Modified magnetohydrodynamics model with wave turbulence: astrophysical applications

Abstract

Modeling astrophysical flows in the framework of classical magnetohydrodynamics often encounters significant difficulties due to high (up to relativistic) Alfvén wave velocities. Such situations can arise in modeling the magnetosphere of planets and stars and accretion flows in polars, intermediate polars, and near-neutron stars. In a strongly magnetized plasma, wave turbulence can develop, which can significantly affect the energy balance and the forces determining the plasma dynamics. In this paper, a closed system of equations is obtained for modified magnetohydrodynamics with wave turbulence for a wide range of magnetic fields and turbulence energies. The turbulent flow is described as the sum of the mean flow and perturbations induced by relativistic Alfvén waves. Expressions are derived for the turbulence-induced body force, viscosity, and dissipative heating. An analysis of equations in certain limit cases is performed. It is shown that the proposed approach can be used for modeling a broad class of astrophysical plasma flows.

Alfvénic Fluctuations Associated With Jupiter's Auroral Emissions

“…However, in Jupiter's polar magnetosphere, the field was sufficiently strong to require a semirelativistic description Alfvén wave propagation. In this regime, the Alfvén mode remained nearly dispersionless at fluid scales but propagated with speed V A /√(1+( V A / c ) 2 ), where c is the speed of light and V A is the typical Alfvén speed of B /( mn μ o ), with B , m , n , and μ o representing to the magnetic field magnitude, particle mass, number density, and vacuum permeability, respectively (Gombosi et al, ; Kurbatov et al, ; Su et al, ). In the high‐latitude regions considered here, the Alfvén speed was ~ c .…”

A Possible Mechanism for the Radio Emission of Polars

“…The presence of fluctuations is associated with the setting of wave Alfvén turbulence in the plasma. This paper continues investigation of the effects of Alfvén turbulence in cataclysmic binary systems [8].…”

“…In the paper [8] we considered the problems of simulation of plasma flows in strong magnetic fields. Under such conditions, Alfvén and magnetosonic waves may significantly affect dynamics of the flow.…”

“…Turbulence of this type is characterized by the magnitude of the background magnetic field, power spectrum, longitudinal and diagonal spatial scales. In the paper [8] we proposed a model of modified magnetic hydrodynamics in which Alfvén turbulence is taken into account via stochastic sources of momentum and magnetic field acting on the average medium flow. The model was confined to the case of the so-called balanced turbulence, for which the energy spectra of Alfvén fluctuations of both families coincide.…”

“…The energy spectrum was calculated by [18]. For the given spectrum P (k), let denote the energy of the turbulent fluctuations of the magnetic field, per unit mass, as in [8]…”