Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 118

latitude of alpha ventus. West and east of the wind farm, local extreme of

cooler water were observed influencing the surface at both ends of that section. A
zone of around 7.90 C dominates down to 10-m depth (Fig. 5.44 ).
These measured results can be reasonably well reproduced by the HAMSOM
simulations. Despite divergences between model and reality, the model results after
3 days of simulation are used for comparison. This time step is based on the fact that
on May 10-12, similar wind conditions were discovered, so till the CTD measure-
ments, the ocean system had around 2.5-3 days to react on the OWF influence
under nearly constant wind conditions.
Simulated temperature distributions within a distance of 6 km to the wind farm
are displayed in Fig. 5.45 along each section (west, north, east, south) through the
whole model area. While measurements show a clear temperature transition from
surface to bottom, the model results are blocked by a too strong thermocline as a
separation frontier, which leads to nearly two main ocean layers, although the
starting TS profile is based on the CTD data. A layer of mostly 7.65 C exists
above 12 m, a dominant layer of 7 C below 20 m. The discrepancies are a result of
tidal mixing. In the here used model simulation of the ocean, box tides are
neglected. Tides would support vertical mixing in the lower layers due to bottom
friction. But still a strong agreement of temperature distribution between model and
measurements can be identified between 10 and 22 m, especially around the OWF
area. The realistically used distance to the OWF of 6 km shows a temperature
distribution comparable with measurements, although the 3-km horizontal resolu-
tion of model is quite coarse. The model also provides little details depending on
warmer zones within the wind farm sector. These zones have temperatures of
7.73 C, which means a difference of 0.1 C, compared to the not OWF-affected
areas (between

bubbles

' '

45 and 90 km and 45 and 90 km), and are of the same dimension

as that of the CTD.
Especially in the northern section (Fig. 5.45b ), the model simulates the warmer
extrema easterly displaced from wind farm sector, which was also measured. That
extremum can be identified in the model by a 6-km distance to OWF, but at 18-km
distance, the structure is closer to measure (Fig. 5.44b , north section).
In the case of the south section (Fig 5.45c ), the maximum with depth is shifted to
the front of the wind farm zone, while CTD data show a maximum within the wind
farm sector. The overall maximum occurred close to surface, east of the OWF zone,
which can also be found in simulations. The wave formation in sections with peaks
and troughs is overestimated along the sections by the model, while the structure
gives a comprehensive agreement.
The west section (Fig. 5.45a ) shows a wave formation with one minimum and
two peaks, whereby the maximum peak in the south is wider and stronger then the
northern one. The model results in a horizontal width of the southern peak of 15-
20 km; the horizontal dimension by measurements leads to around 5 km.
At the north section (Fig. 5.45b ), one trough is easily observable, followed by a
rudiment of a long persistent peak, between 20 and 75 km, where colder water is
upwelling. Over that peak, at and close to the surface, the mentioned warmer
extreme is located. Here, the model gives a horizontal dimension of the trough