1. Global Wind Patterns

2. Caused by uneven heating
The circulations of the atmosphere (winds) and oceans (currents) are driven by sunlight hitting the earth’s surface more directly near the equator a LOT of this sunlight energy hits the tropics, between North and South of the equator.

3. InterTropical Convergence Zone ITCZ
the “doldrums”

4. If Earth did not rotate, wind patterns would be simply N to South along the surface
Thermal convection leads to formation of convection cell in each hemisphere
Heat Energy is transported from the tropics toward poles in upper atmosphere
Cold air sinks and shuttles back toward equator along surface

5. Coriolis effect
But the earth rotates, so there is a tendency for objects moving over long distance (like air masses) to curve due to “coriolis effect”
Curve to right in N. Hemisphere
Curve to left in S. Hemisphere
This leads to winds generally blowing in east/west directions and having spin to them

6. CORIOLIS EFFECT
THE ROTATION OF THE EARTH CAUSES THE AIR TO MOVE AT ANGLES FROM THE EQUATOR TO THE POLES AND BACK.

7. See coriolis effect as high pressure wind blows into a low pressure air mass
Wind blowing in curve to the right in N. hemisphere
Thus, low pressure system has air spinning counterclockwise
This pattern creates tornadoes and hurricanes as well

8. Heat Exchange in air masses
Warm, humid air rises, dry clear air sinks Creates 3 huge convection/circulation cells in each hemisphere

9. Prevailing winds are created by coriolis effect curving their paths
Add these prevailing winds to your globe from north to south:
Polar Northeasterlies
Westerlies
Northeasterly Tradewinds
Doldrums
Southeasterly Tradewinds
Polar Southeasterlies

10. Wind Wind blows from high pressure air masses to low pressure
Winds named westerly wind IF blowing from the West
Wind spead increases as pressure gradient increases (steeper isobars)

11. Low pressure areas
Warm, humid air rises, expands and condenses = causing a low pres air mass at surface and condensation above (lots of rain or snow)
Equator and polar front, 00 and 600 N and S.

12. High Pressure Areas
Dense, dry air (can by cold dense or hot arid) sinks due to gravity = creating high pressure at surface and outward blowing wind, very little precipiation
30° N and S; 90° N and S at poles

13. dry
wet
dry
wet
dry
wet
dry

14. Notice location of major deserts near 30 Latitude

15. Ferrel
cell
Hadley Cells

16. Key features of three cell model
Hadley cell takes heated air away from the tropics
- TROPICS: low pressure air rises near equator - MUCH RAIN
-DESERT ZONE: condensed, high pressure air descends near 30 degrees - clear skies!
Ferrel Cell - driven by heat transports of eddies
- Polar air rises near 60 degrees and descends near 30 degrees
- explains surface westerlies from 30-60
Weak (WUSSIE-BABIES) winds found near
Equator (doldrums)
30 degrees (horse latitudes)
Boundary between cold polar air and mid-latitude warmer air is the polar front

17. Understanding the General Circulation
1. Unequal solar heating between the equator and poles. Atmospheric general circulation moves heat toward the north and south poles..
2. In a Hadley cell, warmer air rises and moves poleward. Equator-to-pole Hadley cell is impossible. The Earth rotates!
3. In the Northern Hemisphere, air is pushed to the right as it moves; in the Southern Hemisphere, air is deflected toward the left. The Coriolis effect.
- rotation produces trade winds; surface westerlies in NH; upper tropospheric jet streams.
4. Ferrel cell runs backwards! Transports heat the wrong way, towards the equator!
5. The Ferrel cell is weak, so does not move as much energy as the other cells.

18. Global Wind and Pressure Patterns
Deserts: belts of persistent high atmospheric pressure centered at about lat. 30º N and S
Polar Front: front lying between cold polar air masses and warm tropical air masses
Intertropical Convergence Zone (ITCZ): Where convergence of air masses along the equatorial trough
Hadley Cell: low-latitude atmospheric circulation cell with rising air over the equatorial trough and sinking air over the subtropical high-pressure belts

19. Thermal Wind Balance Produces Jet Streams
Hot tropics and cold poles produce westerly high altitude jet streams at middle latitudes like ours.