Environmental Engineering Reference
In-Depth Information
Table 7.1
The near-neutral estimation of aerodynamic roughness length and displacement height
for Sodankylä and Basel-Sperrtrasse
Present values
Literature values
Site
|
z
3
/L
|
z
oo
(m)
d
oo
(m)
z
oo
(m)
d
oo
(m)
Sodankylä
<0.125
1.1
±
0.3
9.8
±
3.2
0.8 (Zilitinkevich
et al., 2001)
1.4 (Joffre et al.,
2001)
-
∼
12 (Christen,
2005)
Basel-Sperrtrasse
280
◦
-360
◦
wind sector.
<0.3
1.2
±
0.4
11.8
±
3.6
∼
1.7 (Christen, 2005)
collected by the Finnish Meteorological Institute in an area typical of the sub-arctic
Northern Finland with Scots pine forests are used. The Sodankylä Meteorological
Observatory (67
◦
22
N, 26
◦
38
E, 180m) is located in Finnish Lapland, 100 km
north of the arctic polar circle (Gryning et al., 2001; Joffre et al., 2001). For the
convective regime an urban canopy dataset collected in the Basel Urban Boundary
Layer Experiment (BUBBLE) between summer 2001 and summer 2002, are used
(Rotach et al., 2005). For this analysis, wind and average turbulence data from the
main urban tower “Basel-Sperrstrasse” (32m high) located in a heavily build-up
area in the city centre.
Figure 7.2 compares (7.7) with data for stable stratification from the mean-profile
and turbulence measurements [providing
U
(
z
) and
u
∗
] at a 48m tower during July
2003-June 2004 over a boreal forest at the Sodankylä Observatory. To determine
z
0
u
the log-linear velocity profile was employed (Monin and Obukhov, 1954):
k
−
1
u
∗
ln (
z
L
.
U
(
z
)
=
/
z
0
u
)
+
C
u
z
/
Using data from three levels (23, 25, 47m)
z
0
u
and
C
u
were determined for each
profile. This analysis confirms (7.7) with confidence and allows determination of
C
SS
=
0.05).
For unstable stratification, using data of a similar kind measurements at three lev-
els (17.9, 22.4, 31.7m) at the “Basel-Sperrstrasse” meteorological tower, To achieve
a pronounced effect, only cases of strong convection (
8.13
±
0.21 (a side product was a reasonable estimate of
C
u
=
3
±
−
h
0
/L
> 0.5) when
U
and
profiles in the entire surface layer followed the
−
1/3 power law are used (Fig. 7.3):
(
L
)
−
1
/
3
,
L
)
−
1
/
3
U
(
z
)
=
3
C
U
u
∗
−
z
0
u
/
−
(
−
z
/
(7.10a)
)
(
L
)
−
1
/
3
,
L
)
−
1
/
3
(
z
2
)
−
(
z
1
)
=
3
C
(
−
F
/
u
−
z
1
/
−
(
−
z
2
/
(7.10b)
∗
where
C
U
=
1.1 (Kader and Yaglom, 1990; Zilitinkevich, 2006a).
Resolving (7.10a) allows determining
z
0
u
from measured
U
and
u
1.7 and
C
=
. Unfor-
∗
tunately
z
0
u
appears in this algorithm in the combination
z
0
u
/
L
. Because
L
is
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