Abstract:
We investigate the solar origin and heliospheric evolution of an intense geomagnetic storm that occurred on 2023 March 23─24. Despite multiple candidate coronal mass ejections (CMEs) observed between March 19 and 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 the center of the Sun. The channel underwent a smooth transition to the 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 ≍640 km s−1. 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 hr delay between STEREO-A (STA) 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 0.08 au at SolO to 0.18 au at STA), a decrease in magnetic field strength with distance; Bav∝RH−1.97 (SolO-STA) and Bav∝RH−1.53 (SolO-WIND). The MC axis is inclined with the ecliptic at −69° at SolO, −25° at STA, and −34° at WIND, indicating rotation during heliospheric transit. Importantly, the storm's main phase leads to a peak intensity (SYM-H= −169 nT) occurring at 24/02:40 UT, followed by a second peak (SYM-H = −170 nT) at 24/05:20 UT due to density enhancement toward MC's tail. The study emphasizes the significant geoeffectiveness of weak, stealth CMEs with southward Bz and density enhancements.
