Flagged data of the Langmuir probes onboard Swarm satellites related extremely low plasma density environment

Abstract

As a widely used instrument for in situ electron density and temperature measurements, the spaceborne Langmuir Probe (LP) provides critical insights into ionospheric structure and dynamics. In this study, we investigate a specific type of anomalous disturbance in the plasma density data recorded by the LP onboard Swarm satellites. In the official Swarm data product, these anomalous disturbances have been flagged as invalid data. Comprehensive analysis shows that these flagged disturbances predominantly occur in regions of extremely low background electron density, such as inside the post-sunset equatorial plasma bubbles (EPBs) and low-density regions at high latitudes. Their occurrence rates are notably higher during nighttime, local winter, and periods of low solar activity, but show no clear dependence on geomagnetic activity. In addition to space environment factors, differences in satellite platforms and payload configurations also contribute to statistical discrepancies in such disturbances. The average background electron densities during these events for Swarm A, B, and C are 440 cm⁻³, 449 cm⁻³, and 692 cm⁻³, respectively. These differences in background levels are likely related to subtle inter-satellite variations in the LP onboard Swarm A, B, and C. Furthermore, there is a clear hemispheric asymmetry in the occurrence of these disturbance events, with many more detected in the Southern Hemisphere than in the Northern Hemisphere. This result indicates that much deeper and more frequent low electron density appear in the southern high-latitude regions, which might be associated with the southern mid-latitude trough. These findings highlight how both space environment and satellite hardware can influence the interpretation of ionospheric measurements.