1. Robert W. Christopherson Charlie Thomsen Chapter 6 Atmospheric 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 Anemometer measures wind direction and speed Figure 6.4 N S W E NE SW NEN ENE SE NW ESE SES SWS WSW WNW NWN

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

8. Pressure Gradient : changes in air pressure over a horizontal distance Pressure 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 equater 3) 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 1016mb 1012mb PGF COF Vg

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 1016mb 1012mb PGF Vs 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. Figure 6.8 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

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

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

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

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

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

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

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

30. Oceanic Currents Surface Currents Deep Currents

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

32. Deep-Ocean Thermohaline Circulation Figure 6.22