Drift wave turbulence and zonal flow development measured by information rate

Generation of zonal flows (ZF) by drift wave turbulence in numerical simulations based on the modified Hasegawa–Wakatani model is investigated using probability density functions (PDFs) and information rate which quantifies the number of statistically distinct states generated per unit time in the non-equilibrium system. The evolution of time-dependent PDFs of the electrostatic potential, density, and vorticity is quantified by the information rate and is directly compared. We examine this evolution for the system dominated by the isotropic turbulence as well as the system dominated by anisotropic ZF. Impact of ZF on turbulence is captured by a narrower PDF of fluctuating velocity perpendicular to ZF. The information rates of the turbulent potential and density, which are coupled via fast electron parallel transport, are similar confirming the strong coupling between these quantities during their evolution. In contrast, zonal parts of these fields exhibit a distinct information rate evolution. This suggests that the zonal density structure may develop independently of ZF, consistent with recent finding in gyrokinetic simulations.