Influence of ICME-driven Magnetic Cloud-like and Sheath Region induced Geomagnetic Storms in causing anomalous responses of the Low-latitude Ionosphere: A Case Study

TL;DR

This study investigates how non-fluctuating penetration electric fields and neutral wind variations, rather than storm strength, cause anomalous low-latitude ionospheric responses during ICME-driven geomagnetic events.

Contribution

It highlights the significant role of non-fluctuating penetration electric fields in causing ionospheric enhancements under weak geomagnetic conditions, challenging the focus on storm intensity alone.

Findings

Enhanced TEC during weak geomagnetic conditions linked to non-fluctuating IMF.

Storm intensity alone does not determine ionospheric impact.

Penetration electric fields and neutral winds are key drivers of anomalies.

Abstract

This work shows an anomalously enhanced response of the low-latitude ionosphere over the Indian sector under weak geomagnetic conditions (October 31, 2021) in comparison to a stronger event (November 04, 2021) under the influence of an Interplanetary Coronal Mass Ejection (ICME)-driven Magnetic Cloud (MC)-like and sheath regions respectively. The investigation is based on measurements of the Total Electron Content (TEC) from Ahmedabad (23.06$^\circ$N, 72.54$^\circ$E, geographic; dip angle: 35.20$^\circ$), a location near the northern crest of the Equatorial Ionization Anomaly (EIA) over the Indian region. During the weaker event, the observed TEC from the Geostationary Earth Orbit (GEO) satellites of Navigation with Indian Constellation (NavIC), showed diurnal maximum enhancements of about 20 TECU over quiet-time variations, as compared to the stronger event where no such enhancements are present. It is shown that storm intensity (SYM-H) or magnitude of the southward Interplanetary Magnetic Field (IMF) alone is unable to determine the ionospheric impacts of this space weather event. However, it is the non-fluctuating southward IMF and the corresponding penetration electric fields, for a sufficient interval of time, in tandem with the poleward neutral wind variations, that determines the strengthening of low-latitude electrodynamics of this anomalous event of October 31, 2021. Therefore, the present investigation highlights a case for further investigations of the important roles played by non-fluctuating penetration electric fields in determining a higher response of the low-latitude ionosphere even if the geomagnetic storm intensities are significantly low.