Collections of water droplets that appear as cloud can form at many different altitudes. They often appear down here at ground level, when they are known as fog. But the ice crystals that make up higher clouds are far less common at low altitudes. Few have been lucky enough to see the beautiful ice-crystal equivalent to fog, shown in March’s Cloud of the Month, which goes by the appealing name of ‘diamond dust’.

Diamond dust is rarely thick enough to reduce visibility much. Its presence is then only revealed by the way the ice crystals glint in the light as they tumble through the air, producing a magical sparkling effect. It is sometimes also known as ‘ice fog’, though this term usually refers to a thicker ice-crystal fog. For classic diamond dust to appear, temperatures need to be lower than –20˚C. When the ice crystals grow slowly in such temperatures, they take the form of tiny, regularly shaped hexagonal prisms. As well as glittering, these can also produce some of the most dramatic and beautiful ‘halo phenomena’.

This is the name for the rings, arcs and bands of colour that appear when sunlight is refracted and reflected as it passes through a cloud’s ice crystals. If diamond dust is made of particularly regular crystals, as is often the case in polar regions, it produces better halo phenomena than the high clouds do. But cloudspotters needn’t travel all the way to the Poles to see these light effects. The onset of the skiing season brings diamond-dust observing opportunities much closer to home, for the same tiny ice-crystal prisms often form downwind of snow machines at ski resorts. Just remember to take cover when they do so on a black run. Fellow cloudspotters will be so distracted by the beautiful halo effects that they are bound to be completely out of control.
 

Current Cloud of the Month:
March 2010

Previous Clouds of the Month:
February 2010
January 2010
Cloud Reflections (December 09)
Numbers in the Clouds (November 09)
Sun Pillar (October 09)
Convection Clouds (September 09)
‘Pile d’Assiettes’ (August 09)
Cumulus congestus (July 09)
‘Asperatus’ (June 09)
Clouds at Night (May 09)
Sundogs (April 09)
Diamond Dust (March 09)
Cloud Streets (February 09)
Crepuscular Rays (Jan 09)
Valley Fog (December 08)
Cloud Shadows (November 08)
Contrails (October 08)
Mamma (September 08)
Kármán Vortex (August 08)
The Summertime Halo (July 08)
The Nor’west Arch (June 08)
Microbursts (May 08)
Irridescent Clouds (April 08)
Northern Lights – Aurora Borealis (March 08)
Ice halos (February 08)
Lightning (January 08)
Roll Cloud (December 07)
Banner Cloud (November 07)
Stratocumulus (October 07)
The Unclassified Cloud (September 07)
Alexander’s Dark Band (August 07)
Fumulus Snail (July 07)
Distrail (June 07)
Altocumulus undulatus (May 07)
Cumulonimbus capillatus (April 07)
Lacunosus (March 07)
Horseshoe Vortex Cloud (February 07)
Jet-Stream Cirrus (Janurary 07)
Altostratus/Altocumulus/Altowhateveritis (December 06)
Anti-Crepuscular Rays (November 06)
Stratocumulus (October 06)
Altocumulus (September ’06)
The Kelvin-Helmholtz Wave Cloud (August ’06)
The ‘Brocken Spectre’ (July ’06)
‘Whale’s Mouth’ (June ’06)
Noctilucent (May ’06)
Cirrus (April ’06)
Cap Cloud (March ’06)
Fallstreak Holes (February ’06)
Nacreous (January ’06)
Cirrostratus (December ’05)
Tuba (November ’05)
Virga (October ’05)
Cirrocumulus (September ’05)
Altostratus (August ’05)
Cumulus (July ’05)
Mamma (June ’05)
Pileus (May ’05)
Lenticularis (April ’05)
Stratus (March ’05)
Cumulonimbus (February ’05)
Contrails (January ’05)


To contribute a Cloud of the Month,
go to our Photograph Submissions page.

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