Abstract:
When the velocity field of a magneto-fluid is accorded an intrinsically equal status with the magnetic field, standard magnetohydrodynamics (MHD) must be replaced by the dispersive or Hall MHD which retains some crucial two-fluid effects, in particular the physics on the ion skin depth scale. The larger system has three quadratic invariants: the generalized helicity (a sum of the cross and fluid helicities) is added to the ranks of the standard total energy and the magnetic helicity invariants. Based on this extended set, dimensional arguments à la Kolmogorov are invoked to derive the turbulent spectral distributions of the kinetic and the magnetic energy densities in the inertial range. By using the selective dissipation hypothesis, we construct the spectra on three different scales within the inertial range, and acknowledge the possible role of the dual cascade of the kinetic and the magnetic energy densities. The additional structure imparted to the spectral laws (by the inclusion of the generalized helicity) allows us to reproduce, remarkably well, the essentials as well as details of the observed spectra of the motions and of the magnetic fields of the solar atmosphere on the scales of a few thousand km.
