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General Atmospheric Circulation

General Atmospheric Circulation. V1003 - Science and Society. Take away concepts and ideas. The Earth is heated unevenly. Why there are seasons. Global-scale wind patterns.

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General Atmospheric Circulation

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  1. General Atmospheric Circulation V1003 - Science and Society

  2. Take away concepts and ideas The Earth is heated unevenly. Why there are seasons. Global-scale wind patterns. Geostrophic flow: Balance of forces that act on atmospheric flow (Pressure gradients & gravity balanced by Coriolis force) Wind belts and climate zones. Monsoonal climate.

  3. As a sphere, the Earth is unevenly heated,equator to poles

  4. 2. As a tilted sphere, the Earth has seasons

  5. Seasonal changes in solar energy winter summer winter summer winter summer

  6. The equation of state (air) Atmospheric Pressure is a function of temperature and density Ideal Gas Law: P =  R T if pressure is constant, then what happens to  as T increases?

  7. Concept of horizontal motion:Sea Breeze

  8. Pressure imbalance = flow 1. Pressure imbalance is a FORCE (F = m x a) 2. Law of mass continuity (empty spaces not tolerated in fluids)

  9. Earth’s uneven radiation • Earth is a sphere (uneven radiation) • Tilted (there are seasons) Sphere means equator gets more radiation than poles. Tilt mean the amount of radiation at one location changes with time (seasons).

  10. Incoming (and outgoing) radiation

  11. Heating imbalance (∆T) = Pressure imbalance (∆P) = Winds

  12. Q1: Knowing uneven heating and P = R T • Poles have low pressure, equator has high pressure? b) Equator has low pressure, poles have high pressure?

  13. BUT - The Earth rotates Apparent (inertial) forces control the flow of air in response to these pressure gradients. Centripedal force is the force acting on body by string Centrifugal force is the opposite force acted on by the ball (by its own inertia)

  14. Imagine a satellite in orbit Centripetal force = Gravity Centrifugal force = mass and acceleration of satellite Exact balance sets the angular velocity of the satellite

  15. The Coriolis Force Artifact of Earth’s rotation An apparent force which acts on motion on the earth’s surface Conservation of angular momentum Fcoriolis = 0 on equator, increases poleward

  16. Coriolis ForceCons. of Angular Momentum

  17. … the pressure gradient force (∆P) is balanced by Coriolis force. Applies to atmosphere and ocean circulation where friction can be ignored. Geostrophic Balance

  18. Geostrophic balanceBalance between pressure and coriolis forces

  19. Geostrophic Balance NORTHERN HEMISPHERE

  20. Geostrophic flow in the Northern Hemisphere Counter-clockwise around low pressure cells Clockwise around high pressure cells

  21. Opposite Coriolis deflection for opposite hemispheres

  22. An example of Geostrophic flow Low High

  23. Burlington Q2: What direction is the wind coming FROM in Burlington, VT today? • North • East • West • South

  24. Application to Earth Geostrophic flow gives rise to banded circulation zones

  25. Trade Winds and the Intertropical Convergence Zone (ITCZ) ITCZ

  26. Hadley Cell Tropical convection cells westerlies Trade winds Hadley Cell Trade winds

  27. Global vegetation patterns Rising limb of Hadley Cell (ITCZ) = Rainforest Descending limb of Hadley Cell = Deserts

  28. Global Vegetation

  29. Incoming (and outgoing) radiation

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