Abstract:Helicities as well as the turbulent energies are key players of the dynamo process. From viewpoint of turbulent transport, helicities mainly suppress the effective transports. In the presence of inhomogeneous large-scale flow, the turbulent cross helicity (cross-correlation between the velocity and magnetic-field fluctuations) enters the turbulent electromotive force and its suppression/generation effect tends to be balanced with the turbulent magnetic diffusivity. At the same time, the turbulent cross helicity coupled with the mean magnetic strain affects the momentum transport. In addition to these effects of helicities, in strong compressible magnetohydrodynamic (MHD) turbulence, the density variance contributes to the turbulent electromotive force as the coupling coefficient of the obliqueness of the mean magnetic field to the density gradient. This means that the density variance as well as the helicities alters the turbulent transport. This density-variance effect is expected to enhance the intensity of turbulence across the slow MHD shock, which may contribute to the realization of a localized fast magnetic reconnection.
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