Flow structures and kinetic-potential exchange in forced rotating stratified turbulence

We investigate the long-time evolution of flow structures and the kinetic-potential energy exchange in rotating stratified turbulence, which is of great significance in geophysical flows. Numerical simulations of forced three-dimensional homogeneous rotating stratified turbulence in transient state with different Froude numbers are performed. Numerous small vortices spread in the flow, besides a cyclone and an anticyclone that fill up the domain after a very long time. Cyclonic vortices, though being less numerous than anticyclonic vortices, grow faster, thus becoming comparable to the domain scale at an earlier time. When the strength of stratification is varied, we find that in the case with weak stratification, the intensity of global kinetic-potential energy exchange is nearly constant in earlier times, while it oscillates in time at later times. Moreover, for the simulation with weak stratification, the areas of intense kinetic-potential energy exchange tend to concentrate in segmented cylinders. In contrasts, when the strength of stratification is comparable to that of rotation, the areas of intense kinetic-potential energy exchange populate the flow as quadrupoles. For both simulations with stratification, the intense kinetic-potential energy exchange is found to be associated with the cyclonic structures. A possible relation between the sign of ωz and the spatial distribution of the density field θ is proposed, and the conditional average (∂θ/∂z|ωz) is found to be almost time-invariant throughout most of the domain.