Download Global Circulation

Global Circulation and Winds
(Stewart Cap. 4)
Outline
1.
2.
3.
4.
Atmospheric pressure
Winds
Global circulation patterns
Ocean circulation patterns
1. Atmospheric Pressure
Atmospheric Pressure
Density of the
atmosphere
decreases with
altitude
Earth
Atmospheric
Pressure:
Force exerted by the
atmospheric per unit
area
Measuring Atmospheric Pressure
At sea level:
• 101,320 Pascals (101 kPa)
• 1013.2 millibars
• 76 cm Hg (30 in Hg)
Atmospheric Pressure
Atmospheric Pressure
Isobar map
Differences in atmospheric
pressure cause air to move …
820
820
830
830
840
840
850
860
850
870
880
860
weak pressure
gradient
890
strong pressure
gradient
Winds are named for the direction
they originate from
Local winds
Land – sea breezes
Daytime: sea breeze
Night time: land breeze
3. Global circulation patterns
http://www.bergonia.org/History/Hist-maps/columbusmap.gif
Cold
High
Pressure
90oN
Solar radiation creates
variation in heating /
atmospheric pressure
60oN
30oN
SUN
0o
30oS
60oS
90oN
Earth
Warm
Low Pressure
90oN
60oN
30oN
L
0o
30oS
60oS
90oN
Warm air rises at
equator and flows
towards the poles
90oN
Cold air sinks at 30o N and
S latitude
creating high pressure
60oN
30oN
0o
30oS
60oS
90oN
H
L
H
Low pressure at
0o , 60o latitude
high pressure at
30o , 90o latitude
Doldrums: strong vertical
uplift, little horizontal wind
Hadley cells: well
developed low
pressure cells in
the tropics
H
90oN
60oN
L
30oN
H
0o
L
30oS
60oS
90oN
H
H
L
Pressure
gradients
influence
development of
global wind
patterns
Easterly winds
90oN
60oN
30oN
0o
30oS
60oS
90oN
H
L
Westerly winds
Easterly winds (trade winds)
H
Westerly winds
Easterly winds
4. Ocean circulation patterns
Ocean currents
• large continuously moving loops (gyres)
• produced by winds, Coriolis effect and land masses
Ocean circulation exposes east coasts
of continents to warm currents,
west coasts to cold currents
Ocean upwelling
Summary
• Variation in heating causes variation in
atmospheric pressure conditions
• Variation in atmospheric pressure causes
air to move (H  L)
• Local-scale wind patterns occur with
variation in heating, pressure
Summary (continued)
• Direction of air movement affected by
pressure gradient, Coriolis effect, and
friction
• In No. Hemisphere L pressure systems
(cyclones) circulate counterclockwise in, H
pressures systems (anticyclones) circulate
clockwise out
Summary (continued)
• Global variation in heating produces L
pressure at 0o and 60o, H pressure at 30o
and 90o
• H and L pressure systems drive global
wind patterns (easterlies between 30o N
and 30o S; westerlies between 30-60o N
and S)
Summary (continued)
• Ocean currents influenced by winds,
Coriolis effect and land masses
• Ocean circulation exposes east coasts of
continents to warm currents, west coasts
to cold currents