Air Pressure and Wind

1. Air Pressure and Wind Chapter 19

2. What is Air Pressure? • Air pressure weight of air above • Exerted in all directions (up, down, and sideways)

3. Measuring Air Pressure • Unit: called the millibar • Barometer: device used for measuring air pressure

4. Types of barometers • Mercury • When air pressure increases, the mercury in the tube rises • When air pressure decreases, the mercury in the tube goes down • Aneroid • recording mechanism providing a continuous record of pressure change over time

5. Wind • The result of horizontal differences in air pressure • Air flows from areas of high to low. • The unequal heating of Earth’s surface generates pressure differences. • Solar energy is the ultimate energy source for most wind.

6. Three Factors that Combine to Control Wind • Pressure Differences • Coriolis Effect • Friction

7. Pressure Differences • Wind is created from differences in pressure. • The greater the difference the greater the wind speed. • Shown using isobars: • Lines on a map that connect places of equal air pressure • Closely spaced isobars indicate high winds.

8. Isobars • Closely spaced isobars: indicatea steep pressure gradient and high winds. • Widely spaced isobars: indicate a weak pressure gradient and light winds.

9. Coriolis Effect • The Coriolis effect describes how Earth’s rotation affects moving objects. • Northern Hemisphere • Deflected to right • Southern Hemisphere • Deflected to the left • Strongest at the poles, weakest at the equator Coriolis video

10. Friction • Important only within a few km of Earth’s surface • Slows air movement, which changes wind direction

11. Jet Streams • Jet streams: fast-moving rivers of air • Travel between 120 and 240 kilometers per hour

12. High and Low Pressure System

13. Global Winds • Underlying cause of wind is the unequal heating of Earth’s surface • Atmosphere balances these differences by acting as a giant heat-transferring system • Warm air towards the poles • Cool air toward equator

14. Global Winds • Trade winds • Blow constantly from east • Westerlies • Middle latitudes • Blow from the west • Polar Easterlies • Not constant • Blow east to west • Polar Front: • Interaction of war and cool air masses produces a stormy belt

15. Four Pressure Zones • Highs: Subtropical and Polar • Dry subsiding air • Prevailing winds • Lows: Equatorial and Subpolar • Inward and upward air • Clouds and precipitation

16. Influence of Continents • Only true continuous pressure belt is the subpolar low. • Uninterrupted by landmasses • Can produce seasonal temperature differences • Monsoons • Seasonal changes in wind direction • Summers: rainy • Winters: dry

17. Local Winds • Caused by topographic effects or variations in surface composition • Types of Local Winds • Land Breezes • Sea Breezes • Valley Breezes • Mountain Breezes

18. Sea and Land Breezes • Sea Breezes • Day • Land heated more intensely • So air above the land: heats, expands, and rises • Cool air over water moves toward land. • Land Breezes • Night • Land cools more quickly. • Cooler Air over land moves to the sea

19. Valley and Mountain Breezes • Valley • Day • Land is heated more intensely • Air moves up along the slop • Mountain • Night • Rapidly cooling air along the slopes • Moves downward

20. Measuring Wind • Direction • Always labeled by the direction from which they blow • Prevailing Wind: wind consistently blows from one direction.

21. Wind Speed • Anemometer • Measures how fast wind is blowing

22. El Nino El Niño • Episodes of ocean warming that affect the eastern tropical Pacific. • Warm countercurrents replace normally cold offshore waters.