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Transcript 
Chapter 7
Circulation of the Atmosphere
Scales of Atmospheric Motion
tornado
Planetary scale motion (Large-scale motion)
Trade-wind
Synoptic scale motion
cyclone
Front
Anti-cyclone
Hurricane
Meso-scale motion
kilometer to 10 kilometers
Local Winds
Sea and Land Breeze
Valley and Mountain Breeze
Tornadoe, 10 2 m
Dust devils, 1 - 10 m.
Global circulation
Single-cell Model
Thermally driven circulation (direct circulation)
ITCZ: Intertropical Convergence Zone
North
South
30 degree
Polar cell: direct cell
Ferrel cell:
indirect cell
Global Atmospheric Circulation Model
Summary
1. ITCZ: a rapidly upward moving air forms a narrow band
of convection.
2. Trade Winds: the steady northeast and southeast winds in
the tropics.
3. Hadley cell. a direct thermally driven circulation.
4. Subtropical high: descending branch of the Hadley cell
causes high pressure at the surface near 30 degree.
5. Mid-latitude westerly: prevailing winds between 30 degree
and 60 degree.
6. Ferrel cell: an indirect circulation in the mid-latitudes.
7. Polar front: the boundary between the cold polar air flowing
to the equator and the warm subtropical air moving poleward.
8. Polar easterly: prevailing winds in high latitude beyond 60
degree.
Monsoons
Does not mean “rainy season”, it refers to a wind system that exhibits
a pronounced seasonal reversal in direction.
Asian Monsoon
The raining season begins around the beginning of June and fade away
by the end of September
The North American Monsoon
The North American Monsoon occurs from late May or early June into
September, originating over Mexico and spreading into the southwest
United States by mid July.
The Westerlies in the mid-latitude
Thermal wind
Caused by horizontal
temperature gradient
Jet stream
Rossby Waves
Rotation, Circulation, and Vorticity


f
Planetary (entraining) vorticity
Latitude  : 0  90
0
Planetary vorticity f : 0  max
 effect :

Planetary vorticity changes with latitude

Relative vrticity


f
f is defined as positive
 0
 0
Cyclone
Anti-cyclone
Absolute vorticity=Planetary vorticity + Relative vrticity
a

f


Absolute vorticity is not conserved
Absolute vorticity
Potential vorticity 
Depth
 f
 constant
H
is conserved
P-1
H
h
P
S (warm)
N (cold)
Northward motion:
 0
anti-cyclonic circulation
Southward motion:
 0
cyclonic circulation
Westward propagation
Westerly winds
Changes in Upper-level Airflow
Wave
breaking
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