Morphology Of Coronal Mass Ejections Research Articles

Filament Eruption from Active Region 13283 Leading to a Fast Halo-CME and an Intense Geomagnetic Storm on 2023 April 23

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 R ⊙. 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.

SoloHI observations of coronal mass ejections observed by multiple spacecraft

Context. The Solar Orbiter Heliospheric Imager (SoloHI) instrument of the Solar Orbiter mission is a next-generation heliospheric imager. New observations from SoloHI demonstrate the improved spatial and temporal resolution compared to previous observations of the heliosphere and corona. At perihelion, the field of view (FoV) of SoloHI covers the transition between the coronagraph (COR2) and heliospheric imager (HI1) Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite. In this paper, we focus on an active solar period following the first Solar Orbiter science perihelion that resulted in a number of well-observed large coronal mass ejections (CMEs) in SoloHI data in March and April 2022. Specifically, we highlight a series of events produced by AR12795 between 28 March and 2 April and show overlapping observations with SECCHI/COR2 and HI1 and LASCO/C3. Aims. We compare the performance of the SoloHI instrument against similar observations from 1 au imagers. We describe CME observations, highlighting the unique structural features captured within the SoloHI FoV. These observations demonstrate that SoloHI will provide new insights into CME morphology and evolution from a unique vantage point. Methods. To provide a direct and relevant comparison, images from all the telescopes we used in the paper are presented in FoVs common to each and with minimal processing applied. The J-maps we used to highlight outflowing features are also presented to show that the CME kinematics can be tracked through the SoloHI FoV, and also to report how the rest of the Heliophysics Systems Observatory (HSO) can be used to support the SoloHI data. Results. The high-resolution SoloHI images of these eruptions, taken from ∼0.3 au, reveal a number of detailed structural CME features, including internal cavities or cores of the CME flux rope(s). They also show the surrounding material and associated sheath region of the compressed upstream solar wind plasma. Many features that could not have been observed by other instruments are highlighted and discussed. Conclusions. The SoloHI instrument is performing well and has already provided detailed observations of CMEs that can help us understand the details of the internal structure and magnetic field of CMEs. These new observations in combination with synoptic observations from 1 au offer new opportunities for CME propagation from the corona to the heliosphere.

Asymmetric expansion of coronal mass ejections in the low corona

Aims. Understanding how magnetic fields are structured within coronal mass ejections (CMEs), and how they evolve from the low corona into the heliosphere, is a major challenge for space weather forecasting and for solar physics. The study of CME morphology is a particularly auspicious approach to this problem, given that it holds a close relationship with the CME magnetic field configuration. Although earlier studies have suggested an asymmetry in the width of CMEs in orthogonal directions, this has not been inspected using multi-viewpoint observations. Methods. The improved spatial, temporal, and spectral resolution, added to the multiple vantage points offered by missions of the Heliophysics System Observatory, constitute a unique opportunity to gain insight into this regard. We inspect the early evolution (below ten solar radii) of the morphology of a dozen CMEs occurring under specific conditions of observing spacecraft location and CME trajectory, favorable to reduce uncertainties typically involved in the 3D reconstruction used here. These events are carefully reconstructed by means of a forward modeling tool using simultaneous observations of the Solar-Terrestrial Relations Observatory (STEREO) Extreme Ultraviolet Imager and the Solar Dynamics Observatory Atmospheric Imaging Assembly as input when originating low in the corona, and followed up in the outer fields of view of the STEREO and the Solar and Heliospheric Observatory coronagraphs. We then examine the height evolution of the morphological parameters arising from the reconstructions. Results. The multi-viewpoint analysis of this set of CMEs revealed that their initial expansion – below three solar radii – is considerably asymmetric and non-self-similar. Both angular widths, namely along the main axes of CMEs (AWL) and in the orthogonal direction (AWD, representative of the flux rope diameter), exhibit much steeper change rates below this height, with the growth rate of AWL found to be larger than that of AWD, also below that height. Angular widths along the main axes of CMEs are on average ≈1.8 times larger than widths in the orthogonal direction AWD. The ratios of the two expansion speeds, namely in the directions of CMEs main axes and in their orthogonal, are nearly constant in time after ∼4 solar radii, with an average ratio ≈1.6. Heights at which the width change rate is defined to stabilize are greater for AWL than for AWD.

