Wind is caused by changing air pressure. The earth is divided into imaginary lines of latitude and longitude. Latitude lines go east and west around the earth parallel to the equator. The longitude lines go north and south from the north and south poles. The tilt of the earth means the sun is always most directly over the region 23 degrees north and south of the equator. This warms the air there (check out this cool site for a simulator showing this).
Since warm air is lighter than cool air, it rises up into atmosphere. As the warm air goes upward, the cool air over the north and south poles moves toward the equator and fills in the space. This movement causes wind.
Peter Mercator Wikipedia Commons
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The wind doesn't just blow in a straight line from the poles to the equator, however. There is something else affecting it, the Coriolis effect. As the earth rotates, the movement also affects the wind. The winds nearest the equator are called the trade winds. The Coriolis effect causes the trade winds to blow toward the west.
In the area near the equator, the winds from the north and the winds from the south meet at the equator where they are warmed enough they travel upward. There are often no steady winds at the surface of the earth here. This is called the doldrums and sailors are often stuck in this area, unable to move because there is no wind.
WESTERLIES AND EASTERLIES
The area between about 30º and 60º latitude is known as prevailing westerlies because the wind comes from the west (winds are named for the direction they come from). In the area above 60º the cool air over the poles flows south and because of the Coriolis effect. It curves toward the west from the east so they are known as polar easterlies.
Make your own wind pattern map
- Label the equator, the tropic of Cancer, the tropic of Capricorn, the Arctic Circle and the Antarctic Circle.
- Use a red crayon to draw arrows showing the trade winds.
- Use a green crayon to draw arrows showing the westerlies.
- Use a blue crayon to draw arrows showing the polar easterlies.
- Label the doldrums and color the area yellow.
- Create a key for your map.
Dunbar, Brian. "What Is the Coriolis Effect?" NASA. NASA, 10 Apr. 2008. Web. 26 Apr. 2015.
Mercator, Peter. December Solstice Geometry. Digital image. Wikimedia Commons. Wikimedia Foundation, 14 Dec. 2011. Web. 2 May 2015.
O'Connor, J J, and E. F. Robertson. "Gaspard Gustave De Coriolis." The MacTutor History of Mathematics Archive. School of Mathematics and Statistics University of St Andrews, Scotland, July 2000. Web. 26 Apr. 2015.
Pearson Scott Foresman. Compass3. Digital image. Wikimedia Commons. Wikimedia Foundation, 15 Dec. 2007. Web. 26 Apr. 2015.
"Seasons and Ecliptic Simulator." University of Nebraska-Lincoln. Nebraska Astronomy Applet Project/National Science Foundation, 19 Mar. 2009. Web. 8 Jan.
"What Is the Coriolis Effect?" ESchool Today. ESchool Today, 2010. Web. 26 Apr. 2015. <http://www.eschooltoday.com/winds/the-coriolis-effect.html>.
Wicker, Crystal. "Weather Wiz Kids Weather Information for Kids." Weather Wiz Kids Weather Information for Kids. N.p., n.d. Web. 02 May 2015.