Geoscience Reference
In-Depth Information
Chapter 5
Offshore Winds
This Chapter deals with the marine atmospheric boundary (MABL). The special
features of wind and turbulence profiles over the sea are very important, since an
increasingly larger fraction of wind energy will be generated at offshore wind
parks in the future. Although the sea surface is perfectly flat, these wind features
partly differ from profiles over homogeneous land presented in
Chap. 3
. Unless
otherwise stated, the examples for the state of the MABL presented in this Chapter
are based on Türk (
2008
). Türk (
2008
)'s analysis was based on data from the
100 m tower FINO1 in the German Bight. This offshore tower, which is about
45 km away from the German coast, provides wind information from cup
anemometers in heights between 30 and 100 m with a vertical resolution of 10 m.
Sonics data are available at 40, 60 and 80 m from this tower. So, some of the
presented features may be specific for the German Bight at the site of FINO1.
Nevertheless, they can serve as an indication for typical behaviour in the MABL in
contrast to an onshore boundary layer. There are more measurement towers near
offshore wind parks, e.g., the 62 and 70 m masts at Horns Rev off the Danish west
coast or the 116 m mast ''NoordzeeWind'' off the Dutch coast near Egmond aan
Zee. In Germany there are the towers FINO2 in the Baltic and FINO3 in the
German Bight off the island of Sylt as well. These latter two towers are quite
similar to the tower FINO1.
Section 5.1
explains the special features of the sea surface.
Section 5.2
then
presents mean vertical profiles before
Sect. 5.3
deals with extreme wind speeds and
Sect. 5.4
with turbulence parameters in the MABL. Weibull parameters charac-
terizing the marine boundary layer are discussed in
Sect. 5.5
. In coastal areas, which
are the subject of
Sect. 5.6
, internal boundary layers (see
Sect. 3.5
) can form which
exhibit marine boundary characteristics in the internal boundary layer and onshore
boundary layer characteristics in the layer above. Especially for stable thermal
stratification when warmer air is advected over colder water, such internal boundary
layers can persist for long distances of several tens of kilometres.
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