1. High and Low Pressure Systems
Lecture 7
High and Low Pressure Systems
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

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= /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 advects the 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 pattern of convergence and divergence

10. Curvature vs. Speed convergence

11. Imbalance between upper-level convergence/divergence and compensating surface divergence/convergence leads 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