WIND

What causes wind? All winds are caused by differences in air pressure. Wind is the horizontal movement of air from an area of high pressure to an area of low pressure. Differences in air pressure is caused by unequal heating of the atmosphere.

Measuring Wind South winds blow from the south toward the north. North winds blow from the north toward the south. An anemometer measures wind speed. An example of wind chill factor is if it is 20 F and the wind speed is 30 mph the wind chill factor makes it feel like -18 F.

Local Winds They blow over a short distance. They are caused by unequal heating of Earth’s surface within a small area. They form only when no winds are blowing from far away.

Sea Breezes Occur during the day. The land will heat up faster during the day than the water. The cool air blows inland from the water pushing up the warm air. The wind that blows from the water is known as sea breezes.

Land Breezes Occur during the night. The land cools off more quickly than the water. Therefore the cool air moves over the water causing the warmer air to rise.

Global Winds They are long distance winds that blow steadily from specific directions. The movement of air between the equator and the poles produces global winds. The Coriolis effect is wind curvature due to Earth’s rotation. If the Earth didn’t rotate, the wind would blow in a straight line from the poles toward the equator.

Global Wind Belts Major wind belts are trade winds, prevailing westerlies, and polar easterlies.

Doldrums Very little horizontal movement. Region near equator with little or no wind.

Doldrum

Horse Latitude 30 degrees N latitude 30 degrees S latitude

Horse Latitude Doldrum

Trade Winds Winds in the Northern hemisphere between 30 degrees N latitude and the equator blow generally from the northeast. Winds in the southern hemisphere between 30 degrees S latitude and the equator blow generally from the southeast. Hundreds of years ago, sailors relied on the trade winds to carry cargo from Europe to the West Indies and South America.

Trade Winds Horse Latitude Doldrum Trade Winds

Prevailing Westerlies They blow generally from the Southwest between 30 degrees N and 60 degrees N latitude. They blow from the northwest between 30 degrees S and 60 degrees S latitude. They play an important role in the weather of the United States.

Doldrum Prevailing Westerlies Trade Winds Horse Latitude Trade Winds

Polar Easterlies The coriolis effect shifts polar winds to the west. They meet the prevailing westerlies at about 60 degrees N and 60 degrees S latitude.

Doldrum Polar Easterlies Prevailing Westerlies Trade Winds Horse Latitude Doldrum Trade Winds Prevailing Westerlies Polar Easterlies

Jet Streams 10 km above the earth’s surface are bands of high-speed winds. They blow from the west to the east at speeds of 200-400km/h. Airplanes are aided by the jet stream when traveling east. Airplanes flying at jet stream altitudes are slowed down when traveling west against the jet stream winds.