High and Low Pressure Systems

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Lecture 9

• High and Low Pressure Systems
• (Read Chapter 22 For Friday)

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300 mb vs. Surface(GFS output from AOS site)
300mb height speed
Surface pressure, Temperature, precipitation
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Divergence vs. Convergence
Directional Convergence
Directional Divergence
Speed Convergence
Speed Divergence
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Convergence at one height tends to be balanced by
divergence at anotherbut not completely!
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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
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In a wave pattern, winds spped up and slow down
from curvature of flow
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Jet Streak 4 Celled Pattern
Jet Streak
Jet Streak
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Curvature vs. Speed convergence
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Imbalance between upper-level convergence/diverge
nce and compensating surface
divergence/convergence leads to surface
pressure rises/falls
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Surface Friction forces upward motion in low and
sinking motion in high
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Todays weather

• http//www.atmos.albany.edu/weather/difax.html

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How surface heating affects pressure
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Formation of surface pressure low and highs as a
result of jet movement