Transcript Lecture 9 - UW-Madison Department of Atmospheric and

Lecture 9
High and Low Pressure Systems
(Read Chapter 22 For Friday)
300 mb vs. Surface
(GFS output from AOS site)
300mb height + speed
Surface pressure, Temperature,
precipitation
Divergence vs. Convergence
Directional
Convergence
Speed
Convergence
Directional
Divergence
Speed
Divergence
Convergence at one height tends to be balanced by divergence at
another…but not completely!
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 supergeostrophic because centrifugal
acceleration (relative to the curved flow)
adds to the pressure gradient
acceleration
In a wave pattern, winds spped up
and slow down from curvature of
flow
Jet Streak 4 Celled Pattern
Jet Streak
Jet Streak
Curvature vs. Speed convergence
Imbalance between
upper-level convergence/divergence
and compensating
surface divergence/convergence
leads to
surface pressure rises/falls
Surface Friction forces upward
motion in low and sinking motion in
high
Today’s weather
http://www.atmos.albany.edu/weather/difax.html
How surface heating affects
pressure
Formation of surface pressure low
and highs as a result of jet
movement