Study on the Suppression of Equatorial Ionization Anomaly Crest Observed by CSES‐01

Abstract

The Langmuir Probe (LAP) on board the China Seismo‐Electromagnetic Satellite (CSES‐01) has repeatedly observed an unexpected suppression of the equatorial ionization anomaly (EIA) crest in its retrieved electron density (Ne) data. This study systematically investigates this phenomenon using five years of Ne observations from CSES‐01 descending orbits (∼14:00 local time, LT). Through multi‐source data intercomparison, including simultaneous in situ Ne from Swarm‐B, electron density profiles from CSES‐01 and COSMIC‐2, and the fixed‐bias current (Iflat) from LAP itself, the crest suppression is confirmed as an instrumental artifact during the daytime. Statistical analysis reveals a clear seasonal dependence: being most frequent in winter, least in summer, and intermediate during equinoxes. Spatially, the suppression events are predominantly occurring in the Northern Hemisphere, and exhibit a global distribution with no pronounced longitudinal preference. The analysis of current‐voltage (I–V) curves shows that the suppression originates from distortion in the electron saturation region, which leads to the misidentification of the plasma potential ( Vp ) and consequent bias of the Ne estimates. To address this issue, a correction method has been developed and validated based on the stable Iflat. The method effectively restores the normal morphology of the EIA crests. This work provides a diagnostic and corrective framework for a key instrumental artifact in CSES‐01 LAP data, significantly improving the reliability of its Ne data set for ionospheric research.