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Chapter 6
Atmospheric and
Oceanic
Circulations
Robert W. Christopherson
Charlie Thomsen
Wind Essentials
Air Pressure and Its Measurement
Mercury barometer
Aneroid barometer
Wind: Description and Measurement
Wind
Anemometer
Wind vane
Global Winds
Barometers
Figure 6.2
Air Pressure Readings
Figure 6.3
Wind Vane and
Anemometer
measures wind
direction and speed
NEN
N
NE
NW NWN
WNW
W
WSW
ENE
E
ESE
SE
SW
SWS S SES
Figure 6.4
Driving Forces within the
Atmosphere
Pressure Gradient Force
Coriolis Force
Friction Force
Pressure Gradient : changes in air pressure
over a horizontal distance
Pressure gradient force (PGF): points from
higher to lower pressure, perpendicular to
isobars.
Isobars: lines of equal air pressure.
Figure 6.7
Coriolis Force: an
apparent force caused by
the rotation of the earth;
1) deflects to the right (of
the movement) in
northern hemisphere.
2) Maximum in the poles
and zero in the equater
3) Proportional to the
wind speed.
Figure 6.9
Geostrophic wind (Vg)
Results from the balance
between the PGF and
Coriolis force
Flows parallel to straight
isobars at a constant
speed
Speed in determined by
the PGF
PGF
1012mb
Vg
1016mb
COF
Frictional force
Opposite to the wind direction
Slows down the wind speed
Reduces Coriolis force
Creates surface wind (Vs):
Flows from high to low pressure
across isobars at an angle
PGF
Vs
1012mb
1016mb
COF
Cyclone (low pressure) and
Anticyclone (high pressure)
In northern hemisphere:
Cyclone: wind flows counterclockwise towards the center across
isobars at an angle
Anticyclone: wind flows clockwise
away from the center across isobars
at an angle
Cyclone: air converges on the surface and moves upwards over the center; clouds
forms and is likely to be associated with precipitation
Anticyclone: air diverges away and subsides over the center; clear sky and sunny
Figure 6.8
Atmospheric Patterns of Motion
Primary High-Pressure and Low-Pressure
Areas
Upper Atmospheric Circulation
Local Winds
Monsoonal Winds
cold
warm
N. Pole
H
L
General circulation:
If the earth were not
rotating: simple one
cell model
equator
General circulation pattern with rotation
H
L
H
L
H
L
H
60N
30N
equator
General Atmospheric Circulation
Hadley Cell:
rises from
equator
subsides over
Subtropical
High
Figure 6.12
Primary High-Pressure and
Low-Pressure Areas
Inter-tropical convergence zone-ITCZ
(equator)
Polar High Pressure (poles)
Subtropical high pressure (30N/S)
Subpolar low-pressure cells (60N/S)
June–July ITCZ
Figure 6.11
Global wind pattern
Northeast trade wind (between equator and
30N/S)
Westerlies (between 30N/S-60N/S)
Polar northeasterly (between 60N/S-poles)
Global Barometric Pressure -winter
Figure 6.10
Global Barometric Pressure-summer
Figure 6.10
Semi-permanent system associated
with Subtropical High
Bermuda high
(Azores high;
Atlantic high)
Pacific high
(Hawaii high)
Figure 6.13
Semi-permanent system associated
with Subpolar Low Pressure
Aleutian low
Icelandic low
General Atmospheric Circulation
Figure 6.12
Local Winds
Land-sea breezes
Mountain-valley breezes
Katabatic winds
Land-Sea
Breezes
Sea breeze: wind flows from
ocean to land; occurs during the
day.
Land breeze: wind flows from
land to ocean; occurs during the
night
Figure 6.18
Mountain-Valley
Breezes
Wind flows from valley to
hill during the daytime
Wind flows from high to
valley during the night
Figure 6.19
Monsoonal Winds: reversal of wind
directions between seasons
Figure 6.20
Oceanic Currents
Surface Currents
Deep Currents
Major Ocean Currents
Gyre: a circular flow pattern occupies the entire
ocean basin
Figure 6.21
Deep-Ocean Thermohaline
Circulation
Figure 6.22