Jie Zhang

The radial and lateral dimensions of coronal mass ejections (CMEs) influence their duration and probability of encounter at Earth. These properties are linked to the expansion speeds of CMEs in different radial and lateral directions; however, most earlier studies modeled CME evolution using a projected full ice-cream-cone geometry, which does not distinguish between radial and lateral expansion. Our study investigates the asymmetric expansion (relative radial and lateral components) and kinematics of seven fast and seven slow CMEs within coronagraphic heights using the graduated cylindrical shell model. Our study confirms that CMEs expand asymmetrically, with lateral expansion exceeding radial expansion in both CME populations. This asymmetry limits the accuracy of the full ice-cream-cone model. For both fast and slow CMEs, higher leading-edge speeds are associated with higher expansion speeds. At a height of 10 R _⊙ , slow CMEs with larger expansion speeds (lateral and radial) have larger angular widths (face-on and edge-on), whereas fast CMEs exhibit a negative correlation between lateral expansion speed and face-on angular width. We find that the expansion and propagation speeds of slow CMEs exhibit a two-phase evolution, whereas those of fast CMEs display more diverse trends. Overall, this study suggests that fast and slow CMEs evolve differently and should not be treated as a single population in statistical estimates of their physical parameters. Our study highlights the importance of estimating CME angular widths and expansion speeds along different directions, and beyond standard coronagraphic heights, to capture their complete physical evolution.

Severe space weather is caused by coronal mass ejections (CMEs). While the chain of CME activities from the Sun to Earth has been well tracked for some individual events, the statistical relations between the physical properties of CMEs near the Sun and those of their counterpart interplanetary CMEs (ICMEs) have not been well investigated. In this article, we provide a comprehensive study of a large set of properties for all 66 Earth-affecting CMEs during 2011–2013. Among them, 32 (48%) CMEs originated from compact and stronger magnetic field regions, i.e., active regions (ARs), while 34 (52%) CMEs originated from larger but weaker-field quiescent regions (QRs). The AR-CMEs are much faster than QR-CMEs near the Sun, with average true speeds of 1086 and 711 km s ⁻¹ , respectively. We find that, at 1 au or near Earth, the differences between the two contrasting types are no longer prominent, but not fully diminished. While the charge states and velocities remain statistically different, other ICME properties, including magnetic field strength, plasma β , proton temperature, helium abundance, and others, do not differ with statistical significance. Interestingly, QR-CMEs and AR-CMEs have nearly equal chances of driving a forward shock at 1 au (68% versus 69%). These results indicate that the evolution of CMEs during their propagation from the Sun to Earth has significantly reduced many differences in properties near the Sun between the two types of events.

Coronal cavities are low-density regions in the solar corona surrounding prominences that often erupt into coronal mass ejections. Therefore, understanding the magnetic field in these preeruptive structures is important for understanding the process of magnetic energy storage and release in the solar corona, with implications for space weather modeling and predictions. The Daniel K. Inouye Solar Telescope/CryoNIRSP instrument acquired spectropolarimetric observations of the Fe xiii 10747 Å forbidden emission line in two coronal cavities, one on the northwest limb on 2025 August 8 and the other on the southwest limb on 2025 October 5. For the first time, we detect the circularly polarized emission in the Stokes V parameter in the coronal cavities and their embedded structures, which could be resolved such that the line-of-sight (LOS) magnetic field intensity could be estimated using the weak-field approximation. It is found that the inferred LOS magnetic field strength varies from ∼5 to 20 G in the cavity, with the strongest field strength above the prominence in the hornlike substructure of the cavity.

Multivariate time series classification is a crucial task in data mining, attracting growing research interest due to its broad applications. While many existing methods focus on discovering discriminative patterns in time series, real-world data does not always present such patterns, and sometimes raw numerical values can also serve as discriminative features. Additionally, the recent success of Transformer models has inspired many studies. However, when applying to time series classification, the self-attention mechanisms in Transformer models could introduce classification-irrelevant features, thereby compromising accuracy. To address these challenges, we propose a novel method, VSFormer, that incorporates both discriminative patterns (shape) and numerical information (value). In addition, we extract class-specific prior information derived from supervised information to enrich the positional encoding and provide classification-oriented self-attention learning, thereby enhancing its effectiveness. Extensive experiments on all 30 UEA archived datasets demonstrate the superior performance of our method compared to SOTA models. Through ablation studies, we demonstrate the effectiveness of the improved encoding layer and the proposed self-attention mechanism. Finally, We provide a case study on a real-world time series dataset without discriminative patterns to interpret our model.

