Geoscience Reference
In-Depth Information
u
∗
h
E
∼
1
/
2
,
conventionally neutral ABL
;
(12.56)
|
fN
|
u
∗
L
|
1
/
2
h
E
∼
,
nocturnal stable ABL
.
f
|
The first of
Eqs. (12.56)
is the Rossby-Montgomery (
1935
) expression for the
equilibrium depth of a neutral ABL; the second is due to
Pollard
et al
.
(
1973
); the
third is the
Zilitinkevich
(
1972
)form,
Eq. (12.50)
.
Zilitinkevich
et al
.
(
2007
) then suggest the ABL height
h
E
across this neutral
and stable regime can be obtained from the interpolation formula
f
2
(C
R
u
∗
)
2
+
1
h
E
=
|
(C
CN
u
∗
)
2
+
N
|
f
|
C
NS
ku
∗
L
.
|
f
(12.57)
Here
C
R
,
C
CN
,and
C
NS
are constants associated with the truly neutral, convention-
ally neutral, and nocturnal stable states. From a variety of observations and LES
results they suggest that
C
R
0
.
6,
C
CN
1
.
36, and
C
NS
0
.
51. The last implies
the constant in the Zilitinkevich expression
(12.50)
is
0
.
3.
Questions on key concepts
12.1 Explain some of the prominent differences between the SBL and the CBL.
What is their common, root cause?
12.2 Explain why and how the late-afternoon transition process depends on clear
weather.
12.3 Sketch the dynamics of the low-level jet. Explain why it can be most intense
in a clear-weather, baroclinic situation.
12.4 Discuss why geophysical turbulence is more sensitive to stable stratification
than is engineering turbulence.
12.5 What are the two broad classes of SBL? How are they different?
12.6 Discuss how stable stratification of the ABL develops in late afternoon and
early evening in clear weather.
12.7 Discuss the positive and negative impacts of the low-level jet on wind-power
generation.
12.8 Explain why and how the dynamics of stably stratified turbulence is
“delicate.”
12.9 Discuss and interpret the sensitivity of the SBL to terrain slope.
12.10 Discuss the generalization of the traditional ensemble-mean-plus-fluctuation
decomposition of turbulent fields to include a wave component.
12.11 Interpret the buoyancy length scale
(12.41)
physically.
12.12 Explain why the nocturnal SBL is unlikely to achieve a quasi-steady state.
