Observations of Night‐Time Equatorial Ionosphere Structure with the FPMU on board the International Space Station

Electron density measurements from the Floating Potential Measurement Unit (FPMU) onboard the International Space Station allow us to observe the structure of the equatorial ionosphere. During two geomagnetically quiet time periods, we examined the equatorial F-region structure at night using FPMU electron density measurements along with Swarm spacecraft electron density measurements and Total Electron Content from ground-based Global Navigation Satellite System receivers for comparison. During these time periods, the equatorial ionization anomaly (EIA) extended to local times late as post-midnight in some cases. The EIA occurrences at night showed a longitudinal dependence. The mean density of the EIA peaks exhibited a 3-wave pattern in longitude likely due to lower atmospheric planetary wave activity, similar to the longitudinal dependence previously observed in the EIA.