Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 89

a b

Fig. 5.25 Position of (a) extremes of variable w in 12-m depth and (b) extremes of w in the
vertical along the y -section based on different wind speed forcing. In the depth of the thermocline,
that is, 12 m, the position of positive extreme is comparable between different wind speeds, while
the negative extreme swifts into the OWF with increased wind forcing. Negative maxima are
slightly higher than the positive ones and are positioned in deeper layers

Figure 5.25 illustrates that maximal upwelling velocity at 12 m nearly fits the
same position; only the run based on UG16 forcing has its maximal upwelling one
grid box (~3 km) easterly of the result based on UG5 and UG8 forcing. Regarding
maximal downwelling, the effect at 12 m of run with UG16 forcing has its extreme
within the OWF, while extremes of UG5 and UG8 forced runs are placed more
northeasterly. It seems that with increased wind forcing, the position of
downwelling switches more towards midpoint of the OWF, but only based on
three cases, it is not possible to make a statistical fundamental statement. Never-
theless, it can be underlined that the stronger the wind speed forcing is the stronger
the vertical motion will be, especially in deeper layers. The strongest upwelling at
2 m, at position P 1, is identified by simulation with forcing UG8 (Fig. 5.24a ).

This does not enervate the termed relation because at the surface, extrema are also
affected by horizontal flow, and so positions of extrema are not defined at the same
location, which also causes a bad correlation. That is why here run, forced with
UG16, gives only the lowest upwelling. However, maxima/minima of vertical
velocity w is 1.04 10 5 / 10 5 m/s (for forcing UG5), 1.54 10 5 / 0.77

10 5 m/s (for UG8), and 0.0246/ 1.10 0.0194 mm/s (for UG16) over the

whole area and within first 2-m depths.
Further, an increase in wind speed forcing results in a swift of positions of
maximal and minimal vertical velocities into higher depths. Figure 5.25 clarifies the
dependence between induced wind speed, depth, and extrema. Additionally, it can
be said that the upwelling effect is a little bit more dominant than the downwelling
effect and that the discrepancy between these two motions increases with wind
speed.