2-D Total Electron Content and 3-D Ionospheric Electron Density Variations During the 14 October 2023 Annular Solar Eclipse

This study investigates the ionospheric total electron content (TEC) responses in the 2-D spatial domain and electron density variations in the 3-D spatial domain during the annular solar eclipse on 14 October 2023, using ground-based Global Navigation Satellite System (GNSS) observations, a novel TEC-based ionospheric data assimilation system (TIDAS), ionosonde measurements, and satellite in situ data. The main results are summarized as follows: (a) The 2-D TEC responses exhibited distinct latitudinal differences. The mid-latitude ionosphere exhibited a more substantial TEC decrease of 25%-40% along with an extended recovery time of 3-4 hr. In contrast, the equatorial and low-latitude ionosphere experienced a smaller TEC reduction of 10%-25% and a faster recovery time of 20-50 min. The minimal eclipse effect was observed near the northern equatorial ionization anomaly crest region. (b) The ionospheric electron density variations during the eclipse were effectively reconstructed by TIDAS data assimilation in the 3-D domain, providing important altitude information with validity. (c) The ionospheric electron density variations showed a notable altitude-dependent feature. The eclipse led to a substantial electron density reduction of 30%-50%, with the maximum depletion occurring around the ionospheric F2-layer peak height (hmF2) of 250-350 km. The post-eclipse recovery of electron density exhibited a relatively slower pace near the F2-layer peak height than that at lower and higher altitudes. On 14 October 2023, the Great American annular solar eclipse traversed North, Central, and South America with dense observational network in place, presenting a valuable opportunity for exploring the eclipse-induced ionospheric responses from mid-latitude to equatorial regions. This paper presents a comprehensive analysis of the 2-D ionospheric TEC and 3-D electron density responses during the eclipse, utilizing dense ground-based GNSS observations, a new TEC-based ionospheric data assimilation system (TIDAS), and ionosonde and satellite data sets. The TIDAS data assimilation system provides accurate and reliable regional ionospheric electron density reconstruction, which can effectively reproduce the electron density variations during the eclipse in the 3-D domain with important altitude information and high-fidelity details. This multi-instrumental and data assimilation study highlights the latitudinal and altitudinal dependencies of the eclipse-induced ionospheric responses, advancing the current understanding of how a solar eclipse event impacts the ionosphere. The TEC response showed latitudinal variances, with a 25%-40% decrease in midlatitudes but only a 10%-25% reduction in the equatorial region The Ne response showed altitudinal dependencies, with a larger depletion and a slower recovery near the F2 peak height than below and above The NmF2 exhibited a 30%-50% reduction, and the hmF2 exhibited a 20-30 km decrease in the recovery phase after the maximum obscuration