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obvious soil-atmosphere interface. It was assumed that the thermal
capacitance of the soil at the surface was negligible when compared to
the magnitudes of the fluxes which occur. Therefore, the net flux of
energy must be zero at the soil surface. The ability of the soil to
maintain a significant rate of evaporation at the soil surface was
assumed to be small as well. This assumption required the water to
evaporate at a finite distance below the soil surface rather than at
the soil surface. The boundary conditions for the energy, vapor and
liquid continuity were
(2-31a)
(2-31b)
(2-31c)
where:
Cpw = specific heat of water [J-kg'1*^'1]
CpV specific heat of water vapor [J*kg'l*K"l]
D[_ hydraulic diffusivity [m2*s_1]
Dv = diffusivity of water vapor in soil [m2*s"l]
hf, = boundary layer heat transfer coefficient [W*m'2*K_1]
hm = boundary layer mass transfer coefficient [m*sl]
P = precipitation or irrigation rate [m3*m'2*s-1]
Rn = net radiation incident upon soil surface [W*m"2]
soil temperature [K]
- X
3T
ST
z=0
99 ^/*v
(PwcpwL + cpvv tfz )^avg
Rn ^h(Tz=0 Ta)
n 30
-L ST
= P
Z=0
3pv
3v Sz~
z=0
= hm(pV0" hz )
T