Post on 15-Jan-2016
Atmosphere structure, Solar Inputs and the Transport of Heat
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.
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.
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
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.
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
Troposphere
• Temperature determined by surface heating
• Well mixed by weather
Troposphere: lowest layer in atmosphere, temperature decreases with altitude
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.
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
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
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
No tilt Tilted
Shortwave radiation
Earth has seasons because its axis is tilted 23.5º with respect to the plane of the ecliptic
Why do we have seasons?
Seasonal variations in insolation are greatest at high latitudes
Dec-Jan-Feb. Jun-Jul-Aug
Shortwave radiation
Earth receives more solar radiation at low latitudes than high latitudes
Longwave radiation
Earth emits more longwave radiation at low latitudes than high latitudes
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?
Net radiation
Net radiation: total radiation• Net radiation: shortwave - longwave• There is an energy imbalance!
Global Energy Balance
Global Energy Balance
Global Energy Balance
Global Energy Balance
• 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
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
• 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
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
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.
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.
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.
Pressure DifferencesPressure differences arise from temperature differences.
General Circulation of the Atmosphere
Circulation on a non-rotating Earth
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
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
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
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
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
General Circulation of the Atmosphere
• Trade winds• Mid-latitude westerlies• Polar easterlies
Circulation on a rotating Earth
DESERTS – THE CONVERGENCE OF ATMOSPHERIC CIRCULATION CELLS AND THE SURFACE OF THE EARTH
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
Circulation of the OceanThermohaline Driving Mechanism
THE ATLANTIC GULF STREAMWARMING THE POLES – COOLING THE TROPICS
MAJOR OCEAN CURRENT SYSTEMS
GLOBAL SCALE CIRCULATION OF OCEANS – A THERMAL TRANSFER.
SURFACE TEMPERATURE ANOMOLIES