the journal Earth and Space Science.

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