Bifurcation of drift wave turbulence trapping by zonal flows near density limit

Abstract We investigate drift wave—zonal flow interactions near the density limit and demonstrate transitions of turbulence trapping states. Nonlinear simulations of the modified Hasegawa–Wakatani model reveal two robust types of turbulence energy localization: valley-trapping near zonal flow troughs at small adiabaticity (hydrodynamic regime) and hill-trapping near crests at large adiabaticity (adiabatic regime). Around the transition, turbulence exhibits bistability, dynamically switching between valley- and hill-trapping, and also shows indications of multi-stable behavior depending on the adiabaticity. The Lagrangian auto-correlation time of turbulence changes markedly across the bifurcation between the trapping states, indicating that turbulent vortices become long-lived in the adiabatic limit and short-lived in the hydrodynamic limit. Eigenmode analysis reproduces these patterns and shows that the selection is governed by the relative magnitude of the drift wave phase velocity and the zonal flow amplitude. These findings provide a simple selection rule for turbulence energy localization and offer new insight into drift wave—zonal flow dynamics in regimes relevant to the density limit.