Responses of the African-European equatorial-, low-, mid-, and high-latitude ionosphere to geomagnetic storms of 2013, 2015 St Patrick’s Days, 1 June 2013, and 7 October 2015

Abstract

This study investigates ionospheric responses to 2013 and 2015 St. Patrick’s Days (CME-driven), 1 June 2013 and 7 October 2015 (CIR-driven) geomagnetic storms over the African-European equatorial-, low-, mid-, and high-latitude regions. We constructed the Equatorial Ionization Anomaly (EIA) of Total Electron Content (TEC) and ionospheric irregularities using data derived from Global Navigation Satellite System (GNSS) receivers along 30°–45°E meridian lines. TEC intensities and EIA crests’ locations were significantly influenced by geomagnetic storms. Asymmetries in EIA crests’ locations, attributable to neutral wind effect were generally observed, consistently higher in the northern hemisphere than the southern hemisphere. Of all the four geomagnetic storms, storm of 17 March 2015 was the most intense and most impactful on the ionosphere. Generally, the two CME-driven storms were more geoeffective than the two CIR-driven storms. The phases of responses of the ionosphere to storms were dependent on geomagnetic storms’ onset time. Daytime onset time produced eastward PPEF which intensified forward plasma fountain to cause pole-ward expansion of the African-European EIA structure, while night-time westward PPEF reversed plasma fountain to cause equator-ward shrinking of the EIA structure. At the equatorial/low-latitude regions, ionospheric irregularities were influenced by PPEF orientation, and they were confined to night-time and early morning hours. At high latitudes, ionospheric irregularities were related to auroral activities, and they spread across both daytime and night-time hours at storm-time period.