Circulation of the Atmosphere


Published on

  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Circulation of the Atmosphere

  1. 1. +Circulation of the AtmosphereChapter 7 © 2011 Pearson Education, Inc.
  2. 2. +7.1 Scales of Atmospheric Motion © 2011 Pearson Education, Inc.
  3. 3. + Scales of Atmospheric Motion Small- and large-scale circulation:  Microscale  Mesoscale  Macroscale
  4. 4. + Scales of Atmospheric Motion Microscale winds:  The circulation is small and chaotic.  They can last from seconds to minutes.  They can be simple gusts, downdrafts, and small vortices, such as dust devils.
  5. 5. + Scales of Atmospheric Motion Mesoscale winds:  They can last from minutes to hours.  They are usually less than 100 km across.  Some mesoscale winds (thunderstorms and tornadoes) also have a strong vertical component.
  6. 6. + Scales of Atmospheric Motion  Macroscale winds:  These winds are the largest wind patterns.  These planetary-scale patterns can remain unchanged for weeks at a time.  Smaller macroscale circulation is called synoptic scale.  These wind systems are about 1000 km in diameter.  Smaller macroscale systems are tropical storms and hurricanes.
  7. 7. + Scales of Atmospheric Motion
  8. 8. + Scales of Atmospheric Motion Structure of wind patterns:  Global winds are a composite of motion on all scales.  Hurricanes appear as a large cloud moving slowly across the ocean.  The large cloud contains many mesoscale thunderstorms.  The thunderstorms consist of numerous microscale bursts.
  9. 9. +7.2 Local Winds © 2011 Pearson Education, Inc.
  10. 10. + Local Winds Land and sea breezes
  11. 11. + Local Winds Mountain and valley breezes
  12. 12. + Local Winds Valley Breeze:  Air along Mt. slopes is heated more intensely than air at the same elevation over the valley floor. This warm air glides up the Mt. slope and generates a valley breeze. Mt. Breeze:  After sunset process is reversed. Rapid heat loss along the mountain slopes cool the air. Which drain into the valley.© 2011 Pearson Education, Inc.
  13. 13. +7.3 Global Circulation © 2011 Pearson Education, Inc.
  14. 14. + Global Circulation Single-cell circulation model Hadley model  Hadley proposed that the contrast in temperatures between the poles and the equator creates a large convection cell in both the Northern and Southern hemispheres.
  15. 15. + Global Circulation Hadley Model  Warm equatorial air rises until it reaches the tropopause. Where it spreads towards the poles. Eventually this uplift level flow reaches the poles, where cooling causes it to sink and spread out at the surface as equatorward moving winds.  It reaches the equator warms and they cycle repeats.© 2011 Pearson Education, Inc.
  16. 16. + Global Circulation Three-cell model
  17. 17. + Global Circulation  A three-cell circulation model was proposed in the 1920s.  Warm air rises at the equator (Hadley cell).  As the flow moves poleward, it begins to cool and sinks at 20°–35° latitude.  Trade winds meet at the equator, in a region with a weak pressure gradient, called the doldrums.
  18. 18. + Global Circulation The westerly circulation of surface winds (prevailing westerlies) between 30°–60° latitude is called the Ferrel cell.  Not a good model for winds aloft because it predicts winds that flow from east to west. Just opposite of what is observed. Circulation (at 60°–90°) within a polar cell produces polar easterlies; surface flows that move toward the equator.© 2011 Pearson Education, Inc.
  19. 19. +7.4 Pressure Zones Drive the Wind © 2011 Pearson Education, Inc.
  20. 20. + Pressure Zones Drive Winds Idealized zonal pressure belts: 1. The equatorial low is an intertropical convergence zone (ITCZ).  Low pressure and trade winds converge 1. Subtropical highs (STH) are high-pressure zones in the belts about 20°–35° latitude on either side of the equator.  Where westerlies and trade winds originate.
  21. 21. + Pressure Zones Drive Winds 3. Subpolar low is a low pressure region about 50°-60° latitude. Polar easterlies and westerlies clash in low pressure convergence zone; this is the reason for bad weather in our area in the winter 4. Polar highs near the Earth’s poles are where the polar easterlies originate.  Higher than average pressure.© 2011 Pearson Education, Inc.
  22. 22. + Pressure Zones Drive Winds
  23. 23. + Pressure Zones Drive Winds Semi permanent pressure systems: The real world
  24. 24. + Pressure Zones Drive Winds January pressure and wind patterns  Siberian high- a very strong high pressure center positioned over frozen area in northern Asia.  As highs over the continents grow the lows over oceans grow weak.© 2011 Pearson Education, Inc.
  25. 25. + Pressure Zones Drive Winds In Jan but not in July; 2 intense semipermenant low pressure centers  Aleutian low- by Alaska  Icelandic Low Areas are frequently clouds and get lots of winter precipitation.© 2011 Pearson Education, Inc.
  26. 26. + Pressure Zones Drive Winds Semi permanent pressure systems: The real world
  27. 27. + July pressure and wind pattern July pressure and wind pattern  In the summer months, the subtropical high in the northern hemisphere migrate west and become stronger than during the winter.© 2011 Pearson Education, Inc.
