How meteor smoke can turn into a dazzling display of glowing clouds at dusk
If you’ve ever been up early for the sunrise or stayed up late past sunset around the heart of summer, you might just be treated to a stunning display of bluish clouds that appear to have luminescence.
Rare noctilucent clouds shine brightly across Whitley Bay beach over St Mary's Lighthouse on the North East coast overnight, as heavy rain is predicted to lash parts of the UK again as flood-hit communities continue to clear up after last week's downpours. (Photo by Owen Humphreys/PA Images via Getty Images)
If you’ve ever been up early for the sunrise or stayed up late past sunset around the heart of summer, you might just be treated to a stunning display of bluish clouds that appear to have luminescence.
These "Polar Mesospheric Clouds" — informally known as noctilucent clouds, or "night-shining" clouds, glow with a beautiful blue hue as the sun sits just below the horizon. But they are not the typical ones that portend rain; instead, they are in the highest reaches of the atmosphere.
"PMCs are water-ice clouds that form about 50 miles above the surface of the Earth, primarily in the summer hemisphere polar region," says Prof. Cora Randall at the University of Colorado. She is also the principal investigator of the NASA Aeronomy of Ice in the Mesosphere Cloud Imaging and Particle Size instrument.
Like regular clouds, they are formed from condensed water vapor, but instead of dust or other Earth-born particles, these clouds coalesce around leftover meteor smoke! The resulting ice particles are just 50 nanometers in size — that is 0.000002 inches across.
![]()
Image 1 of 16UNITED KINGDOM - JULY 15: Noctilucent clouds over Northamptonshire, UK. Taken 17 June 2009. Noctilucent clouds, are tenuous cloud-like phenomena that are the 'ragged-edge' of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. The name means roughly night shining in Latin. They are most commonly observed in the summer months at latitudes between 50° and 70° north and south of the equator. (Photo by Jamie Cooper/SSPL/Getty Images) ( )
![]()
Image 2 of 16Comet NEOWISE (C/2020 F3) low in the northeastern sky at dawn on July 7, 2020 with it amid bright noctilucent clouds this morning and over a prairie pond. Even so, the tail is visible. So this is a juxtaposition of an icy comet amid icy clouds. This is a stack of 6 exposures for the ground to smooth noise and a single 1-second untracked shot for the sky, all with the 135mm telephoto at f/2.8 and Canon 6D MkII at ISO 400. (Photo by: Alan Dyer/VW PICS/Universal Images Group via Getty Images) ( )
![]()
Image 3 of 16Noctilucent clouds or night clouds forming over Seaton Sluice watchhouse early this morning. Picture date: Saturday June 5, 2021. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 4 of 16Noctilucent clouds or night clouds forming over Seaton Sluice watchhouse early this morning. Picture date: Saturday June 5, 2021. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 5 of 16Noctilucent clouds or night clouds forming over Seaton Sluice watchhouse early this morning. Picture date: Saturday June 5, 2021. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 6 of 16Noctilucent clouds gather over Whitley Bay above St Mary's Lighthouse in the early hours. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 7 of 16Noctilucent clouds gather over Whitley Bay above St Mary's Lighthouse in the early hours. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 8 of 16Noctilucent clouds gather over The Bathing House, a grade II listed cottage that sits on the cliff edge on the Northumberland coast. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 9 of 16Noctilucent clouds or night clouds forming over Bamburgh Lighthouse in Northumberland. The clouds appear when the sun is 6-16 degrees below the Horizon. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 10 of 16Rare noctilucent clouds shine brightly over Blyth pier in Northumberland. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 11 of 16Rare noctilucent clouds shine brightly across Whitley Bay beach over St Mary's Lighthouse on the North East coast overnight, as heavy rain is predicted to lash parts of the UK again as flood-hit communities continue to clear up after last week's downpours. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 12 of 16Rare noctilucent clouds appear over the famous Sycamore Gap tree on Hadrian's Wall in Northumberland. (Photo by Owen Humphreys/PA Images via Getty Images) ( )
![]()
Image 13 of 16UNITED KINGDOM - JULY 15: Noctilucent clouds over Northamptonshire, UK. Taken 17 June 2009 Noctilucent clouds are tenuous cloud-like phenomena that are the ragged-edge of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. The name means roughly night shining in Latin. They are most commonly observed in the summer months at latitudes between 50° and 70° north and south of the equator. (Photo by Jamie Cooper/SSPL/Getty Images) ( )
![]()
