Séminaire
Geostrophic turbulence is a key paradigm in the current understanding of the large-scale planetary circulations. It implies that a flow is turbulent, rotating, stably stratified and in near-geostrophic balance. When a small-scale forcing is present, geostrophic turbulence features an inverse energy cascade.When the meridional variation of the Coriolis parameter (or a beta-effect) is included, the horizontal flow symmetry breaks down giving rise to the emergence of jet flows. The presence of a large-scale drag ensures that the flow attains a steady state. Dependent on the governing parameters, four steady state flow regimes are possible two of which are considered in this study. In one of these regimes, a flow is dominated by the drag while in the other one, the recently discovered regime of zonostrophic turbulence, a flow becomes strongly anisotropic and features slowly evolving systems of alternating zonal jets. Zonostrophic turbulence is distinguished by anisotropic inverse energy cascade and emergence of a new class of nonlinear waves known as zonons. In addition, meridional scalar diffusion is strongly modified in this regime. An overview of various regimes of turbulence with a beta-effect will be provided. Main characteristics of friction-dominated and zonostrophic regimes will be elaborated along with the physical nature of the zonons. Meridional diffusion processes in different regimes will be discussed and connections of these results to oceanic observations will be underscored.
Riwal Plougonven
Laboratoire de Météorologie Dynamique, Ecole Normale Supérieure, Paris 75005
(01 44 32 27 31)