Cool air flowing over the Earth's poles sinks and spreads over the surface of the planet. When air flows away from the poles, it goes to the west due to the Coriolis effect. When this air, known as the polar easterlies, meets prevailing winds at lower latitudes, the air's upward motion is reduced. This polar cooling and spreading occurs at 60 degrees of latitude on both poles.
Polar easterlies are normally weak winds that form high pressure systems and flow toward the equator. These winds go toward low pressure areas of the prevailing westerlies at latitudes between 30 and 60 degrees. Polar easterlies are so named because they originate in the east and blow towards the west due to the Coriolis effect caused by the Earth's rotation.
Prevailing winds out of the west are responsible for much of North America's weather patterns. Westerlies are strongest in the winter when pressure over the poles is lower. Prevailing westerlies are weakest in the summer because winds create stronger polar easterlies.
When cooler air from the poles reaches the equator, the air is heated and turns into low pressure areas. Warm winds then rise and go towards the poles while cool air heads towards the equator.