High-Resolution and Accurate Low-Latitude Gridded Electron Density Generation and Evaluation

The accurate specification of three-dimensional (3-D) ionosphere states is crucial to positioning, navigation, and communication systems, especially in low-latitude and equatorial regions. In this work, the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2) radio occultation total electron content was assimilated around a whole year from October 2020 to September 2021 via the Kalman filter (KF) data assimilation system. This system includes an empirical ionosphere background model and the KF data assimilation algorithm. Accurate 3-D ionosphere data assimilation results were produced hourly with spatial resolutions of 2° latitude, 5° longitude, and 20 km height in low-latitude and equatorial regions. First, the results were validated by Massachusetts Institute of Technology vertical total electron content and global ionosonde data. The ionosphere vertical total electron content and the critical frequency at the F2 layer agree well with the independent observations. Then, a general ionosphere climatological pattern is found in the reconstructed 3D ionosphere results, including seasonal variation, annual asymmetry, and December anomaly. In addition, the results can well capture the daily spatial and temporal ionospheric variations in the day-to-day variability, the longitudinal wave 4 structures, and the interhemispheric asymmetry transition of the equatorial ionization anomaly crests. The current results demonstrate that assimilating COSMIC-2 TEC observations can further improve the 3D ionosphere specification in low-latitude and equatorial regions and can also contribute to physical research on ionosphere variability characteristics.