Remote Sensing Estimates of CME Density in the Ecliptic Using the STEREO Heliospheric Imagers

AbstractWe present a method to estimate electron densities in the ecliptic plane using the STEREO Heliospheric Imagers (HIs). The nature of Thomson scattering of photospheric light by solar wind electrons is such that visible‐light observations by HI provide a means to infer information about plasma density from afar. This is achieved using discrete tomography, whereby line‐of‐sight integrals from HI are used to estimate electron density in the heliosphere over a predefined grid. The technique is applied to the Earth‐impacting coronal mass ejection (CME) launched on 12 December 2008. The two vantage points afforded by STEREO are insufficient to reproduce the density structure of the CME in detail; however, the technique is successful in locating the presence of a density enhancement associated with the CME. When applied to consecutive images, we are able to use the technique as a means to track the CME through interplanetary space. From these observations we make estimates of the CME radial velocity and density profiles, the results of which are consistent with measurements made in situ by Wind at L1. This method is presented as a new approach to determine CME propagation from HI observations, one that avoids many of the assumptions of CME morphology and dynamics that are often applied when tracking CMEs in such data. We also expect that this technique will prove useful, and a test of the long‐standing heliospheric reconstruction technique employed by using single images over time (Jackson et al., 2006, https://doi.org/10.1029/2004JA010942) when views from many wide‐angle imagers become available.

How Reliable Are the Properties of Coronal Mass Ejections Measured from a Single Viewpoint?

We present an analysis of widths and kinematic properties of coronal mass ejections (CMEs) obtained via a supervised image segmentation algorithm, the CORonal SEgmentation Technique (CORSET), on simultaneous observations from the two COR2 telescopes on the Solar Terrestrial Relations Observatory (STEREO) mission, from 2007 May to 2014 September. The sample of 460 events with measurements from two vantage points offers the opportunity to test the accuracy and constraints of single-viewpoint properties that underlie the bulk of CME research to date. In addition, we examine the dependence of the properties on the morphology of the events. The main findings are as follows. (1) The radial speeds derived from different perspectives are in good agreement with a relatively low intrinsic uncertainty of 39%. (2) Projection effects are more important for determination of CME width rather than for speed. (3) The expansion speeds depend on CME morphology, with loop-type CMEs expanding twice as fast as flux-rope CMEs, possibly underpinning the more explosive nature. (4) Triangulations of CME speed and propagation direction are optimal from viewpoints separated by 60??90?; e.g., between the Lagrangian points L1 and L5 (or L4). (5) The projected speeds are underestimated, on average, by at least 20% when compared to their deprojected (triangulated) values. We also discuss in detail the lessons learned from the application of the CORSET algorithm to event tracking. Our findings should hopefully be a useful guide in the use of (semi)automated algorithms for extraction of CME physical parameters and in the interpretation of single-viewpoint observations (likely to be the norm after the end of the STEREO mission).

Prospective Out-of-ecliptic White-light Imaging of Coronal Mass Ejections Traveling through the Corona and Heliosphere

