A cloud, at least to the untrained observer, is merely an atmospheric accumulation of water particles that fills portions of the sky overhead.
However, within the annals of nephology, which comprises the science of cloud formations and their physics, no two clouds are alike, and each falls into its very own specific category of atmospheric phenomena.
Recently, the nephological community has had more than enough reason for rejoice, with the identification of a dozen new types of clouds; among these are an unusual, seldom-observed formation known as the asperitas cloud, which has now been finally recognized by the International Cloud Atlas for the very first time.
The Atlas, which first appeared in the 19th century as the "Manual on the Observation of Clouds and Other Meteors", is published by the World Meteorological Organization, has not been revised since 1987. However, thanks to the efforts of cloud-gazing citizen scientists around the world, these "asperitas" have finally secured their official designation.
The BBC reports that a handful of other additions will be included as well. Also new to the lineup will be "volutus" clouds, which are similar to long, tubular formations known as roll-clouds.
However, perhaps the most unusual addition to the Atlas will be contrails, which of course represent the vapor trails left by airplanes passing through the sky (these aren't to be confused with chemtrails, long held as an item of controversy among conspiracy theorists). Vapor residues from aircraft are not natural formations, per se, though the nephological community now appears to be in agreement that they will nonetheless be classified among varieties of clouds.
Arguably, the massive, eerie looking Roll Clouds are among the most unusual varieties of cloud formations known to exist. These represent a variety of arcus cloud, and often appear near coastal regions, as well as in conjunction with thunderstorms and other larger-scale storm activity.
In December of 1970, pilot Bruce Gernon and his copilots claimed to have experienced an unusual "transportation" of their aircraft, in which the plane and its occupants were allegedly transported across a large distance during an inconceivably short period of time. This occurred, according to Gernon's account, after flying into an anomalous cloud formation that resembled a long tunnel. One odd theory about Gernon's experience involves the idea that he and his crew had somehow managed to pass through a roll cloud formation, which could have carried the plane along at speeds faster than anticipated.
This, however, is a rather speculative explanation for the alleged phenomenon Gernon and his company described experiencing, and there may be other ways the circumstances might be interpreted.
Apart from clouds alone, a number of interesting varieties of phenomenon have been observed and recorded by the International Cloud Atlas over the last century. Some of the more esoteric among these phenomena are Saint Elmo's Fire, as well as Polar Aurora. "In the case of Saint Elmo's fire," past editions of the Atlas have advised, "it should be stated whether the phenomenon appears in a cloud, in precipitation or in clear air, etc. Exceptional polar aurorae should be described in detail."
According to the new Atlas, this tradition of non-cloud weather features being included for skywatchers seems to be ongoing; the new edition will also be including rainbows, halos, snow devils and hailstones among the varieties of "meteors" for which it helps categorize and collect new data.