Eulerian space-time correlation of strong magnetohydrodynamic turbulence

The Eulerian space-time correlation of strong magnetohydrodynamic (MHD) turbulence in strongly magnetized plasmas is investigated by means of direct numerical simulations of reduced MHD turbulence and phenomenological modeling. Two important results follow from the simulations: (1) Counterpropagating Alfvénic fluctuations at each scale decorrelate in time at the same rate in both balanced and imbalanced turbulence and (2) the scaling with wave number of the decorrelation rate is consistent with pure hydrodynamic sweeping of small-scale structures by the fluctuating velocity of the energy-containing scales. An explanation of the simulation results is proposed in the context of a recent phenomenological MHD model introduced by Bourouaine and Perez [Astrophys. J., Lett. 879, L16 (2019)2041-821310.3847/2041-8213/ab288a] when restricted to the strong turbulence regime. The model predicts that the two-time power spectrum exhibits universal, self-similar behavior that is solely determined by the probability distribution function of random velocities in the energy-containing range. Understanding the scale-dependent temporal decorrelation of MHD turbulence as well as its possible universal properties is essential in the analysis and interpretation of spacecraft observations when the Taylor's hypothesis may not be valid, which could well be the case in near-Sun regions to be explored by the recently launched Parker Solar Probe (PSP).