In the simplest situations, air temperature is dictated by energy balance at the underlying surface. The following is the basic form of a surface energy balance equation:
asQ + asq + aiL + Qf = egT4 + hc(Ta – Ta)
+ kdT0/dz |z=0 + le,
where as and al are the absorptivities for short – and long-wave radiation, respectively; Q and q are the direct and diffuse short-wave radiative fluxes, respectively; L is incoming long-wave flux; Qf is anthropogenic heat flux; e is emissivity; s is the Stefan-Boltzmann constant; To and Ta are surface and air temperatures, respectively; hc is the convective heat transfer coefficient; k is thermal conductivity; l is latent heat of vaporization; and e is
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evaporation rate (mass flux). Thus, the first and second terms on the left side represent the total absorbed short-wave (e. g., solar) radiation flux at the surface (both direct and diffuse), and the third term is the absorbed long-wave (e. g., near infrared) flux. The fourth term on the left is the anthropogenic heat flux (e. g., from motor vehicles, building equipment, and other heat sources) into the surface or near-surface atmospheric layer. On the right side of the equation, the first term represents long-wave radiative flux from the surface, the second term is the sensible heat flux, the third term is ground heat flux (heat conduction through the surface), and the last term is latent heat flux. Some of the terms in this equation are discussed directly or indirectly in the following sections.
