This article presents the recent extreme and rare G5-level geomagnetic storm (Mother’s Day Storm) effects on the equatorial and low-latitude ionosphere observed at the Peruvian sector by the Jicamarca (11.9°S, 76.8°W, magnetic dip 1°N) incoherent scatter radar and associated instruments. This storm was produced by multiple Earth-directed coronal mass ejections, which generated significant modifications in the Earth’s magnetic field, leading to the Sym-H of ~-518 nT. On the dayside, due to the strong eastward penetration electric field, vertical plasma drift and equatorial electrojet (EEJ) enhanced for 2-3 hours and remained consistent at values of ~95 m/s and 260 nT between 1700 and 1900 UT (1200 and 1500 LT). At the same time, vertical E B plasma drift uplifted the equatorial ionosphere, producing the dusk-side super plasma fountain and transferring electron density to higher latitudes. A huge increase (~1325 %) in electron density (from 11 to 142 TECu) is observed at low and mid-latitudes from ~20o S to 50oS between 2000-0400 UT (1500-2300 LT). The strong westward penetration electric field suppressed pre-reversal enhancement, leading to downward plasma drift (~-96 m/s) at around 2400 UT (1900LT). Overnight, the vertical plasma drift fluctuated between ±90 m/s owing to under- and over-shielding electric fields. On May 11, a long-duration (~6-8 hours) westward penetration electric field induced downward plasma drift and a strong westward EEJ (-240 nT). In the main and early recovery phase, consistent short- and long-duration penetration electric fields persisted for approximately 30 hours, with periods of 48 and 90 minutes.

We found the signatures of the multiple prompt penetration electric fields (PPEF) and the disturbance dynamo (DD) electric field having impacts on the East Asian sector ionosphere along the meridional chain thoroughly from the equator, low-mid to high latitudes during the space weather event of 03-05 November 2021. The observation is made on GPS-TEC, digisonde, and magnetometer stations. In the main phase of the storm, intense modulations of VTEC (vertical total electron content) and foF2 (critical frequency) are observed as coherently fluctuating with IEF (interplanetary electric field) and IMF Bz reorientations. It is diagnosed that the oscillations in the DP2 (disturbance polar current 2) current system directly penetrate meridianally from high to equatorial latitudes, leading to the significant changes in ionospheric electrodynamics that governs the density fluctuations. The wavelet spectra of VTEC, foF2, h’F (virtual height), H-components and IEF give a result of common and dominant periodicity occurring at ~1hr. This result suggests that the wavelike oscillations of VTEC and foF2 and H component are associated with PP electric fields.

This study presents ultra-low frequency (ULF) Pc5 discrete spectrum simultaneously observed in the magnetosphere and high- to low-latitude ionospheres near noon hours (~10-14 MLT) during the recovery phase of geomagnetic storm on November 4, 2021. During the recovery phase, magnetospheric toroidal mode oscillations (GOES-16 Bn) appeared according to solar wind dynamic pressure enhancements after GOES Bp and Be (poloidal mode) oscillations precede during high solar wind speeds. When Bn oscillates, the ionospheric line-of-sight (LOS) velocity and echo power oscillate at the same discrete frequencies of 1.7 and 2.2 mHz (9.7 and 7.5 min), observed by Super Dual Auroral Radar Network (SuperDARN) at Saskatoon (eastward LOS). The period of negative LOS velocity (away from the radar) for 7.5 min or 9.7 min corresponds to echo power increase. This signifies that both the ionospheric density and poleward convection velocity increase are driven by the periodic forcing of the convection electric field and energetic electron precipitation. The same frequency pulsations have also been observed in the geomagnetic field (H-component) and Global Positioning System (GPS) total electron content (TEC) from high- to low-latitude ionosphere. The oscillation frequency of the H-component is consistently preserved at 1.7 mHz (9.7 min) down to low latitudes. The Pc5 oscillations at high to low latitudes can be attributed to toroidal mode Alfven waves and the compressional mode propagating across magnetic field lines as well as the fast magnetosonic waveguide mode at work by the solar wind dynamic pressure enhancements at high solar wind speeds.enhancements at high solar wind speeds.enhancements at high solar wind speeds.enhancements at high solar wind speeds.enhancements at high solar wind speeds.