  Synthetic-aperture radar images and mesoscale model results show that
wind-farm wakes behave very differently than single-turbine wakes, e.g. with
wakes that seemingly narrow and do not disperse over long distances. In the
current work, we aim at better understanding the physical mechanisms that
govern wind-farm wake behaviour and recovery. Hence, we study the wake
properties of a 1.6 GW wind-farm operating in conventionally neutral boundary
layers with four capping-inversion heights, i.e. 203, 319, 507 and 1001 m. In
shallow boundary layers, we find strong flow decelerations which reduce the
Coriolis force magnitude, leading to an anticlockwise wake deflection in the
Northern Hemisphere. In deep boundary layers, the vertical turbulent
entrainment of momentum adds clockwise-turning flow from aloft into the wake
region, leading to a faster recovery rate and a clockwise wake deflection. To
estimate the wake properties, we develop a simple model that fits the velocity
magnitude profiles along the spanwise direction. Based on this, we observe that
the wake narrows along the downstream direction in all cases. Further, a
detailed momentum budget analysis shows that the wake is mostly replenished by
turbulent vertical entrainment in deep boundary layers. In shallow boundary
layers, the capping inversion limits vertical motions and wakes are mostly
replenished by mean flow entrainment in the spanwise direction. Moreover, in
these cases, we observe a counterclockwise flow rotation near the left edge of
the wake, which persists at each location downstream of the farm, giving rise
to local strong streamwise velocity gradients along the spanwise direction.
