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Chapter 4 Atmospheric Circulation

Chapter 4 Atmospheric Circulation. Regions near the equator receive light at 90 o High latitudes receive light at low angles. Earth. Regions near the equator receive light at 90 o High latitudes receive light at low angles

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Chapter 4 Atmospheric Circulation

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  1. Chapter 4 Atmospheric Circulation

  2. Regions near the equator receive light at 90o High latitudes receive light at low angles Earth

  3. Regions near the equator receive light at 90o High latitudes receive light at low angles Light energy is more concentrated near the equator. In other words, there is a greater flux per unit area (W/m2) Earth

  4. Solar energy is concentrated near the equator Image: Netherlands Center for Climate Research

  5. absorbed solar energy Energy 90 45 0 45 90 Latitude

  6. absorbed solar energy Emitted IR energy Energy 90 45 0 45 90 Latitude

  7. More energy is absorbed near the equator than emitted And more energy is emitted near the poles than is absorbed. absorbed solar energy Emitted IR energy Energy 90 45 0 45 90 Latitude

  8. net radiation surplus Energy 90 45 0 45 90 Latitude

  9. Excess energy at the equator is transferred towards the poles by convection cells net radiation surplus Energy net radiation deficit 90 45 0 45 90 Latitude

  10. Solar energy received is greatest near the equator. Energy is moved from the equator to the poles.

  11. Solar energy received is greatest near the equator. Energy is moved from the equator to the poles. Energy is transferred by wind and ocean currents

  12. Air near the equator is warmed, and rises solar radiation

  13. The rising air creates a circulation cell, called a Hadley Cell H L solar radiation H Rising air  low pressure Sinking air  high pressure

  14. Hadley Circulation Cell Rising air is replaced Warm air rises

  15. Hadley Circulation Cell Air cools, sinks Rising air is replaced Warm air rises

  16. Hadley Circulation Cell Air cools, sinks Rising air is replaced Warm air rises HIGH HIGH LOW

  17. The Earth would have two large Hadley cells, if it did not rotate. --This is exactly what we think occurs on Venus (which rotates very slowly)! Rotation of the Earth leads to the Coriolis Effect This causes winds (and all moving objects) to be deflected: to the right in the Northern Hemisphere to the left in the Southern Hemisphere

  18. The Coriolis Effect Based on conservation ofangular momentum We experience linear momentum when we are in a car that is traveling fast and then stops suddenly.

  19. Planet Earth rotates once per day. Objects near the poles travel slower than those near the equator.

  20. Angular Momentum v r m L = mvr Angular momentum is conserved unless some force (a torque) is applied

  21. Objects near the poles have less angular momentum than those near the equator. When objects move poleward, their angular momentum causes them to go faster than the surrounding air. Conversely, they slow as they move towards the equator.

  22. When objects move north or south, their angular momentum causes them to appear to go slower or faster. This is why traveling objects (or air parcels) deflect to the right in the northern hemisphere and to the left in the southern hemisphere.

  23. L Example of Coriolis effect: hurricanes H H isobar (line of constant pressure) • Hurricanes are low pressure centers • Air moves from high pressure towards low • pressure

  24. L Hurricanes: Northern hemisphere H H • As the air moves in, it is deflected towards the • right in the NH • Resulting circulation is counter-clockwise

  25. The Coriolis effect causes winds to deflect as they travel within circulation cells This breaks up the two large Hadley cells into six smaller cells.

  26. In the tropics, surface air is moving equatorward. It is deflected to the right in the NH (left in the SH), giving rise to easterly flow (the trade winds) Easterlies

  27. At midlatitudes, surface air is moving poleward. It is deflected to the right in the NH (left in the SH), giving rise to westerly flow (the prevailing westerlies) Westerlies Westerlies

  28. Credit: NASA Credit: NASA

  29. Hadley Circulation Cell Air cools, sinks Rising air is replaced Warm air rises HIGH HIGH LOW

  30. Rising air cools; the air’s capacity to hold water drops. Rain! Air cools, sinks No rain in regions where air is descending Rising air is replaced Warm air rises HIGH HIGH LOW

  31. : orbit-net.nesdis.noaa.gov/arad/ gpcp/maps/frontmap.gif

  32. Intertropical Convergence Zone (ITCZ) http://en.wikipedia.org/wiki/File:IntertropicalConvergenceZone-EO.jpg

  33. Caution: Zonal weather pattern is not completely true The pattern is disrupted by land-sea contrasts

  34. Land heats and cools rapidly Water heats and cools slowly

  35. Warm air rises Onshore wind Sea Breezes DAY

  36. Warm air rises Onshore wind Sea Breezes Offshore wind DAY NIGHT

  37. Tibetian Plateau--Monsoon Circulation

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