In honour of World Meteorological Day on March 23, the World Meteorological Organisation has announced the addition of new species to the International Cloud Atlas. This Cloud Atlas is used as a reference document for meteorologists around the world and is an important guide for those working in aviation and at sea.
Dating back to the 19th Century, the was last revised in 1987. Today's additions feature on the new, fully-digital edition and include the rare asperitas, which was added after campaigns by citizen scientists. WIRED takes a look at some of the most intricate new formations:
A long, typically low, horizontal, tube-shaped mass, this cloud often appears to roll slowly through the sky on a horizontal axis. It is a soliton, meaning it is not attached to other clouds. This has been offically recognised by the Met Office and included on the Cloud Atlas for the first time.
These clouds develop as a consequence of forest fires, wildfires or volcanic activity. They originate from localised natural heat sources which, at least in part, consist of water droplets.
These clouds are formed through human activity such as aircraft condensation trails (contrails), or clouds resulting from industrial processes, such as cumuliform clouds generated by power station cooling towers.
These clouds have well-defined, wave-like structures in the underside, in more chaotic patterns than the variety undulatus. Asperitas is characterised by localised waves in the cloud base, either smooth or dappled, sometimes descending into sharp points, as if viewing a roughened sea surface from below.
The cavum is a well-defined, generally circular hole in a thin layer of a supercooled water droplet cloud. Wisps of Cirrus clouds typically fall from the central part of the hole, which will generally grow larger with time. It's circular feature is clearest when viewed from directly beneath, but can often appear oval-shaped when viewed from a distance or at an angle.
A relatively short-lived wave formation, the Fluctus usually sits on the top surface of the cloud, in the form of curls or breaking waves.
These bands of low clouds are associated with a severe supercell convective storm (Cumulonimbus). They are arranged parallel to low-level winds and usually move into or towards the supercell.
These accessory clouds form on an inflow band into a supercell storm along the pseudo-warm front. This can often give it the striking appearance known as a 'beaver tail'.
A localised, persistent, and often abrupt lowering of cloud from the base of a Cumulonimbus. It is usually associated with a supercell or severe multi-cell storm. It typically develops in the rain-free portion of a Cumulonimbus and indicates an area of strong updraft. It is commonly referred to as a 'wall cloud'.
A horizontal, tail-shaped cloud that extends from the main precipitation region of a supercell Cumulonimbus to a wall cloud (see above, murus). Cloud motion is away from the precipitation area and towards the murus, with rapid upward motion often observed near the junction of the tail and wall clouds - the reason it is also known as a 'tail cloud'.
These clouds often develop near large waterfalls as a consequence of water broken up into spray by the falls.
The Silvagenitus develops locally over forests as a result of increased humidity due to evaporation and evapotranspiration from the tree canopy.
Persistent contrails (of the Cirrus variety) are formed over a period of time under the influence of strong upper winds. They grow and spread out over a larger portion of sky, and eventually take on the appearance of more natural cirri-form clouds.
This article was originally published by WIRED UK
