Shock-triggered Magnetic Activity Downstream of Coronal Shocks Interacting with Preexisting Turbulence

We perform 2.5D viscous-resistive magnetohydrodynamic (MHD) simulations to study shock-turbulence interaction at 1 R ⊙ above the photosphere, driven by coronal mass ejections. Using identical upstream fluctuation amplitudes and spectra in three simulation cases, we investigate how different shock magnetosonic Mach numbers ( M f = 1.5, 3, and 5) affect downstream fluctuations and magnetic activity signatures. The energy spectra in both upstream and downstream regions after shock passage exhibit three distinct wavenumber ranges: a low- k inertial range with slope −5/3, a mid- k subinertial range mediated by magnetic reconnection, and a high- k diffusive range. These features are consistent with those previously simulated in interplanetary plasmas. Downstream of the shock, the number densities of magnetic null points and vortices, as well as the magnetic reconnection rate per unit area, initially rise to a peak and then gradually decline with increasing distance from the shock front, with higher M f producing higher peaks in all these quantities. The shock acts as a trigger for magnetic activity downstream, manifested as enhanced magnetic reconnection per unit area, accompanied by the increase and decrease of magnetic null points and vortex populations. We find that the ratios of downstream-to-upstream mean quantities follow the Rankine–Hugoniot relations. While the downstream-to-upstream fluctuation ratios of ρ and T grow as M f increases from 1.5 to 3 and then flatten over M f = 3–5, those of u x [ SKF ] , u y , and fluctuation ratios of all components of B continue to increase over the investigated M f range, whereas the fluctuation ratio of u z varies only within a narrow range.