Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 72

a b c

OWFr: temperature [ ° C], src54 OWFr: temperature [ ° C], src56 OWFr−REFr: temperature [ ° C], src(54 −5 6)

0 0 0

1 5.00 1 5.00 0.010

max: 12.00 max: 12.00 max: 0.04

min: 7.00 min: 7.00 min: −0.17 0 .008

1 4.00 1 4.00

10 10 10

0 .006

1 3.00 1 3.00

20 20 20 0 .004

1 2.00 1 2.00

0 .002

30 30 30

1 1.00 1 1.00 0 .000

− 0.002

1 0.00 1 0.00

40 40 40

− 0.004

9 .00 9 .00

− 0.006

50 50 50

8 .00 8 .00

− 0.008

S N S N

S N

7.00 7.00 −0.010

60 60 60

−90 −60 −30 0 30 60 90 −90 −60 −30 0 30 60 90 −90 −60 −30 0 30 60 90

y (km) y (km) y (km)

Fig. 5.14 Impact of the vertical diffusion (run src54: neglecting vertical advection) on the (a)
OWFr temperature stratification, compared to (b) the sensitivity run without advection and
diffusion (src56 after 1 day of OWF operation; the difference is pictured in (c). The diffusion
leads to a diffusive transition at the thermocline but without a sharper thermocline. The heat
transport is supported by diffusion within the OWF. Sensitivity run src54, in comparison with
src56, depicts the single effect of vertical diffusion. The dashed horizontal line marks the depth of
the thermocline, the dashed-dotted lines mark the OWF area, and the solid lines accent the effect
dimension

For this reason, the vertical advection dominates the TS effect based on the
velocity component w . But with time, the temperature/density gradient around the
thermocline within the up- and downwelling cells become weaker due to intensified
vertical advection, which leads to reduced vertical velocities in the normal run
(Fig. 5.11 ). Without vertical TS advection, the up- and downwelling cells have
intensified magnitudes of extrema, which are in average three times stronger than in
the case of the normal simulation.
Figure 5.15 illustrates the single impact of the vertical TS diffusion and the
vertical TS advection on the vertical velocity component w . As mentioned, the
vertical advection reduces up- and downwelling by an average of 64.38 %, while
diffusion only supports the vertical motion by around 1.21 % in relation to src56
(no vertical TS advection and diffusion).
Summarizing, the OWF effect on the hydrography based on vertical advection
and diffusion acts by the same means but a difference in the velocity field, mostly
contradictory.
The last vertical exchange mode here, simulation run src51 , considers
HAMSOM vertical eddy viscosity coefficient A vc and so the vertical exchange of
momentum .
Regarding hydrography, coefficient A vc increases the OWF effect by 10.94 % for
the negative effect and by 17.51 % for the positive effect, which means an average
impact of 14.23 % (Fig. 5.11 ). The vertical velocity component w is greater in
the sensitivity run than in the normal run, exactly by 49.45 %, as well as the
v -component with a 77.03 % greater increase and the u -component with a wake
increase of 28.25 % (Fig. 5.11 ). Generally, A vc supports changes in hydrographic
fields due to stronger vertical motion and triggers the dimension of the wake in the
velocity field. These results here also strengthen the thesis of the vertical motion
having its origin in changed barotropic conditions. Minimizing the vertical eddy
viscosity, coefficient A vc, almost neglects the vertical exchange of momentum,