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. We’ll discuss how heating by the Sun generates air flow.
• What influence does the Earth’s rotation have on winds?Earth’s rotation causes the winds and currents to turn…without 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,
Sun’s energy can heat air molecules to very high temperatures (2500 °C) during the day. But there are so few, it doesn’t reallymatter Auroras occur in thermosphere
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Mesosphere
• Temperatures as low as -100 C
• Million of meteors burn up daily in the mesosphere, due to collision with air molecules
Mesosphere: middle atmospheric layers where temperature decreases with altitude
Noctilucent clouds (blue-white) over Finland.
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Stratosphere
• Ozone is concentrated around an altitude of 25 km in the “ozone layer”
• Ozone layer protects surface from harmful UV radiation
Stratosphere: temperature increases with altitude due to absorption of UV by ozone
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Troposphere
• Temperature determined by surface heating
• Well mixed by weather
Troposphere: lowest layer in atmosphere, temperature decreases with altitude
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ANNUAL
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 Earth’s surface that controls winds and currents.
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Shortwave radiation
• Beam spreading: each unit of shortwave radiation is spread over a larger area away from the equator
3 factors influence the shortwave radiation received at Earth’s surface
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Shortwave radiation
• 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
3 factors influence the shortwave radiation received at Earth’s surface
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Shortwave radiation
• 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
3 factors influence the shortwave radiation received at Earth’s surface
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No tilt Tilted
Shortwave radiation
Earth has seasons because its axis is tilted 23.5º with respect to the plane of the ecliptic
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Why do we have seasons?
Seasonal variations in insolation are greatest at high latitudes
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Dec-Jan-Feb. Jun-Jul-Aug
Shortwave radiation
Earth receives more solar radiation at low latitudes than high latitudes
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Longwave radiation
Earth emits more longwave radiation at low latitudes than high latitudes
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Dec-Jan-Feb. Jun-Jul-Aug
Longwave radiation
Earth emits more longwave radiation at low latitudes than high latitudes
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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• 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 --> liquid --> gas)
Energy Transport
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Newton’s 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
• Fluid flow is driven by forces
• Forces include- Pressure- Coriolis- Friction
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• Pressure gradient force: fluid flows from high pressure to low pressure
Fluid Flow
Pressure: force exerted against a surface due to the weight of air
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Fluid Flow
• Pressure gradient force: fluid flows from high pressure to low pressure
- Flow in direction from H to L- Larger gradient = faster flow
Pressure: force exerted against a surface due to the weight of air
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Heating air causes it to expand
In this example, the masses ofthe 2 air columns, A and B, are equal
Equal masses of air
SURFACE
HOTCOLD
A B
Pressure DifferencesPressure differences arise from temperature differences.
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SURFACE
HOTCOLD
Top of Atmos.
COLD COLD
The mass of air overlying column A is greater than that overlying column B
> mass< mass
A B
Pressure DifferencesPressure differences arise from temperature differences.
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HOTCOLD
COLD COLD
BONUS!
HIGH LOW
Because the massis greater in column A, the surfacepressure (i.e., the weightof the overlying air) isgreater.
Top of Atmos.A B
Pressure DifferencesPressure differences arise from temperature differences.
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Pressure DifferencesPressure differences arise from temperature differences.
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General Circulation of the Atmosphere
Circulation on a non-rotating Earth
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Coriolis force is an artificial forcethat arises because we are ridingon a rotating rock.
Fluid Flow
Coriolis force: an apparent deflection of moving objects when observed from a rotating reference frame
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Consider two children throwinga ball on a moving merry-go-round.
Stationary Observer’s Perspective
Rotating Observer’s Perspective
Fluid Flow
Coriolis force: an apparent deflection of moving objects when observed from a rotating reference frame
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The stationary observer sees the ball moving in a straight line, and Johnny and Jill moving in a circle.
Stationary observer
Fluid Flow
Coriolis force: an apparent deflection of moving objects when observed from a rotating reference frame
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Johnny and Jill on the merry-go-round perceive that they arestationary. They see the ballmove to the right.
Moving observer
Fluid Flow
Coriolis force: an apparent deflection of moving objects when observed from a rotating reference frame
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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/crls.rxml
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General Circulation of the Atmosphere
• Trade winds• Mid-latitude westerlies• Polar easterlies
Circulation on a rotating Earth
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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 OceanThermohaline Driving Mechanism
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THE ATLANTIC GULF STREAMWARMING 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