Rare Noctilucent Clouds Seen Over Northern Ireland

Noctilucent clouds as photographed by Mark Bailey from Lisdoart on 14th July 2006 at 11.30 pm.
An unusual display of mysterious luminous clouds appeared over Northern Ireland during the night of 14/15th July. These so-called noctilucent (night glowing) clouds (NLCs), are formed by sunlight reflecting off ice crystals high in the atmosphere, and usually appear in the northwest, through north to northeast during twilight in the late spring and summer months at our latitude. The clouds have a silvery, electric-blue colour and take various forms from feathery streamers to waves.

NLCs occur at very high altitudes, in excess of 50 miles high, in the region above the stratosphere known as the mesosphere and at first sight they look like cirrus clouds. However, they are far higher than any normal clouds and are believed to be made of water-ice crystals. They appear to be self luminous, but in fact shine by reflected sunlight when the Sun is a few degrees below the observer's horizon. Any visible lower clouds appear dark and silhouetted against the NLCs because they are not illuminated by the Sun. and stars can often be seen twinkling through them.

NLCs appear first to have noticed as a distinct cloud phenomenon in 1885, by the astronomer and meteorologist Thomas William Backhouse, and were then thought to have resulted from the Krakatoa volcanic eruption of August 1883. However, more recent studies have indicated that they are primarily caused by meteoric particles that become covered with ice as they fall through our atmosphere.

Noctilucent clouds as photographed by John McFarland from Richhill on 14th July 2006 at 11.30 pm.

One of the mysteries of NLCs is why they were not reported earlier. However, in the climate archive of the Armagh Observatory, Dr Thomas Romney Robinson, then the chief Armagh Astronomer, made two observations of seeing "strange luminous clouds in the northwest, not aurorae" around 10pm on 1st and 4th May 1850. Although these may have been the first recorded sightings of noctilucent clouds it is still a puzzle why no-one appears to have seen them before 1850 (Robinson's Observations - PDF Document).

NASA plans to launch a mission called Aeronomy of Ice in the Mesosphere (AIM) in March 2007. The spacecraft will be placed into a polar orbit for just over two years to try to determine what factors are responsible for the formation of the enigmatic NLCs.

Robert Cobain has made a time lapse movie of nocticlucent clouds seen at Bangor Northern Ireland on 15th June 2006 from 12.00-12.30. It covers a period of 30 minutes with each frame lasting about 6.5 seconds. The full size 4.7MB mpg file can be downloaded here.

NLC images by Martin McKenna

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

Last Revised: 2010 March 1st