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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. We present measurements of the electron density in the ionized part of the terrestrial atmosphere using the Floating Potential Measurement Unit plasma instrument on board the International Space Station, at an altitude around 400 km. Near the geomagnetic equator, these measurements show that a well‐known daytime structure in the electron density extends all the way past midnight. This structure is the equatorial ionization anomaly, which consists of a trough at the equator and two peaks at approximately ±15° latitude. We also show that values of electron density in this structure are modulated in longitude, varying as a 3‐wave pattern, likely due to the underlying action of tidal planetary waves in the lower atmosphere. During two geomagnetically quiet time periods, the equatorial ionization anomaly (EIA) was observed at local times as late as post‐midnightThe mean density of the EIA crests at night appears to exhibit a 3‐wave pattern in longitudeThis variation in longitude is consistent with previous observations from IMAGE During two geomagnetically quiet time periods, the equatorial ionization anomaly (EIA) was observed at local times as late as post‐midnight The mean density of the EIA crests at night appears to exhibit a 3‐wave pattern in longitude This variation in longitude is consistent with previous observations from IMAGE

The Floating Potential Measurement Unit (FPMU) has been operational on board the International Space Station (ISS) since 2006. One of the instruments in the FPMU suite is a spherical wide‐sweeping Langmuir probe, referred to as the WLP, which is sampled at a temporal cadence of 1 s giving in‐situ measurements of the plasma density and electron temperature. In this study we present our refinements to the Langmuir probe analysis algorithm that address the uncertainties associated with photoelectron emission current from the metal probe. We also derive the fraction of O+ions as a secondary data product, which shows decrease in O+abundance in the post‐midnight sector during solar minimum. The derived plasma parameters are compared and validated with an independent in‐situ measurement technique, overlapping ground‐based incoherent scatter radar measurements, as well as International Reference Ionosphere model output. The reduced data set spans the entire solar cycle 24 and shows the F‐region ionosphere variance at ISS altitudes. Langmuir probe measurements of plasma parameters in Earth's F‐region ionosphere over Solar Cycle 24Reduced parameters include plasma density, electron temperature, and O+fraction which are validated using plasma impedance probe and Incoherent Scatter Radar observationsAlgorithm details of analyzing a Langmuir probe IV curve in ionospheric space plasma are provided Langmuir probe measurements of plasma parameters in Earth's F‐region ionosphere over Solar Cycle 24 Reduced parameters include plasma density, electron temperature, and O+fraction which are validated using plasma impedance probe and Incoherent Scatter Radar observations Algorithm details of analyzing a Langmuir probe IV curve in ionospheric space plasma are provided