Zonostrophic Turbulence in Two-layer Quasi-geotrophic Model

Abstract:

Zonostrophic turbulence was discovered in the one-layer shallow water model forced by random stirring and has since been related to Jovian atmosphere for the appearance of very strong and steady zonal jets. This study shows that such zonostrophic turbulence can also exist in a two-layer QG model driven by baroclinic instability. The kinetic energy spectrum shows a clear transition from the inertial inverse cascade regime with energy spectrum slope -5/3 at small scales to the zonostrophic regime with slope -5 at the largest scales. The turbulent regime is characterized by two non-dimensional numbers criticality and non-dimensional surface friction. The zonostrophic regime is reached and is most clear in the corner of low friction and low criticality. A new dependency of eddy diffusivity on surface friction is founded when surface friction is low enough, that eddy diffusivity decreases with surface friction regardless of criticality. The zonal jets are found to be strong mixing barriers, especially in the upper layer, and therefore potential vorticity (PV) and tracer staircases are formed. Time-space spectrum shows that the strong zonal jet traps waves within the critical latitudes so that the waves do not break. The longest waves are trapped as edge waves, and the shorter waves are trapped by Rossby wave reflection. Both are a result of the PV gradient created by the jet core.