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Atmospheric Pressure and Winds. Pgs. 14 - 19. Why Air Moves?. Wind – moving air Wind is created by differences in air pressure. Bigger differences in air pressure results in faster moving winds. Differences in air pressure are caused by unequal heating of the Earth.
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Atmospheric Pressure and Winds Pgs. 14 - 19
Why Air Moves? • Wind – moving air • Wind is created by differences in air pressure. • Bigger differences in air pressure results in faster moving winds. • Differences in air pressure are caused by unequal heating of the Earth. • The equator is filled with warm air that is less dense and lower pressure, while the poles are filled with cool air that is more dense and higher pressure. • Winds generally move from the poles to the equator.
Pressure Belts • Wind movement is more complicated than just moving from the poles toward the equator. • As warm air rises over the equator, it begins to cool. • At 30 degrees north and south latitude, the air is cool and begins to sink. • The sinking air produces high pressure at 30 degrees north and south latitude. • At the poles cool air moves toward the equator and is heated. • By 60 degrees north and south latitude, warm air is rising in an area of low pressure. • This high and low pressure pattern continues.
Coriolis Effect • To make things more complicated, you may have noticed that winds don’t typically blow directly north or south. • The rotation of the Earth affects the winds direction. • The curving of moving objects by the Earth’s rotation is the Coriolis effect. • Think of trying to roll a ball across a spinning merry-go-round. • You may intend for it to go straight, but is curves due to the spinning.
Types of Wind • There are two main types of wind: local and global. • They are both caused by the uneven heating of the Earth’s surface. • Local winds will move short distances and in any direction. • Global winds are part of a pattern of air circulation that moves across the Earth. • They travel farther and in a specific direction.
Trade Winds • Winds that blow from 30 degrees north or south to the equator are called trade winds. • The rotation of the Earth causes trade winds to curve to the west from the east. • They are either the northeast trade winds or southeast trade winds. • They are known as the trade winds because early traders would sail from Europe to the Americas to trade goods.
Doldrums and Horse Latitudes • The trade winds meet at the equator in an area of low pressure called the doldrums. • There is very little wind because the heated air rises. • Doldrums comes from an old English word meaning foolish because it was foolish to sail where there was no wind. • At 30 degrees north or south latitude is an area of high pressure called the horse latitudes. • They are called horse latitudes because ships would carry horses to the Americas but there was little wind. • To save supplies, they would throw horses overboard in order to survive.
Westerlies • Wind belts found between 30 and 60 degrees north or south latitudes are called westerlies. • These winds flow toward the poles. • They flow from the west to the east due to the rotation of the Earth. • Early explorers and sailors would use the westerlies to sail to Europe.
Polar Easterlies • Wind belts that extend from the poles to 60 degrees north or south latitude are called polar easterlies. • Cold sinking air from the poles moves toward the equator and warms. • The wind curves to the west from the east due to the rotation of the Earth.
Jet Streams • Jet streams are narrow belts of high-speed winds that blow in the upper troposphere and lower stratosphere. • These winds often change direction and can reach speeds of 500km/hr. • Knowing the position of the jet stream is useful. • Pilots can save time and fuel by flying with the jet stream. • Meteorologists use the jet stream to predict the movement of storms.
Local Winds • Local winds are influence by an area’s geography. • Land and sea breezes occur near the shoreline. • During the day, the land heats up quicker than the water and warm air on land rises. • Cool air from over the ocean moves toward land. • At night, the water retains its heat and so its warm air rises up. • The land cools off and the air cools and moves from land to the water.
Mountain and Valley Breezes • During the day, the sun heats the air on the valley floor and it rises up the sides of the mountain. • This is a valley breeze. • At night, the mountain cools faster than the valley and a the cool air sinks down the sides of the mountain to the valley. • This is a mountain breeze.
