Solar and interplanetary events that drove two CIR-related geomagnetic storms of 1 June 2013 and 7 October 2015, and their ionospheric responses at the American and African equatorial ionization Anomaly regions

• Published in: Advances in space research 2022-03, Vol.69 (5), p.2168-2181
• Main Authors: Oyedokun, Oluwole J., Amaechi, P.O., Akala, A.O., Simi, K.G., Ogwala, Aghogho, Oyeyemi, E.O.
• Format: Article
• Language: English
• Subjects: Corotating Interacting Region; Geomagnetic storm; Ionospheric irregularities; Total electron content
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/j.asr.2021.12.027

•1 June 2013 geomagnetic storm was driven by weak CME and HSSs, while 7 October 2015 storm was HSS driven.•Storm at day side location had enhancement in plasma and poleward movement of EIA crests & vice versa.•Daytime eastward PPEF intensifies plasma fountain to cause positive ionospheric response & vice versa.•The season of storm’s occurrence is a factor that also dictates ionospheric response to a storm.•Stronger and well-developed EIA crests were observed over the American sector than African sector. This study investigates the sequence of solar and interplanetary events that drove the 1 June 2013 and October 2015 geomagnetic storms and how the American (68°–78oE) and African (32°–42oE) Equatorial Ionization Anomaly (EIA) regions responded to them. We constructed the EIA structures by using Total Electron Content (TEC) and ionospheric irregularities derived from Global Navigation Satellite System (GNSS) receivers along with the study locations. We also analyzed disturbed time ionospheric electric field and model data alongside the GNSS data. The 1 June 2013 geomagnetic storm was driven by a combination of a weak CME and HSSs from solar coronal holes, while the 7 October 2015 storm was solely driven by HSSs. Storm-time hemispherical asymmetry in ionospheric TEC and irregularities distributions was consistently observed. Storm with minimum SYM-H value at day-side locations caused enhancement in plasma ionization and pole-ward movement of EIA crests, while storm with minimum SYM-H value at night-side locations caused reduction in plasma ionization and equator-ward movement of EIA crests. The phase of responses of the ionosphere to geomagnetic storms depends on the local time of storm’s onset and local time of the storm’s main phase minimum which also determine the orientation of Prompt Penetration Electric Field (PPEF). At storm’s onset time in the low latitude regions, the main storm-induced electric field is PPEF. Daytime eastward PPEF intensified plasma fountain to increase the EIA crests locations, while nighttime westward PPEF reversed plasma fountain to cause equator-ward collapse of the EIA crests. However, around the storm’s recovery phase, under southward turning of IMF Bz, depending on their orientations, PPEF and Disturbed Dynamo Electric Field (DDEF) collectively influenced low latitude ionosphere. Eastward PPEF at the Pre-Reversal Enhancement (PRE) time enhanced irregularities generation, while westward DDEF at PRE time inhibited irregularitie