Lateral Deformation of Large-scale Coronal Mass Ejections during the Transition from Non-radial to Radial Propagation

TL;DR

This study investigates how large limb CMEs transition from non-radial to radial propagation in the low corona by analyzing two events from the same active region with multi-wavelength data. It reveals that lateral deformation—specifically bulging of the upper CME flank toward the higher corona—drives the directional shift, after which the bulged flank becomes the radial leading edge. PFSS-based ambient fields show strong loop tension constraining radial expansion during the transition, while a high magnetic-pressure region near the eruption interacts with the CME evolution. The filament associated with the eruption is largely displaced south during the transition, highlighting the complex, non-self-similar evolution of CMEs and the challenges this poses for space-weather forecasting.

Abstract

Many coronal mass ejections (CMEs) initially propagate non-radially, and then transition to radial propagation in the corona. This directional transition is a significant process that determines a CME's space weather effects but remains poorly understood. Based on multi-wavelength observations, we investigate the transition from non-radial to radial propagation in the low corona for two large-scale CMEs from the same active region on the solar limb. In the beginning, both CMEs move in a non-radial direction, beneath a system of overlying loops that are roughly parallel to the flux-rope axis. The CMEs laterally deform by bulging their upper flanks in the non-radial stage toward the higher corona, which results in the transition to a radial propagation direction approximately 25$^\circ$ away from the eruption site. After the directional transition, the non-radial-stage upper flank becomes the leading edge in the radial stage. Although the overlying loops do not strap over the flux rope, their strong magnetic tension force constrains the radial expansion of part of the CME during the transition by acting on the flux-rope legs. A major portion of the filament is displaced to the southern part of a CME in the radial stage, which implies the complexity of observational CME features. This study presents the first investigation of the lateral deformation during the transition of CMEs from non-radial to radial in the low corona, and makes an essential contribution to the complete CME evolution picture.

Figures (9)

