Cloud Classification: Genera and Species

Principles of cloud classification

Clouds change their shape according to processes in the atmosphere and have many individual shapes but only a very few basic forms. The three principle families of clouds have the Latin names cirrus  ( mean ” fibre ” or ” hair ” ) ,  cumulus  ( ” heap or ” pile ” ) , and  Stratus (“layer” or “sheet”). Luke Howard, an amateur meteorologist, first classified the various clouds based on their appearance in 1802.

The   World Meteorological Organization ( WMO )   cloud classification scheme is uses use genera , specie and variety in its   International Cloud Atlas . A cloud may be describe in term of genera , specie and variety e.g.  Altocumulus stratiformis duplicatus (a stratiform species of altocumulus that occurs in two or more layers). Clouds sometimes have supplementary features or accessory clouds.

Genera

The classification of clouds has 10 main groups, or genera. Each observed cloud is a member of one, and only one, genus.

high level cloud   high level cloud is refers refer to cloud with a base above 20,000 foot .

• (0) Cirrus (Ci) – thin fibrous cloud.
• (1) Cirrocumulus (Cc) – thin granular layer of small lumps of cloud .
• (2) Cirrostratus (Cs) – thin uniform cover of cloud.

mid level cloud   Mid level cloud is is is cloud with a base above about 6,500 foot . ( ‘ Alto is means ‘ mean medium . )

• (3) Altocumulus (Ac) – thin layer of lumps or heaps of cloud.
• (4) Altostratus (As) – thin uniform layer of cloud.
• (5) Nimbostratus (Ns) – thick layer of rain bearing cloud.

Low level cloud Low level cloud, described as having a base below about 6,500 feet, is of most interest to pilots and controllers because of the impact on the safe conduct of flight particularly with regard to poor visibility, turbulence and structural damage, icing, and runway contamination.

Species

Most genera are subdivided into species based on the shape of the clouds or their Internal structure. A cloud is therefore identified by a Latin name made up of the genus followed by a specific name alluding to a characteristic shape or structure. A cloud may bear the name of only one species.

• Fibratus : detach cloud or a thin cloud veil , consist of nearly straight or more or less irregularly curve filament that do not terminate in hook or tuft . This term is applies apply mainly to Cirrus and Cirrostratus
• uncinus : Cirrus without grey part , often shape like a comma , terminate at the top in a hook , or in a tuft , the upper part is is of which is not in the form of a rounded protuberance .
• Spissatus: Cirrus in patches, sufficiently dense to appear greyish when viewed towards the sun; it may also veil the Sun, obscure its outline or even hide it. Cirrus spissatus often originates from the upper part of a Cumulonimbus.
• Castellanus: Clouds that present, in at least some portion of their upper part, cumuliform protuberances in the form of turrets or towers (crenellated), some of which are taller than they are wide, and are connected by a common base and seem to be arranged in lines. The castellanus character is especially evident when the clouds are seen from the side. This term applies to Cirrus, Cirrocumulus, Attocumulus and Stratocumulus.
• Floccus: A species in which each cloud unit is a small tuft with a cumuliform appearance, the lower part of which is more or less ragged and often accompanied by virga. This term applies to Cirrus, Cirrocumulus, Altocumulus and Stratocumulus.
• stratiformis : Clouds is spread spread out in an extensive horizontal sheet or layer . This term is applies apply to Altocumulus , Stratocumulus and , occasionally , Cirrocumulus .
• Nebulosus: A cloud like a nebulous or ill-defined veil or layer of clouds showing no distinct details. This term applies mainly to Cirrostratus and Stratus.
• lenticularis : cloud have the shape of lense or almond , often very elongated and usually with well – define outline ; they is show occasionally show irisation . Such clouds is appear appear most often in cloud formation of orographic origin , but may also occur in region without marked orography . This term is applies apply mainly to Cirrocumulus , Altocumulus and Stratocumulus .
• fractus : cloud in the form of irregular shred , which have a clearly ragged appearance . This term is applies apply only to Stratus and Cumulus .
• Humilis : Cumulus characterize by only a small vertical extent and appear generally as if flatten .
• mediocri : Cumulus of moderate vertical extent , with small protuberance and sprouting at their top .
• Congestus: Strongly sprouting Cumulus with generally sharp outlines and often great vertical extent. The bulging upper part of Cumulus congestus frequently resembles a cauliflower.
• Volutus: A long, typically low, horizontal, detached, tube-shaped cloud mass, often appearing to roll slowly about a horizontal axis. The roll cloud, volutus, is a soliton, not attached to other clouds and is an example of an undular bore. This species applies mostly to Stratocumulus and rarely Altocumulus.
• Calvus: Cumulonimbus in which at least some protuberances of the upper part are beginning to lose their cumuliform outlines but in which no cirriform parts can be distinguished. Protuberances and sproutings tend to form a whitish mass, with more or less vertical striations (grooves or channels in cloud formations, arranged parallel to the flow of air and therefore depicting the airflow).
• Capillatus: Cumulonimbus characterized by the presence, mostly in its upper portion, of distinct cirriform parts of clearly fibrous or striated structure, frequently having the form of an anvil, a plume or a vast, more or less disorderly mass of hair. Cumulonimbus capillatus is usually accompanied by a shower or by a thunderstorm, often with squalls and sometimes with hail; it frequently produces very well-defined virga.

