Abstract
In this work the scale-dependent temporal decorrelation of incompressible MHD turbulence is investigated by means of high-resolution numerical simulations and phenomenological modeling. The simulations show that counterpropagating Alfv\'enic fluctuations at each scale decorrelate at the same rate in both balanced and imbalanced turbulence, and consistent with random advection of small-scale eddies by the velocity of the energy containing scales.
Highlights
Since the first observations by Belcher and Davis [1] that noncompressive Alfvén-like fluctuations of velocity and magnetic field dominate the solar wind, incompressible magnetohydrodynamics (MHD) [2] has been often invoked to describe the observed Kolmogorov-like power spectrum of low-frequency fluctuations of the solar wind plasma; for extensive reviews, see Refs. [3,4,5]
We show that when the BP19 model is applied in strong MHD turbulence, the Eulerian space-time correlation is solely dominated by HD sweeping, which we confirm in numerical simulations of homogeneous MHD turbulence
The modeled scale-dependent time correlations for strong MHD turbulence given in Eq (15) have the following important features: (1) temporal decorrelation is solely due to the random sweeping by the large-scale flow, (2) the decorrelation rates are the same for both Elsasser fluctuations z±, whether the turbulence is balanced or imbalanced, and scale linearly with k⊥ as γ ± = k⊥u0/2 in the inertial range, and (3) they exhibit universal, self-similar behavior as they can all be written in terms of the characteristic function associated with the random distribution of large-scale velocities with a simple rescaling of the wavenumber k⊥
Summary
Since the first observations by Belcher and Davis [1] that noncompressive Alfvén-like fluctuations of velocity and magnetic field dominate the solar wind, incompressible magnetohydrodynamics (MHD) [2] has been often invoked to describe the observed Kolmogorov-like power spectrum of low-frequency fluctuations of the solar wind plasma; for extensive reviews, see Refs. [3,4,5]. Bourouaine and Perez [23] measured the Eulerian correlation of Elsasser fields in highly imbalanced, reflection-driven MHD turbulence simulations with high space-time resolution and found that the decorrelation of both fields is consistent with sweeping by large-scale fluctuations at a common speed that is comparable to the root mean squared (rms) value of the fluctuating velocity, suggesting that the sweeping is hydrodynamic in nature. It is worth noting that the RMHD model is commonly invoked to describe the dominant nonlinear interactions and resulting turbulence of noncompressive Alfvén-like fluctuations, which account for most of the energy in the solar wind It has been shown, from gyrokinetics [40] and from comparisons with MHD simulations [14,41], that RMHD accurately describes the essential nonlinear interactions responsible for the turbulence cascade of noncompressive Alfvénic fluctuations. The correlation in Eq (2) can be expressed in terms of its spatial Fourier transform
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
