Evidence of a complex structure within the 2013 August 19 coronal mass ejection

Abstract

Context. Late on 2013 August 19, a coronal mass ejection (CME) erupted from an active region located near the far-side central meridian from Earth’s perspective. The event and its accompanying shock were remotely observed by the STEREO-A, STEREO-B, and SOHO spacecraft. The interplanetary counterpart (ICME) was intercepted by MESSENGER near 0.3 au and by both STEREO-A and STEREO-B near 1 au, which were separated from each other by 78° in heliolongitude. Aims. The main objective of this study is to follow the radial and longitudinal evolution of the ICME throughout the inner heliosphere and to examine possible scenarios for the different magnetic flux-rope configuration observed on the solar disk and measured in situ at the locations of MESSENGER and STEREO-A, separated by 15° in heliolongitude, and at STEREO-B, which detected the ICME flank. Methods. Solar disk observations are used to estimate the “magnetic flux-rope type”, namely, the magnetic helicity, axis orientation, and axial magnetic field direction of the flux rope. The graduated cylindrical shell model is used to reconstruct the CME in the corona. The analysis of in situ data, specifically the plasma and magnetic field, is used to estimate the global interplanetary shock geometry and to derive the magnetic flux-rope type at different in situ locations, which is compared to the type estimated from solar disk observations. The elliptical cylindrical analytical model is used for the in situ magnetic flux-rope reconstruction. Results. Based on the CME geometry and on the spacecraft configuration, we find that the magnetic flux-rope structure detected at STEREO-B belongs to the same ICME detected at MESSENGER and STEREO-A. The opposite helicity deduced at STEREO-B might be due to that fact that it intercepted one of the legs of the structure far from the flux-rope axis, in contrast to STEREO-A and MESSENGER, which were crossing through the core of the magnetic flux rope. The different flux-rope orientations measured at MESSENGER and STEREO-A probably arise because the two spacecraft measure a curved, highly distorted, and rather complex magnetic flux-rope topology. The ICME may have suffered additional distortion in its evolution in the inner heliosphere, such as the west flank propagating faster than the east flank when arriving near 1 au. Conclusions. This work illustrates how a wide, curved, highly distorted, and rather complex CME showed different orientations as observed on the solar disk and measured in situ at 0.3 au and near 1 au. Furthermore, the work shows how the ambient conditions can significantly affect the expansion and propagation of the CME and ICME, introducing additional irregularities to the already asymmetric eruption. The study also manifests how these complex structures cannot be directly reconstructed with the currently available models and that multi-point analysis is of the utmost importance in such complex events.

On the Mesoscale Structure of Coronal Mass Ejections at Mercury’s Orbit: BepiColombo and Parker Solar Probe Observations

“…The GCS model consists of a parameterized shell (described by six variables) that can be projected onto nearly simultaneous coronagraph images from different perspectives and is then manually adjusted to best match the CME structures seen in the data. Despite being associated with uncertainties due to the user's subjectivity when performing a fit (e.g., Verbeke et al 2023), the GCS model is widely used in CME and space weather research (see, e.g., Palmerio et al 2022a;Nieves-Chinchilla et al 2022;Rodríguez-García et al 2022, for some recent applications). An example of GCS fitting applied to the 2022 February 15 CME is shown in the right panels of Figure 3.…”

“…The power of multispacecraft observations of CMEs in situ has been known for several decades (e.g., Burlaga et al 1981), and because of data availability in recent years, multiprobe studies have been gaining increasing attention. However, most multipoint measurements are attained over arbitrary radial and angular separations of the spacecraft involved (e.g., Davies et al 2022;Möstl et al 2022;Rodríguez-García et al 2022), making it particularly difficult to attribute structural and compositional differences of the investigated CMEs to radial evolution, longitudinal (local) variations, or both. Even more so, the difficulties only increase as CMEs are probed beyond 1 au and toward the outer heliosphere, mainly due to heightened chances of interactions and mergers of initially separated structures (e.g., Rodriguez et al 2008;Witasse et al 2017;Palmerio et al 2021).…”

Counter‐Helical Magnetic Flux Ropes From Magnetic Reconnections in Space Plasmas

“…Additionally, MFRs with varying helicities along their axes, although unstable, have been proposed based on particle time‐of‐flight data in ICMEs (Cane et al., 1997; Owens, 2016). A recent multi‐spacecraft observation, despite certain uncertainties, found opposite helicity from different parts of an ICME (Rodríguez‐García et al., 2022). We recommend further examination of such cases because CHFR is a plausible, likely, and important phenomenon.…”

Global Morphology Distortion of the 2021 October 9 Coronal Mass Ejection from an Ellipsoid to a Concave Shape

“…On one hand, it is expected that initial circular cross sections of CMEs can evolve into flattened, elliptical objects as a result of expansion in spherical geometry (Riley & Crooker 2004). This distorting is often referred to as "pancaking," which can be directly observed in simulations (Riley & Crooker 2004;Savani et al 2011a;Kay & Nieves-Chinchilla 2021) and can also be deduced from in situ observations (Russell & Mulligan 2002;Owens & Cargill 2004;Liu et al 2006;Savani et al 2011b;Nieves-Chinchilla et al 2018;Wang et al 2018;Rodríguez-García et al 2022). On the other hand, large gradients in ambient solar wind speed over CMEs' latitudinal extent can make concave CME fronts, where CME central regions are overtaken by the faster-propagating edges (Odstrcil et al 2004;Manchester et al 2004b;Owens 2006;Liu et al 2009;Savani et al 2010;Howard & DeForest 2012;Török et al 2018;Chi et al 2021;Braga et al 2022).…”