SURFACE HEAT BUDGET

•   Consider a layer of air within the surface layer, as shown to the right (panel a). 
• Within this layer of air:
  • sensible heat is transported through to top of the layer - this is called the sensible heat flux (Q_H = w'q').
  • latent heat is transported through the top of the layer - this is called the latent heat flux (Q_E = L_v/C_p(w'q'))
  • short wave radiation passes through the layer and is partially absorbed by the surface.  Long wave radiation passes up through the layer.  The net upward radiation is the sum of the upward and downward short wave and long wave radiative fluxes (-Q^*_s).  Note that an upward flux is defined as a positive number, hence this flux is negative for being downward directed.
  • -Q_G represents the molecular heat flux into the ground
  • Some of the heat is stored within the layer (increase in internal energy, chemical storage by photosynthesis, etc.).  In addition, many complex processes occur within the our layer (radiative transfer between leaves, plants, buildings, etc., vertical variations of sensible and latent heat fluxes, evaporation, condensation, transpiration, etc).  These processes are lumped into this term as well and  is called the storage term (DQ_s).
• The overall energy budget for this layer of air near the earth's surface is:

-Q^*_s = Q_H + Q_E -Q_G + DQ_s  (1)

• This equation is simply a statement of energy in = energy out. 
• The external forcing term (energy in) is -Q^*_s  while all the other terms (energy out) are response terms.
• If our layer becomes infinitely small, then the storage term becomes 0 (panel b in Fig. 7.2). 
  • Q:  For what kind of surfaces could this approximation be valid for? Answer    
• Q:  Given a barren land surface, create sketches similar to Fig. 7.2 illustrating the heat budget near the earths surface at:
  • 3PM local time on a sunny day.
  • 2 AM local time on a clear night.