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Anisotropy in Hall MHD turbulence due to a mean magnetic field

Published online by Cambridge University Press:  01 January 1997

S. GHOSH
Affiliation:
Applied Research Corporation, 8201 Corporate Drive, Suite 1120, Landover, Maryland 20785, USA Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
M. L. GOLDSTEIN
Affiliation:
Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

Abstract

The development of anisotropies in an initially isotropic spectrum is studied numerically for compressible magnetohydrodynamic (MHD) turbulence in the presence of the Hall term. Building on a previous study where it was shown that spectral cascades in the Hall MHD system differ from the standard MHD case, particularly at high cross-helicities, we use an isotropic high cross-helicity initial state to study anisotropies of the Hall MHD system for a variety of mean magnetic field strengths and sonic Mach numbers. Strong anisotropies, which maximize at the ion-inertial length scale, appear for several plasma states and are categorized according to their plasma beta β: high-β Hall MHD simulations (β>1) show strong anisotropies relative to the standard MHD case, intermediate-β Hall MHD simulations (β≈1) show smaller anisotropy differences relative to the standard MHD case, and low-β Hall MHD simulations (β<1) again show strong anisotropies relative to the standard model. It is suggested that these anisotropy enhancements are due to nonlinear cascade suppression of propagating Alfvén waves in the field-aligned direction. This is different from the dynamics in the highly oblique directions, where non-propagating density and magnetic-energy anticorrelations appear.

Type
Research Article
Copyright
1997 Cambridge University Press

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