1 / 46

Atmospheric and Oceanic Circulations (continued) Chapter 6

Atmospheric and Oceanic Circulations (continued) Chapter 6. Lecture 14 4 February 2005. Figure Credit: “Earth’s Climate” by W. Ruddiman. Figure Credit: “Earth’s Climate” by W. Ruddiman. Credit: www.physicalgeography.net. Wind.

bianca-cole
Download Presentation

Atmospheric and Oceanic Circulations (continued) Chapter 6

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Atmospheric and Oceanic Circulations(continued)Chapter 6 • Lecture 14 • 4 February 2005

  2. Figure Credit: “Earth’s Climate” by W. Ruddiman

  3. Figure Credit: “Earth’s Climate” by W. Ruddiman

  4. Credit: www.physicalgeography.net Wind simply put, wind is the horizontal flow of air in response to differences in air pressure these pressure differences are usually due to uneven solar heating at the surface ‘heat rises’ wind flows because of pressure gradient

  5. wind compass Wind winds are designated as direction from not direction to (oceanographers do it the opposite) so, a westerly wind would be coming from what angular direction?

  6. Four forces that determine winds 1. Gravity - pulls gas molecules close to Earth density & pressure decrease with height 2. Pressure gradient force - the difference in air pressure between areas 3. Coriolis force - deflects wind from a straight line to the right or left depending on hemisphere 4. Friction force - the drag on air flow from the Earth’s surface

  7. Pressure vs. Pressure Gradient • The value of pressure itself is NOT important • The CHANGE in pressure over DISTANCE is • Change over distance is a GRADIENT • The GRADIENT in pressure gives winds & ocean currents their “push”

  8. Pressure Gradient Force (PGF) isobar - a line of equal pressure (analogous to isotherm) gradient is 16 mb (note the closer isobars) the PGF acts at right (90º) angles to the isobars

  9. Pressure Gradient Force note the 1008 mb isobar

  10. Credit: www.physicalgeography.net Wind speed = Const * Pressure Gradient Here, a 4x increase in PGF corresponds to a 4x increase in wind speed

  11. Pressure Gradient Force and Isobars if there were no other forces acting on wind, it would flow in straight lines (perpendicular to isobars) from high to low pressure zones

  12. Coriolis Force (just the facts) • Rotation of Earth acts to deflect any motion from a straight line • Deflection is to right (NH) to the left (SH) • Coriolis “force” act on a right angle to the motion • Coriolis Force is NOT a real “force” but is caused by viewing motion on a rotating planet

  13. Coriolis Force • Show the merry-go-round video

  14. the amount of rotation about a vertical axis (’spinning’) is maximum at the poles and minimum at the equator Figure Credit: “Earth’s Climate” by W. Ruddiman

  15. Earth’s Rotation every point on earth rotates around a central axis at 15 degrees/hour

  16. Coriolis Force an object with an initial east-west velocity will maintain that velocity, even as it passes over surfaces with different velocities as a result, it appears to be deflected over that surface (right in NH, left in SH)

  17. Coriolis Force and Deflection of Flight Path

  18. Coriolis Force and Deflection of Flight Path

  19. Coriolis Force and Flight Paths II. Airplane animation

  20. The Coriolis Force affects air flow in response to pressure gradients in the atmosphere Figure Credit: “Earth’s Climate” by W. Ruddiman

  21. geostrophic winds - PGF and Coriolis forces are opposite and balanced in the northern hemisphere (upper troposphere), the CF deflects the wind to the right until wind flows parallel to isobars ~7km Credit: www.physicalgeography.net

  22. Geostrophic Winds Balance between Pressure Gradient & Coriolis Forces Flow along isobars not across Works for upper atmosphere winds & ocean currents

  23. 500 mb Pressure Map

  24. isobars PGF, CF & isobars in upper troposphere

  25. Friction Force surface friction reduces wind speed and reduces the Coriolis force (remember CF increases with wind speed) because of this, it causes winds to move across isobars at an angle the friction force operates only in the bottom 0.5-1 km of the atmosphere, and it acts opposite to the direction of motion

  26. Figure Credit: “Earth’s Climate” by W. Ruddiman

  27. isobars PGF + Coriolis + Friction Forces

  28. average density of air is 1.3 kg/m^3 average molecular weight of air is ~29 g/mol The inter-tropical convergence zone (ITCZ) solar heating in the tropics expands air and decreases its density - leading to increased buoyancy It also gets more humid (adding water vapor) How would this change the average molecular weight of air? what happens to air density if you add water vapor?

  29. Convection on your Stove

  30. Convection on Earth

  31. Credit: http://ess.geology.ufl.edu/ess/Notes/AtmosphericCirculation/convect.jpeg as this air rises, it cools and water condenses out, leading to intense precipitation

  32. A satellite (GOES) view of the ITCZ over the eastern Pacific Credit: http://www.geog.ucsb.edu/~jeff/wallpaper/itcz_goes11_lrg.jpg

  33. the position of the ITCZ tracks the sun (it is found in the summer hemisphere) - the location of the ITCZ determines the rainy season in many tropical countries, especially those in Africa the horizontal winds within the ITCZ are calm - the doldrums

  34. Credit: NASA JPL The C in ITCZ the intense uplift of air creates horizontal pressure gradients at the surface as a result, winds converge towards the equator from both hemispheres what about the complete cycle - where does the uplifted air go?

  35. Equator-to-pole cross section of circulation

  36. Hadley cell circulation this circulation refers to the complete circulation of rising air in the tropics, descending air over 30 °N and °S, and trade winds converging at the equator the descending branch of the Hadley circulation brings hot, dry air to the surface - leading to high pressure areas and suppressed precipitation

  37. Subtropical high-pressure cells these cells occur where the tropical air descends in either hemisphere

  38. Monsoon Circulation Figure Credit: “Earth’s Climate” by W. Ruddiman

  39. Monsoon Circulation Figure Credit: “Earth’s Climate” by W. Ruddiman

  40. Monsoon Circulation Figure Credit: physicalgeography.net

  41. Asian monsoon intense, dry winds flow from the Asian interior in response to the gradient between the continental high pressure and the equatorial (ITCZ) low pressure

  42. Asian monsoon in summer, the subsolar point and the ITCZ shift northward, reversing the pressure gradient - as the winds flow over the Indian ocean they gain moisture

  43. Daytime land-sea breeze results from differential heating of land and sea - not from radiation differences - but from the different specific heats of land and water

  44. Nighttime land-sea breeze at night, the land cools more rapidly than the sea and thus overlying air becomes more dense and has a higher pressure

More Related