Construction and Application of Global Middle- and Low-Latitude Bottomside Electron Density Profile Model Based on Multisource Satellite Geodetic Data and International Reference Ionosphere Model

To improve the bottomside ionospheric electron density profile (EDP) described by the International Reference Ionosphere (IRI), a global bottomside EDP updated model for geographic latitudes between +/- 40 degrees is constructed. This model is based on the spherical harmonic analysis (SHA) method and utilizes radio occultation (RO) data from Formosa Satellite 7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (Formosat-7/COSMIC-2) to improve IRI. Using incoherent scatter radar (ISR) and ionosonde data as references, the corrected parameters and the bottomside EDP of the SHA model were compared with the IRI data. The results show that the time-series curve trends of hmF2 and NmF2 corrected by the SHA model are closer to those of the ISR/ionosonde curve. The standard deviation (STD) of hmF2 and NmF2 at different time segments improved, with the highest improvement ranges of 41.41% and 57.58%, respectively. The total time period statistical results for individual stations also showed an average reduction in STD of 18.80% and 10.11% for hmF2 and NmF2, respectively. Furthermore, the bottomside EDPs of the IRI and SHA models were compared with the ISR data, and we found that owing to the improvements in thickness parameter ${B}0$ and shape parameter ${B}1$ , the bottomside profile shape was also significantly improved. Finally, the bottomside EDPs generated by SHA model were used as vertical constraints to improve the existing computerized ionosphere tomography (CIT) algorithm. The 3-D evolution process of a moderate geomagnetic storm on February 2-3, 2022, was quantified. The 3-D ionospheric morphological changes and evolution characteristics in the region of 18 degrees-36 degrees N and 98 degrees-123 degrees E are clearly demonstrated.