Atmospheric Pressure and Winds

1. Atmospheric Pressure and Winds

2. 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

3. 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

4. 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

5. The Coriolis Effect Coriolis Cannonball

6. 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

7. Global Winds • Trade Winds • Westerlies • Polar Easterlies • Each hemisphere has three main wind belts or prevailing winds (areas of similar wind patterns)

8. Air moves from high to low pressure Doldrums and Horse Latitudes • Areas of weak and slow moving air

9. Jet Stream • Narrow bands of high speed winds that blow in the upper troposphere and lower stratosphere are jet streas.

10. 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.

11. Local Winds