Atmosphere structure, Solar Inputs and the Transport of Heat

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Atmosphere structure, Solar Inputs and the
Transport of Heat
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Heat, winds, and currents

• We will address the following topics....
• Why do the winds blow?
• The source of the winds is ultimately the Sun.
  Well discuss how heating by the Sun generates
  air flow.
• What influence does the Earths rotation have on
  winds?
• Earths rotation causes the winds and currents
  to turnwithout this rotation the climate would
  be very different.
• Solar Insolation controls almost everything
  But it is not just what we get, it is what we
  keep that defines the thermal balances.

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Structure of the Modern Atmosphere

• Pressure force exerted per unit area by the
  weight of overlying air (1 mb 100 Pa 1000 mb
  1bar 1 atm)
• Temperature measure of the molecular kinetic
  energy.

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Thermosphere
Thermosphere upper atmospheric layer with
temperature increasing with altitude

• Heated by absorption of high-energy radiation by
  oxygen
• Atmosphere is extremely thin, nearly a vacuum. As
  a result, Suns energy can heat air molecules to
  very high temperatures (2500 C) during the day.
  But there are so few, it doesnt reallymatter

Auroras occur in thermosphere
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Mesosphere
Mesosphere middle atmospheric layers where
temperature decreases with altitude

• Temperatures as low as -100 C
• Million of meteors burn up daily in the
  mesosphere, due to collision with air molecules

Noctilucent clouds (blue-white) over Finland.
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Stratosphere
Stratosphere temperature increases with altitude
due to absorption of UV by ozone

• Ozone is concentrated around an altitude of 25 km
  in the ozone layer
• Ozone layer protects surface from harmful UV
  radiation

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Troposphere
Troposphere lowest layer in atmosphere,
temperature decreases with altitude

• Temperature determined by surface heating
• Well mixed by weather

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Shortwave radiation

• Earth receives more solar radiation at low
  latitudes than high latitudes.
• Ultimately, it is this solar insolation that
  provides the heat that controls weather and
  climate. It is the imbalance across the Earths
  surface that controls winds and currents.

ANNUAL
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Shortwave radiation
3 factors influence the shortwave radiation
received at Earths surface

• Beam spreading each unit of shortwave radiation
  is spread over a larger area away from the
  equator

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Shortwave radiation
3 factors influence the shortwave radiation
received at Earths surface

• Beam spreading each unit of shortwave radiation
  is spread over a larger area away from the
  equator
• Beam depletion radiation is absorbed and
  reflected as it passes through atmosphere

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Shortwave radiation
3 factors influence the shortwave radiation
received at Earths surface

• Beam spreading each unit of shortwave radiation
  is spread over a larger area away from the
  equator
• Beam depletion radiation is absorbed and
  reflected as it passes through atmosphere
• Day length hours of daylight varies with
  latitude and season

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Shortwave radiation
Earth has seasons because its axis is tilted
23.5º with respect to the plane of the ecliptic
Tilted
No tilt
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Why do we have seasons?
Seasonal variations in insolation are greatest at
high latitudes
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Shortwave radiation
Earth receives more solar radiation at low
latitudes than high latitudes
Jun-Jul-Aug
Dec-Jan-Feb.
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Longwave radiation
Earth emits more longwave radiation at low
latitudes than high latitudes
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Longwave radiation
Earth emits more longwave radiation at low
latitudes than high latitudes
Jun-Jul-Aug
Dec-Jan-Feb.
Why is there a difference between Winter and
Summer?
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Net radiation
Net radiation total radiation

• Net radiation shortwave - longwave
• There is an energy imbalance!

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Global Energy Balance
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Global Energy Balance
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Global Energy Balance
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Global Energy Balance
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Energy Transport

• To make the energy balance, there must be a
  transport of energy from low to high latitudes.
• Radiation is converted to other forms of energy
  that can be transported by winds and currents
• Sensible heat heat that you can feel (stored in
  a substance as a change in temperature)
• Latent heat heat required to changes phases
  (solid --gt liquid --gt gas)

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Fluid Flow
Newtons first law A body at rest remains at
rest and a body in motion remains in constant
motion unless acted upon by an external force

• Fluid flow is driven by forces
• Forces include
• Pressure
• Coriolis
• Friction

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Fluid Flow
Pressure force exerted against a surface due to
the weight of air

• Pressure gradient force fluid flows from high
  pressure to low pressure

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Fluid Flow
Pressure force exerted against a surface due to
the weight of air

• Pressure gradient force fluid flows from high
  pressure to low pressure
• Flow in direction from H to L
• Larger gradient faster flow

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Pressure Differences
Pressure differences arise from temperature
differences.
A
B
Heating air causes it to expand In this example,
the masses of the 2 air columns, A and B, are
equal
Equal masses of air
SURFACE
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Pressure Differences
Pressure differences arise from temperature
differences.
A
B
Top of Atmos.
lt mass
COLD
COLD
gt mass
The mass of air overlying column A is greater
than that overlying column B
SURFACE
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Pressure Differences
Pressure differences arise from temperature
differences.
A
B
Top of Atmos.
COLD
COLD
Because the mass is greater in column A, the
surface pressure (i.e., the weight of the
overlying air) is greater.
BONUS!
HIGH
LOW
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Pressure Differences
Pressure differences arise from temperature
differences.
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General Circulation of the Atmosphere
Circulation on a non-rotating Earth
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Fluid Flow
Coriolis force an apparent deflection of moving
objects when observed from a rotating reference
frame
Coriolis force is an artificial force that arises
because we are riding on a rotating rock.
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Fluid Flow
Coriolis force an apparent deflection of moving
objects when observed from a rotating reference
frame
Stationary Observers Perspective

• Consider two children throwing
• a ball on a moving merry-go-
• round.

Rotating Observers Perspective
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Fluid Flow
Coriolis force an apparent deflection of moving
objects when observed from a rotating reference
frame
Stationary observer

• The stationary observer sees
• the ball moving in a straight
• line, and Johnny and Jill
• moving in a circle.

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Fluid Flow
Coriolis force an apparent deflection of moving
objects when observed from a rotating reference
frame
Moving observer

• Johnny and Jill on the merry-
• go-round perceive that they are
• stationary. They see the ball
• move to the right.

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Fluid Flow
Coriolis force an apparent deflection of moving
objects when observed from a rotating reference
frame
http//ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/cr
ls.rxml
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General Circulation of the Atmosphere
Circulation on a rotating Earth

• Trade winds
• Mid-latitude westerlies
• Polar easterlies

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DESERTS THE CONVERGENCE OF ATMOSPHERIC
CIRCULATION CELLS AND THE SURFACE OF THE EARTH
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Net radiation
Net radiation total radiation

• Net radiation shortwave - longwave
• There is an energy imbalance!
• Cold Poles and Hot Tropics the drive for
  circulation in both the atmosphere and the ocean
  systems

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Circulation of the Ocean Thermohaline Driving
Mechanism
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THE ATLANTIC GULF STREAM WARMING THE POLES
COOLING THE TROPICS
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MAJOR OCEAN CURRENT SYSTEMS
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GLOBAL SCALE CIRCULATION OF OCEANS A THERMAL
TRANSFER.
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SURFACE TEMPERATURE ANOMOLIES