New cloud species added to International Cloud Atlas

New cloud species added to International Cloud Atlas
Asperitas (Source: WTOC)
Asperitas (Source: WTOC)

SAVANNAH, GA (WTOC) - Hot off the presses!!  A new edition of the International Cloud Atlas is out!  Well, not necessarily "presses", the ICA was last updated in 1987, before the internet era.

For the first time, the 2017 edition will primarily be a web-based portal, allowing for much richer content and presentation. However, it may be published in hard copy at a later date.

The International Cloud Atlas was first published in the late 19th century. It contains a detailed manual of standards and numerous plates of photographs of clouds and certain other weather phenomena.

The World Meteorological Organization (WMO) has released its new, long-awaited, digitized International Cloud Atlas. It's THE global reference for observing and identifying clouds, which are an essential part of weather, the climate system and the water cycle. It was released for the World Meteorological Day on March 23. The new Atlas combines 19th-century traditions with 21st-century technology. It contains hundreds of images submitted by meteorologists, photographers and cloud lovers from around the globe.

It includes new classifications, including volutus, a roll cloud; clouds from human activities such as the contrail, a vapour trail sometimes produced by airplanes; and asperitas, a dramatic undulated cloud which captured the public imagination. It also features meteorological phenomena like rainbows, halos, snow devils and hailstones.

"The International Cloud Atlas is the single most authoritative and comprehensive reference for identifying clouds. Its reputation is legendary among cloud enthusiasts and it serves as an essential training tool for professionals working in meteorological services, and in sectors such as aviation and shipping," said WMO Secretary General Petteri Taalas.

The present international system of Latin-based cloud classification dates back to 1803, when amateur meteorologist Luke Howard wrote "The Essay on the Modifications of Clouds."

"This new edition brings together for the first time all types of measurements, including  very high-tech surface-based, in situ and space observations and remote sensing, thus giving to the human observer a revolutionary tool to understand clouds," said Bertrand Calpini, president of WMO's Commission for Instruments and Methods of Observation (CIMO), which oversaw the revision process.

There are ten basic cloud "genera," which are defined according to where in the sky they form and their approximate appearance. The new International Cloud Atlas has made no additions to these 10 genera.

The 10 genera are subdivided into "species," which describe shape and internal structure, and "varieties," which describe the transparency and arrangement of the clouds. In total there are about 100 combinations.

The new International Cloud Atlas has added a new species: volutus or roll cloud (from the Latin volutus which means rolled), which occurs within the genera Altocumulus and Stratocumulus. It describes a long, typically low, horizontal tube-shaped cloud mass that often appeals to roll about a horizontal axis.

Five new supplementary features have been added: asperitas, cavum, cauda (often known as tail cloud), fluctus (widely known as Kelvin-Helmholz wave) and murus (known as wall cloud).

Best known of these is asperitas (from the Latin meaning roughness), Photographs of the dramatic, wave-like cloud captured the popular imagination around the world. The Cloud Appreciation Society argued for a new classification to be used to describe clouds with this appearance. The Atlas includes the winning photograph from a Cloud Appreciation Society's competition on asperitas.

A new accessory cloud, flumen, has been included. Commonly known as "beaver's tail," it is associated with a supercell severe convective storm.

The International Cloud Atlas also proposes five new "special clouds:" cataractagenitus, flammagenitus, homogenitus, silvagenitus and homomutatus. The suffix genitus indicates localized factors that led to cloud formation or growth, while mutatus is added when these caused the cloud to change from a different form. These special clouds are influenced by large waterfalls, localized heat from wildfires, saturation of air above forests and humans. Thus, a common example of homogenitus is contrails, sometimes seen after aircraft.

The International Cloud Atlas is available here.

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