  28. 28. +7.5 Monsoons © 2011 Pearson Education, Inc.
  29. 29. + Monsoons  Monsoon refers to a seasonal reversal of winds.  The Asian monsoon, which affects India and its surrounding areas, China, Korea, and Japan.  The monsoon is driven by pressure differences.  The North American monsoon occurs in the southwestern U.S. and northwestern Mexico.  This monsoon is driven by the extreme temperatures, which generate a low-pressure center over Arizona and results in a circulation pattern that brings moist air from the Gulf of California and from the Gulf of Mexico, to a lesser degree.
  30. 30. + Monsoons
  31. 31. + Monsoons
  32. 32. +7.6 The Westerlies © 2011 Pearson Education, Inc.
  33. 33. + The WesterliesWhy Westerlies?  Difference between pole and equator drive these winds  Pressure gradient from equator to pole and Coriolis force deflects winds and a balance is reached.
  34. 34. + The Westerlies Waves in the westerlies:  Westerliesflow in wavy paths that have long wavelengths.  The longest wave patterns are known as Rossby waves, which usually consist of 4–6 waves that encircle the globe.  Rossby waves can have a large impact on weather.
  35. 35. +7.7 Jet Streams © 2011 Pearson Education, Inc.
  36. 36. + Jet Streams Jet streams:  Embedded in westerlies  Widths vary from less than 100 km to more than 500 km.  Speeds can attain 100–400 kph. (60-240 mph)  Polar and subtropical
  37. 37. + Jet Streams The polar jet stream is the most prevalent.  It occurs along a major frontal zone, the polar front.  The jet stream moves faster in winter.  During the winter, occasionally it moves north– south.  If the jet stream is more equatorward weather will be colder and drier than normal. More poleward, weather will be warmer and more humid.
  38. 38. +© 2011 Pearson Education, Inc.
  39. 39. + Jet Streams The subtropical jet stream is a semipermanent jet stream over the subtropics.  It is a west-to-east current, centered at 25° N and S.  It is mainly a winter phenomenon.  The subtropical jet stream is slower than the polar.
  40. 40. + Jet Streams Jetstreams and Earth’s heat budget Relatively mild temperature occur south of jet stream and cold temperature north of jet stream the waves begin to meander.
  41. 41. +7.8 Global Winds and Ocean Currents © 2011 Pearson Education, Inc.
  42. 42. + Global Winds and Ocean Currents Energy is passed from moving air to the surface of the ocean through friction. Resulting in water being dragged by the wind. The Coriolis force deflects surface currents poleward, which form nearly circular patterns of ocean currents called gyres.© 2011 Pearson Education, Inc.
  43. 43. + Global Winds and Ocean Currents Gyres are found in each major ocean basin centered around subtropical high-pressure systems The Gulf stream is strengthened by westerly winds and continues northeastward.
  44. 44. + Global Winds and Ocean Currents© 2011 Pearson Education, Inc.
  45. 45. + Global Winds and Ocean Currents Importance of ocean currents:  Ocean currents have an important on climate, which helps maintain the Earth’s heat balance.  Cold currents offshore result in a dry climate.  Warm offshore current produce a warm moist climate.  Ocean currents account for ¼ of total heat transport. Wind accounts for the other ¾.
  46. 46. + Global Winds and Ocean Currents Ocean currents and upwelling:  Upwelling is the rising of cold water from deeper layers to replace warmer surface water.  A wind-induced vertical movement  It occurs where winds blow parallel to the coast toward the equator.
  47. 47. +7.9 El Nino and La Nina and the SouthernOscillation © 2011 Pearson Education, Inc.
  48. 48. + El Niño and La Niña and the Southern Ocean
  49. 49. + El Niño and La Niña and the Southern Ocean ElNiño is a gradual warming of eastern Pacific waters in December or January.  Periodof abnormal warming happen at irregular intervals of 2-7 years and persist for spans of 9 months to 2 years. La Niña is the opposite of El Niño and refers to colder-than-normal ocean temperatures along the coast of Ecuador and Peru
  50. 50. + El Niño and La Niña and the Southern Ocean Impact of El Niño:  It is noted for its potentially catastrophic impact on weather and economies of Chile, Peru, Australia, and other countries.  Arid areas can receive a lot of precipitation.  A change in surface water temperature can kill fish.  El Niño has been recognized as part of the global atmospheric circulation pattern.
  51. 51. + El Niño and La Niña and the Southern Ocean Impact of La Niña:  La Niña is also an important atmospheric phenomenon.  In the western Pacific, wetter than normal conditions occur.  There are also more frequent hurricanes in Atlantic.
  52. 52. + El Niño and La Niña and the Southern Ocean Southern oscillation:  This is the seesaw pattern of atmospheric pressure between the eastern and western Pacific.  Winds are the link between pressure changes and the ocean warming and cooling associated with El Niño and La Niña.© 2011 Pearson Education, Inc.
  53. 53. +7.10 Global Distribution of Precipitation © 2011 Pearson Education, Inc.
  54. 54. + Global Distribution of Precipitation Zonal Distribution of precipitation
  55. 55. + Global Distribution of Precipitation Distribution of precipitation over the continents