International Cloud Atlas
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Tabular guide: Genus

(Section 2.7.2.1.1)

Table 12. Guide for the identification of the genera of clouds

Legend
E

The feature is essential to the genus
U

The feature is usual
P

The feature is possible, occurring sometimes in certain species
S

The feature may occur only at the summit or upper portion of the clouds

Consider these criteria in succession
 

Distinctive features

Genera in which the features occur
Ci Cc Cs Ac As Ns Sc St Cu Cb

General shape and grouping of cloud and cloud elements

Detected with a flattened appearance

                

P

  

More or less developed vertivally

Detached

P

P

  

P

    

P

  

U

U

With a common base

P

P

  

P

    

P

      

Thin, with detached filaments

U

                  

Thin, grouped in sheaves, or ending in a hook or tuft

U

                  

Spread out in a patch, sheet or layer, subdivided into more or less regularly arranged layers or rounded masses, the apparent width of most elements being:

Less than 1° (< 1 finger)

  

E

                

Between 1° and 5°

      

U

            

More than 5° (> 3 fingers)

            

E

      

Spread out as a veil totally or partially covering the sky

    

E

  

E

E

  

U

    

Structure and texture

Silky sheen

U

P

P

            

S

Fibrous (hair like)

U

  

P

P

P

        

S

Granular

  

U

  

P

            

Undulated or rippled

  

U

P

P

P

  

P

P

    

Ragged

              

P

P

  

Uniform base

    

U

  

U

U

  

U

U

P

Diffuse base

        

P

U

  

P

  

P

Optical thickness

Thin clouds, through which the disc of the Sun or Moon can be seen

U

U

E

P

    

P

P

P

  

Translucent clouds, revealing only the position of the Sun or Moon

P

P

  

U

U

  

P

P

P

  

Opaque clouds

      

P

U

U

P

U

  

P

Shading

Without shading

U

E

U

P

    

P

P

P

  

Partly shaded

P

  

P

U

P

P

U

P

U

U

Shaded throughout

      

P

U

U

P

U

  

P

Supplementary features and accessory clouds

Incus (inc)

                  

S

Mamma (mam)

P

P

  

P

P

  

P

    

P

Virga (vir)

  

P

  

P

U

U

P

  

P

P

Praecipitatio (pra)

Uniform (intermittent or continuous)

        

P

U

P

P

    

In the form of showers

                

P

U

Arcus (arc)

                

P

P

Tuba (tub)

                

P

P

Pileus (pil)

                

P

P

Velum (vel)

                

P

P

Pannus (pan)

        

P

U

    

P

U

Asperitas (asp)

      

P

    

P

      

Cauda (cau)

                  

P

Cavum (cav)

  

P

  

P

    

P

      

Fluctus (flu)

S

    

S

    

S

S

S

  

Flumen (flm)

                  

P

Murus (mur)

                  

P

Hydrometeors

Rain

        

P

U

P

  

P

U

Drizzle

              

P

    

Snow

        

P

P

P

P

P

P

Snow pellets

            

P

  

P

P

Snow grains

              

P

    

Ice pellets

        

P

P

        

Hail

                  

P

Photometeors

Halo phenomena

P

  

U

P

      

P

  

S

Corona

  

P

P

U

P

  

P

P

P

  

Irisation on clouds

  

P

  

P

    

P

      

Rainbow

                

P

P

Electrometeors

Lightning

                  

P

Thunder

                  

P

Thunderstorm

                  

P
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