Open AccessOn the validity of quasi‐linear kinematic mean‐field electrodynamics in astrophysical flows
Author(s) -
K. Petrovay,
Janos Zsargó
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01231.x
Subject(s) - physics , intermittency , turbulence , strouhal number , magnetic diffusivity , kinematics , magnetic field , classical mechanics , mechanics , computational physics , magnetohydrodynamics , statistical physics , quantum mechanics , reynolds number
Mean‐field theory in its kinematic form with the quasi‐linear approximation is widely used for the modelling of the transport of weak magnetic fields in turbulent media. The validity of this approach to real astrophysical flows is discussed. Numerically evaluating the turbulent electromotive force using Lagrangian analysis for a set of simple, prescribed 2D flow patterns with a wide range of parameters, we find that quasi‐linear expressions for the turbulent diffusivities and for the pumping velocities are correct within a factor of 2 for a wide variety of flow types with order of unity (or even higher) effective Strouhal numbers. The degree of the non‐linear quenching of turbulent transport by a weak magnetic field is also discussed. We argue that, owing to the intermittency and small filling factors of magnetic fields in realistic astrophysical media, diffusivity and pumping effects are not quenched to order of magnitude, while a more moderate quenching of order 10 per cent is still present.