Abstract
We present results of a multiscale study of Hall-magnetohydrodynamic (MHD) turbulence, carried out on a dataset of compressible nonlinear 2D Hall-MHD numerical simulations of decaying Alfvénic turbulence. For the first time, we identify two distinct regimes of fully developed turbulence. In the first one, the power spectrum of the turbulent magnetic fluctuations at sub-ion scales exhibits a power law with a slope of ∼−2.9, typically observed both in solar wind and in magnetosheath turbulence. The second regime, instead, shows a slope of −7/3, in agreement with classical theoretical models of Hall-MHD turbulence. A spectral-transfer analysis reveals that the latter regime occurs when the energy transfer rate at sub-ion scales is dominated by the Hall term, whereas in the former regime, the governing process is the dissipation (and the system exhibits large intermittency). Results of this work are relevant to the space plasma community, as they may potentially reconcile predictions from theoretical models with results from numerical simulations and spacecraft observations.
Highlights
Space and astrophysical plasmas are often found in a highly turbulent state
In the typical case, exemplified by Run d16, the energy injection scales are much larger than the ion characteristic scales; a proper MHD inertial range cascade is established and vortices and coherent structures can form at scales larger than the ion characteristic ones
At sub-ion scales, the cross-scale energy transfer takes place in localized regions of enhanced dissipation. This is in agreement with our previous findings [48] and is coherent with the fact that in Run d16 the dissipation term Dk gives the dominant contribution to the total energy transfer ∂t Ek
Summary
Space and astrophysical plasmas are often found in a highly turbulent state. At large scales, where the solar wind behaves as a fluid and can be modeled within the framework of magnetohydrodynamics (MHD), the power spectrum of the magnetic field exhibits a power-law behavior with a spectral index close to −5/3 (the so-called inertial range), analogous to the Kolmogorov cascade in hydrodynamic turbulence [2]. When approaching the ion characteristic scales, the spectrum steepens, with a slope ranging from −2 to −4. The origin of such transition (possibly related to the onset of Hall currents and ion-kinetic dissipation, e.g., [3–5]) and the nature of sub-ion scales turbulence are still unknown
Sign-in/Register to view highlights & summary 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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