Abstract The in-flight performance of the Coriolis/SMEI and STEREO/HI instruments substantiates the high-technology readiness level of white-light (WL) imaging of coronal mass ejections (CMEs) in the inner heliosphere. The WL intensity of a propagating CME is jointly determined by its evolving mass distribution and the fixed Thomson-scattering geometry. From their in-ecliptic viewpoints, SMEI and HI, the only heliospheric imagers that have been flown to date, integrate the longitudinal dimension of CMEs. In this paper, using forward magnetohydrodynamic modeling, we synthesize the WL radiance pattern of a typical halo CME viewed from an out-of-ecliptic (OOE) vantage point. The major anatomical elements of the CME identified in WL imagery are a leading sheath and a trailing ejecta; the ejecta-driven sheath is the brightest feature of the CME. The sheath, a three-dimensional (3D) dome-like density structure, occupies a wide angular extent ahead of the ejecta itself. The 2D radiance pattern of the sheath depends critically on viewpoint. For a CME modeled under solar minimum conditions, the WL radiance pattern of the sheath is generally a quasi-straight band when viewed from an in-ecliptic viewpoint and a semicircular arc from an OOE viewpoint. The dependence of the radiance pattern of the ejecta-driven sheath on viewpoint is attributed to the bimodal nature of the 3D background solar wind flow. Our forward-modeling results suggest that OOE imaging in WL radiance can enable (1) a near-ecliptic CME to be continuously tracked from its coronal initiation, (2) the longitudinal span of the CME to be readily charted, and (3) the transporting speed of the CME to be reliably determined. Additional WL polarization measurements can significantly limit the ambiguity of localizing CMEs. We assert that a panoramic OOE view in WL would be highly beneficial in revealing CME morphology and kinematics in the hitherto-unresolved longitudinal dimension and hence for monitoring the propagation and evolution of near-ecliptic CMEs for space weather operations.

Development of a Full Ice-cream Cone Model for Halo Coronal Mass Ejections

Abstract It is essential to determine three-dimensional parameters (e.g., radial speed, angular width, and source location) of coronal mass ejections (CMEs) for the space weather forecast. In this study, we investigate which cone type represents a halo CME morphology using 29 CMEs (12 Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) halo CMEs and 17 Solar Terrestrial Relations Observatory (STEREO)/Sun–Earth Connection Coronal and Heliospheric Investigation COR2 halo CMEs) from 2010 December to 2011 June. These CMEs are identified as halo CMEs by one spacecraft (SOHO or one of STEREO A and B) and limb ones by the other spacecraft (One of STEREO A and B or SOHO). From cone shape parameters of these CMEs, such as their front curvature, we find that the CME observational structures are much closer to a full ice-cream cone type than a shallow ice-cream cone type. Thus, we develop a full ice-cream cone model based on a new methodology that the full ice-cream cone consists of many flat cones with different heights and angular widths to estimate the three-dimensional parameters of the halo CMEs. This model is constructed by carrying out the following steps: (1) construct a cone for a given height and angular width, (2) project the cone onto the sky plane, (3) select points comprising the outer boundary, and (4) minimize the difference between the estimated projection speeds with the observed ones. By applying this model to 12 SOHO/LASCO halo CMEs, we find that 3D parameters from our method are similar to those from other stereoscopic methods (i.e., a triangulation method and a Graduated Cylindrical Shell model).

A FULL STUDY ON THE SUN–EARTH CONNECTION OF AN EARTH-DIRECTED CME MAGNETIC FLUX ROPE

We present an investigation of an eruption event of coronal mass ejection (CME) magnetic flux rope (MFR) from source active region (AR) NOAA 11719 on 11 April 2013 utilizing observations from SDO, STEREO, SOHO, and WIND spacecraft. The source AR consists of pre-existing sigmoidal structure stacked over a filament channel which is regarded as MFR system. EUV observations of low corona suggest a further development of this MFR system by added axial flux through tether-cutting reconnection of loops at the middle of sigmoid under the influence of continuous slow flux motions during past two days. Our study implies that the MFR system in the AR is initiated to upward motion by kink-instability and further driven by torus-instability. The CME morphology, captured in simultaneous three-point coronagraph observations, is fitted with Graduated Cylindrical Shell (GCS) model and discerns an MFR topology with orientation aligning with magnetic neutral line in the source AR. This MFR expands self-similarly and is found to have source AR twist signatures in the associated near Earth magnetic cloud (MC). We further derived kinematics of this CME propagation by employing a plethora of stereoscopic as well as single spacecraft reconstruction techniques. While stereoscopic methods perform relatively poorly compared to other methods, fitting methods worked best in estimating the arrival time of the CME compared to in-situ measurements. Supplied with values of constrained solar wind velocity, drag parameter and 3D kinematics from GCS fit, we construct CME kinematics from the drag based model consistent with in-situ MC arrival.

