Atmospheric circulation pattern, III, The polar zone
Air rises to tropopause in Ferrell cell; flows N or S
Air moving along tropopause toward the poles cools, & eventually becomes dense enough that it sinks over poles
This creates a region of dry, cold air centered over each pole called the polar high
Between 60° & 90°N or S, air at surface moves from polar highs to sub-polar lows
Coriolis effect leads to the polar easterlies
This large-scale pattern of circulating air is the Polar cell