THE WATER VAPOR OF THE AIR 



231 



CLOUDS 



Chief Characteristics 



Striated or filament structure (Figs. 155, 156). 

 Casts no shadow. Usually moves from west- 

 erly points. Usually 5 to 7 miles high. Speed, 

 to 120 miles per hour. 



The heap cloud common in summer. Usually 

 dense; shaded on side away from sun. Height, 

 base Y to 1; top y 2 to 3 miles (Figs. 158 to 161). 



The sheet or layer cloud of all seasons. Dark 

 color, often more or less broken. Usually 

 K to M mile high (Figs. 155, 164). 

 Combination Types 



Structure of cirrus. Filaments interlaced or 

 interwoven in sheet or layer form ; merges into 

 alto-stratus; 2 to 6 miles high (Figs. 155, 157). 



(Alto means high) A high layer cloud, sometimes 

 resembling dense cirro-stratus, and sometimes 

 of a lumpy structure; 3 to 5 miles high (Fig. 155). 



Balls or heaps or " fleeces" showing some of 

 the striated texture of cirrus, and casting no 

 shadow. Usually 3 to 6 miles high (Fig. 155). 



A high cumulus; often does not move in same 

 direction as ground wind. 2 to 4 miles high, 

 (Fig. 155). 



8. Strato-cumulus. Lower surface often like stratus; tops resemble 



cumulus grouped together in mass. Sometimes 

 broken showing clear sky or higher clouds above ; 

 often appears in long rolls with gaps between. 

 Grades all the way from stratus to cumulus, 

 K to 3 miles high (Figs. 155, 164, 165). 



9. Cumulu- A cumulus cloud that is raining; is generally 



nimbus. of large size. This is the thunder shower cloud. 



Base usually % to 1^ miles high; top 3 to 8 

 miles (Figs. 160, B, and 162). 



10. Nimbus. Any cloud from which precipitation is falling. 



Has no special form. May be of any stratus 

 or cumulus forms except cirro-stratus or cirro- 

 cumulus (Figs. 155, 162). 



Class 

 1. Cirrus. 



2. Cumulus. 



3. Stratus. 



4. Cirro-stratus. 



5. Alto-stratus. 



6. Cirro-cumulus. 



7. Alto-cumulus. 



