The sky at night yields spectacular sight

By SHÂN ROSS
Published on 26/06/2012 01:03

SHIMMERING blue and silver, rare “night shining” clouds – which can only be spotted over the night skies in the summer months – were captured in these stunning images over Glasgow just after midnight yesterday morning.

Known as noctilucent clouds, they are the highest clouds in the Earth’s atmosphere, made up of tiny ice droplets. The phenomenon, captured by photographer Mark Runnacles, forms in an area known as the mesosphere, the coldest region of the Earth’s atmosphere, at a temperature of -150C.

At a height of 50-60 miles, this is approximately ten times higher than the troposphere, where weather clouds form.

Experts said Scotland is the best place to see them in the UK due to the country’s northern latitude. Depending on weather conditions, they can be seen between sunset and sunrise.

They are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth’s shadow.

They were first observed in 1885 and are a relatively recent classification. Although rare, there have been an increasing number of sightings over the past few years.

But Dr Liz Bentley at the Royal Meteorological Society said the greater number of sightings did not necessarily indicate the phenomenon was happening more frequently.

“There is a general feeling that there have been more sightings. There has been lots of discussion about this being because there is more dust in the mesosphere from volcanos or from rocket fuel particles.

“But it is like anything people become more familiar with, such as tornados, and take photos and share the information online, making it seem as though it is happening more than it is.”

Gavin Pretor-Pinney, founder of the Cloud Appreciation Society, which has more than 30,000 members worldwide, said noctilucent clouds had always been regarded as mysterious, with some observers pointing towards the eruption of the Krakatoa volcano in Indonesia in 1883 and its ash as their origin.

“They were first recorded after Krakatoa and some people thought they had something to do with the ash,” he said.

“Nowaways, scientists are speculating that the more and more frequent reportings are due to changes in the climate. There is an argument that as more heat is trapped in the stratosphere, the converse happens above.

“Whatever the explanation, noctilucent clouds have an eerie, ghostly appearance and Scotland is a great place to see them, the best in the UK, because of the higher latitude.

“They are rather mysterious clouds because they are at an altitude which makes them difficult to study.”

In the years following Krakatoa, global temperatures fell by as much as 1.2C for a few years, with large quantities of sulphur dioxide being pumped into the atmosphere resulting in clouds that reflected a greater amount of incoming light from the sun.