Cloud - Tropospheric Class - Summary of Families, Genera, Species, Varieties, Supplementary Features, Mother Clouds, and Associat - Low Stratocumuliform, Stratiform, and Cumuliform

Low Stratocumuliform, Stratiform, and Cumuliform

  • Genus stratocumulus (Sc):
This genus type is a stratocumuliform cloud layer of limited convection, usually in the form of irregular patches or rounded masses similar to altocumulus but having larger elements with deeper-gray shading. Opaque stratocumulus associated with a weak frontal or low-pressure disturbance can produce very light intermittent precipitation. This cloud often forms under a precipitating deck of altostratus or high-based nimbostratus associated with a well-developed warm front, slow-moving cold front, or low-pressure area. This can create the illusion of continuous precipitation of more than very light intensity falling from stratocumulus. All species are coded CL5 except when formed from free convective mother clouds (CL4) or when formed separately from co-existing cumulus (CL8).
  • Species: Stratocumulus has three species which it shares in common with the other stratocumuliform genus types. The stratiformis species (Sc str) consists of sheets or relatively flat patches of low cloud similar if thicker in structure to the higher altocumulus and cirrocumulus types. Stratocumulus lenticularis (Sc len) and castellanus (Sc cas) also have similar structures to their Ac and Cc counterparts.
  • Opacity-based varieties: The translucidus, perlucidus, and opacus varieties are the same for stratocumulus stratiformis as for Ac stratiformis. Varieties based on opacity are not commonly associated with species lenticularis or castellanus.
  • Pattern-based varieties: Parallel bands of radiatus are occasionally seen with the stratiformis species. Duplicatus and undulatus varieties are sometimes associated with stratocumulus stratiformis and lenticularis. With increased airmass instability, lacunosus downdraft holes may appear in layers of stratocumulus stratiformis and castellanus.
  • Precipitation-based supplementary features: Virga or praecipitatio features of weak intensity may be seen with stratocumulus.
  • Accessory cloud: Mamma in the form of downward facing bubble-like protuberances may form as a result of localized downdrafts in the cloud layer..
  • Genitus mother clouds: Stratocumulus may form from the spreading of cumulus or cumulonimbus (CL4), or the partial transformation of altostratus or nimbostratus.
  • Mutatus mother clouds: This genus type may also result from the complete transformation of altocumulus, nimbostratus, or stratus.
  • Genus stratus (St):
This low cloud is a uniform layer of low non-convective cloud resembling fog but not resting on the ground. Only very weak precipitation can fall from this cloud (usually drizzle or snow grains), although heavier rain or snow may fall through a stratus layer from a higher precipitating cloud deck.
  • Species: There are two species of stratus. The nebulosus species (St neb) is a featureless veil of low cloud sometimes producing light drizzle that is coded CL6 in the SYNOP report. Stratus fractus (St fra) appears as a ragged broken up sheet that often forms as an accessory cloud in precipitation falling from a higher cloud deck. It is coded CL7 when assoociated with bad weather. This species may also result from a continuous sheet of stratus in clear air becoming broken up by the wind, in which case it is coded CL6, the same as for stratus nebulosis not associated with bad weather.
  • Opacity-based varieties: Stratus nebulosus can appear as translucidus or opacus depending on its thickness. The perlucidus variety is not usually associated with this species because of its relatively even structure.
  • Pattern-based variety: Stratus nebulosus usually shows no patterns. However a slightly disturbed gentle wind current can create a mild undulatus pattern, but this is rarely seen. Varieties of any kind are not commonly associated with stratus fractus because of the highly fragmented structure that identifies this species.
  • Precipitation-based supplementary feature: Stratus cloud is too low to produce virga, but the praecipitatio feature can bee seen in the form of drizzle or snow grains.
  • Accessory clouds: Stratus does not have any accessory clouds as such, but may form in precipitation as a cloud based supplementary feature associated with other precipitating clouds.
  • Genitus mother clouds: Stratus can form from the spreading or thinning of the base of clouds with significant vertical development, particularly nimbostratus, cumulus, or cumulonimbus.
  • Mutatus mother clouds: This genus type can form as the result of the fusing of stratocumulus elements into an even featureless sheet.
  • Genus cumulus (Cu) - little vertical extent:
These are small fair-weather cumuliform clouds of limited convection that do not grow vertically and generally do not produce rain showers.
  • Species: Cumulus species are mainly indicators of degrees of vertical development. The smallest type is cumulus fractus (Cu fra) which consists of cumulus broken up into ragged and changing fragments. Fair weather Cu fractus is coded CL1. It can also form in precipitation as a pannus accessory cloud which is coded CL7. Cumulus humilis (Cu hum) is the smallest non-ragged cloud and usually shows a light-grey shading underneath. Fair weather Cu humilis is also coded CL1 in the SYNOP code. Cumulus fractus and humilis are two species that cannot be described as vertical in the true sense of the word. Being at or near the beginning of the convective cloud's daily life cycle, they lack the moderate vertical extent of cumulus mediocris. Consequently they are commonly classified as low clouds despite the fact their bases can be in the middle height range when the moisture content of the air is very low. When cumulus fractus and cumulus humilis are classified as vertical, it is on the basis of their potential for at least moderate upward growth during their daily cycle.
  • Opacity-based varieties: Cumulus fractus is inherently translucent and the humilis species is generally opaque, so these do not have opacity- based varieties.
  • Pattern-based varieties: Radiatus is occasionally seen with fair-weather cumulus when arranged in parallel rows.
  • Supplementary features: These are not commonly seen with small cumulus, but Cu fractus of bad weather may be seen as a pannus feature with precipitating clouds.
  • Genitus mother clouds: Cumulus fractus or humilis may form as the result of a partial transformation of altocumulus or stratocumulus.
  • Mutatus mother clouds: These cumulus species may also appear due to a complete transformation of stratocumulus or stratus.

Read more about this topic:  Cloud, Tropospheric Class, Summary of Families, Genera, Species, Varieties, Supplementary Features, Mother Clouds, and Associat

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