LORENTZ SELF-FORCE OF AN ELLIPSE CURRENT LOOP MODEL

In this work, the Lorentz self-force of an ellipse current loop model is derived. We are motivated by the fact that it has been reported in the literature that coronal mass ejection morphology can resemble an ellipse in the field of view of coronagraph images. Deriving the Lorentz self-force using an ellipse geometry has the advantage of being able to be solved analytically, as opposed to other more complex geometries. The derived ellipse model is compared with the local curvature approximation, where the Lorentz self-force at the ellipse major/minor axis is compared with the Lorentz self-force of a torus with curvature equal to the local curvature at the ellipses major/minor axis. It is found that the local curvature approximation is valid for moderate values of eccentricity.

Observational Tracking of the 2D Structure of Coronal Mass Ejections Between the Sun and 1 AU

The Solar TErrestrial RElations Observatory (STEREO) provides high cadence and high resolution images of the structure and morphology of coronal mass ejections (CMEs) in the inner heliosphere. CME directions and propagation speeds have often been estimated through the use of time-elongation maps obtained from the STEREO Heliospheric Imager (HI) data. Many of these CMEs have been identified by citizen scientists working within the SolarStormWatch project ( www.solarstormwatch.com ) as they work towards providing robust real-time identification of Earth-directed CMEs. The wide field of view of HI allows scientists to directly observe the two-dimensional (2D) structures, while the relative simplicity of time-elongation analysis means that it can be easily applied to many such events, thereby enabling a much deeper understanding of how CMEs evolve between the Sun and the Earth. For events with certain orientations, both the rear and front edges of the CME can be monitored at varying heliocentric distances (R) between the Sun and 1 AU. Here we take four example events with measurable position angle widths and identified by the citizen scientists. These events were chosen for the clarity of their structure within the HI cameras and their long track lengths in the time-elongation maps. We show a linear dependency with R for the growth of the radial width (W) and the 2D aspect ratio (X) of these CMEs, which are measured out to ~0.7 AU. We estimated the radial width from a linear best fit for the average of the four CMEs. We obtained the relationships W=0.14R+0.04 for the width and X=2.5R+0.86 for the aspect ratio (W and R in units of AU).

Remote and in situ observations of an unusual Earth‐directed coronal mass ejection from multiple viewpoints

During June 16–21, 2010, an Earth‐directed coronal mass ejection (CME) event was observed by instruments onboard STEREO, SOHO, MESSENGER and Wind. This event was the first direct detection of a rotating CME in the middle and outer corona. Here, we carry out a comprehensive analysis of the evolution of the CME in the interplanetary medium comparing in situ and remote observations, with analytical models and three‐dimensional reconstructions. In particular, we investigate the parallel and perpendicular cross section expansion of the CME from the corona through the heliosphere up to 1 AU. We use height‐time measurements and the Gradual Cylindrical Shell (GCS) technique to model the imaging observations, remove the projection effects, and derive the 3‐dimensional extent of the event. Then, we compare the results with in situ analytical Magnetic Cloud (MC) models, and with geometrical predictions from past works. We find that the parallel (along the propagation plane) cross section expansion agrees well with the in situ model and with the Bothmer and Schwenn (1998) empirical relationship based on in situ observations between 0.3 and 1 AU. Our results effectively extend this empirical relationship to about 5 solar radii. The expansion of the perpendicular diameter agrees very well with the in situ results at MESSENGER (∼0.5 AU) but not at 1 AU. We also find a slightly different, from Bothmer and Schwenn (1998), empirical relationship for the perpendicular expansion. More importantly, we find no evidence that the CME undergoes a significant latitudinal over‐expansion as it is commonly assumed. Instead, we find evidence that effects due to CME rotation and expansion can be easily confused in the images leading to a severe overestimation of the proper 3D size of the event. Finally, we find that the reconstructions of the CME morphology from the in situ observations at 1 AU are in agreement with the remote sensing observations but they show a big discrepancy at MESSENGER. We attribute this discrepancy to the ambiguity of selecting the proper boundaries due to the lack of accompanying plasma measurements.

