Rare iridescent clouds spotted over northern England
Nacreous clouds mimic the pearly sheen found inside the shells of mollusks and project it onto the open sky.
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A video shot by Greg Diesel Walck shows pink clouds and a rainbow stretching across the sky. (Courtesy: Greg Diesel Walck via Storyful)
SUNDERLAND, United Kingdom – A stunning type of colorful clouds known as "nacreous clouds" were seen sweeping across the sky in Sunderland, England.
Photos taken at the coastal town show the clouds showcasing shades of pink, purple, blue and gold stretched over a lighthouse, as the Sun is near the horizon.
Iridescent, or nacreous, clouds over Sunderland, England in the United Kingdom.
(Richard R. Clark / FOX Weather)
"Nacreous clouds are rare and very high clouds, known mainly for the coloured light they reflect after sunset and before sunrise," the UK Met Office's website read.
According to the site, the name for the clouds comes from the Old English word "nacre," which means "mother of Pearl."
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Much like their iridescent namesake, nacreous clouds light up the sky with colors. They mimic the pearly sheen found inside the shells of mollusks and project it onto the open sky.
How nacreous clouds form
Iridescent, or nacreous, clouds over Sunderland, England in the United Kingdom.
(Richard R. Clark / FOX Weather)
Nacreous clouds form due to a couple of variables: the height at which they form and the size of particles that form the clouds.
The UK Met Office said that nacreous clouds form in the lower stratosphere, which is the second-lowest layer of the five layers of the atmosphere. In fact, the base of nacreous clouds form at an altitude of between 68,500 and 100,000 feet.
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Because of this high altitude, along with the curvature of the planet’s surface, the UK Met Office said the clouds are able to be illuminated by sunlight from below the horizon.
The iridescent appearance of the sunlight, however, is the result of the ice particles that form nacreous clouds. The UK Met Office noted that these ice particles are much smaller than those that form common clouds, and so they scatter light in a different way, creating a pearlescent appearance.
Why nacreous clouds need the polar vortex
Iridescent, or nacreous, clouds over Sunderland, England in the United Kingdom.
(Richard R. Clark / FOX Weather)
Very low temperatures, specifically below -108 degrees, are necessary for nacreous clouds to form. According to the UK Met Office, these temperatures are most likely to occur during very cold and dry weather and during the polar winter.
"Because of the very low temperatures required, nacreous clouds are usually only visible from the UK when the cold air which circulates around polar regions in the stratosphere (known as the stratospheric polar vortex) is displaced and hovers temporarily over the UK," they said.