Global and Local Winds

What is Wind? The movement of air caused by differences in air pressure. These differences in air pressure are generally caused by the unequal heating of the Earth. The greater the pressure difference the faster the wind.

Uneven Heating of the Earth

Pressure Belts Uneven heating causes pressure belts which occur every 30⁰ latitude. As warm air rises at the equator and moves toward the poles, it cools. As it cools, some of the air sinks around 30⁰ north and south of the equator.

Pressure Belts

At the poles, cold air sinks and moves towards the equator. Around 60⁰ north and south, the air begins to heat up and rise.

The Coriolis Effect The apparent curving of the path of winds and ocean currents due to the Earth’s rotation. In the Northern Hemisphere, winds traveling north curve to the east and winds traveling south curve to the west.

Global Winds The combination of pressure belts and the Coriolis Effect cause global winds. Three types of global winds: polar easterlies, westerlies, and trade winds.

Global Winds

Polar Easterlies Prevailing winds that blow from east to west between 60⁰ and 90⁰ latitude in both hemispheres.

Westerlies Prevailing winds that blow from west to east between 30⁰ and 60⁰ latitude in both hemispheres.

Trade winds Prevailing winds that blow northeast from 30⁰ north latitude to the equator and that blow southeast from 30⁰ south latitude to the equator.

The Doldrums Located along the equator where no wind blows because the warm rising air creates an area of low pressure.

The Horse Latitudes Occur at about 30⁰ north and south of the equator where the winds are very weak. Most deserts on the Earth are located here because of the dry air.

Jet Streams The jet streams are narrow belts of high speed winds that blow in the upper troposphere and lower stratosphere. Separates warm air from cold air.

Jet Streams

Local Winds Generally move short distances and can blow from any direction. Caused by geographic features that produce temperature differences.

Sea Breeze

Land Breeze

Mountain and Valley Breezes