9
3. an energy balance method, or
4. a combination method.
The two mass balance methods (1 and 2 above) focus on the
equations of motion for the atmosphere and require accurate measurement
of velocity and temperature profiles or mass fluxes. The equations of
conservation of momentum, mass, and energy were used in the mass
balance methods to develop expressions for the rate of evaporation of
water and the shear stress between to vertical positions in the lower
atmosphere as
Qv = PaKw q (2-2)
az
S = p aKm aU (2-3)
az
H = cpaaKh aT (2-4)
az
where:
Qv = vertical flux density of water vapor [kg-m-2.s-1
Pa = density of air [kg'm-3]
7 = shear stress rate [N'm-2]
H = vertical flux of heat [J.m-2]
z = vertical distance [m]
q = specific humidity [kgapor/kgdry air]
U = velocity [m's-1]
Cpa = specific heat of dry air [J*kg-1K-l]