Rare Noctilucent Clouds Seen Over Northern Ireland

Armagh Observatory reports that rare noctilucent clouds were observed over Northern Ireland on the night of the 30/31 May. The so-called òÀÜnight shiningòÀÝ clouds take various forms ranging from delicate feathery structures to streamers, ripples and waves, and usually have a silvery grey or electric-blue colour. They are a summer phenomenon which can only be seen at night and when the Sun is between approximately 5 and 15 degrees below the observeròÀÙs horizon. At our latitudes this means that they often appear low towards the northern horizon during the summer months May to August, either after sunset or before sunrise.

The clouds are caused by sunlight reflecting off ice crystals very high in the EarthòÀÙs atmosphere, in the region above the stratosphere known as the mesosphere. They typically lie at a height of around 80 kilometres. Any visible lower clouds appear dark, silhouetted against the luminous noctilucent clouds because they are in the EarthòÀÙs shadow and not illuminated by the Sun.

The origin of noctilucent clouds remains a mystery. The most widely accepted explanation is that they comprise ice crystals that have condensed on tiny meteoric particles, which themselves have come from meteoroids or interplanetary dust impacting the EarthòÀÙs atmosphere.

One of the many puzzles surrounding noctilucent clouds is that they appear to be a relatively recent meteorological phenomenon, first described as a distinct cloud phenomenon by the astronomer and meteorologist Thomas William Backhouse in 1885. The first recorded observation of such clouds appears to be a note in the ObservatoryòÀÙs climate archive made by the third director, the Revd Thomas Romney Robinson, who described òÀÜstrange luminous clouds in NW, not auroralòÀÝ, seen around 10pm on 1st May 1850.

For more information on these clouds, see article by astronomer John Butler Possible Observations of Noctilucent Clouds by Thomas Romney Robinson - PDF.

For Thomas Romney RobinsonòÀÙs early observation of these clouds, see May 1st 1850 - "strange luminous clouds in NW"

Image by Paul Evans, Larne, Northern Ireland, taken at 0025 BST Friday 31st May.

FOR FURTHER INFORMATION PLEASE CONTACT: John McFarland at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; jmfarm.ac.uk; URL: climate.arm.ac.uk.

Links:

Time lapse movie of noctilucent clouds

Some more images

Last Revised: 2013 June 3rd