Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 112

In dependence of vertical motion, two zones of changes in the temperature field
are obvious (Fig. 5.39 c1-c3). Although the vertical velocity component w in run
HD30 is greater for downwelling and mostly for upwelling, the maximal effect of
the temperature within the model box is more dominant in case HD60, but discrep-
ancies in the global mean change between run HD30 and over the upper 30 m of
HD60 counts only

0.0024/+0.004 C for cooling/warming. The vertical position
of extrema occurs in both cases around the thermocline in 10-m depths for cooling
and in 14-m depths for warming. A global maximal change in temperature is

2.70/
+1.92 C for run HD60 and 2.36/+1.68 C for run HD30. In the case of HD30, the
effect on temperature in the vertical is more strongly located around the thermo-
cline due to a decrease of w -component with depths below 12 m. Due to smoother
vertical cells in HD30, the change of temperature is more uniform over the affected
areas than in case HD60, which leads to a smaller global mean over the whole ocean
depth for HD60, compared to HD30. However, a change in the temperature over the
vertical at positions P 1 and P 2 (Fig. 5.40c ) shows the little more dominant effect on
the temperature field by HD60. Temperatures at both positions are more strongly
correlated, with 0.99, than velocities

w -component. In the upwelling region occurs
the highest bias of 0.060 C, compared to 0.004 C for the downwelling position,
due to the fact that in case HD60, advection of cooler water, below 30-m depths,
cools the upper layers.

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Upshot
Summarizing, shallower water depths strengthen the wake in the u -velocity, and
hence a stronger dipole structure of surface elevation occurs. Therefore, we can
expect a stronger downwelling and also a stronger upwelling above the thermocline
in shallow waters. Here, the vertical positions of w -component extrema are inde-
pendent of the ocean depth but strongly depend on ocean stratification. Also, a
shallower water leads to stronger distinct vertical cells from top to bottom, while in
the case of deeper ocean, the formation of the vertical cells vary more in the
horizontal. Nevertheless, the ocean depth plays a secondary factor for the common
OWF impact on the ocean system. Like in the previous analysis, it becomes clear
that the distribution of hydrographic conditions and position of thermocline are
more significant for the OWF effect because at the thermocline the OWF induced
dynamical change effectively impacts the ocean system.

5.4 Evaluation of Modeled OWF Effect on the Ocean

The theoretical approach of using HAMSOM over an ocean box to determine the
effect of an OWF on the ocean s dynamic gives possible dynamical changes.

Although HAMSOM is a well physically proofed model, the here used restrictions
of a model box and its forcing lead to the question on how realistic the dimension of
arising phenomenon, treated in the last sections, is. Hence, a snapshot of conditions
around the offshore wind farm alpha ventus was taken owing to BSH

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s support,

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