Global atmospheric circulation

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Global atmospheric circulation
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Poles Cold Decending Air
Tropics Hot Rising Air
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Single circulation cell
Poles Cold Decending Air
Tropics Hot Rising Air
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Coriolis Due to the rotation of the earth
Poles Cold Decending Air
Tropics Hot Rising Air
Rotation
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Coriolis Due to the rotation of the earth
Poles Cold Decending Air
Tropics Hot Rising Air
Rotation
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Coriolis Due to the rotation of the earth
Poles Cold Decending Air
Tropics Hot Rising Air
Rotation
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3 circulation cells
Poles Cold Decending Air
Tropics Hot Rising Air
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3 circulation cells per hemisphere
Tropics Hot Rising Air
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3 circulation cells per hemisphere
Tropics Hadley Cells
NE Trade Winds
ITCZ - doldroms
SE Trade Winds
ITCZ - Inter Tropical Convergence Zone
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Subtropical Jet Stream
Westerlies
Mid-latitudes
Sub-tropical high Horse Lat.
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Cloud Cover
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Surface Pressure
Polar High
Polar Low
Subtropical High
Tropical Low
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Figure 6.13
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General Atmospheric Circulation
Figure 6.13
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Rossby Waves
Undulations in the polar front
Polar Jet Stream
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Jet Streams
Polar Jet stream
Subtropical Jet
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Driving Forces Within the Atmosphere  

• Gravity
• Pressure Gradient Force  
• Coriolis Force  
• Friction Force  

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Barometer
Instrument used to measure air pressure
Figure 6.2
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Weather Map www.weather.com
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Isobaric pressure maps

• Show the elevation in the atmosphere that is (in
  this example) at a pressure of 500 mb.

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Isobaric pressure maps
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Pressure Gradient
Figure 6.7
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Pressure Gradient
Figure 6.7
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Pressure wind
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Geostrophic wind
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Wind movement because of Pressure gradient alone
Map view
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Pressure Coriolis
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Pressure Coriolis Friction
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Pressure Coriolis Friction
Figure 6.8
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Pressure gradient and wind
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Surface vs. high winds

• Surface winds interact with the surface so there
  is more friction.
• High level winds do not interact as much with the
  surface so they tend to be geostrophic winds.

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500 mb Pressure Map (approx.5500m)
Figure 6.10
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Atmospheric Patterns of Motion  

• Primary High-Pressure and Low-Pressure Areas  
• Upper Atmospheric Circulation  
• Local Winds  
• Monsoonal Winds  

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Global Barometric Pressure
Figure 6.11
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Global Barometric Pressure
Figure 6.11
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Primary High-Pressure and Low-Pressure Areas

• Equatorial low-pressure trough
• Polar high-pressure cells
• Subtropical high-pressure cells
• Subpolar low-pressure cells

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Equatorial low-pressure trough

• Intertropical convergence zone (ITCZ)
• Trade winds

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Polar high-pressure cells

• Polar easterlies
• Antarctic high

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Subtropical high-pressure cells

• Westerlies
• Bermuda high
• Azores high
• Pacific high

Figure 6.14
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Subpolar low-pressure cells

• Aleutian low
• Icelandic low
• Polar front

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Figure 6.13
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Upper Atmospheric Circulation

• Rossby waves
• Jet stream

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Local Winds

• Land-sea breezes
• Mountain-valley breezes
• Katabatic winds

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Land-Sea Breezes
Figure 6.19
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Monsoonal Winds
Figure 6.21
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Mountain WindsKatabaticWinds
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Mountain Winds KatabaticWinds
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Oceanic Currents

• Surface Currents  
• Deep Currents  

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Major Ocean Currents
Figure 6.22
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Deep Currents
Thermohaline circulation A function of both
Temperature and Salinity
Figure 6.23
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Thermo-haline circulation

• Temperature
• and
• density

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Temperature and salinity
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North Atlantic Deepwater Formation
Mediterranean saline water Cooling in the North
Atlantic
http//cleo1.phys.tue.nl/michel/Utrecht/use/thc.h
tml
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Turning off thermohaline circulation Hadley
Centre The figure shows that with increased
surface freshening the meridional overturning
collapses and the sea-surface temperature (SST)
and surface air temperature become significantly
cooler.
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Change in annual temperature 30 years after a
collapse of the thermohaline circulation Figure
courtesy of Michael Vellinga, Hadley Centre.