Multi-flux-rope system in solar active regions

2019 ◽  
Vol 15 (S354) ◽  
pp. 443-447
Author(s):  
Yijun Hou ◽  
Jun Zhang ◽  
Ting Li ◽  
Shuhong Yang
Keyword(s):  
Magnetic Energy ◽  
Flux Rope ◽  
Active Regions ◽  
Flux Emergence ◽  
Magnetic Flux Rope ◽  
Solar Eruptions ◽  
Cycle 24 ◽  
A Chain ◽  
Rope System ◽  
Significant Flux

AbstractMagnetic flux rope (MFR) is closely connected with solar eruptions, such as flares and coronal mass ejections. The classical scenario assumes a single MFR for each eruption, but it is reasonable to expect multiple MFRs in a complex active region (AR). Statistically investigating AR 11897, we verify the existence of multiple MFR proxies during the AR evolution. Recently, AR 12673 in 2017 September produced the two largest flares in Solar Cycle 24. The evolutions of the AR magnetic fields and the two large flares reveal that significant flux emergence and successive interactions between different emerging dipoles resulted in the formations of multiple MFRs and twisted loop bundles, which successively erupted like a chain reaction within several minutes before the peaks of the two flares. We propose that the eruptions of a multi-flux-rope system can rapidly release enormous magnetic energy and result in large flares in solar AR.

scholarly journals Relative magnetic helicity as a diagnostic of solar eruptivity

2017 ◽  
Vol 601 ◽  
pp. A125 ◽  
Author(s):  
E. Pariat ◽  
J. E. Leake ◽  
G. Valori ◽  
M. G. Linton ◽  
F. P. Zuccarello ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Magnetic Energy ◽  
Numerical Study ◽  
Three Dimensional ◽  
Flux Rope ◽  
Magnetic Helicity ◽  
Free Energies ◽  
Magnetic Flux Rope ◽  
Solar Eruptions

Context. The discovery of clear criteria that can deterministically describe the eruptive state of a solar active region would lead to major improvements on space weather predictions. Aims. Using series of numerical simulations of the emergence of a magnetic flux rope in a magnetized coronal, leading either to eruptions or to stable configurations, we test several global scalar quantities for the ability to discriminate between the eruptive and the non-eruptive simulations. Methods. From the magnetic field generated by the three-dimensional magnetohydrodynamical simulations, we compute and analyze the evolution of the magnetic flux, of the magnetic energy and its decomposition into potential and free energies, and of the relative magnetic helicity and its decomposition. Results. Unlike the magnetic flux and magnetic energies, magnetic helicities are able to markedly distinguish the eruptive from the non-eruptive simulations. We find that the ratio of the magnetic helicity of the current-carrying magnetic field to the total relative helicity presents the highest values for the eruptive simulations, in the pre-eruptive phase only. We observe that the eruptive simulations do not possess the highest value of total magnetic helicity. Conclusions. In the framework of our numerical study, the magnetic energies and the total relative helicity do not correspond to good eruptivity proxies. Our study highlights that the ratio of magnetic helicities diagnoses very clearly the eruptive potential of our parametric simulations. Our study shows that magnetic-helicity-based quantities may be very efficient for the prediction of solar eruptions.

scholarly journals Observations of flux rope formation prior to coronal mass ejections

2013 ◽  
Vol 8 (S300) ◽  
pp. 209-214 ◽  
Author(s):  
Lucie M. Green ◽  
Bernhard Kliem
Keyword(s):  
Magnetic Flux ◽  
Magnetic Structure ◽  
Solar Atmosphere ◽  
Coronal Mass Ejections ◽  
Flux Rope ◽  
Active Regions ◽  
Magnetic Configuration ◽  
Magnetic Flux Rope ◽  
Source Regions ◽  
Flux Ropes

AbstractUnderstanding the magnetic configuration of the source regions of coronal mass ejections (CMEs) is vital in order to determine the trigger and driver of these events. Observations of four CME productive active regions are presented here, which indicate that the pre-eruption magnetic configuration is that of a magnetic flux rope. The flux ropes are formed in the solar atmosphere by the process known as flux cancellation and are stable for several hours before the eruption. The observations also indicate that the magnetic structure that erupts is not the entire flux rope as initially formed, raising the question of whether the flux rope is able to undergo a partial eruption or whether it undergoes a transition in specific flux rope configuration shortly before the CME.

