with the result that there is a piling up of cold, heavy air. When 

 a sufficient amount of air has accumulated at the North Pole so 

 that a balance no longer exists, a gradual flow of air out of this 

 cold air dome takes place. While the direction of this outflowing 

 air is at first from the north, it soon assumes an easterly com- 

 ponent, due to the rotation of the earth. Velocities associated 

 with the central core of this arctic air mass would be small. It is 

 believed that the vertical extent of high pressure is not great in 

 the polar anticyclone and that above the first few kilometers the 

 pressure field is probably reversed, with low pressure present. If 

 the above assertion is true, the motion of the air in the Polar 

 Anticyclone above the first few kilometers must be anticlockwise 

 or westerly about the North Pole, with a slight component in the 

 direction of the Pole to compensate for the loss of air at the lowest 

 levels. 



While there is a more or less steady flow of air out of this cold 

 air dome, the process is greatly accelerated at times by the passage 

 along its periphery of areas of low pressure which upset the bal- 

 ance and induce large masses of the cold air to break away from 

 the parent mass and move out of the polar region along certain 

 well-defined continual paths. 



Those periodic mass outbreaks of cold air are not limited to the 

 lowest levels, but embrace the entire troposphere, disrupting 

 the shallow easterly circulation of the lower levels and also the 

 westerly circulation above 6,000 feet. At times low pressure 



Figure 3-2. — Blizzard. 



