Geoscience Reference
In-Depth Information
Fig. 4.16
Mean monthly vertical profiles of turbulence intensity over a town (Hannover, Germany)
for April 2003 from SODAR measurements (
bold full line
: all data,
bold dashed line
: nocturnal
data,
bold dash-dotted line
: daytime data,
thin lines
: data from the four wind direction sectors)
it cannot be described by the stationary
eq. (2.27)
. The three additional free param-
eters in the second and third equation of
(2.27)
in comparison to the first equation
are tuned in order to improve the agreement to the measured wind profiles. The first
three parameters have been kept. For the approximation shown, the Prandtl-layer
height,
z
p
is set to 30 m at night. Below this height both profile laws (first equation
and all three equations of
(2.27)
give identical values. The roughness length,
z
0
is
set to 1 m, the Monin-Obukhov length,
L
∗
is chosen in order to represent the profile
below
z
p
properly, and the geostrophic wind speed is set equal to the wind speed at
500 m. The friction velocity,
u
must be iterated as described after
eq. (2.16)
.From
this iteration the friction velocity at night-time is
u
∗
0.18 m s
−
1
. The turning
∗
=
angle of the wind direction is around 32
◦
at night.
4.3.1.2 Optical Techniques
The aforementioned acoustic sounding has a limited height range, usually less than
one kilometre. Wind LIDARs are an alternative, if data from larger ranges should
be obtained. One of the available LIDARs is the scanning High-Resolution Doppler
LIDAR (HRDL) recently developed at the Earth System Research Laboratory of the
U.S. National Oceanic and Atmospheric Administration (NOAA/ESRL; formerly
Environmental Technology Laboratory). HRDL operates at 2.02
μ
m in the infrared
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