1. Winds Chapter 2, Section 3, p.46-52

2. What Is Wind? Air is a fluid so it can move easily – Winds are caused by differences in air pressure Wind: horizontal movement of air from areas of high pressure to areas of lower pressure Unequal heating of atmosphere causes differences in air pressure – Convection currents form when surface is heated by sun Air over heated surface expands – becomes less dense Less dense air has less pressure Cooler areas nearby have more dense air Cooler, denser air flows under warmer, less dense air Warm air forced to rise

3. Measuring Wind Winds are described by their direction and speed – Wind vanes determine wind direction Spins and one end points into the wind – Winds are named by where they come from North wind – blowing from north to south Southeast wind – blowing from southeast to northwest – Anemometer: an instrument with 3-4 cups mounted on the ends of spokes that spin on an axle and can measure wind speed As wind speed increases; the anemometer will spin __?__ As wind speed decreases; the anemometer will spin __?___

4. Wind-Chill Factor Wind-chill factor: the increased cooling a wind can cause – Wind blowing over your skin removes body heat The stronger the wind blows; the cooler/hotter you feel Weather report: – “The temperature outside is 20°F, but the 30 mph wind makes the wind-chill factor seem like 1°F

5. Local Winds Local winds are caused by the unequal heating of Earth’s surface within a small area – Local winds: winds that blow over short distances – Local winds only form when large scale winds are weak

6. Sea Breeze Unequal heating along the shore of a body of water – Sun heats Earth’s surface during day Land warms up faster than water – More energy needed to heat up body of water than body of land Air over land becomes warmer than air over water Warm air expands & rises creating low pressure Cooler, more dense air over water blows in under rising air – Sea breeze: a local wind that blows from an ocean or lake

7. Land Breeze Unequal cooling along the shore of a body of water – Land cools more quickly than water at night Warmer air over the water expands and rises Cooler, more dense air over land blows in under rising air – Land breeze: the flow of air from land to a body of water

8. Global Winds Global winds: winds that blow steadily from specific directions over long distances – Global winds are caused by the unequal heating of Earth’s surface similar to local winds – Global winds occur over a large area Sun’s radiation hitting Earth – Most direct over equator » Direct rays heat Earth’s surface intensely » Temperatures are higher near equator – Low angle at the poles » Sun’s energy spread out over larger area heating surface less » Temperatures are lower near poles

9. Global Convection Currents Temperature differences between the equator and poles produce giant convection currents in the atmosphere – Global winds produced by this air movement pattern Difference in air pressure causes winds on Earth’s surface to blow from poles to equator – Warm air rises at equator » Lower air pressure – Cool air sinks at poles » Higher air pressure Higher in atmosphere air flows away from equator

10. The Coriolis Effect Coriolis effect: the way Earth’s rotation makes winds curve – Global winds would move in a straight line from poles to equator ff Earth didn’t rotate Earth rotates from west to east Making it seem like winds have curved – Northern hemisphere – wind blowing south turns toward southwest » Facing equator – turns right – Southern hemisphere – wind blowing north turns toward northwest » Facing equator – turns right

11. Global Wind Belts Pattern of calm areas and wind belts around Earth – Caused by Coriolis effect and other factors – Calm areas: Doldrums Horse latitudes – The major wind belts are: Trade winds Prevailing westerlies Polar easterlies

12. Global Winds Active Art Activity – (cfp-4023)

13. Doldrums Sun heats surface strongly at equator – Warm air rises creating area of low pressure – Cool air moves into area but is heated before it can move far Little horizontal movement of air Weak winds near equator Doldrums – regions with little to no win dnear the equator

14. Horse Latitudes Horse latitudes – 30°N & 30°S latitudes – Latitude: distance from the equator, measured in degrees – Warm air rises at equator flows north & south – 30°N & S, air stops moving toward poles & falls Area of calm air located here Hundreds of years ago sailors became stuck in area – Ran out of food and water for horses – Threw them over board – “Horse latitudes”

15. Trade Winds Winds blowing from 30°N & 30°S to equator – Cold air over horse latitudes sinks producing area of high pressure – Causes surface winds to blow away from 30°N & S – toward equator & away from it Winds blowing toward equator turned west by Coriolis effect Northern hemisphere – trade winds blow southwest Southern hemisphere – trade winds blow northwest – Hundreds of years – sailors used these winds to carry cargo from Europe to West Indies and South America – Steady winds called trade winds

16. Prevailing Westerlies Winds between 30° and 60° N & S – Winds blow toward poles Coriolis effect turns them east Westerlies because they blow from westerly direction – Northern hemisphere – blow from southwest – Southern hemisphere – blow from northwest Prevailing westerlies play important part in weather of U.S.

17. Polar Easterlies Winds blowing from poles to 60°N or 60°S – Cold air sinks at poles and flows toward lower latitudes – Coriolis effect shifts winds to the west = “polar easterlies” – Polar front Polar easterlies meet prevailing westerlies Warm & cold air mix Major effect on U.S. weather

18. Jet Streams Jet streams: bands of high speed winds 10 km above Earth’s surface – Hundreds of km wide – Blow west to east 200 – 400 km / hr – Wander north and south along wavy path Polar Jet Stream Subtropical Jet Stream

19. Homework Read Chapter 2, Section 3, p46-52 Answer ?s 1-3 p52