  We apply the proper orthogonal decomposition (POD) to large eddy simulation
data of a wind turbine wake in a turbulent atmospheric boundary layer. The
turbine is modeled as an actuator disk. Our analyis mainly focuses on the
question whether POD could be a useful tool to develop a simplified dynamic
wake model. The extracted POD modes are used to obtain approximate descriptions
of the velocity field. To assess the quality of these POD reconstructions, we
define simple measures which are believed to be relevant for a sequential
turbine in the wake such as the energy flux through a disk in the wake. It is
shown that only a few modes are necessary to capture basic dynamical aspects of
these measures even though only a small part of the turbulent kinetic energy is
restored. Furthermore, we show that the importance of the individual modes
depends on the measure chosen. Therefore, the optimal choice of modes for a
possible model could in principle depend on the application of interest. We
additionally present a possible interpretation of the POD modes relating them
to specific properties of the wake. For example the first mode is related to
the horizontal large scale movement. Besides yielding a deeper understanding,
this also enables us to view our results in comparison to existing dynamic wake
models.
