Nikolaos Bakas (University of Ioannina, Greece)
"Symmetry breaking in quasi-geostrophic baroclinic turbulence by the emergence of coherent structures
We investigate the organization of turbulence in a quasi-geostrophic two-layer model in the limit of no mean imposed baroclinic shear, in which turbulence is sustained by spatially homogeneous random stirring. Direct numerical simulations of this model show that as the energy input rate of the forcing is increased the translational symmetry of the flow is broken. For forcing scales comparable to the deformation radius the horizontal symmetry is first broken by the emergence of barotropic non-zonal, coherent, westward propagating waves; while for larger energy input rates, barotropic zonal jets emerge which coexist with large-scale waves. For forcing scales smaller than the deformation radius, both the horizontal and the vertical translational symmetry is broken by baroclinic waves that emerge along with their barotropic counterparts; while for larger energy input rates zonation occurs only for the barotropic component of the flow and baroclinic zonal jets are found to be sustained only in the limit in which the forcing scale is far smaller than the deformation scale. We present here a theory called S3T that studies the statistical state dynamics of the flow. This theory enables us to study the stability of the turbulent flow and therefore predicts both the symmetry breaking as well as the structures that emerge. "