2024/05/26 by James R. Beattie, Christoph Federrath, Beattie, James R. +7 · 5 citations
Biochemistry, Genetics and Molecular Biology · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics of Galaxies (astro-ph.GA) #Classical mechanics #Compressibility #Computational Physics (physics.comp-ph) #Dynamo #Dynamo theory #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Geomagnetism and Paleomagnetism Studies #Geophysics and Gravity Measurements #K-epsilon turbulence model #K-omega turbulence model #Magnetic Reynolds number #Magnetic field #Magnetohydrodynamic turbulence #Magnetohydrodynamics #Mechanics #Physics #Plasma Physics (physics.plasm-ph) #Quantum mechanics #Reynolds decomposition #Reynolds equation #Reynolds number #Reynolds stress equation model #Solar and Space Plasma Dynamics #Solar and Stellar Astrophysics (astro-ph.SR) #Statistical physics #Turbulence
paper · pdf · doi:10.48550/arxiv.2405.16626
published in arXiv (Cornell University) (Cornell University)
openalex publication_date 2024/05/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Supersonic magnetohydrodynamic (MHD) turbulence is a ubiquitous state for many astrophysical plasmas. However, even the basic statistics for this type of turbulence remains uncertain. We present results from supersonic MHD turbulence simulations at unparalleled resolutions, with plasma Reynolds numbers of over a million. In the kinetic energy spectrum we find a break between the scales that are dominated by kinetic energy, with spectral index -2, and those that become strongly magnetized, with spectral index -3/2. By analyzing the Helmholtz decomposed kinetic energy spectrum, we find that the compressible modes are not passively mixed through the cascade of the incompressible modes. At high magnetic Reynolds number, above 105, we find a power law in the magnetic energy spectrum with spectral index -9/5. On the strongly magnetized, subsonic scales the plasma tends to self-organize into locally relaxed regions, where there is strong alignment between the current density, magnetic field, velocity field and vorticity field, depleting both the nonlinearities and magnetic terms in the MHD equations, which we attribute to plasma relaxation on scales where the magnetic fluctuations evolve on shorter timescales than the velocity fluctuations. This process constrains the cascade to inhomogenous, volume-poor, fractal surfaces between relaxed regions, which has significant repercussions for understanding the nature of magnetized turbulence in astrophysical plasmas and the saturation of the fluctuation dynamo.