Publishers version - DTU Orbit

Figure 17: Newly developed models tested against data from the Høvsøre site in Denmark.
The broken line are the extrapolations of the ASL models presented in fig. 14, the solid curves
reflect models developed by (Gryning et al., 2007), involving the boundary layer height and
one more height scale.
vapor into eq. 12 as well.
2.4 Surface Characteristics of real ABLs
We shall consider characteristic real ABLs in the light of the ideal one considered in the
former section. Characteristics of a flat homogeneous land surface, a marine ABL, the effect
of moderate inhomogeneity, and finally steep surfaces and complex terrain.
To understand some of the differences, we must consider layers below the turbulent ASL,
because this is where the frictional processes resulting in a roughness takes place, and where
the surface temperature is a result the heat flux properties. The roughness length z0 is the
height, where the logarithmic profile extrapolates to zero due to surface friction. However,
below a height of about 10 z0 the real profile is not logarithmic anymore, because of the
molecular friction and because of the flow impacting on irregularities of the surface roughness
elements.
Tracking the momentum transport through the viscous layer reveals that the momentum
and heat transport is taken over by the surface and can be written as:
−w ′ u ′ z = u 2 ∗z =
−w ′ θ ′ z
p ∂η
ρ ∂x
∂θ = νθ ∂z
η
η +ν
∂u
∂z
η
The real irregular surface as indicated on the figure and denoted, η, while ν and ν0 are the
molecular diffusivity of momentum and heat respectively. On the left hand side of eq. 16 the
transport taking place in the turbulent ASL have been indexed with a z. In the viscous layer
ASL turbulence cannot exist due to the nearness of the surface, and the transport is taken
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