Shock--turbulence interaction in magnetic reconnection: Density variance effects

Abstract:

Effects of density variance (, : density fluctuation, : mean) in magnetic reconnection shocks are theoretically investigated. Shock--turbulence interaction is one of the most challenging problems in turbulence modeling. A strong variation of the mean density () leads to a strong density variance. The expressions for the turbulent correlations such as the Reynolds and turbulent Maxwell stresses, the turbulent electromotive force, etc. are examined in a compressible magnetohydrodynamic (MHD) turbulence. It is shown that in the presence of the density variance, a mean density gradient () oblique or perpendicular to the mean magnetic field gives rise to the turbulent electromotive force. Since the electric current density induced by this effect is in the direction of the reconnection electric current density, the turbulent energy near the slow shock in the fast magnetic reconnection is expected to be enhanced. The physical origin of this effect is discussed. A turbulence model incorporating this effect is proposed. This model is expected to reproduce the spatial distribution of the turbulent energy around the fast magnetic reconnection.