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Abstract. Super-elastic collision is an abnormal collisional process, in which some particular mechanisms cause the kinetic energy of the system increasing. Most studies in this aspect focus on solid-like objects, but they rarely consider gases or liquids, as the collision of the latter is primarily a mixing process. With cross-field diffusion being effectively prohibited, magnetized plasmoids are different from ordinary gases. But it remains unclear how they act during a collision. Here we present the global picture of a unique collision between two coronal mass ejections in the heliosphere, which are the largest magnetized plasmoids erupting from the Sun. Our analysis for the first time reveals that these two magnetized plasmoids collided like solid-like objects with a 73% likelihood of being super-elastic. Their total kinetic energy surprisingly increased by about 6.6% through the collision, which significantly influenced the dynamics of the plasmoids.

In this paper, ten CME events viewed by the STEREO twin spacecraft are analyzed to study the deflections of CMEs during their propagation in the corona. Based on the three-dimensional information of the CMEs derived by the graduated cylindrical shell (GCS) model [Thernisien et al., 2006], it is found that the propagation directions of eight CMEs had changed. By applying the theoretical method proposed by Shen et al. [2011] to all the CMEs, we found that the deflections are consistent, in strength and direction, with the gradient of the magnetic energy density. There is a positive correlation between the deflection rate and the strength of the magnetic energy density gradient and a weak anti-correlation between the deflection rate and the CME speed. Our results suggest that the deflections of CMEs are mainly controlled by the background magnetic field and can be quantitatively described by the magnetic energy density gradient (MEDG) model.Comment: 19 pages, 20 figure

[1] In this study, we utilize a recently introduced relativistic kappa-type (KT) distribution function to model the omnidirectional differential flux of energetic electrons observed by the SOPA instrument on board the 1989-046 and LANL-01A satellites at geosynchronous orbit. We derive a useful correlation between the differential flux and the distribution of particles which can directly offer those best fitting parameters (e.g., the number density N, the thermal characteristic speed q and the spectral index k) strongly associated with evaluation of the electromagnetic wave instability. We adopt the assumption of a nearly isotropic pitch angle distribution (PAD) and the typical LMFIT function in the program IDL to perform a non-linear least squared fitting, and find that the new KT distribution fits well with the observed data during different universal times both in the lower and higher energies. We also carry out the direct comparisons with the generalized Lorentzian (kappa) distribution and find that kappa distribution fits well with observational data at the relatively lower energies but display deviations at higher energies, typically above hundreds of keV. Furthermore, the fitting spectral index k basically takes 4, 5 or 6 while the fitting parameters N and q are quite different due to different differential fluxes of electrons at different universal times. These results, which are applied to the case of a nearly isotropic PAD, demonstrate that the particle flux satisfies the power law not only at the lower energies but also at the relativistic energies, and the new KT distribution may present valuable insights into the dynamical features in those space plasmas (e.g., the Earth's outer radiation belts and the inner Jovian magnetosphere) where highly energetic particles exist.

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How to properly understand coronal mass ejections (CMEs) viewed in white light coronagraphs is crucial to many relative researches in solar and space physics. The issue is now particularly addressed in this paper through studying the source locations of all the 1078 Large Angle and Spectrometric Coronagraph (LASCO) CMEs listed in Coordinated Data Analysis Workshop (CDAW) CME catalog during 1997–1998 and their correlation with CMEs' apparent parameters. By manually checking LASCO and Extreme Ultraviolet Imaging Telescope (EIT) movies of these CMEs, we find that, except 231 CMEs whose source locations cannot be identified due to poor data, there are 288 CMEs with location identified on the frontside solar disk, 234 CMEs appearing above solar limb, and 325 CMEs without evident eruptive signatures in the field of view of EIT. On the basis of the statistical results of CMEs' source locations, there are four physical issues: (1) the missing rate of CMEs by SOHO LASCO and EIT, (2) the mass of CMEs, (3) the causes of halo CMEs, and (4) the deflections of CMEs in the corona, are exhaustively analyzed. It is found that (1) about 32% frontside CMEs cannot be recognized by SOHO, (2) the brightness of a CME at any heliocentric distance is roughly positively correlated with its speed, and the CME mass derived from the brightness is probably overestimated, (3) both projection effect and violent eruption are the major causes of halo CMEs, and especially for limb halo CMEs the latter is the primary one, and (4) most CMEs deflected toward equator near the solar minimum; these deflections can be classified into three types: the asymmetrical expansion, the nonradial ejection, and the deflected propagation.

Magnetic flux ropes (MFRs) are one kind of fundamental structures in the solar/space physics and involved in various eruption phenomena. Twist, characterizing how the magnetic field lines wind around a main axis, is an intrinsic property of MFRs, closely related to the magnetic free energy and stableness. Although the effect of the twist on the behavior of MFRs had been widely studied in observations, theory, modeling, and numerical simulations, it is still unclear how much amount of twist is carried by MFRs in the solar atmosphere and in heliosphere and what role the twist played in the eruptions of MFRs. Contrasting to the solar MFRs, there are lots of in situ measurements of magnetic clouds (MCs), the large‐scale MFRs in interplanetary space, providing some important information of the twist of MFRs. Thus, starting from MCs, we investigate the twist of interplanetary MFRs with the aid of a velocity‐modified uniform‐twist force‐free flux rope model. It is found that most of MCs can be roughly fitted by the model and nearly half of them can be fitted fairly well though the derived twist is probably overestimated by a factor of 2.5. By applying the model to 115 MCs observed at 1 AU, we find that (1) the twist angles of interplanetary MFRs generally follow a trend of about 0.6lR radians, where lR is the aspect ratio of a MFR, with a cutoff at about 12π radians AU−1, (2) most of them are significantly larger than 2.5π radians but well bounded by 2lR radians, (3) strongly twisted magnetic field lines probably limit the expansion and size of MFRs, and (4) the magnetic field lines in the legs wind more tightly than those in the leading part of MFRs. These results not only advance our understanding of the properties and behavior of interplanetary MFRs but also shed light on the formation and eruption of MFRs in the solar atmosphere. A discussion about the twist and stableness of solar MFRs are therefore given.