Chapter 4
Atmospheric and Oceanic
Circulation
Supplemental notes are drawn from Lutgens and
Tarbuck, The Atmosphere
Interesting
- An individual molecule of air weights almost nothing
- Through their motion, size and number they create air
pressure
- The atmosphere as a whole has considerable mass and
exerts an average pressure of 14.7 lb/sq.in at sea level
… called “one atmosphere” or
“standard atmosphere” or an “ATA”
[a somewhat confusing concept]
We are seldom aware of this atmospheric pressure
- it is exerted on all surfaces
- we are structurally evolved to cope
--- we only become aware if great change (+/-)
occurs
- abstract concept --– cannot “see” or “touch” it
- atmospheric pressure is “relative”
Aside
In 1641, Evangelista Torricelli was working on a mine
drainage problem
- He knew that pumps in the mines could “pull” water
upward only about 33’
[with a little variation]
- In an experiment he was able to determine that the
reason was not the pumps, but that pressure of the
surrounding air counter balanced the pumps
- he replicated the effect using denser mercury
[we use mercury to designate pressure – water would be impractical]
Barometers
Figure 4.2
Air Pressure Readings
Figure 4.3
Air pressure is important for the mechanics of
weather
… pressure differences create the forces of
convection and advection
… in doing this it transfers large
amounts of mass and energy across the
globe
Pressure Difference
Generally the result of change in two
related factors:
(1) temperature
(2) density
The atmosphere adds:
(3) altitude/elevation
… the relationship 1/2n
Pressure change on the Earth is both
vertical and horizontal
- vertical change is thermal in origin
- horizontal change can be thermal or
dynamic
Interesting
horizontal and vertical variations in
pressure create a seeming paradox in
pressure and airflow between high and
low pressures
convergence and divergence
The Hadley Cell
First attempt to characterize
pressure/circulation patterns on the
Earth
Later modified to a three-cell Hadley
Assumed some non-Real World factors
Primary High-Pressure and Low-Pressure
Areas
-
Equatorial Low-Pressure Trough
Polar High-Pressure Cells
Subtropical High-Pressure Cells
Subpolar Low-Pressure Cells
Global Barometric Pressure
Figure 4.11a
Global Barometric Pressure
Figure 4.11b
Factors Affecting Wind
Wind – the horizontal movement of air
(advection) results from difference in air
pressure between two locations
air flow always high to low pressure in
attempt to equalize pressure
Sun is the “driving” force in creating these
pressure differences
Wind
Portrait
of the
Pacific
Ocean
Figure 4.6
Driving Forces Within the Atmosphere
Major
- Pressure Gradient Force
- Coriolis Force (Effect)
- Friction Force
Minor
- centripetal / centrifugal
- gravity
Pressure Gradient
Figure 4.7
Coriolis Force
Figure 4.9
Pressure + Coriolis + Friction =
Wind
Figure 4.8
500-mb Pressure Map
Figure 4.10
Atmospheric Patterns of Motion
- Primary High-Pressure and Low-Pressure
Areas
- Upper Atmospheric Circulation
- Multi-year Oscillations in Global Circulation
- Local Winds
General Atmospheric Circulation
Figure 4.13a
General Atmospheric Circulation
Figure 4.13b
The Asian Monsoon(s)
Figure 4.20
Jet Streams
Figure 4.17
Local Winds
-
Land-Sea Breezes
Mountain-Valley Breezes
Katabatic Winds
Chinook Winds
Land-Sea
Breezes
Figure 4.18
Mountain-Valley
Breezes
Figure 4.19
Oceanic Currents
- Surface Currents
- Upwelling and Downwelling Flows
- Thermohaline Circulation―The Deep
Currents
Major Ocean Currents
Figure 4.21
Thermohaline
Circulation
Figure 4.22