Global Circulation and Winds

1. Global Circulation and Winds

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) • 1013.2 millibars • 76 cm Hg (30 in Hg)

7. Atmospheric Pressure

8. Atmospheric Pressure Isobar map

9. Pressure variation results from uneven heating in the atmosphere

10. 820 830 840 850 860 820 830 840 850 860 870 880 890 Differences in atmospheric pressure cause air to move … weak pressure gradient strong pressure gradient

11. Winds are named for the direction they originate from

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

13. Local winds Mountain-valley breezes

14. Local winds Santa-Ana winds (interior desert region of So. California)

15. 2. Winds

16. Factors affecting wind movement Pressure gradient force Air moves perpendicular to isobars

17. Factors affecting wind movement Coriolis effect Air is deflected; moves parallel to isobars deflection: right in no. hemisphere left in so. hemisphere

18. Factors affecting wind movement Friction Drag on air as it moves across the earth’s surface (reduced with altitude) Earth

19. Factors affecting wind movement H L

20. Combined effects of pressure gradient, Coriolis effect and friction

21. Geostrophic winds Operate in the upper atmosphere Not affected by friction

22. Geostrophic winds – jet stream

23. Rossby waves Smooth westward flow of upper atmosphere air Periodic undulations develop forcing cold air southward, warm air northward

24. 3. Global circulation patterns http://www.bergonia.org/History/Hist-maps/columbusmap.gif

25. 90oN 60oN 30oN 0o 30oS 60oS 90oN Cold High Pressure Solar radiation creates variation in heating / atmospheric pressure Warm Low Pressure SUN Earth

26. 90oN 60oN 30oN 0o 30oS 60oS 90oN Warm air rises at equator and flows towards the poles L

27. 90oN 60oN 30oN 0o 30oS 60oS 90oN Cold air sinks at 30o N and S latitude creating high pressure H L H

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

29. 90oN 60oN 30oN 0o 30oS 60oS 90oN H L Pressure gradients influence development of global wind patterns H L H L H

30. 90oN Easterly winds 60oN Westerly winds 30oN Easterly winds (trade winds) 0o 30oS Westerly winds 60oS 90oN Easterly winds H L H

32. 4. Ocean circulation patterns

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

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

35. Ocean upwelling

36. 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

37. 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

38. 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)

39. 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