Solar Origins of August 26, 2018 Geomagnetic Storm: Responses of the Interplanetary Medium and Equatorial/Low‐Latitude Ionosphere to the Storm. Issue 10 (5th October 2021) - Akala, A. O.
Abstract: This study investigates the solar origins of August 26, 2018 geomagnetic storm and the responses of the interplanetary medium and equatorial/low‐latitude ionosphere to it. We used a multiinstrument approach, with observations right from the solar surface to the Earth. Our results showed that the G3 geomagnetic storm of August 26, 2018 was initiated by a solar filament eruption of August 20, 2018. The storm was driven by an aggregation of weak Coronal Mass Ejection (CME) transients and Corotating Interaction Regions/High Speed Streams (CIR/HSSs). The solar wind energy which got transferred into the magnetosphere drove electrical currents, that penetrated down into the ionosphere to produce weak Prompt Penetration Electric Field (PPEF) (0.3 mV/m). For this reason, during the storm, at daytime, plasma densities of the Equatorial Ionization Anomaly (EIA) crests were localized within the inner flank of ±15° magnetic latitude strip. We attributed this to the extreme quietness of year 2018. There was a clear hemispherical asymmetry, with higher Total Electron Content (TEC) in the northern hemisphere. The major determining factors of the ionospheric responses during the various phases of this storm were the local time of the storm's onset, local time of storm's minimum SYM‐H, and changes in thermospheric O/N2 . Plain Language Summary: This geomagnetic storm was initiated by a solar filament eruption of August 20, 2018, and driven by an aggregation of weak CME transients and CIR/HSSs. The weak PPEF during the storm, which is associated with the extreme quietness of year 2018 caused plasma densities to localize at locations that are not up to the EIA crests. A clear hemispherical asymmetry, with higher TEC in the northern hemisphere was observed. The determining factors for ionospheric responses to this storm are; local time of the storm's onset, local time of storm's minimum SYM‐H, and changes in thermospheric O/N2 . Furthermore, one major factor that is hindering our progress in developing robust prediction capabilities for geomagnetic storm is the characteristic peculiarity of each storm. August 26, 2018 geomagnetic storm is peculiar due to the intertwined physical processes that led to its occurrence. To develop future forecasting capabilities for this type of a complex storm, a comprehensive understanding of the intertwined physical processes is required, which this study provided. Key Points: August 26, 2018 geomagnetic storm was initiated by a solar filament eruption of August 20, 2018 On the whole, this storm was driven by an aggregation of CME transients and CIR/HSSs The resultant ionospheric electric field and PPEF was too week during the storm to support a superfountain effect