Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 61

Additionally, topographic irregularities can be excluded as a mechanism for
incipient vertical velocities because of using a flat ground in simulations. But
what exactly triggers changes in the vertical?
On the basis of the OWF induced wind change and related changes of surface
elevation and considering time analysis, we can assume that vertical motion is
driven by these horizontal changes at the surface, which affects the barotropic
pressure field. To review, the importance of stratification under barotropic
conditions is presented in Sect. 5.2.1 .
ii) An OWF results in an increase and decrease of hydrographic values
(around the thermocline).
The main processes supporting changes in the hydrography on short time
scales are diffusion and advection of temperature, respectively salinity. The
question is now whether horizontal gradients dominantly impact the OWF effect
on hydrography or whether vertical advection mainly causes such changes.
Hence, the impact factor of diffusion and advection and the exchange of
momentum in the vertical and in the horizontal are analyzed in Sect. 5.2.2 .

Sensitivity Analysis
On these grounds, the physical analysis comprises various sensitivity runs, which
are listed in Table 5.1 . All runs underlie the main setup of TOS-01 (Box-Model)
with a 12-turbine wind farm over grid cells in the middle of the model domain and a
prescribed geostrophic wind of ug

¼ 8 m/s. To analyze the physics of the emerging

phenomenon, HAMSOM s equation within the source code (src) was prepared so

far to receive the impact of different physical processes.
The simulation name for simulation under barotropic conditions is T012ug08
TS01HD60F01_BTM (BTM). The corresponding effect-reference simulation is
T012ug08 TS01HD60F01 (BC). BC is the master simulation presented in the
previous chapter considering the full HAMSOM code with 3D baroclinic primitive
equations and an undisturbed diffusion and advection scheme.
Simulations considering vertical and horizontal exchanges are designated as
T012ug08 TS02HD60F01_src* (

'

stands for modification listed in Table 5.1 )
and are explained in context. The corresponding effect-reference simulation is
T012ug08 TS02HD60F01 . That effect-reference run differs from master run BC
by temperature and salinity stratification. Here, temperature and salinity start field
TS02 (Fig. 3.5 ) is used. That TS stratification consists only of two layers. The
reason for another TS description is the fact that the vertical exchange processes
affect layers above and around the thermocline. Those layers can become indistinct
due to the fact that such processes leads to a vertical mixing and so to a change on
the conditions of the TS stratification. Hence, the impact of each process at the
thermocline is not clearly identifiable. Therefore, the temperature and salinity field
was simplified to two main layers, which allows a distinctive detection and analyses
of the influence of exchange processes via and around the thermocline.
All setups listed in Table 5.1 were simulated in the case of OWF and in the case
of no OWF to picture the sole effect after 1 day of the simulation.

*

' '