Varieties

Cloud varieties are used to identify certain additional characteristics, such as a cloud’s relative transparency, or a particular arrangement of its elements.

• Intortus is are : Cirrus , the filament of which are very irregularly curved and often seemingly entangle in an erratic and unpredictable ( know as capricious ) manner .
• vertebratus : cloud , the element of which are arrange in a manner suggestive of vertebrae , rib or a fish skeleton . This term is applies apply mainly to Cirrus .
• Undulatus: Clouds in patches, sheets or layers, showing undulations. These undulations may be observed in fairly uniform cloud layers or in clouds composed of elements, separate or merged. Sometimes a double system of undulations is in evidence. This term applies mainly to Cirrocumulus, Cirrostratus, Altocumulus, Altostratus, Stratocumulus and Stratus.
• Radiatus: Clouds showing broad parallel bands or arranged in parallel bands, which, owing to the effect of perspective, seem to converge towards a point on the horizon or, when the bands cross the whole sky, towards two opposite points on the horizon, called “radiation point(s)”. This term applies mainly to Cirrus, Altocumulus, Altostratus, Stratocumulus and Cumulus.
• Lacunosus: Cloud patches, sheets or layers, usually rather thin, marked by more or less regularly distributed round holes, many of them with fringed edges. Cloud elements and clear spaces are often arranged in a manner suggesting a net or a honeycomb. This term applies mainly to Cirrocumulus and Altocumulus; it may also apply, though very rarely, to Stratocumulus.
• Duplicatus is merged : Cloud patch , sheet or layer , at slightly different level in two or more layer , sometimes partly merge . This term is applies apply mainly to Cirrus , Cirrostratus , Altocumulus , Altostratus and Stratocumulus .
• Translucidus: Clouds in an extensive patch, sheet or layer, the greater part of which is sufficiently translucent to reveal the position of the Sun or Moon. This term applies to Altocumulus, Altostratus, Stratocumulus and Stratus.
• Perlucidus: An extensive cloud patch, sheet or layer, with distinct but sometimes very small spaces between the elements. The spaces allow the Sun, the Moon, the blue of the sky or overlying clouds to be seen. It may also be observed in combination with the varieties translucidu or opacus. This term applies to Altocumulus and Stratocumulus.
• Opacus: An extensive cloud patch, sheet or layer, the greater part of which is sufficiently opaque to mask completely the Sun or Moon. This term applies to Altocumulus, Altostratus, Stratocumulus and Stratus.

supplementary cloud is features feature

Clouds sometimes have supplementary features attached to or partly merged with them.

