Multi-instrument investigation of the longitudinal variability of ionospheric irregularities during the 23–24 April 2023 geomagnetic storm

This study reports an event-specific longitudinal asymmetry of ionospheric irregularities during 23-24 April 2023 geomagnetic storm (SYM-H: −233 nT), utilizing multi-instrument observations (ground-based GNSS and magnetometer along with space-borne Swarm and GOLD satellites). The rate of change of total electron content index (ROTI) is used as a proxy for ionospheric irregularities. Irregularities were largely absent over most western longitudes, except over the Western African sector, where they persisted from 22 to 26 April. On 24 April, these were restricted to 90 °–70 °W during post-midnight hours. On the contrary, over eastern longitudes, irregularities were observed on all days except 24 April. Electron density depletions near ∼12 °W and ∼35 °W reached beyond ∼40 °N and 30 °S Glat on 23 April. Persistence of irregularities observed at GNSS stations YKRO, ACRG, and NKLG over the African longitude sector suggests a decoupling from storm-time magnetospheric electric fields, however suggests dominance of local-time control, background electrodynamics, or trans-equatorial winds, which is relatively a rare observation and strengthens the regional resilience of EPB generation mechanisms. By applying a moving average filter to the magnetic H-component, contributions of prompt penetration (DP2) and disturbance dynamo (Ddyn) currents are separated, with peak activity during southward IMF Bz. Simultaneous DP2 across different local time sectors and anti-Sq patterns illustrate the roles of storm time ionospheric currents. There is a clear sector-dependent phase reversal (main vs. recovery phase) within the storm, highlighting the roles of storm-time drivers, and storm phase alone cannot predict irregularities occurrence without longitude context.