Chapter 15 — METEOROLOGICAL ELEMENTS 



Figure 15-4. — Nimbostratus. 



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bases become lower until they become a layer 

 of nimbostratus. 



LOW CLOUDS. — Low clouds are described 

 as follows: 



1. Stratocumulus (SC). Stratocumulus (fig. 

 15-3(B)) are a layer (or patches) of clouds 

 composed of globular masses or rolls. The 

 smallest of the regularly arranged elements are 

 fairly large. They are soft and gray, with darker 

 spots. 



2. Stratus (ST). Stratus (fig. 15-5) are a 

 low, uniform layer of clouds, resembling fog, 

 but not resting on the ground. When a layer 

 of stratus is broken up into irregular shreds, 

 it is designated as stratus fracto. 



Figure 15-5. — Stratus. 



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A veil of stratus gives the sky a character- 

 istically hazy appearance . Usually , drizzle is 

 the only precipitation associated with stratus. 

 When there is no precipitation, the stratus cloud 

 form appears drier than other similar forms, 

 and it shows some contrasts and some lighter 

 transparent parts. 



3. Cumulus (CU). Cumulus (fig. 15-6 (A)) are 

 dense clouds with vertical development. Their 

 upper surfaces are dome shaped and exhibit 

 rounded protuberances, while their bases are 

 nearly horizontal. Cumulus fractus or fracto- 

 cumulus resemble ragged cumulus in which the 

 different parts show constant change. 



4. Cumulonimbus (CB). Cumulonimbus (fig. 

 15-6(B)) are heavy masses of cumulus-type 

 clouds, with great vertical development, whose 

 cumuliform summits resemble mountains or 

 towers. Tops may extend higher than 60,000 

 feet. Their upper parts are composed of ice 

 crystals and have a fibrous texture; often they 

 spread out in the shape of an anvil. Cumulonim- 

 bus are the familiar thunderclouds, and their 

 precipitation is of a violent, intermittent, showery 

 character. Hail often falls from well-developed 

 cumulonimbus. These clouds also display on 

 occasion several readily apparent supplementary 

 features, such as (1) mamma or hanging pro- 

 tuberances, like pouches, on the under surface 

 of the cloud; (2) tuba (commonly called the 

 funnel cloud) resembling a cloud column or in- 

 verted cloud cone, pendant from the cloud base; 

 and (3) virga, wisps or streaks of water or ice 



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