Abstract

For a collisionless plasma, the magnetic field Ḇ enables fluidlike behavior in the directions perpendicular to B; however, fluid behavior along Ḇ may fail. The magnetic field also introduces an Alfven-wave nature to flows perpendicular to Ḇ. All Alfven waves are subject to Landau damping, which introduces a flow dissipation (viscosity) in collisionless plasmas. For three magnetized plasmas (the solar wind, the Earth’s magnetosheath, and the Earth’s plasma sheet), shear viscosity by Landau damping, Bohm diffusion, and by Coulomb collisions are investigated. For magnetohydrodynamicturbulence in those three plasmas, integral-scale Reynolds numbers are estimated, Kolmogorov dissipation scales are calculated, and Reynolds-number scaling is discussed. Strongly anisotropic Kolmogorov k−5/3 and mildly anisotropic Kraichnan k−3/2turbulences are both considered and the effect of the degree of wavevector anisotropy on quantities such as Reynolds numbers and spectral-transfer rates are calculated. For all three plasmas, Braginskii shear viscosity is much weaker than shear viscosity due to Landau damping, which is somewhat weaker than Bohm diffusion.