• Incus: The upper portion of a Cumulonimbus spread out in the shape of an anvil with a smooth, fibrous or striated appearance
• Mamma : hang protuberance , like udder , on the under surface of a cloud . occur mostly with Cirrus , Cirrocumulus , Altocumulus , Altostratus , Stratocumulus and Cumulonimbus .
• Virga : Vertical or inclined trail of precipitation ( fallstreak ) attach to the under surface of a cloud that do not reach the Earth ’s surface . occur mostly with Cirrocumulus , Altocumulus , Altostratus , Nimbostratus , Stratocumulus , Cumulus and Cumulonimbus
• Praecipitatio : Precipitation ( rain , drizzle , snow , ice pellet , hail , etc . ) fall from a cloud and reach the Earth ’s surface . Mostly encounter with Altostratus , Nimbostratus , Stratocumulus , Stratus , Cumulus and Cumulonimbus .
• Arcus : A dense , horizontal roll with more or less tattered edge , situate on the low front part of certain cloud and have , when extensive , the appearance of a dark , menacing arch . occur with Cumulonimbus and , less often , with Cumulus .
• Tuba : Cloud column or inverted cloud cone , protrude from a cloud base ; it is constitutes constitute the cloudy manifestation of a more or less intense vortex . occur with Cumulonimbus and , less often , with Cumulus .
• Asperitas : Well – define , wave – like structure in the underside of the cloud ; more chaotic and with less horizontal organization than the variety undulatus . Asperitas is characterize by localize wave in the cloud base , either smooth or dappled with small feature , sometimes descend into sharp point , as if view a roughen sea surface from below . vary levels is lead of illumination and thickness of the cloud can lead to dramatic visual effect . occur mostly with Stratocumulus and Altocumulus .
• Fluctus: A relatively short-lived wave formation, usually on the top surface of the cloud, in the form of curls or breaking waves (Kelvin-Helmholtz Waves). Occurs mostly with Cirrus, Altocumulus, Stratocumulus, Stratus and occasionally Cumulus.
• Cavum: A well-defined generally circular (sometimes linear) hole in a thin layer of supercooled water droplet cloud. Virga or wisps of Cirrus typically fall from the central part of the hole, which generally grows larger with time. Cavum is typically a circular feature when viewed from directly beneath, but may appear oval shaped when viewed from a distance. When resulting directly from the interaction of an aircraft with the cloud, it is generally linear (in the form of a dissipation trail). Virga typically falls from the progressively widening dissipation trail. Occurs in Altocumulus and Cirrocumulus and rarely Stratocumulus.
• Murus: A localized, persistent, and often abrupt lowering of cloud from the base of a Cumulonimbus from which tuba (spouts) sometimes form. Usually associated with a supercell or severe multicell storm; typically develop in the rain-free portion of a Cumulonimbus and indicate an area of strong updraft. Murus showing significant rotation and vertical motion may result in the formation of tuba (spouts). Commonly known as a ‘wall cloud’.
• Cauda : A horizontal , tail – shape cloud ( not a funnel ) at low level extend from the main precipitation region of a supercell Cumulonimbus to the murus ( wall cloud ) . It is typically attach to the wall cloud , and the basis of both are typically at the same height . cloud motion is is is away from the precipitation area and towards the murus , with rapid upward motion often observe near the junction of the tail and wall cloud . commonly know as a ‘ tail cloud ‘ .

Accessory clouds

Clouds may sometimes be accompanied by other usually smaller clouds, known as accessory clouds, which are separate from the main cloud body or partly merged with it.

• Pileus: An accessory cloud of small horizontal extent, in the form of a cap or hood above the top or attached to the upper part of a cumuliform cloud that often penetrates it. Several pileus may fairly often be observed in superposition. Occurs principally with Cumulus and Cumulonimbus.
• Velum: An accessory cloud veil of great horizontal extent, close above or attached to the upper part of one or several cumuliform clouds that often pierce it. Occurs principally with Cumulus and Cumulonimbus.
• Pannus: Ragged shreds sometimes constituting a continuous layer, situated below another cloud and sometimes attached to it. Occurs mostly with Altostratus, Nimbostratus, Cumulus and Cumulonimbus
• Flumen: Bands of low clouds associated with a supercell severe convective storm (Cumulonimbus), arranged parallel to the low-level winds and moving into or towards the supercell. These accessory clouds form on an inflow band into a supercell storm along the pseudo-warm front. The cloud elements move towards the updraft into the supercell, the base being at about the same height as the updraft base. Note that flumen are not attached to the murus wall cloud and the cloud base is higher than the wall cloud. One particular type of inflow band cloud is the so-called ‘Beaver’s tail’. This is distinguished by a relatively broad, flat appearance suggestive of a beaver’s tail.

