Analysis of Substorm Auroral Electrojet Signatures in EZIE Observations using Ground-Based Instruments

The Electrojet Zeeman Imaging Explorer (EZIE) mission aims to map the two-dimensional structure of the auroral and equatorial electrojets. Three satellites provide four simultaneous remote sensing vector magnetic field measurements at ~80 km altitude using the Zeeman splitting of the atmospheric O2 thermal emissions. Each orbit provides three maps of the electrojet current, one per satellite, to reveal spatial structure and temporal evolution along four lines of sight. These multipoint measurements provide improved spatial resolution of mesoscale current structures compared to traditional observations from ground-based instruments. Furthermore, the spacing between satellites (varying from 2 and 7 minutes) captures the current system’s temporal evolution over several minutes. In this study, we analyze several days during the summer of 2025 when EZIE was taking measurements of the Northern Hemisphere auroral zone. In particular, we focus on the signature of the auroral electrojet during periods with high substorm activity. We compare and validate EZIE observations with measurements from ground magnetometer stations located near the satellite track. To provide broader context of the ionospheric state during these substorm events, we also use global maps of GNSS total electron content and measurements from the Poker Flat incoherent scatter radar during several close conjunctions.