What causes wind?

• The wind is moving air caused by differences in air pressure.

• Air moves from areas of high pressure to areas of low pressure.

• The greater the pressure difference, the

faster the air moves, and the stronger the wind blows.

What Are the Major Global Wind Systems?

Global winds are large-scale wind systems. There are three pairs of major global wind systems, or wind belts: trade winds, westerlies, and polar easterlies.

These Are the Major Global Wind Systems

Trade winds are wind belts that blow from 30° latitude almost to the equator. They curve to the west as they blow toward the equator.

Westerlies are wind belts that are found between 30° and 60° latitude. The westerlies blow toward the poles from west to east. Most of the United States is located in the belt of westerly winds. These winds can carry moist air over the United States, producing rain and snow.

Polar easterlies are wind belts that extend from the poles to 60° latitude. They form as cold, sinking air moves away from the poles. In the Northern Hemisphere, polar easterlies can carry cold arctic air over the United States. This can produce snow and freezing weather.

Why Do Global Winds Curve?

• If Earth did not rotate, these winds would blow in straight lines. However, because the Earth does rotate, the winds follow curved paths.

• The Earth’s rotation is called the Coriolis effect

• As Earth rotates, places near the equator travel faster than places closer to the poles.

• This difference in speed causes the Coriolis effect.

• Wind moving from the poles to the equator is deflected to the west.

• Wind moving from the equator to the poles is deflected east.

What Are Local Winds?

The United State is mostly under the westerlies wind which means it blows from west to east.

• Local winds are also important:
  winds that generally move over short distances and can blow from any direction.

• local winds are caused by differences in temperature.

• Many of these temperature differences are caused by geographic features, such as mountains and bodies of water.

MOUNTAIN BREEZES AND VALLEY BREEZES

• Mountain and valley breezes are other examples of local winds caused by geography.

• During the day, the sun warms the air on mountain slopes. The warm air rises up the mountain slopes, producing a warm valley breeze.

• At night, the air on the slopes cools. The cool air moves down the slopes, producing a cool mountain breeze.