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Energy Balance

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Energy Balance Energy Balance Presentation Transcript

  • Energy and the Atmosphere
  • Overview
    • Insolation-Atmosphere Interactions
      • Scattering
      • Refraction
      • Reflection
      • Absorption
      • Heat Transfer
        • Conduction
        • Convection
        • Advection
      • Greenhouse Effect
    • Energy Balances
      • Atmospheric Radiation Balance
      • Surface Energy Budget
  • Energy Budget
    • Open Systems model: Shortwave Energy in, Longwave Energy out
    • The Energy Budget describes what happens to insolation after it passes the thermopause, passes through the atmosphere and reaches the surface.
      • Atmospheric effects
      • Ground effects
  • Insolation-Atmosphere Interaction
    • Refers to what happens after the intercepted solar radiation enters the atmosphere
      • Transmission
      • Both short and long wave radiation
    • As light encounters gas molecules and particulates in the atmosphere, the pathway that the light follows changes
      • Diffusion (scattering)
      • Refraction
      • Reflection
      • Absorption
  • Diffusion
    • The Sun’s rays are essentially parallel as they reach the Earth’s surface.
    • As they encounter various particles in the atmosphere, some light rays are bounced in all the different directions.
      • Diffusion, or scattering
      • Some light scattered back into space (7%)
      • Some light scattered to the Earth’s surface (20%)
    • Diffusion increases as sun angle decreases
  • Incoming rays Scattered rays Gaseous medium
  • Refraction
    • Occurs when light passes from one medium to another
      • From air to water droplets
      • From air masses of varying temperature and density
    • Light ray slows and changes direction
      • Short wavelengths are refracted more than long wavelengths
        • Breaks light into a spectrum; rainbows
      • Convection currents in the air (rising hot air) cause refraction, creating a shimmery distortion
        • mirages
  • Medium 1 Medium 2 Incoming rays Refracted rays
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  • Reflection
    • Light that bounces off a surface
    • Albedo refers to the amount of light reflected back to space
      • 31% of incoming sunlight is reflected
        • 21% by clouds
        • 7% by diffuse scattering
        • 3% by the Earth’s surface
      • Mainly short wave radiation
    • Factors that increase albedo
      • Light color
      • Smooth surfaces
      • Low sun angle
  • Medium 1 Medium 2 Incoming rays Reflected rays
  •  
  • Absorption
    • Light that is not part of Earth’s albedo
    • Light that is assimilated by matter (69%)
      • Ozone in the stratosphere (3%)
      • Clouds (3%)
      • Atmospheric gases and dust (18%)
      • Earth’s surface (45%)
        • Including photosynthesis
    • Causes the matter to increase in temperature
      • short wave energy is converted to long wave (infrared)
        • including respiration
    • Absorbed heat energy can be transferred in the atmosphere
      • Heat energy flows from high to low heat
      • conduction
        • transfer of heat energy between two objects through physical contact
        • Phase changes: Latent heat
      • convection
        • occurs in mobile media (liquids, gases)
        • currents: molecules near heat source rise (and cool) while cooler molecules fall (and become heated)
      • advection
        • similar to convection, but occurs horizontally
      • radiation
        • heat transmitted as infrared radiation
  • Greenhouse Effect
    • Clouds
      • Are variable in cover
      • Exert tremendous influence on energy budget
        • Increase albedo (albedo forcing)
        • Increase greenhouse warming (greenhouse forcing)
          • Certain gases in clouds absorb and reradiate infrared radiation
            • Carbon dioxide, water vapor, methane
          • Creates an insulating effect
    • Different cloud types affect the greenhouse effect differently
      • High thin clouds allow more diffuse light through, causing more heat to be trapped (net greenhouse forcing)
      • Low thick clouds reflect more light out, causing less heat to be trapped (net albedo forcing)
    • The greenhouse effect has been identified as the main cause of global warming
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  • Energy Balances
    • Atmospheric radiation balance
    • Surface radiation balance
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    • Surface Radiation Balance
      • Refers to 45% of insolation that reaches the Earth’s surface
      • Daily Pattern
        • Insolation peaks at noon
          • varies seasonally, with maximum on the summer solstice
        • Absorbing the insolation heats the ground, which in turn heats the air
          • Maximum air temperature reached between 3-4 pm
          • Minimum air temperature reached around dawn
  •