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Coriolis Force Misconception

Coriolis Force Misconception. Coriolis force explains why toilets flow differently in different hemispheres right?. Outline for Coriolis mini lecture. Review of last weeks lab and concepts. Forces acting on wind. Factors Affecting Wind. Winds Aloft and Geostrophic Flow. Surface winds.

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Coriolis Force Misconception

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  1. Coriolis ForceMisconception • Coriolis force explains why toilets flow differently in different hemispheres right?

  2. Outline for Coriolis mini lecture Review of last weeks lab and concepts Forces acting on wind Factors Affecting Wind Winds Aloft and Geostrophic Flow Surface winds How Winds Generate Vertical Air Motion

  3. Pressure Gradient Force • Last week we learned: • horizontal differences in pressure result in a force causing • horizontal motions with the motion directed from high pressure to low pressure • the motions are at right angles to the isobars. The magnitue of the PGF can b e inferred from the spacing of the isobars = tightly packed isobars = strong winds!

  4. Pressure Gradient Force • Over the same distance: • a large pressure difference will result in a greater PGF and a stronger wind flowing from high pressure to low pressure. • a small pressure difference will result in a weak PGF and a slower winds

  5. Forces expressed as Vectors • Forces have two properties • Magnitude (length of arrow) • Direction (direction of arrow) • Force balance

  6. How to forces can change objects directions or motions • Acting parallel to motion • will speed up or slow down a moving object Force in direction of motion – result is a faster moving parcel Force in opposite direction of motion – result is a slower moving parcel

  7. How to forces can change objects directions or motions • Acting perpendicular • Moves the parcel in direction of force Force acting on parcel perpendicular to the motion of the parcel New motion of parcel after force acted on it

  8. The Coriolis Force Named after the French Scientist Gaspard Gustave Coriolis free moving objects are deflected to the right of their path in the Northern Hemisphere (to the left of their path in the Southern Hemisphere) because of the Earth’s rotation. It depends on an object’s speed—higher speed means stronger Coriolis Force.

  9. The Coriolis Force Coriolis deflection of winds blowing eastward at different latitudes Coriolis force also increases with increasing Latitude… strong over poles, no effect over equator. Strong Middling Weak None

  10. Friction acts at the surface. winds at the surface aren’t as strong as those at higher altitudes Air is a little viscous, so the layer next to the surface is also affected, but not as much. Friction Altitude

  11. Winds Aloft and Geostrophic Flow Balance pressure gradient force Coriolis Force: Geostrophic Flow. • Geostrophic winds: • go in a straight line • go parallel to the isobars • have speeds proportional to the pressure gradient force.

  12. Geostrophic Flow • WHAT!?!? • pressure difference starts wind • wind gets going a little, starts being deflected by Coriolis force • wind goes faster in response to pressure difference, gets deflected more by Coriolis Force • Eventually, the two balance

  13. Put down the pencils Let’s break down the forces

  14. Start with just a pressure gradient Then wind blows straight from High P to Low P And accelerates as it goes Just a Pressure Gradient View from top H L Pressure 1017 1015 1013 1011 1009 1007 1005 return

  15. Wind blows straight from High to Low, eventually evening out the pressure and stopping the wind. Just a Pressure Gradient H L Pressure 1014 1012 1010 1008

  16. The wind would blow at the same speed regardless of altitude. Just a Pressure Gradient H L Pressure 1013 1011 1009 1007 1005 return

  17. Then wind still blows straight from High P to Low P, but it doesn’t get moving as fast as soon, especially near the ground Now add Friction View from top H L Pressure 1017 1015 1013 1011 1009 1007 1005 back up

  18. The pressure difference also evens out eventually, though it might take a bit longer. Friction and Pressure Gradient H L Pressure 1014 1012 1010 1008

  19. Friction slows the wind at the ground—its effects decrease as you go up in the atmosphere. Friction and Pressure Gradient H L Pressure 1013 1011 1009 1007 1005

  20. Friction slows the wind at the ground—its effects decrease as you go up in the atmosphere. Friction and Pressure Gradient H L Pressure 1013 1011 1009 1007 1005 back up

