  When a fluid system is subject to strong rotation, centrifugal fluid motion
is expected, i.e., denser (lighter) fluid moves outward (inward) from (toward)
the axis of rotation. Here we demonstrate, both experimentally and numerically,
the existence of an unexpected outward motion of warm and lighter vortices in
rotating turbulent convection. This anomalous vortex motion occurs under rapid
rotations when the centrifugal buoyancy is sufficiently strong to induce a
symmetry-breaking in the vorticity field, i.e., the vorticity of the cold
anticyclones overrides that of the warm cyclones. We show that through
hydrodynamic interactions the densely populated vortices can self-aggregate
into coherent clusters and exhibit collective motion in this flow regime.
Interestingly, the correlation of the vortex velocity fluctuations within a
cluster is scale-free, with the correlation length being about 30% of the
cluster length. Such long-range correlation leads to the collective outward
motion of cyclones. Our study provides new understanding of vortex dynamics
that are widely present in nature.