Image 14 of 16UNITED KINGDOM - JULY 15: Photographs of noctilucent clouds appearing in the night sky over Britain on July, 2009. Noctilucent clouds are rare in that they form high in the atmosphere near the edge of space where normally there is not enough moisture or molecular debris needed to form the water vapours that make up clouds. Such clouds generally appear only during the summer months and so high are the clouds that the sun, having already set below the horizon, can still illuminate them. These photographs were taken more than an hour after sunset when the sky would normally be dark. (Photo by Jamie Cooper/SSPL/Getty Images) ( )
![]()
Image 15 of 16GLASGOW, SCOTLAND - JUNE 23 : Noctilucent Clouds visible on Glasgow's northern horizon just after midnight on June 23, 2015 in Glasgow, Scotland. Noctilucent Clouds are the highest clouds in the earths atmosphere inhabiting a region called the Mesosphere, at an altitude of approximately, 76 to 85 kilometres or (47 to 53 miles). They are composed of water ice crystals up to 100 nanometers in diameter and particles of dust. They are visible only when illuminated by sunlight from below the horizon during the summer months of May - July, Noctilucent clouds are a recent meteorological discovery and there are no records of the phenomenon before 1885. (Photo by Mark Runnacles/Getty Images) ( )
![]()
Image 16 of 16Shortly before midnight, so-called noctilucent clouds are reflected in a puddle in Sieversdorf, Germany, 5 July 2016. Noctilucent clouds can be seen during some clear summer nights in Northern direction as silver screens. They are at an height of around 80-85 kilometres, consist of small ice crystals and are visible when the sun is between 6 and 16 degrees beyond the horizon. Then, noctilucent clouds are still illuminated by the sun while the sky is already dark. Photo: Patrick Pleul/dpa | usage worldwide (Photo by Patrick Pleul/picture alliance via Getty Images) ( )
But for this to happen, temperatures have to be quite cold — at least -190 degrees F, Randall said. Those temperatures can be found near the poles, some 50 miles high in the mesopause area of our atmosphere.
"Which is why they somewhat ironically form in the summer," she said. "The polar mesopause in summer is the coldest region on Earth, even colder than the winter polar mesopause."
These clouds form over the poles but spread south. They can appear at night in summer but are best seen in the 30-60 minutes just before sunrise or after sunset. June and July are the best months to see them.
They used to be rare sightings and relegated to far northern latitudes. But in recent years, it appears sightings are becoming more frequent and farther south. In recent years, those as far south as Los Angeles and Las Vegas have spotted them.
Why?
"The short answer is that we are still investigating this," Randall said. Aside from the meteor smoke, which has remained constant, you need very low temperatures and abundant water vapor at those high altitudes.
Noctilucent clouds gather over Whitley Bay above St Mary's Lighthouse in the early hours. (Photo by Owen Humphreys/PA Images via Getty Images)
"So if polar mesopause temperatures are decreasing or water vapor is increasing, we would expect more (PMC) clouds to form," Randall said.
Could increased carbon dioxide emissions be a key?
Adding carbon dioxide to the lower atmosphere increases temperatures, but it acts as a radiator at those high levels, which cools the mesosphere, Randall said. In addition, increases in methane — another climate change gas — in the lower atmosphere will increase water vapor amounts in the higher atmosphere.
But so far, the observations have only shown minor changes not deemed to be statistically significant, Randall said, "which is why we still aren’t certain of the answer to (the) question."
Satellites have only recently been monitoring the clouds and data, and there isn’t enough data yet to determine trends, she said.
"Yet even very small changes can have dramatic effects on the clouds," Randall added.
Noctilucent Clouds in Hansville, Wash.
Noctilucent clouds come out in Hansville, Wash. in 2019. (Video courtesy: Greg Johnson / SkunkBayWeather.com)
As for sightings farther south in recent years, Randall says anecdotally, there does appear to be more frequent sightings at lower latitudes of late.
"Whether the increase in mid-latitude sightings is because the clouds have been appearing more frequently at mid-latitudes, or because more people have been engaged in observing them, is a question," Randall said. The clouds are more difficult to observe via satellite and measure at lower latitudes because they are typically dimmer.
"At the moment, it is problematic to quantify trends at the mid-latitudes from the satellites," she said.
Why are the clouds blue? A similar reason to why the sky is blue
Part of the beauty of the display is that the clouds seem to give off a glowing blue color, instead of white or gray like traditional clouds.
"It's because of Rayleigh scattering," Randall said. The ice cloud particles are so tiny that they scatter out the shorter light wavelengths like blue light. Light from the sun well below the horizon will shine through the clouds, with the blue light becoming scattered and that's the light you'll see reflected back to your eyes.
So, next time you’re out and about on a warm summer evening, and the sun has just set, take a peek at the skies and see if you will be treated to the surreal display of clouds born from meteors.