  21. Forget friction. The wind starts out straight, but as soon as it starts building up speed, the Coriolis force turns it a bit to the right. Pressure Gradient and Coriolis H L The wind can’t accelerate any more over here because it’s going parallel to the isobars This is the Geostrophic Flow

  22. The Coriolis force limits the wind speed by redirecting it AND it prevents wind from blowing straight from H to L Pressure Gradient and Coriolis H L

  23. Since the wind never really reaches the low, the pressure difference is maintained, and the low never fills! Pressure Gradient and Coriolis H L

  24. Coriolis Force turns the wind some, friction slows the wind some, and the result is roughly a 30º angle between isobars and wind. Reality: Pressure Gradient, Coriolis Force, and Friction H L 30º

  25. The wind doesn’t blow straight from High to Low, but it does eventually get in there and even out the pressure difference, so H and L don’t last forever without a source of energy Reality: Pressure Gradient, Coriolis Force, and Friction H L 30º

  26. Friction slows the wind at the ground—its effects decrease as you go up in the atmosphere. Reality: Pressure Gradient, Coriolis Force, and Friction H L Pressure 1013 1011 1009 1007 1005

  27. Coriolis Force is turning the wind toward us in the right part of the picture. Reality: Pressure Gradient, Coriolis Force, and Friction H L Pressure 1013 1011 1009 1007 1005

  28. Since the Coriolis Force depends on wind speed, its effect decreases toward the ground where the wind speed is slower. Reality: Pressure Gradient, Coriolis Force, and Friction Coriolis H L Friction Pressure 1013 1011 1009 1007 1005

  29. Winds Aloft and Geostrophic Flow Coriolis Force Pressure Gradient Wind flows from high to low pressure. Wind speed Coriolis Force Coriolis Force Latitude “Isobaric packing” P.G.F. Geostrophic winds are up high and go straight: only Coriolis and Pressure Gradient Forces are important. Friction is important down low: below about 1500 meters. How do the Coriolis and Pressure Gradient forces change?

  30. Winds Aloft and Geostrophic Flow Wind direction is directly linked to the prevailing pressure pattern. Dutch meteorologist Buys Ballott, 1857 Buys Ballott’s Law states: In the Northern Hemisphere if you stand with your back to the wind, lower pressure will be found to your left and higher pressure will be found to the right. Best when there are no frictional forces or topography involved .

  31. Surface winds—high pressure(anticyclone) COLD DRY H WARM MOIST

  32. Surface winds—low pressure(cyclone) COLD DRY L WARM MOIST

  33. Upper Level Weather Chart 500mb chart Variations in height are analogous to variations in pressure. High height fields correspond to high pressure fields.

  34. Troughs and Ridges RIDGE RIDGE TROUGH

  35. Troughs and Ridges • An elongated region of low pressure (trough) or high pressure (ridge) • Tend to be quite common at higher altitudes • At the surface, a trough is usually a fairly weak feature

  36. How Winds Generate Vertical Air Motion Around a surface low pressure center, a net inward transport of air causes a shrinking of the area occupied by the mass. This is known as horizontal convergence.

  37. Airflow Associated with Cyclones and Anticyclones “Upper level support” is important in cyclone development

  38. Wind speeds and isobars STRONG WINDS Slack winds Slack winds The tighter they’re packed, the stronger the wind

  39. Northern Hemisphere vs. Southern Hemisphere Coriolis force in different hemispheres

  40. Factors that promote vertical airflow • Friction: • air flow from ocean to land (upward motion) • air flow from land to ocean (downward motion) • Mountain ranges

  41. Wind Measurement Wind roses provide a method of representing prevailing winds by indicating the percentage of time the wind blows from various directions

  42. Formation of A Sea Breeze • No pressure gradient, • no wind. • (b) Unequal heating • creates pressure • differences aloft which • causes air to flow. • The transfer of air aloft • (from the land to the sea) • creates a surface high over • the sea which results in a • flow of air from sea to land • (a.k.a. a sea breeze). Returning air Sea Breeze

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