  One of the most prominent dynamical features of turbulent, rapidly-rotating
convection is the formation of large-scale coherent structures, driven by
Reynolds stresses resulting from the small-scale convective flows. In spherical
geometry, such structures consist of intense zonal flows that are invariant
along the rotation axis. In planar geometry, long-lived, depth-invariant
structures also form at large scales, but, in the absence of horizontal
anisotropy, they consist of vortices that grow to the domain size. In this
work, through the introduction of horizontal anisotropy into a numerical model
of planar rotating convection by the adoption of unequal horizontal box sizes
(i.e. $L_x \le L_y$, where the $xy$-plane is horizontal), we investigate
whether unidirectional flows and large-scale vortices can coexist. We find that
only a small degree of anisotropy is required to bring about a transition from
dynamics dominated by persistent large-scale vortices to dynamics dominated by
persistent unidirectional flows parallel to the shortest horizontal direction.
When the anisotropy is sufficiently large, the unidirectional flow consists of
multiple jets, generated on a timescale smaller than a global viscous
timescale, thus signifying that the upscale energy transfer does not
spontaneously feed the largest available mode in the system. That said, the
multiple jets merge on much longer timescales. Large-scale vortices of size
comparable with $L_x$ systematically form in the flanks of the jets and can be
persistent or intermittent. This indicates that large-scale vortices, either
coexisting with jets or not, are a robust dynamical feature of planar rotating
convection.
