Energy Balance at Earth's Surface
 
 
  •      "boundary layer climate" - the climate at or near the Earth's surface
  •      "microclimatology" - the study of this layer
  •      "net radiation" (NET R) - the net (resultant) flux of all the short and longwave fluxes at the Earths' surface:


    •                                                 SW (down) - SW (up) + LW (down) - LW (up) = NET R (net radiation)
     
     

  •           sw (down) varies by season, latitude, and cloud cover
  •           sw (up) is a function of albedo

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  •           At night Net R is negative because SW (down) = 0, and the surface continues to lose L (up) from the surface

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  •           Net R values are positive ~ equatorward of 70 degrees N & S latitude, and negative poleward of 70 degrees N & S latitude
  •           Net R is expended as sensible heat, latent heat, ground heating, and conversion of heat energy to biochemical energy through photosynthesis
  •           sensible heat; heat that you can sense; it gets transferred from ground to air, and air to ground via conduction and convection (18% of NET R)
  •           latent heat of evaporation; heat energy stored in water vapor after water evaporates (dominant expenditure of NET R)
  •           ground heat; energy that flows into and out of the ground by conduction (is zero overall, because the energy stored in spring & summer is lost in fall &

    •              winter)
  •          Photosynthesis by plants utilizes 8% of NET R, converting it into biochemical energy

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    Specific Site Energy Balances:

    (1) desert site 

    (2) midlatitude moist meadow site

    (3) urban site :

         "urban heat island effect": urban microclimates are warmer on average than areas in the surrounding countryside
         urban surfaces are more conductive and have a higher heat storage capacity; and thus have higher temperatures: higher max and min temps
         urban areas have lower albedos, and thus produce higher NET R's - which is expended in producing higher values of sensible heat (H)
         urban rain water runs off quickly (doesn't soak into the ground); and hence isn't available to be evaporated: thus little transfer of heat by latent heat of
         evaporation (and latent heat of condenstion)
         irregular geometric shapes of cities traps insolation; this energy gets conducted to the surface which leads to higher temperatures
         human activities (anthropogenic activities) exacerbate the urban heat island effect (e.g., through the burning of fossil fuels)
         air pollution (gases & aersols) create a higher albedo, but increase L (down); also air pollution may lead to precipitation downwind from urban areas (more
         condensation nuclei).