GNSS-derived TEC signatures of co-seismic ionospheric disturbances triggered by the Mw 7.6 Cayman Islands earthquake of 8 February 2025
by Sambit Prasanajit Naik, Siva Sai Kumar Rajana, Sampad Kumar Panda, Chiranjeevi G. Vivek & Devanshu GhildiyalThis study examines the Co-seismic Ionospheric Disturbances (CIDs) triggered by Mw 7.6 Cayman Islands earthquake along the transform fault setting in the Caribbean Sea on 8 February 2025 using the GNSS-based Total Electron Content (TEC) observations. The significance of characterizing the effects of this particular earthquake event through probing ionospheric perturbations lies in its occurrence under quiet solar and geomagnetic conditions. This provides unambiguous identification of ionospheric perturbations caused by lithospheric forcing from below, and valuable insights into solid Earth-ionosphere coupling mechanisms. The earthquake exhibited the two-stage rupture process, beginning with a slow initial sub-shear rupture phase followed by a rapid acceleration into the supershear regime. This rupture behavior facilitated the generation of strong ground motion and produced atmospheric acoustic-gravity waves (AGWs) that propagated upward and reached ionospheric altitudes. Notably, filtered TEC data exhibited distinct oscillations following the earthquake, which clearly showed the CIDs signatures with the amplitudes reaching up to 0.8 TECU. The filtered TEC values also exhibited the spatial asymmetry due to the atmospheric effects and the ambient geomagnetic field. Also, spectral analysis confirmed the dominant acoustic wave frequencies (2–4 mHz) and horizontal propagation velocities (~ 1.34 km/s) aligning with the theoretical acoustic wave speeds, which further confirmed the signatures of seismic origin ionospheric disturbances. These findings reinforce the role of CIDs as reliable indicators of seismic activity in transform plate boundary settings and highlight the potential use of GNSS networks for real-time earthquake monitoring. Source: https://doi.org/10.1007/s12145-026-02134-6
Peculiar Storm-Time Dynamics of the Summer Solstice Ionosphere over the Indian Region During the June 2025 Geomagnetic Storm
by Prajakta Chougule, Sugumar Iswariya, Siva Sai Kumar Rajana, Dadaso Shetti, Susmita Chougule, Chiranjeevi G. Vivek, J. R. K. Kumar Dabbakuti, Ajeet K. Maurya,Sudipta Sasmal, and Sampad Kumar PandaThis study investigates the temporal and latitudinal variability of the ionosphere over the Indian longitude region during the intense geomagnetic storm from 1 to 3 June 2025, using GNSS receiver observations and magnetometer recordings, along with space-based measurements from in situ Swarm satellite, COSMIC-2 radio occultation, GUVI/TIMED-derived O/N2 ratios, and model-derived electric fields. This particular event is relatively new and is characterized by the bifurcated variation with two distinct main phases separated by a short-lived recovery phase. The results revealed distinct features associated with the geomagnetic storm, including positive and negative ionospheric phases, thermospheric compositional changes, and the latitudinal propagation of disturbances. On 1 June, the observed strong positive ionospheric storm was driven by Prompt Penetration Electric Fields (PPEFs) and equatorward neutral winds, which triggered the upliftment of F-region plasma to higher altitudes through the enhanced equatorial fountain effect, leading to an unusually long-lasting Total Electron Content (TEC) enhancement from day to night. The analysis also revealed the distinct latitudinal behaviour, exhibiting the clear poleward extension of the Equatorial Ionization Anomaly (EIA) crest and significant TEC enhancements (~150–200% of the quiet day values) from low to mid latitudes as compared to the equatorial location through an efficient plasma redistribution. Conversely, pronounced negative ionospheric storm effect at almost all latitudinal locations on 2 June confirms complex and unusual storm-time dynamics, with inhibited upward plasma drifts due to the presence of Disturbance Dynamo Electric Fields (DDEFs), while the thermospheric O/N2 ratio caused an extensive decrease in electron density over the Indian region. Minor negative storm noticed on 3 June coincides with the storm recovery period, reflecting prolonged disturbance dynamo effects and gradual recovery in thermospheric conditions. Overall, the current study highlights the strong sensitivity of the regional ionosphere to prevailing coupled electrodynamic-thermospheric forcing during the June 2025 geomagnetic storm that has not yet been reported for this event over the Indian longitude sector. Moreover, the findings from this study underscore peculiar storm-time behaviour of summer solstice ionosphere over the Indian longitude sector, driven by complex coupled processes which could be incorporated into ionospheric models and forecasting frameworks.
Source: https://doi.org/10.3390/atmos17020189
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