Numerical Short-Term Solar Activity Forecasting

2017 ◽  
Vol 13 (S335) ◽  
pp. 243-249 ◽  
Author(s):  
Huaning Wang ◽  
Yihua Yan ◽  
Han He ◽  
Xin Huang ◽  
Xinghua Dai ◽  
...  
Keyword(s):  
Solar Activity ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Active Regions ◽  
Short Term ◽  
Solar Active Regions ◽  
Solar Eruptions ◽  
Dimensional Reconstruction

AbstractIt is well known that the energy for solar eruptions comes from magnetic fields in solar active regions. Magnetic energy storage and dissipation are regarded as important physical processes in the solar corona. With incomplete theoretical modeling for eruptions in the solar atmosphere, activity forecasting is mainly supported with statistical models. Solar observations with high temporal and spatial resolution continuously from space well describe the evolution of activities in the solar atmosphere, and combined with three dimensional reconstruction of solar magnetic fields, makes numerical short-term (within hours to days) solar activity forecasting possible. In the current report, we propose the erupting frequency and main attack direction of solar eruptions as new forecasts and present the prospects for numerical short-term solar activity forecasting based on the magnetic topological framework in solar active regions.

scholarly journals A new trigger mechanism for coronal mass ejections

2020 ◽  
Vol 644 ◽  
pp. A137
Author(s):  
A. W. James ◽  
L. M. Green ◽  
L. van Driel-Gesztelyi ◽  
G. Valori
Keyword(s):  
Magnetic Flux ◽  
Magnetic Reconnection ◽  
Extreme Ultraviolet ◽  
Flux Rope ◽  
Active Regions ◽  
Magnetic Activity ◽  
Trigger Mechanism ◽  
Magnetic Flux Rope ◽  
Left Handed ◽  
Flux Ropes

Context. Many previous studies have shown that the magnetic precursor of a coronal mass ejection (CME) takes the form of a magnetic flux rope, and a subset of them have become known as “hot flux ropes” due to their emission signatures in ∼10 MK plasma. Aims. We seek to identify the processes by which these hot flux ropes form, with a view of developing our understanding of CMEs and thereby improving space weather forecasts. Methods. Extreme-ultraviolet observations were used to identify five pre-eruptive hot flux ropes in the solar corona and study how they evolved. Confined flares were observed in the hours and days before each flux rope erupted, and these were used as indicators of episodic bursts of magnetic reconnection by which each flux rope formed. The evolution of the photospheric magnetic field was observed during each formation period to identify the process(es) that enabled magnetic reconnection to occur in the β <  1 corona and form the flux ropes. Results. The confined flares were found to be homologous events and suggest flux rope formation times that range from 18 hours to 5 days. Throughout these periods, fragments of photospheric magnetic flux were observed to orbit around each other in sunspots where the flux ropes had a footpoint. Active regions with right-handed (left-handed) twisted magnetic flux exhibited clockwise (anticlockwise) orbiting motions, and right-handed (left-handed) flux ropes formed. Conclusions. We infer that the orbital motions of photospheric magnetic flux fragments about each other bring magnetic flux tubes together in the corona, enabling component reconnection that forms a magnetic flux rope above a flaring arcade. This represents a novel trigger mechanism for solar eruptions and should be considered when predicting solar magnetic activity.

scholarly journals The emergence of magnetic flux and its role on the onset of solar dynamic events

2019 ◽  
Vol 377 (2148) ◽  
pp. 20180387 ◽  
Author(s):  
V. Archontis ◽  
P. Syntelis
Keyword(s):  
Magnetic Flux ◽  
Large Scale ◽  
Spatial Scales ◽  
Active Regions ◽  
Short Review ◽  
The Sun ◽  
Flux Emergence ◽  
Dynamic Events ◽  
Solar Eruptions ◽  
Solar Dynamics

A plethora of solar dynamic events, such as the formation of active regions, the emission of jets and the occurrence of eruptions is often associated with the emergence of magnetic flux from the interior of the Sun to the surface and above. Here, we present a short review on the onset, driving and/or triggering of such events by magnetic flux emergence. We briefly describe some key observational examples, theoretical aspects and numerical simulations, towards revealing the mechanisms that govern solar dynamics and activity related to flux emergence. We show that the combination of important physical processes like shearing and reconnection of magnetic fieldlines in emerging flux regions or at their vicinity can power some of the most dynamic phenomena in the Sun on various temporal and spatial scales. Based on previous and recent observational and numerical studies, we highlight that, in most cases, none of these processes alone can drive and also trigger explosive phenomena releasing considerable amount of energy towards the outer solar atmosphere and space, such as flares, jets and large-scale eruptions (e.g. coronal mass ejections). In addition, one has to take into account the physical properties of the emerging field (e.g. strength, amount of flux, relative orientation to neighbouring and pre-existing magnetic fields, etc.) in order to better understand the exact role of magnetic flux emergence on the onset of solar dynamic events. This article is part of the theme issue ‘Solar eruptions and their space weather impact’.

scholarly journals Formation of a tiny flux rope in the center of an active region driven by magnetic flux emergence, convergence, and cancellation

2020 ◽  
Vol 642 ◽  
pp. A199
Author(s):  
Ruisheng Zheng ◽  
Yao Chen ◽  
Bing Wang ◽  
Hongqiang Song ◽  
Wenda Cao
Keyword(s):  
Active Region ◽  
Magnetic Flux ◽  
Space Weather ◽  
Source Region ◽  
Flux Rope ◽  
Negative Polarity ◽  
Flux Emergence ◽  
High Quality ◽  
Solar Eruptions ◽  
A Minor

