Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 69

In the following, these three options were applied to HAMSOM in different
combinations. In the first sensitivity run, src60 , all three options are set to mini-
mum/zero. In a second step, in the sensitivity run src51 , only A vc is set to minimum;
vertical advection and diffusion are treated as normal. In the sensitivity run src52 ,
consequences of vertical diffusion are carved out by setting A dc to zero; in src54 ,
TSVA is neglected, and in src56 , TSVA and vertical TS diffusion are set to zero.
For analysis, extrema of variables along the N-S cross section after 1 day of
simulation are used as representative data set. The maximal effect on the ocean due
to an operating OWF is illustrated, separated into positive effect, means an increase
of variable compared to reference run without wind turbines, and opposite effect—
the negative effect. Based on the asymmetric surface elevation, the maxima and
minima are not symmetric. An overview of changes in the OWF effect on the ocean
by vertical exchange processes is pictured in Fig. 5.11 .
The sensitivity run, src60, preventing vertical exchange of momentum, vertical
advection, and diffusion of temperature and salinity (TS), shows a weaker effect in
surface elevation due to a stronger impact on velocities but does not show an effect
in the hydrographic stratification, and the thermocline does not form an excursion
around the OWF. Higher velocities are based on a constant hydrographic field
unpersuaded by additional changes in the density and so the pressure field.
Figure 5.12 illustrates the difference in temperature along the cross section from
S to N through the OWF for the normal simulation src50 and the run src60 without
vertical exchange processes. Runs without vertical TS exchange processes have a
warmer upper layer because the exchange of heat is forbidden, while in the normal
run, the upper layers become cooler due to the exchange via the thermocline. The
other way around is also explained by the exchange via the thermocline, which ends
in warmer layers close below the thermocline.
Ignoring vertical diffusion, src52 , the vertical exchange of temperature and
salinity (TS) is connected with vertical advection. Results show that the negligence
of the diffusion increases the effect on hydrographic conditions, compared to the
normal run (Fig. 5.11 ). On one hand, that leads to the assumption that vertical
advection plays an important role for the exclusion of the thermocline, and on the
other hand, the vertical diffusion seems to break the development of the hydro-
graphic effect. Having a look at the distribution of the temperature in comparison
with the normal run in Fig. 5.13 , less obvious changes are identifiable. The
examination of the OWF effect illustrates that a cooling occurs at and above the
thermocline southerly of the OWF and the warming occurs only below the ther-
mocline northerly of OWF. The change is sharp, in the form of small arrows,

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linked to the direction of the vertical velocity component w , it is stronger limited in
the vertical than in the normal run. So the diffusion supports reduction of the
gradients over the vertical layers. Therefore, in the normal run, the effect has a
more oval form blurred over more layers. Hence, differences between run src52
(no vertical diffusion) and the normal run are located at thermocline

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30 km
around the OWF along the S-N section. Here, we can say that the diffusion does
not cause the exclusion of the thermocline but triggers the form and therewith the
extrema of the OWF effect on temperature.