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Understanding Atmospheric Convergence and Divergence Dynamics

Explore geostrophic balance, Eulerian vs. Lagrangian frameworks, and the impact of jet streaks on atmospheric pressure systems. Learn about surface friction forces and the formation of pressure highs and lows.

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Understanding Atmospheric Convergence and Divergence Dynamics

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  1. Lecture 7 Homework Due Friday, October 3, 2014 TYU Ch 6: 1,2,5,7,11,14,17,18,20; TYPSS Ch 6: 2 TYU Ch 7: 1,5,10,11,13,14,15,18,20; TYPSS Ch 7: 1 TYU Ch 8: 1,2,6,7,12,14,15,18,20; TYPSS Ch 8: 2 High and Low Pressure Systems

  2. Divergence vs. Convergence Directional Convergence Directional Divergence Speed Convergence Speed Divergence

  3. Divergence (Convergence) vs. Diffluence (confluence) • Diffluence is the spreading of height contours on an upper air map. • Speed slows => convergence • Direction is divergent => divergence • Convergence or divergence? • Uncertain • Numerical calculation necessary to tell

  4. Convergence at one height tends to be balanced by divergence at another…but not completely!

  5. Geostrophic Adjustment • Coriolis acceleration is equal wind multiplied by Coriolis parameter (f=.0001 1/s). • Wind at rests accelerates from the sum of these forces until Coriolis and pressure gradient accelerations balance • The final state of balance is called “geostrophic balance”

  6. Eulerian vs. Lagrangian Framework • Eulerian framework is when we stand in one place and the wind blows by us. • Lagrangian framework, is when we are riding on a parcel • Consider flow moving at a constant speed in a circle around a low pressure center • Lagrangian framework • parcel is continuously accelerating, i.e. its velocity (speed and direction) is constantly changing • The pressure gradient force is the only real force acting on the parcel and is responsible for its acceleration • Eulerian framework, • the wind is blowing at a constant speed and direction • Inertia advectsthe upstream wind which has a radial component outward, hence an inertial acceleration outward (centrifugal acceleration) . This advection is countered by the PGF L CF PGF

  7. Gradient Wind Balance takes centrifugal force* into account Winds moving around a cyclone tend to be sub-geostrophic because centrifugal acceleration (relative to the curved flow) opposes the pressure gradient acceleration Winds moving around a synoptic-scale anticyclone tend to be super-geostrophic because centrifugal acceleration (relative to the curved flow) adds to the pressure gradient acceleration

  8. In a wave pattern, winds spped up and slow down from curvature of flow

  9. Jet Streak has a 4 celled patternof convergence and divergence Jet Streak Jet Streak

  10. Curvature vs. Speed convergence

  11. Imbalance between upper-level convergence/divergenceand compensating surface divergence/convergenceleads to surface pressure rises/falls

  12. Surface Friction forces upward motion in low and sinking motion in high

  13. How surface heating affects pressure

  14. Formation of surface pressure low and highs as a result of jet movement

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