Geoscience Reference
In-Depth Information
Table 2.6 Typical roughness values for various surfaces
Surface description
z
0
(m)
Large water surfaces (“average”)
Snow, mud flats
0.0001-0.0005
Smooth runways
Short grass
0.008-0.02
Long grass, prairie
0.02-0.06
Short agricultural crops
0.05-0.10
Tall agricultural crops
0.10-0.20
Prairie or short crops with scattered bushes and tree clumps
0.20-0.40
Continuous bushland
Bushland in rugged and hilly (50-100 m) terrain
1.0-2.0
Mature pine forest
0.80-1.5
Tropical forest
1.5-2.5
Fore-Alpine terrain (200-300 m) with scattered tree stands
3.0-4.0
ln(z
−
d
0
)
Fig. 2.10 Schematic illustration
of the mean specific
h
umi
d
ity profile
q
=
q
(
z
)inthe
dynamic sublayer
and in the
atmos
ph
eric surface
layer;
q
s
is its value at
the surface.
unstable
neutral
stable
Surface
sublayer
(ASL)
Dynamic
sublayer
ln(z
0v
)
Mean specific humidity difference,
(
q
s
−
q
)
z
0v
and
d
0
are best deter-
mined experimentally for each specific surface. However, in the absence of measure-
ments, it may be necessary to estimate them from simple geometric characteristics of
the surface; numerous such relationships have appeared in the literature (e.g. Brutsaert,
1982). Wieringa (1993) has presented a review of available experimental determinations
of
z
0
over homogeneous terrain. A few typical values of
z
0
taken from the literature
for various surfaces are given in Table 2.6. As a useful first approximation for surfaces
In practical applications the roughness parameters
z
0
,
z
0h
,