EVOLUTION OF CORONAL MASS EJECTION MORPHOLOGY WITH INCREASING HELIOCENTRIC DISTANCE. I. GEOMETRICAL ANALYSIS

At launch, coronal mass ejections (CMEs) are often approximated as locally cylindrical objects with circular cross sections. However, CMEs have long been known to propagate almost radially away from the Sun along with the bulk solar wind. This has important consequences for the structure of CMEs; an initially circular cross section will be severely flattened by this radial motion. Yet calculations of total flux and helicity transport by CMEs based on in situ observations still use the assumption of a locally cylindrical object. In this paper, we investigate the morphology of an interplanetary CME based upon geometric arguments. By radially propagating an initial cylindrical object that maintains a constant ratio between its expansion speed and bulk flow, A, we show that the flattening, or pancaking, of the two-dimensional cross section effectively ceases; the aspect ratios of these CMEs converge to a fixed value as they propagate further into the heliosphere. Thereafter the CME morphology is scale invariant. We predict aspect ratios of 5 ± 1 at terrestrial distances. By correlating a planetary shock with an interplanetary shock linked to a CME, these aspect ratios are estimated using in situ measurements in Paper II. These estimates are made at various heliocentric distances.

CME reconstruction: Pre-STEREO and STEREO era

Since the first observations of coronal mass ejections (CMEs) in 1970s, their three-dimensional (3D) morphology has been a key ingredient for understanding their origin and evolution. The determination of their 3D structure using a single viewpoint, however posed a challenge because only their 2D projection on the sky plane is observed. The operation of the STEREO mission with its unique capability of imaging the inner heliosphere from two viewpoints has greatly improved this situation. It is therefore timely to review the pre-STEREO efforts in 3D CME reconstruction and compare them with the first STEREO results in this area. Our paper focuses on the techniques relevant to the CME morphology: forward modeling, polarimetric, spectroscopic, direct inversion. We also discuss the limitations and considerations involved in each technique.

OBSERVATIONAL EVIDENCE OF A CORONAL MASS EJECTION DISTORTION DIRECTLY ATTRIBUTABLE TO A STRUCTURED SOLAR WIND

We present the first observational evidence of the near-Sun distortion of the leading edge of a coronal mass ejection (CME) by the ambient solar wind into a concave structure. On 2007 November 14, a CME was observed by coronagraphs onboard the STEREO-B spacecraft, possessing a circular cross section. Subsequently the CME passed through the field of view of the STEREO-B Heliospheric Imagers where the leading edge was observed to distort into an increasingly concave structure. The CME observations are compared to an analytical flux rope model constrained by a magnetohydrodynamic solar wind solution. The resultant bimodal speed profile is used to kinematically distort a circular structure that replicates the initial shape of the CME. The CME morphology is found to change rapidly over a relatively short distance. This indicates an approximate radial distance in the heliosphere where the solar wind forces begin to dominate over the magnetic forces of the CME influencing the shape of the CME.

Multiscale Edge Detection in the Corona

Coronal Mass Ejections (CMEs) are challenging objects to detect using automated techniques, due to their high velocity and diffuse, irregular morphology. A necessary step to automating the detection process is to first remove the subjectivity introduced by the observer used in the current, standard, CME detection and tracking method. Here we describe and demonstrate a multiscale edge detection technique that addresses this step and could serve as one part of an automated CME detection system. This method provides a way to objectively define a CME front with associated error estimates. These fronts can then be used to extract CME morphology and kinematics. We apply this technique to a CME observed on 18 April 2000 by the Large Angle Solar COronagraph experiment (LASCO) C2/C3 and a CME observed on 21 April 2002 by LASCO C2/C3 and the Transition Region and Coronal Explorer (TRACE). For the two examples in this work, the heights determined by the standard manual method are larger than those determined with the multiscale method by ≈10% using LASCO data and ≈20% using TRACE data.

Fuzzy set theory applied to CME importance classification

In this paper, fuzzy set theory is applied to a quantitative way of assigning importance class to coronal mass ejection (CME) events based on four observed characteristics, i.e. velocity, span, mass and kinetic energy. The weights to be associated with each of the characteristics and the membership functions of belonging to one of the three importance classes are determined from the correlations between the characteristics and the CME morphology properties. A useful software of data reduction has been successfully compiled. The results show that the fuzzy comprehensive evaluation is better than the classic statistical analysis.