Multi-Spacecraft Observations of the Rotation and Non-Radial Motion of a CME Flux Rope causing an intense geomagnetic storm

TL;DR

This study analyzes the rotation and non-radial motion of a CME flux rope from multiple spacecraft observations, revealing how coronal magnetic fields influence CME trajectory and rotation, ultimately causing a severe geomagnetic storm.

Contribution

It provides new insights into the role of coronal magnetic energy gradients in CME rotation and deflection, using multi-spacecraft data and advanced magnetic field modeling.

Findings

CME deviated by about 45° in longitude and 30° in latitude from source region.

The flux rope rotated approximately 95° in the low corona.

The flux rope's orientation at 1 AU matched the low corona rotation, linking the two.

Abstract

We present an investigation of the rotation and non-radial motion of a coronal mass ejection (CME) from AR 12468 on 2015 December 16 using observations from SDO, SOHO, STEREO A and Wind. The EUV and HMI observations of the source region show that the associated magnetic flux rope (MFR) axis pointed to the east before the eruption. We use a nonlinear fore-free field (NLFFF) extrapolation to determine the configuration of the coronal magnetic field and calculate the magnetic energy density distributions at different heights. The distribution of the magnetic energy density shows a strong gradient toward the northeast. The propagation direction of the CME from a Graduated Cylindrical Shell (GCS) modeling deviates from the radial direction of the source region by about 45 degr in longitude and about 30 degr in latitude, which is consistent with the gradient of the magnetic energy distribution around the AR.The MFR axis determined by the GCS modeling points southward, which has rotated counterclockwise by about 95 degr compared with the orientation of the MFR in the low corona.The MFR reconstructed by a Grad-Shafranov (GS) method at 1 AU has almost the same orientation as the MFR from the GCS modeling, which indicates that the MFR rotation occurred in the low corona. It is the rotation of the MFR that caused the intense geomagnetic storm with the minimum Dst of -155 nT. These results suggest that the coronal magnetic field surrounding the MFR plays a crucial role in the MFR rotation and propagation direction.