Observations of the Magnetopause Reconnection Ion Diffusion Region With High‐Density O ⁺ Ions During the May 2024 Superstorm

Abstract Based on high‐resolution measurements from NASA's Magnetospheric Multiscale mission (MMS), we present the first direct observation of an ion diffusion region (IDR) with high number density O + ions within dayside magnetopause reconnection during the May 2024 superstorm. The O + ion density reaches a high value of ∼3.3 cm −3 . It helps study heavy‐ion dynamics in dayside magnetopause reconnection. In the vicinity of IDR, O + ions exhibit distinct acceleration to 300 km/s along the normal direction caused by the enhanced Hall electric field (| E N | max ≈ 80 mV/m). The distorted ion velocity distributions reveal the complex energization processes in the IDR. Crucially, these O + ion dynamics can reduce reconnection rate by ∼10.3%–25.3%, providing the result that heavy‐ion can substantially alter magnetopause reconnection physics during the superstorm. This study advances our understanding of magnetopause reconnection by demonstrating that storm‐enhanced O + populations modify the structure of diffusion regions, particle energization, and reconnection rate.