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Shepherd's delight: Rainbow coloured 'mother-of-pearl' clouds shimmering in the night sky over Scotland
Unusual formation spotted over the Outer Hebrides just before sunriseMethane reacts with ozone in the atmosphere to create the dazzling display
10:13 GMT, 17 December 2012
These breathtaking images show an extremely rare, multi-coloured cloud hovering over a Scottish island at night.
The dazzling sight appeared over the island of Scalpay, in the Outer Hebrides, just before sunrise on December 9.
Amateur photographer Jez Wheeler was lucky enough to be in the right place to capture the perfect shots of the cloud, known as a 'mother-of-pearl' or Nacreous cloud.
Iridescence: The mother-of-pearl cloud glows in a dazzling array of colours in this incredible image
Misty mountains: The unusual cloud is often found downwind of high ground, and can signal wind or waves in the atmosphere
'I woke up early about 8.15am just to have a look outside and there it was,' said Jaz, a mink trapper. 'It was completely unexpected but I managed to get the shot. It was beautiful.'
Atmospheric optics expert Les Cowley said: 'Nacreous clouds, sometimes called mother-of-pearl clouds, are rare but once seen are never forgotten.
'They are mostly visible within two hours after sunset or before dawn, when they blaze unbelievably bright, with vivid and slowly shifting iridescent colours.
'They are filmy sheets slowly curling and uncurling, stretching and contracting in the semi-dark sky.
UFO: The spectacular cloud hovers high above Scotland like a visitor from space
HEAD IN THE CLOUDS
Nacreous clouds, or mother-of-pearl clouds, form in the very cold regions of the lower stratosphere, 15-25 km (9-16 miles) high and well above tropospheric clouds.
They form when methane in the atmosphere reacts with ozone, and the reason they are so bright after sunset and before dawn is because, at those heights, they are still sunlit.
Dave Clark, of Aberdeen Met Office, said: 'It is unusual to be able to see these nacreous clouds as they are formed in the troposphere, high above our weather. They are a direct consequence of us releasing too much methane into the atmosphere and this reacts with the ozone to form chlorine clouds.
'In the past they could only be seen in the polar countries… But that is worrying because of what it signifies about increased global warming.'
'Compared with dark scudding low altitude
clouds that might be present, nacreous clouds stand majestically in
almost the same place – an indicator of their great height.
'They need the very frigid regions of the lower stratosphere some 15-25 km high and well above tropospheric clouds. They are so bright after sunset and before dawn because at those heights they are still sunlit.'
'They are seen mostly during winter at high latitudes like Scandinavia, Iceland, Alaska and Northern Canada.
'Sometimes, however, they occur as far south as England. They can be less rare downwind of mountain ranges.
'Elsewhere, their appearance is often associated with severe tropospheric winds and storms.
'Nacreous clouds far outshine and have much more vivid colours than ordinary iridescent clouds which are very much poor relations and seen frequently all over the world.
'Nacreous clouds are wave clouds. They are often found downwind of mountain ranges which induce gravity waves in the lower stratosphere.
'Their sheet-like forms slowly undulate and stretch as the waves evolve.
'The clouds can also be associated with very high surface winds which may indicate the presence of, or induce, winds and waves in the stratosphere.
'They form at temperatures of around minus 85C, colder than average lower stratosphere temperatures, and are comprised of ice particles.
'The clouds must be composed of similar sized crystals to produce the characteristic bright iridescent colours by diffraction and interference.'