Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 90

The effect of the forcing of 16 m/s wind speed ends in a temperature increase at
the surface of 0.88 C at position P 0 and a decrease of 0.23 C at position P 1

(Fig. 5.24b ). Maximal temperature decrease at P 1 due to forcing of UG8 is

0.07 C. The temperatures
are higher than in the reference run at the downwelling area. This forcing of UG16
has the strongest effect of 0.88 C increase, compared to 0.19/0.03 C for UG8/5.
Although the vertical velocity component w at the thermocline is more intense for
UG16 forcing than for UG8, the temperature extrema at the thermocline are
maximal in the case of forcing UG8. This underlines the previous analysis that
vertical mixing is not singly driven by vertical velocity component w but also
driven by additional exchange processes. Additionally, a stronger wind forcing
quickens processes; that is also a reason the for weaker temperature effects by
UG16 because the upper layers are quickly mixed, which results in one abundant
upper layer. In turn, the thermocline is pushed into deeper depths.
The shift of the thermocline

0.20 C, and for UG5 forcing, only

slightly weaker,

s position is pictured in Fig. 5.26 . The change from
UG5 to UG16 forcing at thermocline is clearly seen. Excursion increases with wind
speed forcing from 2 (UG5) over 4 (UG8) up to 8 (UG16) meters. In the case of
UG16, the thermocline is switched beginning from 12 to 20-m depths. Correlations
of temperatures with forcing UG16 are around 0.15 higher than for the vertical
velocity component w at the thermocline. Correlations between UG5 and UG8 are
high with 0.94 at the surface and 0.99 at the thermocline.
The effect on salinity forced by the three different wind speeds has a weak
variability in comparison due to goof correlations of around 0.9 at the surface,
Fig. 5.24c, f . Differences of the effect mostly occur in the downwelling region at
positions P 0 and P + 1, especially in the thermocline depth. However, the OWF
effect on salinity increases with wind speed forcing.

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Upshot
Summarizing, the effect of an OWF on the ocean, considering different wind
speeds, does not impact strongly on horizontal dimensions. Dipole structure and
up- and downwelling cells have similar dimension because they depend more on the
OWF arrangement. Positions of maxima and minima vary due to differences in the
horizontal velocity field, which depends on the wake intensity. Here, a trend of
extrema moving towards the OWF grid boxes with higher wind speed forcing was
detected. That behavior is based on the fact that the maximum decrease in wind is
placed close to the OWF and so the effects here are stronger on the ocean. The cells
of vertical motion become more intense with higher wind speeds and the cells

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extrema occur in deeper layers, which more strongly affects vertical layers again.
Stronger OWF induced wind wakes support the vertical mixing and lead to a
stronger exchange of temperature via the thermocline. Hence, the depth of the
thermocline increases with wake intensity. The variation of the OWF effect due to
different wake intensity in temperature is in order of tenths of a degree, even for the
horizontal velocity component u , and variations of the surface elevations count
several millimeters; for the vertical motion, hundredths of mm/s.