Evolution of Plasma Composition in an Eruptive Flux Rope

Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs). However, identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, we show Hinode EUV Imaging Spectrometer observations of sigmoidal active region (AR) 10977. We analyze the coronal plasma composition in the AR and its evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma with photospheric composition was observed in coronal loops close to the main polarity inversion line during episodes of significant flux cancellation, suggestive of the injection of photospheric plasma into these loops driven by photospheric flux cancellation. Concurrently, the increasingly sheared core field contained plasma with coronal composition. As flux cancellation decreased and a sigmoid/flux rope formed, the plasma evolved to an intermediate composition in between photospheric and typical AR coronal compositions. Finally, the flux rope contained predominantly photospheric plasma during and after a failed eruption preceding the CME. Hence, plasma composition observations of AR 10977 strongly support models of flux rope formation by photospheric flux cancellation forcing magnetic reconnection first at the photospheric level then at the coronal level.

Investigation of two coronal mass ejections from circular ribbon source region:Origin, Sun-Earth propagation and Geoeffectiveness

In this article, we compare the properties of two coronal mass ejections (CMEs) that show similar source region characteristics but different evolutionary behaviors in the later phases. We discuss the two events in terms of their near-Sun characteristics, interplanetary evolution and geoeffectiveness. We carefully analyzed the initiation and propagation parameters of these events to establish the precise CME-interplanetary CME (ICME) connection and their near-Earth consequences. The first event is associated with poor geomagnetic storm disturbance index (Dst ≈-20 nT) while the second event is associated with an intense geomagnetic storm of DST ≈-119 nT. The configuration of the sunspots in the active regions and their evolution are observed by Helioseismic and Magnetic Imager (HMI). For source region imaging, we rely on data obtained from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) and Hα filtergrams from the Solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences (ARIES). For both the CMEs, flux rope eruptions from the source region triggered flares of similar intensities (≈M1). At the solar source region of the eruptions,we observed a circular ribbon flare (CRF) for both cases, suggesting fan-spine magnetic configuration in the active region corona. The multi-channel SDO observations confirm that the eruptive flares and subsequent CMEs were intimately related to the filament eruption. Within the Large Angle and Spectrometric Coronograph (LASCO) field of view (FOV) thetwo CMEs propagated with linear speeds of 671 and 631 km s−1, respectively. These CMEs were tracked up to the Earth by Solar Terrestrial Relations Observatory (STEREO) instruments. We find that the source region evolution of CMEs, guided by the large-scale coronal magnetic field configuration, along with near-Sun propagation characteristics, such as CME-CME interactions, played important roles in deciding the evolution of CMEs in the interplanetary medium and subsequently their geoeffectiveness.

Small-scale Magnetic Flux Ropes and Their Properties Based on In Situ Measurements from the Parker Solar Probe

We report small-scale magnetic flux ropes via the in situ measurements from the Parker Solar Probe during the first six encounters, and present additional analyses to supplement our prior work in Chen et al. These flux ropes are detected by the Grad–Shafranov-based algorithm, with their durations and scale sizes ranging from 10 s to ≲1 hr and from a few hundred kilometers to 10−3 au, respectively. They include both static structures and those with significant field-aligned plasma flows. Most structures tend to possess large cross helicity, while the residual energy is distributed over wide ranges. We find that these dynamic flux ropes mostly propagate in the antisunward direction relative to the background solar wind, with no preferential signs of magnetic helicity. The magnetic flux function follows a power law and is proportional to scale size. We also present case studies showing reconstructed two-dimensional (2D) configurations, which confirm that both the static and dynamic flux ropes have a common configuration of spiral magnetic field lines (also streamlines). Moreover, the existence of such events hints at interchange reconnection as a possible mechanism for generating flux rope-like structures near the Sun. Lastly, we summarize the major findings, and discuss the possible correlation between these flux rope-like structures and turbulence due to the process of local Alfvénic alignment.

