Chapter 6 Atmospheric and Oceanic Circulations

1. Chapter 6Atmospheric and Oceanic Circulations

3. Wind Essentials • Air Pressure and Its Measurement   • Mercury barometer • Aneroid barometer • Wind: Description and Measurement   • Wind • Anemometer • Wind vane • Global Winds  

4. Barometers Figure 6.2

5. Air Pressure Readings Figure 6.3

6. Wind Vane and Anemometermeasures wind direction and speed NEN N NWN NE NW ENE WNW E W ESE WSW SE SW S SWS SES Figure 6.4

7. Driving Forces within the Atmosphere   • Pressure Gradient Force   • Coriolis Force   • Friction Force  

8. Pressure Gradient : changes in air pressure over a horizontal distancePressure gradient force (PGF): points from higher to lower pressure, perpendicular to isobars.Isobars: lines of equal air pressure. Figure 6.7

9. Coriolis Force: an apparent force caused by the rotation of the earth;1) deflects to the right (of the movement) in northern hemisphere.2) Maximum in the poles and zero in the equater3) Proportional to the wind speed. Figure 6.9

10. Geostrophic wind (Vg) • Results from the balance between the PGF and Coriolis force • Flows parallel to straight isobars at a constant speed • Speed in determined by the PGF PGF 1012mb Vg 1016mb COF

11. Frictional force • Opposite to the wind direction • Slows down the wind speed • Reduces Coriolis force • Creates surface wind (Vs): Flows from high to low pressure across isobars at an angle PGF Vs 1012mb 1016mb COF

12. Cyclone (low pressure) and Anticyclone (high pressure) In northern hemisphere: Cyclone: wind flows counter-clockwise towards the center across isobars at an angle Anticyclone: wind flows clockwise away from the center across isobars at an angle

13. Cyclone: air converges on the surface and moves upwards over the center; clouds forms and is likely to be associated with precipitation Anticyclone: air diverges away and subsides over the center; clear sky and sunny Figure 6.8

14. Atmospheric Patterns of Motion   • Primary High-Pressure and Low-Pressure Areas   • Upper Atmospheric Circulation   • Local Winds   • Monsoonal Winds  

15. General circulation: If the earth were not rotating: simple one cell model N. Pole cold H L warm equator

16. General circulation pattern with rotation H L 60N L 30N H equator H L H

17. General Atmospheric Circulation Hadley Cell: rises from equator subsides over Subtropical High Figure 6.12

18. Primary High-Pressure and Low-Pressure Areas • Inter-tropical convergence zone-ITCZ (equator) • Polar High Pressure (poles) • Subtropical high pressure (30N/S) • Subpolar low-pressure cells (60N/S)

19. June–July ITCZ Figure 6.11

20. Global wind pattern • Northeast trade wind (between equator and 30N/S) • Westerlies (between 30N/S-60N/S) • Polar northeasterly (between 60N/S-poles)

21. Global Barometric Pressure -winter Figure 6.10

22. Global Barometric Pressure-summer Figure 6.10

23. Semi-permanent system associated with Subtropical High • Bermuda high (Azores high; Atlantic high) • Pacific high (Hawaii high) Figure 6.13

24. Semi-permanent system associated with Subpolar Low Pressure • Aleutian low • Icelandic low

25. General Atmospheric Circulation Figure 6.12

26. Local Winds • Land-sea breezes • Mountain-valley breezes • Katabatic winds

27. Land-Sea Breezes Sea breeze: wind flows from ocean to land; occurs during the day. Land breeze: wind flows from land to ocean; occurs during the night Figure 6.18

28. Mountain-Valley Breezes Wind flows from valley to hill during the daytime Wind flows from high to valley during the night Figure 6.19

29. Monsoonal Winds: reversal of wind directions between seasons Figure 6.20

30. Oceanic Currents • Surface Currents   • Deep Currents  

31. Major Ocean CurrentsGyre: a circular flow pattern occupies the entire ocean basin Figure 6.21

32. Deep-Ocean Thermohaline Circulation Figure 6.22