Dynamics of Null-points across Shocks Interacting with Preexisting Turbulence

Abstract In this study, we utilize 2.5D resistive magnetohydrodynamic (MHD) simulations to examine the generation and evolution of plasmoids resulting from the interaction between shock waves and turbulence in interplanetary space. We focus on (quasi-)perpendicular shock geometries with an out-of-plane mean magnetic field to investigate the impact of preexisting large-scale turbulent magnetic fluctuations upstream on MHD shock waves and on magnetic reconnection in the downstream region. Our findings reveal several key insights. First, the magnetic turbulence spectra exhibit three ranges: a low- k range characterized by cascading, a mid- k range potentially mediated by reconnection, and a high- k range corresponding to resistive diffusion. Importantly, these spectral features, including their characteristic breaks and slopes, remain invariant across the shock transition. Second, in all cases, the downstream occurrence of X-points and O-points increases, saturates to a peak value for a certain interval, and gradually decreases away from the shock. This behavior of X-points is consistent with the in situ measurements taken by the Magnetospheric Multiscale mission at Earth’s bow shocks. Third, the resistive simulations allow for the explicit calculation of the magnetic reconnection rate per unit area in the x–y plane, indicating a higher rate per unit area downstream than upstream. This is consistent with the increased occurrence of X-points.