Radio Spectral Imaging and Magnetohydrodynamic Modeling of a Coronal Mass Ejection–driven Shock: Connecting Solar Type II Radio Bursts with Shock-surface Magnetic Geometry

Solar type II radio bursts are widely regarded as signatures of shock waves propagating in the solar corona and are of particular importance for understanding shock-driven particle acceleration processes. Type II radio bursts often exhibit complex multilane and split-band features. The detailed spectral, temporal, and spatial structures carry key information about the shock properties and evolution. However, the physical origin of the multilane and split-band features remains unclear, largely due to a lack of spatially resolved data and understanding of the concurrent shock morphology and its magnetic-field context. In this work, we combine radio imaging spectroscopy of a multilane, split-band type II burst event with a three-dimensional global magnetohydrodynamic simulation of the associated coronal mass ejection–driven shock using the Alfvén Wave Solar atmosphere Model-Realtime. In this event, the burst intensity evolves from fundamental-emission dominated to harmonic-emission dominated. Meanwhile, the preferential emission source region moves from the Earth-facing side to the limb or farside, coinciding with quasi-perpendicular shock regions with enhanced Mach numbers. The observed spatial offset between the fundamental and harmonic sources is generally aligned with the projected shock-surface magnetic field from the simulation, consistent with anisotropic scattering in a magnetized turbulent plasma. These results establish a physical connection between type II radio sources and coronal shock magnetic geometry, providing new insight into the origin of the multilane features and their diagnostics of coronal shocks.