88o 



Handbook of Nature-Study 



In a cyclone or "low," and also in a tornado, the air blows from all sides 

 spirally inward toward the center where there is a column of ascending air. 



In an anti-cyclone or "high" the air blows outward in every direction 

 in curved lines from a column of descending air. 



X 



Map of a storm. 



In the above map, the curved lines are isobars; the line of crosses from 

 A to B indicates the course of the storm ; the arrows indicate the direction 

 of the wind, note that it is moving counter-clockwise around the area of 

 low pressure; the shaded area indicates the region where it is raining or 

 snowing; note that this is the area where the warm, moist air from the 

 Gulf and the Ocean meets the colder air of the North. 



The weather conditions during the passage of a cyclone are briefly as 

 follows: Small, changing wisps of cirrus clouds appear about 24 hours 

 before rain ; these gradually become larger and cover the whole sky, making 

 a nimbus cloud. The wind changes from northeast to east or southeast to 

 south. The barometer falls ; the thermometer rises, that is, air pressure is 

 less to the square inch, and the temperature of the atmosphere is warmer. 

 Rain begins and falls for a time, varying from an hour to a day or more. 

 After the rain there appear breaks in the great nimbus clouds and finally the 

 blue sky conquers until there are only a few or no clouds. The wind 

 changes to southwest and west; the barometer rises, the temperature falls. 

 The rain ceases, the sun shines out brightly. The low has passed and the 

 high is approaching to last about three days. 



