Lecture 1 - Energy and the Earth System (2)

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  • Created on: 03-05-21 11:27
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  • Lecture 1 - Energy and the Earth System
    • Solar constant
      • Solar energy flux received by the Earth outside of the Earth's atmosphere
        • Earth receives around 1/4 of the solar constant per surface area
      • Depends on total radiation emitted by the Sun and the Sun-Earth distance
        • Geological timescales - Radiation emitted by Sun increases over time
        • Decadal to centennial timescales - 11 years Sun cycle dominates changes in solar output
      • Distribution of radiation at Earth's surface depends on angle between Earth's rotational axis and plane of orbit
        • Variations in orbital parameters causes ice ages (along with other factors)
    • Geometric effects and surface radiation
      • Latitude effect
        • Less heating at higher latitudes (changes across the year)
      • Sun angle effect
        • Light dissipation is greater at shallow angles
      • Optical path effect
      • Together, these lead to seasonal and daily cycles in the amount of solar radiation
        • Sun shifts noon overhead position between 23.5 degrees N and S, producing seasons
    • Earth's response to solar insolation
      • Incoming  energy = outgoing energy
        • Keeps Earth from constantly cooling or heating
      • Receives energy as shortwave radiation, heating planet
      • Emits energy as long wave radiation, cooling planet
        • Before energy is radiated back into space, it undergoes several transformations and redistributions between the subsystems, producing weather and climate
    • Albedo
      • Amount of incoming radiation reflected by an object across all wavelengths
      • 0 = total absorption (black body), 1 = total reflection (white body)
      • Earth albedo = approx 0.3
        • Solar radiation reflected by surface particles in atmosphere e.g. clouds and aerosols and also gas molecules (Rayleigh scattering)
        • High over deserts and snow/ice
        • Low over dense forests and oceans


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