Fast-to-Alfvén mode conversion mediated by Hall current. II Application to the solar atmosphere

Abstract

Coupling between fast magneto-acoustic and Alfvén waves can be observe in fully ionized plasmas mediated by stratification and 3D geometrical effects. In Paper I, Cally & Khomenko (2015) have shown that in a weakly ionized plasma, such as the solar photosphere and chromosphere, the Hall current introduces a new coupling mechanism. The present study extends the results from Paper I to the case of warm plasma. We report on numerical experiments where mode transformation is studied using quasi-realistic stratification in thermodynamic parameters resembling the solar atmosphere. This redresses the limitation of the cold plasma approximation assumed in Paper I, in particular allowing the complete process of coupling between fast and slow magneto-acoustic modes and subsequent coupling of the fast mode to the Alfvén mode through the Hall current. Our results confirm the efficacy of the mechanism proposed in Paper I for the solar case. We observe that the efficiency of the transformation is a sensitive function of the angle between the wave propagation direction and the magnetic field, and of the wave frequency. The efficiency increases when the field direction and the wave direction are aligned for increasing wave frequencies. After scaling our results to typical solar values, the maximum amplitude of the transformed Alfvén waves, for a frequency of 1 Hz, corresponds to an energy flux (measured above the height of peak Hall coupling) of $\sim 10^3$ $\mathrm{W}{\mathrm{m}}^{-2}$, based on an amplitude of 500 $\mathrm{m}{\mathrm{s}}^{-1}$ at $\beta =1$, which is sufficient to play a major role in both quiet and active region coronal heating.

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• Influence of ambipolar and Hall effects on vorticity in 3D simulations of magneto-convection
• Efficient kinetic Lattice Boltzmann simulation of three-dimensional Hall-MHD Turbulence
• Wave Conversion, Decay and Heating in a Partially Ionized Two-Fluid Magneto-Atmosphere
• Observational and numerical characterization of a recurrent arc-shaped front propagating along a coronal fan
• Damping of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere
• Convergence study of ambipolar diffusion in realistic simulations of magneto-convection
• MHD waves in the partially ionized plasma: from single to multi-fluid approach
• Decomposing wave activity in the solar atmosphere: Shocks, jets and swirls in the quiet Sun