Mammatus cloud


Mammatus, meaning "mammary cloud", is a cellular pattern of pouches hanging underneath the base of a cloud, typically cumulonimbus rainclouds, although they may be attached to other classes of parent clouds. The name mammatus is derived from the Latin '. According to the WMO International Cloud Atlas, mamma is a cloud supplementary feature rather than a genus, species or variety of cloud. They are formed by cold air sinking down to form the pockets contrary to the puffs of clouds rising through the convection of warm air. These formations were first described in 1894 by William Clement Ley.

Characteristics

Mammatus are most often associated with anvil clouds and also severe thunderstorms. They often extend from the base of a cumulonimbus, but may also be found under altostratus, and cirrus clouds, as well as volcanic ash clouds. When occurring in cumulonimbus, mammatus are often indicative of a particularly strong storm. Due to the intensely sheared environment in which mammatus form, aviators are strongly cautioned to avoid cumulonimbus with mammatus as they indicate convectively induced turbulence. Contrails may also produce lobes but these are incorrectly termed as mammatus.
Mammatus may appear as smooth, ragged or lumpy lobes and may be opaque or translucent. Because mammatus occur as a grouping of lobes, the way they clump together can vary from an isolated cluster to a field of mammae that spread over hundreds of kilometers to being organized along a line, and may be composed of unequal or similarly-sized lobes. The individual mammatus lobe average diameters of and lengths on average of. A lobe can last an average of 10 minutes, but a whole cluster of mamma can range from 15 minutes to a few hours. They are usually composed of ice, but also can be a mixture of ice and liquid water or be composed of almost entirely liquid water.
True to their ominous appearance, mammatus clouds are often harbingers of a coming storm or other extreme weather system. Typically composed primarily of ice, they can extend for hundreds of miles in each direction and individual formations can remain visibly static for ten to fifteen minutes at a time. While they may appear foreboding they are merely the messengers - appearing around, before or even after severe weather.

Hypothesized formation mechanisms

The existence of many different types of mammatus clouds, each with distinct properties and occurring in distinct environments, has given rise to multiple hypotheses on their formation, which are also relevant to other cloud forms.
One environmental trend is shared by all of the formation mechanisms hypothesized for mammatus clouds: sharp gradients in temperature, moisture and momentum across the anvil cloud/sub-cloud air boundary, which strongly influence interactions therein. The following are the proposed mechanisms, each described with its shortcomings:
This plenitude of proposed formation mechanisms shows, if nothing else, that the mammatus cloud is generally poorly understood.

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