Investigating the impact of the dynamic solar wind on the propagation of a coronal mass ejection with two models and multi-spacecraft measurements

TL;DR

This study addresses how a dynamically evolving solar wind affects CME propagation in the heliosphere. It combines two CME representations—a non-magnetised cone and a linear force-free spheromak—within the Icarus 3D MHD framework to simulate a CME observed on SOL2021-09-23 and compare against multi-spacecraft in situ data. The dynamic wind, driven by time-varying magnetogram inputs, yields greater CME deceleration and reveals that the spheromak flux rope better reproduces magnetic ejecta and sheath signatures across multiple spacecraft, though arrivals at L1 remain challenging to match. The work demonstrates the importance of time-dependent boundary conditions for improving space weather forecasting and sets the stage for modeling CME–high-speed-stream interactions in a realistic solar wind environment.

Abstract

Coronal mass ejections (CMEs) are the main drivers of disturbances in the solar heliosphere because they propagate and interact with the magnetic field of the solar wind. It is crucial to investigate the evolution of CMEs and their deformation for understanding the interaction between the solar wind and CMEs. We quantify the effect of the dynamic solar wind on the propagation of a CME in the heliosphere with a hydrodynamic plasma cloud-cone model and a linear force-free spheromak model at various locations in the heliosphere. We chose a CME event that launched on SOL2021-09-23T04:39:45 and was observed by multiple spacecraft, namely BepiColombo, Parker Solar Probe, Solar Orbiter, Stereo A and ACE. The solar wind was modelled in the steady and dynamic regimes in the Icarus model. The CME parameters were approximated for the selected event, and two CME models (spheromak and cone) were launched from the inner heliosphere boundary. The obtained synthetic in situ measurements were compared to the observed in situ measurements at all spacecraft. The internal magnetic field of the flux rope was better reconstructed by the spheromak model than by the cone CME model. The cone CME model maintained a nearly constant longitudinal angular extension while somewhat contracting in the radial direction. In contrast, the spheromak model contracted in the longitudinal direction while expanding in the radial direction. The CME sheath and magnetic cloud signatures were better reproduced at the four spacecraft clustered around the CME nose by the spheromak CME model. The dynamic solar wind caused a greater deceleration of the modelled CME than the steady-state solar wind solution. Because the background was homogeneous, the modelled CME properties were only mildly affected by the solar wind regime, however.

Figures (15)

• Figure 1: Configuration of the solar atmosphere during the CME eruption for SOL2021-09-23T04:39:45. The left panel represents the HMI magnetogram, which is saturated between $\pm 1000\;$G. The middle panel represents the AIA 171Å image, and the right panel shows the AIA image overlaid on the magnetogram. The red line shows the approximate polarity-inversion line. The figures were created with JHelioviewer.
• Figure 2: Location of the spacecraft in Stonyhurst coordinates during the eruption of the CME in a top-down view on the ecliptic plane. The theoretical Parker spiral passing at each spacecraft was added. The arrow denotes the propagation direction of the CME.
• Figure 3: Steady (left) and dynamic (right) solar wind configurations before the CME injection at 0.1 au. The radial velocity is plotted with colour levels in the solar equatorial plane, along with the contours of the magnetic field component, $B_r$, to identify the heliospheric current sheet (HCS). The spacecraft are plotted on top of the solar wind.
• Figure 4: Base difference of the LASCO C2 and C3 images. The HMI magnetogram is plotted on the solar disk. Green arrows denote the CME extent.
• Figure 5: Magnetic field magnitude and magnetic field components in RTN coordinates at each spacecraft. The observational data are plotted in black, and the two CME models propagated in the steady solar wind, namely a cone and a spheromak CME model, are represented by the red and purple curves, respectively. The blue and pink shaded areas correspond to the sheath and magnetic ejecta regions, as defined by in situ observations. The vertical blue line shows the arrival of the shock, the vertical green line corresponds to the end of the magnetic cloud of the CME, the magenta line corresponds to the end of the second magnetic cloud, and the vertical orange line shows the end of a part of the solar wind following the CME.