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arXiv · 1906.11065

Role of the sonic scale in the growth of magnetic field in compressible turbulence

Itzhak Fouxon·Michael Mond
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Abstract

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.

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Itzhak Fouxon, Michael Mond. 2019-06-24. Role of the sonic scale in the growth of magnetic field in compressible turbulence. https://doi.org/10.1093/mnras/staa582

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