Solar Ultraviolet Bursts in the Joint Footpoints of Multiple Transition Region Loops

Solar Ultraviolet bursts (UBs) associated with flux emergence are expected to help understand the physical processes of the flux emergence itself. In the present study, we analyse imaging and spectroscopic observations of a special group of UBs (including twelve of them) occurring in the joint footpoint regions of multiple transition region loops above the flux emerging regions. Consistent with previous studies of common UBs, we found that the spectral characteristics of this group of UBs are varied. Our results show that the responses of UBs in Ni ii, NUV continuum, Mg ii h and O i are originated from locations differ from that emits Si iv. The imaging data show that UBs have connections with the dynamics in the transition region loops. Brightenings starting from UB-regions and propagating along loops can be seen in SJ 1400/1330 Å and AIA 304 Å images and the corresponding time-space images. The apparent velocities are tens of kilometers per second in AIA 304 Å. For symmetry, the brightenings can propagate from the UB-regions towards opposite directions with similar apparent velocities in some cases. Given that these UBs are magnetic reconnection phenomena, we suggest that the propagating brightenings are the signals of the plasma flows resulted from heatings in the UB-regions.

Human-efficient labeling of a solar flux emergence video dataset by a deep learning model

Machine learning is becoming a critical tool for interrogation of large complex data. However, labeling large datasets is time-consuming. Here we show that convolutional neural networks (CNNs), trained on crudely labeled astronomical videos, can be leveraged to improve the quality of data labeling and reduce the need for human intervention. We use videos of the solar photospheric magnetic field, crudely labeled into two classes: emergence or non-emergence of large bipolar magnetic regions (BMRs). We train the CNN using crude labeling, manually verify, correct labeling vs. CNN disagreements, and repeat this process until convergence. This results in a high-quality labeled dataset requiring the manual verification of only ~50% of all videos. Furthermore, by gradually masking the videos and looking for maximum change in CNN inference, we locate BMR emergence time without retraining the CNN. This demonstrates the versatility of CNNs for simplifying the challenging task of labeling complex dynamic events.

Direct Observation of A Large-scale CME Flux Rope Event Arising from an Unwinding Coronal Jet

<p>Increasing observations show that coronal jets may result in bubble-shaped coronal mass ejections (CMEs), but the genesis of jet-driven CMEs and their nature are not fully understood. Here, we report a direct stereoscopic observation on the magnetic coupling from a coronal blowout jet to a stellar-sized CME.  Observations in the EUV passbands of SDO/AIA show that this whole event starts with a small-scale active-region filament whose eruption occurs at a coronal geyser site due to flux emergence and cancellation. By interacting with an overlying null-point configuration, this erupting filament first breaks one of its legs and triggers an unwinding blowout jet. The release of magnetic twist in its jet spire is estimated at around 1.5−2.0 turns. This prominent twist transport in jet spire rapidly creates a newborn large-scale flux rope from the jet base to a remote site. As a result, the newborn large-scale flux rope erupts into the outer coronae causing an Earth-directed bubble-shaped CME. In particular, two sets of distinct flare post-flare loops form in its source region in sequence, indicating this eruptive event couples with twice flare reconnection. This observation highlights a real pathway for jet-CME magnetic coupling and provides a new hint for the buildup of large-scale CME flux ropes.<span> </span></p>

The Source Locations of Major Flares and CMEs in the Emerging Active Regions

<p>Major flares and coronal mass ejections (CMEs) tend to originate from the compact polarity inversion lines (PILs) in the solar active regions (ARs). Recently, a scenario named as “collisional shearing” is proposed by Chintzoglou et al. (2019) to explain the phenomenon, which suggests that the collision between different emerging bipoles is able to form the compact PIL, driving the shearing and flux cancellation that are responsible to the subsequent large activities. In this work, through tracking the evolution of 19 emerging ARs from their birth until they produce the first major flares or CMEs, we investigated the source PILs of the activities, i.e., the active PILs, to explore the generality of “collisional shearing”. We find that none of the active PILs is the self PIL (sPIL) of a single bipole. We further find that 11 eruptions originate from the collisional PILs (cPILs) formed due to the collision between different bipoles, 6 from the conjoined systems of sPIL and cPIL, and 2 from the conjoined systems of sPIL and ePIL (external  PIL between the AR and the nearby preexisting polarities). Collision accompanied by shearing and flux cancellation is found developing at all PILs prior to the eruptions, with 84% (16/19) cases having collisional length longer than 18 Mm. Moreover, we find that the magnitude of the flares is positively correlated with the collisional length of the active PILs, indicating that the intenser activities tend to originate from the PILs with severer collision. The results suggest that the “collisional shearing”, i.e., bipole-bipole interaction during the flux emergence is a common process in driving the major activities in emerging ARs.</p>

Simulations of Switchback, Fragmentation and Sunspot Pair in δ-Sunspots during Magnetic Flux Emergence

Strong flares and coronal mass ejections (CMEs), launched from δ-sunspots, are the most catastrophic energy-releasing events in the solar system. The formations of δ-sunspots and relevant polarity inversion lines (PILs) are crucial for the understanding of flare eruptions and CMEs. In this work, the kink-stable, spot-spot-type δ-sunspots induced by flux emergence are simulated, under different subphotospheric initial conditions of magnetic field strength, radius, twist, and depth. The time evolution of various plasma variables of the δ-sunspots are simulated and compared with the observation data, including magnetic bipolar structures, relevant PILs, and temperature. The simulation results show that magnetic polarities display switchbacks at a certain stage and then split into numerous fragments. The simulated fragmentation phenomenon in some δ-sunspots may provide leads for future observations in the field.