Anisotropic Dispersion in Rotating Fluids: a Laboratory Model of Large Scale Flows

The variation of the Coriolis parameter with the latitude (beta effect) strongly affects the turbulent inverse cascade. In fact, when this effect holds, energy is preferentially transferred towards zonal modes. The consequent emergence of flow structures along the zonal direction can strongly impact transport and modify both zonal and meridional scalar diffusion. We performed a detailed analysis of Lagrangian tracers dispersion on rotating flows simulated in laboratory. A relatively wide range of the zonostrophy index, a parameter used to characterize flow regimes in the presence of a beta effect, is investigated. The degree of anisotropy and the characteristic scales of the flow have been estimated by means of the zonal and radial components of the Finite Scale Lyapunov Exponents. Moreover, we introduced the Lagrangian Anisotropy Index is in order to describe the onset of anisotropy and to verify the agreement with the theoretical predictions.