The Weather 33 



SUMMARY 



Winds about a low-pressure area moving spirally inward in a 

 counter-clockwise direction, in the northern hemisphere, constitute 

 a cyclone. 



Winds about a high-pressure area moving spirally outward in a 

 clockwise direction, in the northern hemisphere, constitute an anti- 

 cyclone. 



Winds forced from the high-pressure areas directly toward the low- 

 pressure areas are modified in direction by the rotation of the earth 

 and local causes, like mountains. 



The velocity of the wind depends mainly on the pressure gradient, 

 is determined by the anemometer, and is designated in miles per 

 hour, or by such terms as " breeze " and " gale." 



The low-pressure areas follow typical paths across the continent, 

 with an average velocity of about 30 miles an hour. They are likely 

 to be storm centers, the greatest rainfall generally occurring to the 

 south and east of the center. 



The three chief forms of clouds are cirrus, cumulus, and stratus. 

 Clouds from which rain is falling are nimbus clouds. 



Anticyclones, or high-pressure areas, which usually follow the 

 paths of cyclones but travel more slowly, are generally associated with 

 clear weather. In winter they may bring cold waves and blizzards. 



Typhoons of the China Sea, cyclones of the Bay of Bengal, and 

 hurricanes of the West Indies are rotary storms of large dimensions 

 and destructive violence. Hurricanes sometimes enter the United 

 States from the Gulf of Mexico. 



REVIEW QUESTIONS 



1. How is the direction of the wind indicated? 2. (a) What is 

 the direction of the wind between a high and a low? (6) What is 

 its direction about a low? (c) About a high? 3. What does the 

 word " cyclone " mean as used by the Weather Bureau? 4. What 

 does the word " anticyclone " mean? 5. What is the rule for deter- 

 mining the direction of the wind when the position of a high and 

 low are known? 6. Which way are winds deflected in the northern 

 hemisphere? Why? 7. Mention and describe certain local condi- 

 tions that affect the direction of the wind. 8. What are some of the 

 terms used to indicate different wind velocity? 9. With regard to 

 difference in velocity how many winds are named on the Beaufort 

 scale? 10. (a) What is the use of an anemometer? (6) How is it 

 constructed? 11. (a) Is the velocity of winds generally recorded on 



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