Evolution of turbulence in the expanding solar wind, a numerical study

Abstract

We study the evolution of turbulence in the solar wind by solving numerically the full 3D magneto-hydrodynamic (MHD) equations embedded in a radial mean wind. The corresponding equations (expanding box model or EBM) have been considered earlier but never integrated in 3D simulations. Here, we follow the development of turbulence from 0.2 AU up to about 1.5 AU. Starting with isotropic spectra scaling as $k^{-1}$, we observe a steepening toward a $k^{-5/3}$ scaling in the middle of the wavenumber range and formation of spectral anisotropies. The advection of a plasma volume by the expanding solar wind causes a non-trivial stretching of the volume in directions transverse to radial and the selective decay of the components of velocity and magnetic fluctuations. These two effects combine to yield the following results. (i) Spectral anisotropy: gyrotropy is broken, and the radial wavevectors have most of the power. (ii) Coherent structures: radial streams emerge that resemble the observed microjets. (iii) Energy spectra per component: they show an ordering in good agreement with the one observed in the solar wind at 1 AU. The latter point includes a global dominance of the magnetic energy over kinetic energy in the inertial and $f^{-1}$ range and a dominance of the perpendicular-to-the-radial components over the radial components in the inertial range. We conclude that many of the above properties are the result of evolution during transport in the heliosphere, and not just the remnant of the initial turbulence close to the Sun.

arXiv comment14 pages, 12 figures, accepted in ApJ

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Cited by in corpus (29)

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• High-resolution hybrid simulations of kinetic plasma turbulence at proton scales
• Three-dimensional simulation of the fast solar wind driven by compressible magnetohydrodynamic turbulence
• Solar wind turbulent cascade from MHD to sub-ion scales: large-size 3D hybrid particle-in-cell simulations
• Enhanced Energy Transfer Rate in Solar Wind Turbulence Observed near the Sun from Parker Solar Probe
• Anisotropy of third-order structure functions in MHD turbulence
• Solar wind turbulence from MHD to sub-ion scales: high-resolution hybrid simulations
• Alfvénic versus non-Alfvénic turbulence in the inner heliosphere as observed by Parker Solar Probe
• Plasma turbulence and kinetic instabilities at ion scales in the expanding solar wind
• Imprints of expansion onto the local anisotropy of solar wind turbulence
• Parametric decay of parallel and oblique Alfven waves in the expanding solar wind
• Evolving waves and turbulence in the outer corona and inner heliosphere: the accelerating expanding box
• Turbulent Heating between 0.2 and 1 au: A Numerical Study
• Beyond the Maltese cross: geometry of turbulence between 0.2 and 1 AU
• 3D Anisotropy of Solar Wind Turbulence, Tubes, or Ribbons?
• Mirror instability in the turbulent solar wind
• Turbulence vs. fire hose instabilities: 3-D hybrid expanding box simulations
• Reconnection-Driven Magnetohydrodynamic Turbulence in a Simulated Coronal-Hole Jet
• Helios 2 observations of solar wind turbulence decay in the inner heliosphere
• Alfvén-dynamo balance and magnetic excess in MHD turbulence
• Spectral Anisotropy of Elsässer Variables in Two Dimensional Wave-vector Space as Observed in the Fast Solar Wind Turbulence
• Conditions for proton temperature anisotropy to drive instabilities in the solar wind
• Three-dimensional local anisotropy of velocity fluctuations in the solar wind
• Influence of the heliospheric current sheet on the evolution of solar wind turbulence
• Comparing turbulent cascades and heating vs spectral anisotropy in solar wind via direct simulations
• Sub-structure formation in starless cores
• Evolution of MHD turbulence in the expanding solar wind: residual energy and intermittency
• The effects of expansion and turbulence on the interplanetary evolution of a magnetic cloud
• Simulations of Energetic Particles Interacting with Nonlinear Anisotropic Dynamical Turbulence