Research Article
Modeling Equatorial Plasma Depletion and Anisotropic MSTIDs from the April 2024 Eclipse
Belay Sitotaw Goshu*
Issue:
Volume 14, Issue 3, September 2026
Pages:
39-52
Received:
15 July 2026
Accepted:
24 July 2026
Published:
10 August 2026
Abstract: Background: Total solar eclipses provide unique opportunities to study the ionospheric response to sudden solar extreme ultraviolet (EUV) reduction. The April 8, 2024 total solar eclipse occurred near the peak of Solar Cycle 25, offering a rare chance to examine eclipse-driven plasma depletion and traveling ionospheric disturbances under high solar activity. Purpose: This study models the equatorial ionospheric plasma depletion and anisotropic medium-scale traveling ionospheric disturbances (MSTIDs) generated by the 2024 eclipse, using GNSS total electron content (TEC) observations and the SAMI3 ionospheric model. Methods: We analyzed TEC data from ~200 stations spanning North America to equatorial Brazil. SAMI3 simulations incorporated time-dependent EUV reduction along the eclipse path, with neutral atmosphere from NRLMSIS 2.0. MSTID propagation parameters were extracted via wavelet analysis and cross-correlation. Findings: Equatorial TEC depletion reached 20-40%, with the F2 layer showing 60% electron density reduction. The eclipse generated anisotropic MSTIDs: zonal propagation (λ = 1304 km, v = 0.81 km/s) and meridional propagation (λ = 571 km, v = 0.42 km/s), reproduced by SAMI3 within 15% accuracy. Compared to the 2017 solar-minimum eclipse, the 2024 event exhibited deeper depletion (40% vs. 25%) and prolonged recovery (≥7 hours vs. 3.5 hours). Conclusion: High solar activity amplifies eclipse-induced ionospheric effects, including stronger plasma loss and longer-lasting MSTIDs. SAMI3 successfully captures these anisotropic disturbances, validating its use for operational forecasting. Recommendation: Future work should employ coupled ionosphere-neutral atmosphere models (e.g., SAMI3 + WACCM-X) to improve AGW source physics and extend comparisons to other solar-maximum eclipses (e.g., 2026).
Abstract: Background: Total solar eclipses provide unique opportunities to study the ionospheric response to sudden solar extreme ultraviolet (EUV) reduction. The April 8, 2024 total solar eclipse occurred near the peak of Solar Cycle 25, offering a rare chance to examine eclipse-driven plasma depletion and traveling ionospheric disturbances under high solar...
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Research Article
Cosmological Dynamics in Quadratic f(R,G) Gravity with a Periodically Evolving Deceleration Parameter
Dhajendra Rabha,
Rajshekhar Roy Baruah*
Issue:
Volume 14, Issue 3, September 2026
Pages:
53-68
Received:
19 August 2026
Accepted:
19 August 2026
Published:
21 September 2026
Abstract: The late-time accelerated expansion of the Universe remains one of the major challenges in modern cosmology, motivating the exploration of modified theories of gravity as alternatives to the standard ΛCDM framework. In this work, we investigate the cosmological evolution of a spatially flat Friedmann–Lemaitre–Robertson–Walker (FLRW) universe within the framework of f(R,G) gravity, where both the Ricci scalar R and the Gauss–Bonnet invariant G contribute to the gravitational dynamics. We consider quadratic corrections to the Ricci scalar and Gauss-Bonnet invariant, with (ξ) and (λ) denoting the corresponding coupling parameters. To obtain the cosmological solutions, the modified field equations are analyzed by adopting a periodically varying deceleration parameter through a suitable parametrization of the scale factor. The resulting cosmological model is examined in detail in terms of its expansion history, dynamical evolution, scalar field correspondence, and energy conditions. The model describes an initially singular Universe characterized by vanishing volume and divergent energy density, followed by a transition to an accelerated expansion phase. The evolution of the effective equation-of-state parameter indicates a quintessence-like behavior of the dark-energy sector during the relevant stages of cosmic evolution. Furthermore, the model gradually approaches the behavior of the standard ΛCDM cosmology at late times. The analysis of the energy conditions and cosmological parameters demonstrates that the proposed quadratic f(R,G) model provides a physically viable description of the observed late-time cosmic acceleration. These results indicate that the combined quadratic Ricci and Gauss–Bonnet corrections can provide an effective geometric mechanism for describing the accelerated expansion of the Universe without requiring a separate dark-energy component.
Abstract: The late-time accelerated expansion of the Universe remains one of the major challenges in modern cosmology, motivating the exploration of modified theories of gravity as alternatives to the standard ΛCDM framework. In this work, we investigate the cosmological evolution of a spatially flat Friedmann–Lemaitre–Robertson–Walker (FLRW) universe within...
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