This study presents the longitudinal dependence of responses of the equatorial/low‐latitude ionosphere over the oceanic regions to geomagnetic storms of 28 May and 8 September 2017. We investigated the interplanetary origins of the storms. Total electron content (TEC) data were obtained from Global Navigation Satellite System stations, located around the oceanic areas in the equatorial/low‐latitude regions. The Rate of change of TEC Index (ROTI) was used as a proxy for ionospheric irregularities over the study locations. Further, variations of the horizontal component of the Earth's magnetic fields, obtained from ground‐based magnetometers were studied. We used ionospheric disturbance currents, polar cap and auroral electrojet indices to monitor the storm time electric fields. The May 2017 storm was driven by sheath and magnetic cloud fields, while the September 2017 storm was driven by sheath fields. We observed a comparative dominance of TEC intensities over the Oceans than over the landlocked areas. Empirically, our results validated a theoretical suggestion of the existence of a dynamic ocean‐ionosphere coupling made by Godin et al. (2015, http://10.0.4.162/s40623-015-0212-4). Prompt Penetration Electric Fields (PPEF) was observed to be a key factor that controls TEC responses to storms. PPEFs caused TEC enhancements, mainly over the Pacific Ocean longitudes during the May 2017 storm and enhanced TEC over the Atlantic Ocean and the Pacific Oceans longitudes during the September 2017 storm. These PPEFs triggered irregularities over the Pacific Ocean longitudes, particularly during the main phase of May 2017 storm. Irregularities were generally inhibited by the September 2017 storm.
Total electron content (TEC) has been used to study the response of the African equatorial/low‐latitude ionosphere to the 17 March 2015 intense storm. Daily variations of symmetric H index, z component of interplanetary magnetic field, polar cap index, and H component of the Earth's magnetic field were analyzed along with TEC obtained from stations classified into western (11.53°E to 5.24°W) and eastern (25.00°E to 40.20°E) sectors. Storm time behavior of TEC was compared with the mean TEC of quiet days. TEC was enhanced over both sectors at the beginning of the storm while it reduced after the main phase as a result of prompt penetration of electric field and disturbance dynamo electric field (DDEF), respectively. The magnetic effect of the disturbed ionospheric electric current showed oscillations and minima in response to prompt penetration of electric field, which further enhanced the equatorial ionization anomaly. The effect of DDEF estimated from the ionospheric disturbance dynamo manifested in the form of decrease in the amplitude of the horizontal component of the Earth magnetic field (H) several hours after the beginning of the disturbance and during the recovery phase. Consequently, ionospheric irregularities were suppressed over all stations in both sectors on 17 and 18 March due to westward DDEF. On the 19 March, however, there was a difference in the pattern of irregularities over both sectors.
This paper investigated the behavior of ionospheric irregularities over the African equatorial ionization anomaly (EIA) crests during intense geomagnetic storms that occurred from 2012 to 2015. Irregularities were monitored using the rate of change of TEC index along with variations of the horizontal component of the Earth's magnetic field (H) and ionospheric electric current disturbance (Diono). The predictive capability of the Prompt Penetration Equatorial Electric Field Model (PPEFM) was assessed by comparing prompt penetration electric field (PPEF) inferred from interplanetary electric field and Diono with PPEF derived from the PPEFM, with emphasis on how well the model reproduced enhancement/reduction in the prereversal enhancement (PRE). Eastward PPEF triggered short duration irregularities on
Perturbations in the solar atmosphere are the major origins of geomagnetic storms. Reconfiguration of magnetic fields in the solar atmosphere causes uplift of materials from the solar chromosphere into the corona. These relatively cool, but dense materials are suspended against gravity at greater heights by magnetic tension in the dips of the field lines, appearing by absorption against the hotter and brighter background (Carlyle, 2016). These materials could be elongated in structures, to the order of thousands of kilometers in length to form filaments, which could, in turn erupt from the solar coronal surface as Coronal Mass Ejection (CME). CMEs, particularly the Earth-directed ones are the sources of space weather events (e.g., geomagnetic storms) on the Earth. High Speed Streams (HSSs) from the Sun's coronal holes are the sources of the Corotating Interaction Regions (CIRs) which also known to cause geomagnetic storms (Burlaga & Lepping, 1977;Gosling, 1993). The occurrences of geomagnetic storms do influence the electrodynamics of
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