The role of the sonic scale in the growth of magnetic field in compressible turbulence
- Resource Type
- Authors
- Michael Mond; Itzhak Fouxon
- Source
- Monthly Notices of the Royal Astronomical Society. 493:4400-4408
- Subject
- Physics
Field (physics)
Scale (ratio)
Turbulence
Fluid Dynamics (physics.flu-dyn)
FOS: Physical sciences
Astronomy and Astrophysics
Physics - Fluid Dynamics
Mechanics
01 natural sciences
Physics::Fluid Dynamics
symbols.namesake
Astrophysics - Solar and Stellar Astrophysics
Mach number
Space and Planetary Science
Incompressible flow
Physics::Space Physics
0103 physical sciences
symbols
Supersonic speed
Magnetohydrodynamics
010306 general physics
010303 astronomy & astrophysics
Solar and Stellar Astrophysics (astro-ph.SR)
Dynamo
- Language
- ISSN
- 1365-2966
0035-8711
We study the growth of small fluctuations of magnetic field in supersonic turbulence, the small-scale dynamo. The growth is due to the fastest turbulent eddies above the resistive scale. We observe that for supersonic turbulence these eddies are effectively incompressible which creates a robust structure of the growth. The eddies are localised below the sonic scale $l_s$ defined as the scale where the typical velocity of the turbulent eddies equals the speed of sound. Thus the flow below $l_s$ is effectively incompressible and the field growth proceeds as in incompressible flow. At large Mach numbers $l_s$ is much smaller than the integral scale of turbulence so the fastest growing mode of the magnetic field belongs to small-scale turbulence. We derive this mode and the associated growth rate numerically in a white noise in time model of turbulence. The relevance of this model relies on considering evolution time larger than the correlation time of turbulence.
Comment: 5 pages, 2 figures