The Atmosphere-Ocean System: Motion and Energy in the Atmosphere

Global Wind Belts

Remember from the warm-up activity of this section that waves are larger on the west coast of the U.S. than on the east coast. You saw how this is related to wind on the two coasts. What did you decide might be the connection between wind and wave size? You should have noticed that on the west coast, the wind is behind the waves, driving them and giving them more energy. But on the east coast, the wind is blowing against the waves, beating them down and diminishing their energy. This pattern of wind flow derives from the prevailing wind patterns on the globe.

Image of the earth with various global wind patterns. At the poles, arrows indicate movement towards the center of the earth as well as east and west. These winds are called Polar Easterlies. On both the northern and southern sides of the earth, the next wind pattern is shown with arrows pointing east. These winds are called Westerlies. On both the northern and southern sides of the equator, the next wind pattern is shown with arrows pointing west. These winds are called Northeasterly Trades to the north of the equator and Southeasterly Trades to the south of the equator.

Temperature and pressure differences and the Coriolis effect create recognizable global wind patterns that are often predictable. You have learned that these winds are called the prevailing winds. They are found in specific belts around the globe, based on latitude. The map shows the locations of the prevailing winds, which are called the trade winds, Polar Easterlies and Westerlies. You can see that wind is deflected southwestward in the Northern Hemisphere and northwestward in the Southern Hemisphere. On the sides of the globe you also see convection cells, indicating how air flows in convection currents from warm areas to cool areas and back again. Click through the tabs below to learn more about the global wind belts.

Trade Winds

a Spanish exploring ship


Trade wind is the movement of air from subtropical areas just north and south of the equator toward the equator. Note that they are named for the direction FROM which they blow. They move in response to pressure differences. Warm moist air sits above the equator because it has greater solar heating. The warm equatorial air has lower air pressure than the subtropical air, and air will always move from higher pressure to lower pressure areas. The warm air at the equator rises and would flow directly toward the poles except that the Coriolis effect deflects it in the subtropical areas.

The name, trade winds, comes from the fact that these winds are important for ocean navigation. They allowed early exploration around the world as well as the development of trade routes between the Eastern and Western Hemispheres. They were significant in the Age of Discovery and global exploration during the 14th and 15th centuries.

Westerlies

Aerial view of a cyclone

The Westerlies are winds that blow from high pressure areas at about 30° latitude north and south to low pressure areas at about 60° north and south. The name comes from the fact that they blow from the west. This belt that makes up the subtropical areas just north and south of the equator is characterized by dry descending air. Many places on Earth in this area are desert ecosystems. The Westerlies form many of the strongest winds on Earth and are responsible for hurricanes that develop over the oceans and sometimes make their way to land.

Polar Easterlies

Map highlighting the polar regions of the Earth

The Polar Easterlies are made of dry, cold air that moves from the poles toward the area of the Westerlies. At the poles, the cold air sinks and is pushed toward the equator. It would flow directly to the equator in a straight path, except that the Coriolis effect deflects the air once it enters the area of the Westerlies.