July 12, 2022
By Shreesha Ghosh
These are some of the rarest clouds on the planet, a form of the polar stratospheric cloud. The clouds manifest close to the poles during winter; when temperatures plummet below -83C, tiny quantities of moisture in what is usually quite a dry stratosphere condense to create wispy ice crystals clouds.
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These clouds are associated with powerful storm clouds and thunderstorms. The two types of arcus clouds are shelf clouds and roll clouds, which can be spotted underneath fearsome storm clouds or cumulonimbus clouds. They need specific weather conditions to manifest, such as during or just before a storm.
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Altocumulus lenticularis is one of the 'bizarre' cloud types- they don't occur too frequently, so when you see one, take notice. They often form above or near mountains as moist air flows rapidly in elevation. Mt Fuji, Japan’s tallest peak, makes a pretty amazing base for this specific cloud.
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Another rare and easily recognisable variety, mammatocumulus, tends to spill out from the base of massive thunderheads in a characteristic blanket of pouch-like nodules. These clouds refer to distinctive formations set apart by a bunch of protrusions or bulges emerging from the base of another cloud.
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Cumulonimbus clouds are menacing-looking multi-level clouds, extending high into the sky in towers or plumes. More commonly known as thunderclouds, cumulonimbus is the only cloud type that can produce hail, thunder and lightning, all at the same time.
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Altocumulus clouds are small mid-level layers or patches of clouds, called cloudlets, which commonly exist in the shape of rounded clumps. There are many shapes of altocumulus. Its formations usually comprise several individual cloudlets and take shape at heights of 6,500 to 23,000 feet.
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Often called “hole-punch” clouds, fallstreak holes can grow as big as 50 km in just one hour. They appear between layers of mid to high-level clouds in the sky when an area of moisture suddenly begins to freeze and fall. These clouds are circular or elliptical gaps that can also appear in cirrocumulus or altocumulus clouds.
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Asperitas, formerly known as Undulatus asperatus, is a cloud formation first popularised and proposed as a type of cloud in 2009 by Gavin Pretor-Pinney of the Cloud Appreciation Society. Added to the International Cloud Atlas as a supplementary feature in March 2017, it is the first cloud formation added since the cirrus intortus in 1951.
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