Geoscience Reference
In-Depth Information
“Free” atmosphere
Transition or inversion
10
2
to 10
3
m
Outer region or
defect layer
10
1
to 10
2
m
Inner region or
atmospheric
surface layer
(ASL)
Dynamic sublayer
(logarithmic profiles)
(30 /u
*
)
or 3 to 5 h
0
Transition or wake layer
(5 /u
*
) or h
0
Interfacial
sublayer
z
Smooth
Bluff-rough
Permeable-rough
Fig. 2.6
Sketch of the typical structure of the atmospheric boundary layer (ABL) above three different types of
uniform surfaces. The atmospheric surface layer (ASL) is the region where Monin-Obukhov
similarity (MOS) is usually valid;
h
0
is a typical height of the roughness obstacles. Under unstable
conditions the outer region is called the mixed layer, and it is capped by an inversion layer. (The
vertical axis scale is distorted.)
introduced here, is often expressed also as the friction velocity defined as
)
1
/
2
u
∗
≡
(
τ
0
/ρ
(2.32)
This shows that in light of Equation (2.30), under steady or
nearl
y steady conditions,
one has to a good approximation near the ground that
u
2
∗
=−
w
u
.
2.4.2
General structure of the ABL
In the analysis, it is convenient to assume that the atmospheric boundary layer consists
of a number of sublayers, in which different sets of variables are important to different
degrees in governing turbulent transport. The main subdivision is into an inner and an
outer region. In the
outer region
or
defect layer
the flow is strongly dependent on the