We study the relationship between the speed of coronal mass ejections (CMEs) and the height profile of the ambient magnetic field, quantified by its decay index, n ( h ). Our sample is composed of 15 very fast CMEs ( V _CME ≥ 1500 kms ^–1 ; all halo CMEs) and 22 halo CMEs below this speed limit from Solar Cycle 23. The very fast CMEs yield a high correlation of 0.81 between V _CME and the slope of n ( h ) in a height range above the onset height of the torus instability if one extremely fast outlier, which closely followed another very fast CME, is excluded. This is consistent with the hypothesis that the torus instability plays a decisive role in CME acceleration. The whole sample yields a weaker correlation, which is still significant if events with a broad torus-stable dip in n ( h ) are excluded. A parametric simulation study of flux-rope eruptions from quadrupolar and two-scale bipolar source regions confirms the decelerating effect of such dips. Very fast, moderate-velocity, and confined eruptions are found.

The open solar magnetic field refers to field lines that are magnetically connected to the surface of the Sun at one end and continue through the corona into the heliosphere. The open magnetic flux problem is the discrepancy between the total unsigned open magnetic flux determined using in situ measurements and that derived in the corona via remote-sensing observations of the photospheric magnetic field. Recent work has shown that the missing open flux derived by the Wang–Sheeley–Arge (WSA) model is located at coronal hole boundaries, which consist of mixed regions of open and closed field lines. The method for identifying these boundaries is based on field-line tracing, which locates the footpoints of open field lines by tracing them down from the model outer boundary to the photosphere. The approach takes advantage of the intrinsic uncertainty when tracing the field at finite resolution, as it creates a randomly selected boundary surrounding the coronal hole perimeters. In this paper, we first describe an extension of previous work to include data from the Helioseismic and Magnetic Imager, which extends the period of alignment between modeled and in situ derived open flux from 28 to 35 yr. Second, by adjusting the resolution of the model we can adjust the width of the boundary region. We find that at higher resolutions the total open flux predicted decreases, while if the resolution is reduced, the open flux increases. Furthermore, between 1° and 2° the total open flux prediction matches the in situ measurements most closely.

This paper presents Heliospheric conneXions for Coronal mass ejections (HeXCor), a new coronal mass ejection (CME) flux rope (FR) reconstruction model that combines the geometry of the graduated cylindrical shell (GCS) model, defined from remote sensing imagery, with a modified cylindrical magnetic field solution inferred from in situ data. The usage of synergistic remote sensing and in situ data allows HeXCor to reconstruct an advanced magnetic FR model of CMEs with both global 3D geometry and internal magnetic field defined. The model is validated with four case studies of Earth-affecting CMEs from 2010 to 2014 observed in the corona by Solar and Heliospheric Observatory and Solar TErrestrial RElations Observatory’s spacecraft with large separation angles. It is shown that the in situ fitting capability is comparable to traditional cylindrical fittings while uniquely providing global structural context. The model also uniquely defines both the poloidal and toroidal impact parameters to fully describe the characteristics of CME impacts. Two of the events (2012 July 12 and 2011 March 25 CMEs) are found to follow the basic assumptions of radial and self-similar expansion from the Sun to Earth, while the other two (2010 May 23 and 2013 April 11 CMEs) likely experience deflection in the propagation direction and change in axial orientation. These results demonstrate how HeXCor provides a realistic and informative CME model that is comprised of accurate 3D global geometry with internal magnetic fields.

This paper presents a systematic study that focuses on how the number of viewpoints distributed in the heliosphere affects the accuracy and uncertainty of the 3D geometric coronal mass ejection (CME) measurements. An efficient nonmanual minimization-based fitting technique that is different from the manual methods widely used in the community is developed. It uses the MPFIT minimization IDL routine and searches for the optimized model point clouds that best fit the observed CME leading edges from one, two, or three viewpoints using a set of combinations of observations provided by the Solar Terrestrial Relations Observatory and Solar and Heliospheric Observatory. The technique also provides a robust calculation of uncertainties of the CME geometric parameters that is lacking in manual methods. Three well-known geometric models, the cone, graduated cylindrical shell, and spheroid shock, are used. All three models depend on geometric parameters that govern the CME propagation direction and size. Sample cases of a halo, partial halo, and limb CMEs as seen from the Earth are used in the fitting and uncertainty calculation. It is found that, after adding a second viewpoint off the Sun–Earth line, the uncertainties drop significantly, while the addition of the third viewpoint adds limited benefits. This study shows that the minimization fitting method provides a robust, fast, and straightforward way to define the CME geometric parameters along with their uncertainties for individual events, which shall provide the necessary data constraints for ensemble predictions of CME evolution. It also underlines the importance of having a permanent observatory off the Sun–Earth line for operational space weather prediction.