Partial Eruption, Confinement, and Twist Buildup and Release of a Double-decker Filament

We investigate the failed partial eruption of a filament system in NOAA AR 12104 on 2014 July 5, using multiwavelength EUV, magnetogram, and Hα observations, as well as magnetic field modeling. The filament system consists of two almost co-spatial segments with different end points, both resembling a C shape. Following an ejection and a precursor flare related to flux cancellation, only the upper segment rises and then displays a prominent twisted structure, while rolling over toward its footpoints. The lower segment remains undisturbed, indicating that the system possesses a double-decker structure. The erupted segment ends up with a reverse-C shape, with material draining toward its footpoints, while losing its twist. Using the flux rope insertion method, we construct a model of the source region that qualitatively reproduces key elements of the observed evolution. At the eruption onset, the model consists of a flux rope atop a flux bundle with negligible twist, which is consistent with the observational interpretation that the filament possesses a double-decker structure. The flux rope reaches the critical height of the torus instability during its initial relaxation, while the lower flux bundle remains in stable equilibrium. The eruption terminates when the flux rope reaches a dome-shaped quasi-separatrix layer that is reminiscent of a magnetic fan surface, although no magnetic null is found. The flux rope is destroyed by reconnection with the confining overlying flux above the dome, transferring its twist in the process.

Solar Prominence Bubble and Plumes Caused By an Eruptive Magnetic Flux Rope

Prominence bubbles and plumes often form near the lower prominence–corona boundary. They are believed to play an important role in mass supply and evolution of solar prominences. However, how they form is still an open question. In this Letter we present a unique high-resolution Hα observation of a quiescent prominence by the New Vacuum Solar Telescope. Two noteworthy bubble–plume events are studied in detail. The two events are almost identical, except that an erupting mini filament appeared below the prominence–bubble interface in the second event, unlike the first one or any of the reported bubble observations. Analysis of the Hα and extreme-ultraviolet data indicates that the rising magnetic flux rope (MFR) in the mini filament is the cause of bubble expansion and that the interaction between the prominence and MFR results in plume formation. These observations provided clear evidence that emerging MFR may be a common trigger of bubbles and suggested a new mechanism of plumes in addition to Rayleigh–Taylor instability and reconnection.

Internal Structure of the 2019 April 2 CME

We present the first analysis of internal coronal mass ejection (CME) structure observed very close to the Sun by the Wide-field Imager for Solar PRobe (WISPR) instrument on board the Parker Solar Probe (PSP). The transient studied here is a CME observed during PSP’s second perihelion passage on 2019 April 2, when PSP was only 40 R ⊙ from the Sun. The CME was also well observed from 1 au by the STEREO-A spacecraft, which tracks the event all the way from the Sun to 1 au. However, PSP/WISPR observes internal structure not apparent in the images from 1 au. In particular, two linear features are observed, one bright and one dark. We model these features as two loops within the CME flux rope (FR) channel. The loops can be interpreted as bundles of field lines, with the brightness of the bright loop indicative of lots of mass being loaded into those field lines, and with the dark loop being devoid of such mass loading. It is possible that these loops are actually representative of two independent FR structures within the overall CME outline.

A Catalog of Interplanetary Coronal Mass Ejections Observed by Juno between 1 and 5.4 au

We use magnetic field measurements by the Juno spacecraft to catalog and investigate interplanetary coronal mass ejections (ICMEs) beyond 1 au. During its cruise phase, Juno spent about 5 yr in the solar wind between 2011 September and 2016 June, providing measurements of the interplanetary magnetic field (IMF) between 1 and 5.4 au. Juno therefore presents the most recent opportunity for a statistical analysis of ICME properties beyond 1 au since the Ulysses mission (1990–2009). Our catalog includes 80 such ICME events, 32 of which contain associated flux-rope-like structures. We find that the dependency of the mean magnetic field strength of the magnetic flux ropes decreases with heliocentric distance as r −1.24±0.43 between 1 and 5.4 au, in good agreement with previous relationships calculated using ICME catalogs at Ulysses. We combine the Juno catalog with the HELCATS catalog to create a data set of ICMEs covering 0.3–5.4 au. Using a linear regression model to fit the combined data set on a double-logarithmic plot, we find that there is a clear difference between global expansion rates for ICMEs observed at shorter heliocentric distances and those observed farther out beyond 1 au. The cataloged ICMEs at Juno present a good basis for future multispacecraft studies of ICME evolution between the inner heliosphere, 1 au, and beyond.