An Intense Geomagnetic Storm Originated from Stealth Coronal Mass Ejection: Remote and In Situ Observations by Near Radially Aligned Spacecraft

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; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> <mml:mi>v</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>H</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.97</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> (SolO-STA) and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> <mml:mi>v</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>H</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.53</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> (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.