📝 SummarXiv

Abstract

We investigate the solar origin and heliospheric evolution of an intense geomagnetic storm that occurred on March 23-24, 2023. Despite multiple candidate CMEs observed between March 19-21, a weak CME detected on March 19 at 18:00 UT was identified as the cause, originating from the eruption of a longitudinal-filament channel near center of the sun. The channel underwent a smooth transition to eruption phase without detectable low coronal signatures. Wide-angle heliospheric imaging revealed asymmetric expansion and acceleration by solar wind drag, achieving an average CME velocity of $\approx$640 km/s. The radial evolution of the interplanetary coronal mass ejection (ICME) was analyzed by three spacecraft in close radial alignment. Arrival times and propagation speeds were consistent across spacecraft, with a 21 hour delay between STEREO-A and WIND attributed to solar rotation and longitudinal separation. The ICME exhibits magnetic cloud (MC) signatures characterized by right-handed helicity, enhanced density at all three spacecraft. The MC underwent expansion (radial-size increases from 0.08AU at SolO to 0.18AU at STEREO-A), decrease in magnetic field strength with distance; $B_{av}\propto R_H^{-1.97}$ (SolO-STA) and $B_{av}\propto R_H^{-1.53}$ (SolO-WIND). The MC axis is inclined with the ecliptic at $-69^o$ at SolO, $-25^o$ at STA and $-34^o$ at WIND, indicating rotation during heliospheric transit. Importantly, the storm's main phase leads to a peak intensity ($SYM-H=-169$nT) occurring at 24/02:40UT followed by a second peak ($SYM-H=-170$nT) at 24/05:20UT due to density enhancement towards MC's tail. The study emphasizes the significant geoeffectiveness of weak, stealth CMEs with southward Bz and density enhancements.