Investigating Ionospheric Variability During Solar Eclipses Using Multi-Instrument Observations

Solar eclipses provide a unique opportunity to study ionospheric dynamics under controlled solar radiation blockage.This study investigates the response of the ionosphere F-layer during the annular eclipse of 14 October 2023 and the total eclipse of 8 April 2024, both primarily visible across North and South America.Using a multi-instrument approach, we analyse the impact on the ionosphere's Total Electron Content (TEC) and additional parameters, including Very Low Frequency (VLF) signals and the critical frequency of the F2 layer (f0F2), over three-day periods surrounding each eclipse.In this study, we utilised more than sixty GNSS receiver station data from IGS, eleven digisondes from the GIRO network, and four VLF receiver stations along the path of solar eclipses.Vertical TEC (vTEC) and foF2 variations reveal a significant depletion in ionisation during both eclipses, with VLF data exhibiting more pronounced fluctuations.The percentage change in vTEC shows a positive correlation with the degree of solar obscuration.Space-based observations incorporate Swarm and COSMIC-2 satellite data, which consistently demonstrate vTEC depletion along the eclipse trajectories.Additionally, spatiotemporal analyses using the Global Ionospheric Map (GIM) and the German Aerospace Center (DLR) databases further confirm these trends.During the solar eclipse of 14 October 2023, VTEC depletion ranged from 3% to 65%, depending on observation locations and the degree of solar obscuration.In contrast, during the solar eclipse of 8 April 2024, depletion ranged from 20% to 60% based on observation locations.A time delay analysis between the maximum eclipse and maximum TEC modulation highlights ionospheric response time variations at different locations.Geomagnetic data assessments confirm that external disturbances did not significantly influence the results.These findings, derived from two consecutive solar eclipses, enhance our understanding of ionospheric variability under reduced solar radiation and validate existing models of eclipse-induced ionospheric perturbations.This dual approach allows for a detailed characterisation of ionospheric processes, including variations in electron density, production and recombination rates, and propagation effects along eclipse-affected paths.Such an integrative methodology offers new insights into the coupling mechanisms between the ionosphere's layers, enriching the understanding of solar-terrestrial interactions during eclipses.