Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 66

10 5 m/s; the maximum, upwelling, of the barotropic run is
34.29 % lower than the master run.
The effect of the barotropic run, compared to the baroclinic master run, is, under
barotropic conditions, stronger at the thermocline by around 3.0

run, having 1.1

10 5 m/s, which
is equivalent to a 45 % stronger effect for upwelling and downwelling by BTM,
Fig. 5.10 . Stronger vertical mixing over time in the barotropic case results in a
slightly faster compensation of the surface elevation. Thus run BTM shows lower
values after 1 day at surface.
The vertical velocity component of the barotropic run has its maxima in 27.00-m
depth with values of 5.0 10 5 up to 7.0 10 5 m/s (~6 m/d). Here, the vertical
cells around the OWF are more intensified with the depth than in the master run, but
their horizontal dimensions are restricted to 15 km, compared to the 30 km in the
master run along the S-N cross section through the OWF, Fig. 5.10 . The cells in
BTM are smoother and more symmetric than the ones in the master run, especially
along the W-E cross section through the OWF. Therefore, the positions of extrema
in the horizontal are not equal for both cases. At surface, the positions of the
extrema have discrepancies only of one grid box, so 3 km in x -direction, but with
depth, the positions of the positive/negative maximal change switches more to the
north/south in the barotropic mode, with difference to the master run of 3 km (one
grid box). Hence, under barotropic conditions, the extreme changes occur closer to
the OWF.
Finally, the physics behind the vertical motion can be identified as a barotropic
effect caused by changes in the surface elevation and not as an impulse of OWF
induced hydrographic changes.
Overall, the barotropic mode boosts maximal changes of the ocean system over
the whole ocean box by an average of 65 %; thus, the impact due to the baroclinic
mode counts 35 %.
The start of upwelling and downwelling at all is independent of hydrographic
OWF changes, but differences in the simulation of BTM and BCM link to addi-
tional processes triggering the dimension and magnitude of the OWF effect on
ocean dynamics.
Such processes are supposed to be mainly vertical transports due to diffusion and
advection of temperature and salinity, as well as the exchange of momentum, which
in turn influences diffusivities.

5.2.2 Analysis of Vertical and Horizontal Exchanges

Reflection of the OWF effect on the ocean under barotropic conditions yields to the
result of vertical motion being a requirement of mass redisturbance based on wind
wake and reduced surface flow. But besides the barotropic factor, additional
processes have to be considered to describe the final phenomenon on the ocean
impacted by the OWF.