• Figure 1: The CME on 2023 March 3 observed near the Earth. (a)--(b) The erupted filament observed by SDO AIA 304 Å, and (c) by SATech-01 SUTRI 465 Å. In (a)--(c) the symbol "×" marks the eruption site, and the white arrows indicate the erupted filament material and its approximate motion direction. (d)--(h) The CME in GOES SUVI 284 Å running-difference images, where the three short arrows in (e) mark the CME leading edge in the non-radial stage, the rightward arrows in (e)--(h) indicate the bulging upper CME flank, the cyan arrows in (f)--(h) point to the filament, and the downward arrows in (g)--(h) mark the northward expanding part. (i) The CME in a SOHO LASCO C2 running-difference image, where the red arrow indicates the approximate non-radial motion direction of the filament, the dashed arrow points to the radial propagation direction of the CME (along $\sim$$-$1° latitude, which is $\sim$24° away from the eruption site marked by the blue line), and the cyan arrow denotes a CME core ("Core 2", as labeled in Figure \ref{['fig:plot03sta']}(i)). The dashed square in (d) represents the field of view of (a)--(c). For all panels, the abscissa and ordinate are scaled in arcseconds in the helioprojective coordinates. An animation for this figure is available, which contains two parts. The first part is for (a)--(b), which begins at 2023-03-03T17:49 UT and ends at 2023-03-03T18:20 UT. The second part corresponds to (d)--(i), where the GOES SUVI images are overlaid on the LASCO C2 images. The second part runs from 2023-03-03T17:47 UT to 2023-03-03T19:11 UT, with an arrow highlighting the CME leading edge in the LASCO C2 image at 18:11 UT. The real-time animation duration is $\sim$8 s. In the first part of the animation, the time, 0° latitude, and the solar limb are marked, and in the second part, the time and solar limb are shown.
• Figure 2: The CME on 2023 March 3 observed by STEREO A. (a)--(c) Running-difference images of STEREO A EUVI 195 Å, where the rightward white arrows mark the bulging upper flank, and the cyan arrow in (a) indicates the CME leading edge in the non-radial stage. (d)--(f) Running-difference images of STEREO A COR1 overlaid with running-difference images of EUVI 195 Å, where the cyan arrows denote the bulged flank entering COR1 as the leading edge in the radial stage. (g)--(h) Running-difference COR1 images combined with EUVI 304 Å images, where the white arrows mark the trailing part of the erupted filament in EUVI 304 Å, and the cyan arrows indicate a CME core ("Core 1") in COR1 corresponding to the leading part of the filament. (i) STEREO A COR2 image superimposed with a running-difference COR1 image and an EUVI 304 Å image, where the arrow points to another CME core ("Core 2", also shown in Figure \ref{['plot03']}(i)). The axes are labeled similarly to Figure \ref{['plot03']}. An animation for this figure is available, which has the same field of view as (i), where the COR2 images are overlaid with running-difference images of COR1 and EUVI 195 Å. The animation begins at 2023-03-03T17:45 UT and ends at 2023-03-03T19:57 UT, and the real-time duration is $\sim$3 s. The times are displayed in the animation.
• Figure 3: The CME on 2023 March 4 observed near the Earth. (a)--(b) The erupted hot channel/flux rope observed by SDO AIA 131 Å/211 Å, which is indicated by the white arrows. (c)--(h) The CME imaged by GOES SUVI 284 Å, where the arrows in (d) mark the CME leading edge in the non-radial stage, the rightward white arrows in (d)--(h) denote the bulging upper CME flank, the cyan arrows in (f)--(h) indicate the indentation on the CME flank, and the downward white arrow in (h) points to the northward expanding part. (i) The CME observed in SOHO LASCO C2, where the red arrow, dashed arrow and blue line have the same meanings as in Figure \ref{['plot03']}(i). The symbol "×" in (a)--(h) marks the eruption site. The dashed square in (c) represents the field of view of (a)--(b). The coordinate axes are similar to those in Figure \ref{['plot03']}. An animation for this figure is available, which consists of two parts. The first part corresponds to (b), which begins at 2023-03-04T15:05 UT and ends at 2023-03-04T15:33 UT. The second part is for (c)--(i), where the GOES SUVI images are superimposed on the LASCO C2 images. The second part runs from 2023-03-04T15:11 UT to 2023-03-04T16:35 UT, with an arrow indicating the CME leading edge in the LASCO C2 image at 15:35 UT. The real-time animation duration is $\sim$11 s. The annotations in the animation are similar to those in the animation for Figure \ref{['plot03']}.
• Figure 4: The CME on 2023 March 4 observed by STEREO A. (a)--(e) Running-difference images of STEREO A EUVI 195 Å, where the rightward white arrows mark the bulging upper flank, the cyan arrow in (a) indicates the CME leading edge during the non-radial propagation, and the cyan arrows in (c)--(e) point to the indentation on the CME flank, similar to those in Figure \ref{['plot04']}(f)--(h). (f)--(h) Running-difference images of STEREO A COR1 overlaid with running-difference images of EUVI 195 Å, where the cyan arrows denote the bulged flank appearing as the leading edge in the radial stage in COR1. The three pink arrows in (g)--(h) mark a plausible shock ahead of the radial leading edge, but the shock is not definitive due to the noisy imaging. (i) STEREO A COR2 image superimposed with a running-difference COR1 image and an EUVI 304 Å image, showing the CME propagating nearly radially in COR2. The axes are labeled as in Figure \ref{['plot03']}. An animation for this figure is available, which has the same field of view as (i), where the COR2 images are superimposed with running-difference images of COR1 and EUVI 195 Å. The animation runs from 2023-03-04T15:05 UT to 2023-03-04T17:17 UT, and the real-time duration is $\sim$3 s. The times are shown in the animation.
• Figure 5: The magnetic loops overlying the eruption site. (a) PFSS-extrapolated magnetic loops (cyan curves) superimposed on an SDO HMI line-of-sight magnetogram taken around the eruption on 2023 March 3, where the inset shows a zoomed-in view of the magnetogram centered on the eruption site (marked by the symbol "×"). (b) SDO AIA 171 Å image showing the overlying loops, where the symbol "×" denotes the eruption site, and the cyan arrow indicates the brightened erupting filament. (c) A time-distance profile along the slit marked by the white line in (b), where the vertical dashed line marks the image time in (b). (d) Similar to (a), showing the magnetic loops in the view around the eruption on 2023 March 4. (e) Similar to (b), but for the eruption on March 4, where the cyan arrow indicates the erupted flux rope in an edge-on view. (f) Similar to (c), but the time-distance profile is made along the slit in (e) where the dashed line marks the time in (e). The pink arrows in (a) and (d) point to the eruption site denoted by the symbol "+×".