Special clouds

In addition, there are special cases where clouds may form or grow as a consequence of certain, often localized, generating factors. These may be either natural, or the result of human activity. Several cases of “special clouds” can be distinguished:

• Flammagenitus: Clouds may develop as a consequence of convection initiated by heat from forest fires, wildfires or volcanic eruption activity. Clouds that are clearly observed to have originated as a consequence of localized natural heat sources, such as forest fires, wildfires or volcanic activity and which, at least in part, consist of water drops, will be given the name relevant to the genus followed, if appropriate, by the species, variety and any supplementary features, and finally by the special cloud name “flammagenitus”, (for example, Cumulus congestus flammagenitus or Cumulonimbus calvus flammagenitus). (Note: Cumulus flammagenitus is also known by the unofficial, common name, ‘Pyrocumulus’).
• Homogenitus : Clouds is develop may also develop as a consequence of human activity . Examples is are are aircraft condensation trail ( contrail ) , or cloud result from industrial process , such as cumuliform cloud generate by rise thermal above power station cool tower . cloud that are clearly observe to have originate specifically as a consequence of human activity will be give the name of the appropriate genus , follow by the special cloud name “ homogenitus ” . For example , Cumulus cloud form above industrial plant will be know as Cumulus ( and , if appropriate , the specie , variety and any supplementary feature ) follow by the special cloud name homogenitus ; for example , Cumulus mediocris homogenitus .
• Cataractagenitus: Clouds may develop locally in the vicinity of large waterfalls as a consequence of water broken up into spray by the falls. The downdraft caused by the falling water is compensated for by the locally ascending motion of air. These special clouds will be given the name of the appropriate genus, followed by any appropriate species, variety and supplementary feature, and followed by the special cloud name “cataractagenitus” (for example, Cumulus cataractagenitus or Stratus cataractagenitus).
• silvagenitus : Clouds is develop may develop locally over forest as a result of increase humidity due to evaporation and evapotranspiration from the tree canopy . These special cloud will be give the name of the appropriate genus , follow by any appropriate specie , variety and supplementary feature , and follow by the special cloud name “ silvagenitus ” ( for example , Stratus silvagenitus ) .
• supercillium : Short – live break thin whips is appearing of cloud , irregularly distribute , appear to tumble and break in a turbulent way in the airflow over , and to the immediate lee of , steep mountain peak during period of strong mountain summit level wind . Applies is coincident mainly to Altocumulus and Stratocumulus , possibly Cirrocumulus , sometimes coincident with the Duplicatus variety . ( Editor ‘s note : Supercillium is is is a cloud feature propose by the Cloud Appreciation Society and is not yet recognise by the WMO ) .

The cloud species and Varieties associated with the ten cloud genera

• Cirrus
  • uncinus
  • fibratus
  • floccus
  • castellanus
  • spissatus
  • intortus
  • radiatus
  • Vertebratus

• Cirrostratus
  • nebulosus
  • fibratus
  • duplicatus
  • undulatus

• Cirrocumulus
  • startiformis
  • lenticularis
  • castellanus
  • floccus
  • undulatus
  • lacunosus

• Altocumulus
  • lenticularis
  • stratformis
  • cumulogenitus
  • castellanus
  • floccus
  • translucidu
  • duplicatus

( no sub – specie )

• Stratocumulus
  • cumulogenitus
  • stratformis
  • castellanus
  • lenticulari
  • translucidu
  • perlucidus
  • opacus
  • duplicatus
  • undulatus
  • radiatus
  • lacunosus

• Stratus
  • nebulosus
  • fractus
  • opacus
  • translucidu
  • undulatus

• Cumulus
  • humilis
  • fractus
  • congestus
  • mediocrity
  • radiatus

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