Aims. Flux ropes are generally believed to be core structures of solar eruptions that are significant for the space weather, but their formation mechanism remains intensely debated. We report on the formation of a tiny flux rope beneath clusters of active region loops on 2018 August 24. Methods. Combining the high-quality multiwavelength observations from multiple instruments, we studied the event in detail in the photosphere, chromosphere, and corona. Results. In the source region, the continual emergence of two positive polarities (P1 and P2) that appeared as two pores (A and B) is unambiguous. Interestingly, P2 and Pore B slowly approached P1 and Pore A, implying a magnetic flux convergence. During the emergence and convergence, P1 and P2 successively interacted with a minor negative polarity (N3) that emerged, which led to a continuous magnetic flux cancellation. As a result, the overlying loops became much sheared and finally evolved into a tiny twisted flux rope that was evidenced by a transient inverse S-shaped sigmoid, the twisted filament threads with blueshift and redshift signatures, and a hot channel. Conclusions. All the results show that the formation of the tiny flux rope in the center of the active region was closely associated with the continuous magnetic flux emergence, convergence, and cancellation in the photosphere. Hence, we suggest that the magnetic flux emergence, convergence, and cancellation are crucial for the formation of the tiny flux rope.

Dynamical Splitting of Spot-producing Magnetic Rings in a Nonlinear Shallow-water Model

2021 ◽  
Vol 922 (1) ◽  
pp. 46
Author(s):  
Mausumi Dikpati ◽  
Aimee A. Norton ◽  
Scott W. McIntosh ◽  
Peter A. Gilman
Keyword(s):  
Magnetic Fields ◽  
Shallow Water ◽  
High Latitude ◽  
Magnetic Energy ◽  
Active Regions ◽  
Water Model ◽  
Lower Latitude ◽  
Shallow Water Model ◽  
Weather Events ◽  
Solar Eruptions

Abstract We explore the fundamental physics of narrow toroidal rings during their nonlinear magnetohydrodynamic evolution at tachocline depths. Using a shallow-water model, we simulate the nonlinear evolution of spot-producing toroidal rings of 6° latitudinal width and a peak field of 15 kG. We find that the rings split; the split time depends on the latitude of each ring. Ring splitting occurs fastest, within a few weeks, at latitudes 20°–25°. Rossby waves work as perturbations to drive the instability of spot-producing toroidal rings; the ring split is caused by the “mixed stress” or cross-correlations of perturbation velocities and magnetic fields, which carry magnetic energy and flux from the ring peak to its shoulders, leading to the ring split. The two split rings migrate away from each other, the high-latitude counterpart slipping poleward faster due to migrating mixed stress and magnetic curvature stress. Broader toroidal bands do not split. Much stronger rings, despite being narrow, do not split due to rigidity from stronger magnetic fields within the ring. Magnetogram analysis indicates the emergence of active regions sometimes at the same longitudes but separated in latitude by 20° or more, which could be evidence of active regions emerging from split rings, which consistently contribute to observed high-latitude excursions of butterfly wings during the ascending, peak, and descending phases of a solar cycle. Observational studies in the future can determine how often new spots are found at higher latitudes than their lower-latitude counterparts and how the combinations influence solar eruptions and space weather events.

scholarly journals Origin and structures of solar eruptions I: Magnetic flux rope

2017 ◽  
Vol 60 (8) ◽  
pp. 1383-1407 ◽  
Author(s):  
Xin Cheng ◽  
Yang Guo ◽  
MingDe Ding
Keyword(s):  
Magnetic Flux ◽  
Flux Rope ◽  
Magnetic Flux Rope ◽  
Solar Eruptions

Multi-spacecraft Observations of interacting CME flux ropes

2020 ◽  
Author(s):  
Emilia Kilpua ◽  
Simon Good ◽  
Erika Palmerio ◽  
Eleanna Asvestari ◽  
Jens Pomoell ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Significant Interaction ◽  
Interplanetary Space ◽  
Flux Rope ◽  
The Sun ◽  
The Earth ◽  
General Importance ◽  
Solar Cycle 24 ◽  
Solar Eruptions ◽  
Cycle 24

&lt;p&gt;Interactions between coronal mass ejections (CMEs) in interplanetary space are a highly important aspect for understanding their physical dynamics and evolution as well as their space weather consequences. Here we present an analysis of three CMEs that erupted from the Sun on June 12-14, 2012 using almost radially aligned spacecraft at Venus and Earth, complemented by heliospheric imaging and modelling with EUHFORIA. These multi-spacecraft observations were critical for interpreting the event correctly, in particular regarding the last two CMEs in the series (June 13 and June 14). At the orbit of Venus these CMEs were mostly separate with the June 14 CME just about to reach the previous CME. A significant interaction occurred before the CMEs reached the Earth. The shock of the June 14 CME had propagated through the June 13 CME and the two CMEs had coalesced into a single large flux rope structure before they reached the Earth. This merged flux rope had one of the largest magnetic field magnitudes observed in the near-Earth solar wind during Solar Cycle 24. We discuss also the general importance of multi-spacecraft observations and modelling using them in analyzing solar eruptions.&lt;/p&gt;

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