Abstract:
Using multi-instrument and multiwavelength observations, we studied a coronal mass ejection (CME) that led to an
intense geomagnetic storm on 2023 April 23. The eruption occurred on April 21 in solar active region (AR) 13283
near the disk center. The AR was in its decay stage, with fragmented polarities and a preexisting long filament
channel a few days before the eruption. The study of the magnetic field evolution suggests that the flux rope
(filament) was built up by monotonous helicity accumulation over several days, and furthermore, converging and
canceling fluxes led to a change in helicity injection, resulting in an unstable nature of the magnetic flux rope
(MFR) and its further eruption. Importantly, the CME morphology revealed that the MFR apex underwent a
rotation of up to 56°in clockwise direction owing to its positive helicity. The CME decelerates in the field of view
(FOV) of the Large Angle Spectrometric Coronagraph and has a plane-of-sky velocity of 1226 km s−1 at 20 Re. In
the FOV of the Heliospheric Imager, the lateral expansion of the CME is tracked better than the earthward motion.
This implies that the arrival time is difficult to assess. The in situ arrival of the interplanetary CME shock was at
07:30 UT on April 23, and a geomagnetic storm commenced at 08:30 UT. The flux rope fitting to the in situ
magnetic field observations reveals that the magnetic cloud flux rope orientation is consistent with its near-Sun
orientation, which has a strong negative Bz-component. The analysis of this study indicates that the near-Sun
rotation of the filament during its eruption to the CME is the key to the negative Bz-component and consequently
the intense geomagnetic storm.
