A Novel Approach of Reconstructing the Topside Ionosphere Using Ionosonde and COSMIC Scale Height Gradients: Validation With Swarm Measurements

Abstract Accurate estimation of vertical electron density profiles in the electrodynamically complex equatorial and low‐latitude ionosphere remains a persistent challenge, primarily due to the scarcity of direct topside observational data with sufficient temporal and spatial coverage. Therefore, reconstructing topside profiles using bottomside ionosonde parameters is essential for capturing ionospheric behaviour in these regions. In this study, bottomside real height profiles derived from digital ionosonde measurements from Tirunelveli, an equatorial station in India, using the standard POLynomial ANalysis (POLAN) algorithm was used as basis for topside reconstruction. Key ionospheric parameters including the scale height at the F 2 peak were extracted. Reconstruction was performed for two years of contrasting solar activity (2014 (high) and 2020 (low)) using both α‐Chapman and semi‐Epstein formulations, with the latter incorporating a linearly varying topside scale height. Additionally, scale heights derived from the Reinisch‐Huang (R‐H) method were used to validate the POLAN‐derived outputs. All reconstructed profiles were evaluated independently using in situ electron density measurements from Swarm satellites over the Indian region. Results demonstrate that using realistic topside scale height gradients derived from COSMIC Radio Occultation (RO) profiles significantly improves reconstruction accuracy, especially when semi‐Epstein formulation is applied. Further, seasonal analyses indicate better agreement of the reconstruction approach during high solar activity, with a larger fraction of profiles falling within a ±20% deviation from Swarm observations. These findings highlight the potential of integrating empirical topside scale height variations into reconstruction models to achieve a more accurate representation of the topside ionosphere, particularly over the Indian region.