Geoscience Reference
In-Depth Information
Figure 9.1 A laminar boundary layer on a flat plate in a uniform flow. Its thickness
δ(x)
is defined as the distance above the surface where the streamwise velocity
reaches a specified fraction of the free-stream velocity
U
.
∞
Figure 9.2 An acoustic sounder record from a convective ABL. The ABL is about
200 m deep until 1100 MST, grows to about 400 m at 1230, falls to 200 m at 1330,
and grows to 400 m again at 1400. Photo courtesy W. D. Neff. From
Wyngaard
(
1988
).
The first could be approached when the stress-divergence term is small (as in a deep
convective ABL over a smooth surface,
Chapter 11
) and the mean horizontal momentum
balance
(8.65)
, in vector form, nears the nonturbulent flow limit
1
ρ
0
∇
0
=−
p
−
2
×
u
.
(9.1)
Since the Coriolis term is perpendicular to
u
, the dot product of
Eq. (9.1)
with
u
is
simply
1
ρ
0
∇
−
p
·
u
=
0
,
(9.2)
so that
u
is parallel to the isobars, as shown in
Figure 9.3
.
The second bound is approached
in turbulent flow when the Coriolis term is small (as with an inversion at height
z
i
such
