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Atmospheric Pressure and Winds. Low Pressure. Large parcels or pockets of uncompressed air Warmer air Air is “spread out” so fewer air particles push on any given area with less pressure Low density = air molecules spread out
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Low Pressure • Large parcels or pockets of uncompressed air • Warmer air • Air is “spread out” so fewer air particles push on any given area with less pressure • Low density = air molecules spread out • Rising air that circulates in a counterclockwise direction in the Northern Hemisphere • Called Cyclones
High Pressure • Large parcels or pockets of compressed air • Colder air • More air particles pressing on a given surface area • High density = air molecules packed together • Falling air that circulates in a clockwise direction in the Northern Hemisphere • Called Anticyclones H
Wind • What causes the wind? • Differences in air pressure: High Low • Two main wind patterns • Global • local • Does the wind move straight up and down? • Coriolis Effect High Pressure Convection Low Pressure Convection High Pressure
The Coriolis Effect Coriolis Cannonball
Air moves from high to low pressure Coriolis Effect • Circulation of air is affected by the earth’s rotation • Coriolis Effect – deflection of a fluid because of Earth’s rotation • Deflects air in the Northern Hemisphere to the right • Deflects air in the Southern Hemisphere to the left
Global Winds • Trade Winds • Westerlies • Polar Easterlies • Each hemisphere has three main wind belts or prevailing winds (areas of similar wind patterns)
Air moves from high to low pressure Doldrums and Horse Latitudes • Areas of weak and slow moving air
Jet Stream • Narrow bands of high speed winds that blow in the upper troposphere and lower stratosphere are jet streas.
Breezes • Land Breeze • When wind moves from high pressure (over land) to low pressure (over water). • Usually occurs at night. • Sea/Lake Breeze • When wind moves from high pressure (over water) to low pressure (over land). • Usually occurs during the day.