Progresses on refinement of ionospheric bottomside profile thickness (B0) and shape (B1) parameters in IRI model: insights from observations and simulations
Advances in Space Research, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Basım Tarihi: 2026
- Doi Numarası: 10.1016/j.asr.2026.08.085
- Dergi Adı: Advances in Space Research
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Artic & Antarctic Regions, Compendex, INSPEC, MEDLINE, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
- Anahtar Kelimeler: Bottomside thickness (B0) and shape (B1), Electron density profile, Formosat-7/COSMIC-2, International Reference Ionosphere (IRI), Radio Occultation
- Karadeniz Teknik Üniversitesi Adresli: Evet
Özet
In this paper, we review the current understanding of the ionospheric bottomside thickness and shape parameters (B0 and B1), which are fundamental for specifying the electron density profile (EDP) in the most accepted empirical standard International Reference Ionosphere (IRI) model. Drawing on a large number of ground- and space-based observational studies and model simulations, we present a review of the evolution of these parameters across three primary sub-models in the IRI-2020 model: the tabular Bil-2000, functional Gul-1987, and default spherical-harmonic ABT-2009. While models have progressively improved, significant discrepancies persist, which are highlighted in this study through morphological analysis involving diurnal, seasonal, and solar activity dependencies, alongside variations in geographic location and longitudinal differences. The important observations highlight complex spatiotemporal morphologies, including seasonal maxima during summer solstices and positive correlations with solar activity. These patterns influence key ionospheric properties, including the topside scale height and integrated electron content. These findings reinforce the direct implications of B0 and B1 in ionospheric modeling for radio communication, satellite navigation, and space weather monitoring. The ABT-2009 model provides seasonal and solar cycle variations more accurately than the Bil-2000 or Gul-1987 sub-models, though all options systematically underestimate daytime B0 and overestimate B1 compared to the observed diurnal peaks at noon and night, respectively. Furthermore, modeled B0 results often fail to reproduce complex longitudinal wavenumber patterns or maintain accurate geomagnetic control during solstices, where the Gul-1987 option exhibits erroneous spatial distributions. Such discrepancies in the existing models are attributed to several constraints, like uneven underlying data coverage in model formulation, marginal exploitation of space-based observations, and the continued reliance on simplified parameterization schemes. Moreover, the B1 parameter is significantly less understood due to its inherent sensitivity to data quality and fitting uncertainties. The review concludes by discussing emerging opportunities for improving the bottomside formulation in IRI by using modern GNSS RO profiles from the dedicated low latitude mission FORMOSAT-7/COSMIC-2 (F7/C2) and global missions Fengyun-3 (FY-3) and Tianmu-1 (TM-1), which together may yield an unprecedented dense daily coverage of vertical ionospheric electron density profiles. Integrating these datasets through real-time data assimilation (IRTAM) and machine learning will enable IRI to accurately reproduce multiscale ionospheric morphologies, significantly enhancing reliability in global space weather forecasting and navigation applications.