Winds and Global Circulation

1. Winds and Global Circulation • Atmospheric Pressure • Winds • Global Wind and Pressure Patterns • Oceans and Ocean Currents

2. Atmospheric Pressure • As the atmosphere is held down by gravity, it exerts a force upon every surface • Pressure is force per unit area • Atmospheric pressure is the pressure, or force, that the atmosphere is exerting (or pushing) on the earth with.

4. Atmospheric pressure decreases with altitude near the surface • It decreases faster closer to the Earth’s surface • :THUS: a small change in elevation can produce significant changes in air pressure

5. Winds and Global Circulation • Atmospheric Pressure • Winds • Global Wind and Pressure Patterns • Oceans and Ocean Currents

6. What is Wind? • Wind is horizontal air motion with respect to the Earth’s surface • Air motions that are vertical are called updrafts or downdrafts

7. How is Wind Measured? Wind is measured by direction and velocity • Wind direction is always given as the direction wind is coming from • Wind speed is measured in meters per second or miles per hour

8. What Causes Wind? • Wind is caused by differences in atmospheric pressure from place to place. • Air tends to move from areas of high pressure to areas of low pressure until the air pressures are equal

9. What Causes Wind? • When Atmospheric pressure is unequal, a pressure gradientforce will push the air from a high pressure area to a low pressure area. • The greater the pressure differencebetween the two locations, the greater this forcewill be and thus the stronger the wind.

10. Differences in air pressure = a pressure gradient 820 830 840 850 860 870 880 890 820 830 840 850 860 strong pressure gradient weak pressure gradient

11. Differences in air pressure = a pressure gradient 820 830 840 850 860 820 830 840 850 860 870 880 890 The pressure gradient forces acts at right angles to the isobars (90 degrees) strong pressure gradient weak pressure gradient

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13. Wind Wind is the result of three forces: • Pressure Gradient • Surface Friction • Coriolis Effect Coriolis Effect:Due to the rotation of the earth an object in motion appears to be deflected away from it’s course.

14. SEA BREEZES

15. San Diego Sea Breeze and Night Breeze

16. Winds and Global Circulation • Atmospheric Pressure • Winds and the earth • Global Wind and Pressure Patterns • Oceans and Ocean Currents

19. Low Pressure/Cyclones • Winds flow counterclockwise around a low in the northern hemisphere. The opposite in the southern hemisphere • Air swirls inward and upward creating clouds and precipitation, which is why cloudy weather (and likely precipitation) are commonly associated with an area of low pressure.

20. High Pressure/Anti-Cyclones • Winds flow clockwise around a high pressure center in the northern hemisphere, and opposite in the southern hemisphere • Air swirls outward and down in high pressure centers. Sinking air suppresses the upward motion needed to support the development of clouds and precipitation. This is why fair weather is commonly associated with an area of high pressure.

21. Winds and Global Circulation • Atmospheric Pressure • Winds • Global Wind and Pressure Patterns • Oceans and Ocean Currents

22. Heat is transported from the Equator to the Poles - how? 90oN 60oN 30oN 0o 30oS 60oS 90oN Cold High Pressure Warm Low Pressure SUN Earth

23. 90oN 60oN 30oN 0o 30oS 60oS 90oN • Warm air rises at the • equator producing low • pressure (Intertropical • Convergence Zone, • ITCZ) and flows • towards the poles • Very little horizontal air • movement here • (AKA: The Duldrums) L

24. 90oN 60oN 30oN 0o 30oS 60oS 90oN Cold air sinks at 30o N and S latitude Creating high pressure (subtropical high pressure, STH) H L H

25. 90oN 60oN 30oN 0o 30oS 60oS 90oN Northeasterlyandsoutheasterly surface winds flow from the subtropical high pressure belts (30o N and S) to the low pressure belt (ITCZ) at the equator Westerly surface winds flow from the subtropical high pressure belts towards higher latitudes H L H

26. Westerly surface winds are forced to rise around 60o N and S latitude when they encounter cold polar easterly winds from the poles resulting in Subpolar Low pressure (SPL) belts 90oN 60oN 30oN 0o 30oS 60oS 90oN L H L H L

27. 90oN 60oN 30oN 0o 30oS 60oS 90oN H Cold air sinks at the poles producing polar high (PH) pressure regions L H L H L H

28. Hadley Cells are important in the transfer of heat and determining wind patterns (they start everything)

29. 90oN 60oN 30oN 0o 30oS 60oS 90oN H polar jet stream Jet streams are streams of fast moving air aloft that occur where atmospheric temperature gradients are strong L H L subtropical jet streams H L H polar jet stream

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32. Hadley Single Cell and3 Cell Models

36. video

37. Winds and Global Circulation • Atmospheric Pressure • Winds • Global Wind and Pressure Patterns • Oceans and Ocean Currents

38. The Earth’s Oceans Circulation patterns (CURRENTS): Another key component of heat redistribution Winds Density differences in sea water Coriolis force Shape of ocean basins Astronomical factors (TIDES)

39. Ocean Currents Driven mostly by wind blowing over the surface The currents move slower than the wind, they lag behind wind speed so often they are called drifts wind

40. Each hemisphere contains a tropical and subtropical gyre: Large continuously moving loops produced by winds, Coriolis force and land masses N. Subtropical Gyre North Tropical Gyre EQUATOR South Tropical Gyre S. Subtropical Gyre

41. Ocean currents

42. Different Depths of water have different temperatures (deeper=colder)

43. Deep-sea currents • Driven by differences in temperature and salinity (colder saltier water in the north is more dense) • Much slower than surface currents

44. Winds and Global Circulation • Atmospheric Pressure • Winds • Global Wind and Pressure Patterns • Oceans and Ocean Currents