1. Global Circulation and Winds (Stewart Cap. 4)

2. Outline Atmospheric pressure Winds Global circulation patterns
Ocean circulation patterns

3. 1. Atmospheric Pressure

4. Atmospheric Pressure Density of the atmosphere decreases with altitude
Earth

5. Atmospheric Pressure:
Force exerted by the atmospheric per unit area

6. Measuring Atmospheric Pressure
At sea level:
101,320 Pascals (101 kPa)
millibars
76 cm Hg (30 in Hg)

7. Atmospheric Pressure

8. Atmospheric Pressure
Isobar map

9. Differences in atmospheric pressure cause air to move …
820
830
840
850
860
820
830
840
850
860
870
880
890
weak pressure gradient
strong pressure gradient

10. Winds are named for the direction they originate from

11. Local winds Land – sea breezes Daytime: sea breeze
Night time: land breeze

12. 3. Global circulation patterns

13. Cold
High Pressure
Solar radiation creates variation in heating / atmospheric pressure 0o
30oN
60oN
30oS
60oS
90oN
SUN
Warm
Low Pressure
Earth

14. L Warm air rises at equator and flows towards the poles 90oN 60oN 30oN
30oS
60oS
90oN L

15. H L H Cold air sinks at 30o N and S latitude creating high pressure
30oS
60oS
90oN H L H

16. Low pressure at 0o , 60o latitude high pressure at 30o , 90o latitude
Doldrums: strong vertical uplift, little horizontal wind
Hadley cells: well developed low pressure cells in the tropics

17. H 0o
30oN
60oN
30oS
60oS
90oN L
Pressure gradients influence development of global wind patterns H L H L H

18. H L H Easterly winds (trade winds) Westerly winds Easterly winds 90oN
30oS
60oS
90oN
Easterly winds
Westerly winds H
Easterly winds (trade winds) L H

19. 4. Ocean circulation patterns

20. Ocean currents large continuously moving loops (gyres)
produced by winds, Coriolis effect and land masses

21. Ocean circulation exposes east coasts of continents to warm currents, west coasts to cold currents

22. Ocean upwelling

23. Summary
Variation in heating causes variation in atmospheric pressure conditions
Variation in atmospheric pressure causes air to move (H  L)
Local-scale wind patterns occur with variation in heating, pressure

24. Summary (continued)
Direction of air movement affected by pressure gradient, Coriolis effect, and friction
In No. Hemisphere L pressure systems (cyclones) circulate counterclockwise in, H pressures systems (anticyclones) circulate clockwise out

25. Summary (continued)
Global variation in heating produces L pressure at 0o and 60o, H pressure at 30o and 90o
H and L pressure systems drive global wind patterns (easterlies between 30o N and 30o S; westerlies between 30-60o N and S)

26. Summary (continued)
Ocean currents influenced by winds, Coriolis effect and land masses
Ocean circulation exposes east coasts of continents to warm currents, west coasts to cold currents