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![Magnetic configuration after initial relaxation (a), during slow rise phase (b), at time of peak flux rope velocity (c), and during flux rope deceleration (d). The flux rope core is depicted by orange field lines; ambient field lines are green. Bz (z = 0) is shown, with red (blue) corresponding to positive (negative) values. Left panels use a view similar to the observations (see paper I); right panels show a side view. The transparent grey-scales show a logarithmic distribution of |j|/|B| in the plane x = 0, outlining the locations of strongest currents. The sub-volume [−10, 16] × [−11, 11] × [0, 18] is used for all panels. (Kliem and Török 2006; Démoulin and Aulanier 2010), as has been shown under similar conditions in various simulations of erupting flux ropes (Török and Kliem 2007; Fan and Gibson 2007; Schrijver et al. 2008; Aulanier et al. 2010; Török et al. 2011). The right panels in Fig. 4 show that the trajectory of the flux rope is far from being vertical. Such lateral eruptions have been reported frequently in both observations and simulations (see, e.g., Williams et al. 2005; Panasenco et al. 2011; Yang et al. 2012), and are usually attributed to an asymmetric structure of the field overlying the erupting core flux. We believe that this causes the lateral rise also in our case. As the eruption continues, the trajectory of the flux rope becomes increasingly horizontal , resembling the so-called " roll effect " (Panasenco et al. 2011) and indicating that the rope cannot overcome the tension of the large-scale overlying field. Moreover, as a](profile/Gherardo-Valori/publication/313427913/figure/fig4/AS:459275899281411@1486511315273/Magnetic-configuration-after-initial-relaxation-a-during-slow-rise-phase-b-at-time.png)
Magnetic configuration after initial relaxation (a), during slow rise phase (b), at time of peak flux rope velocity (c), and during flux rope deceleration (d). The flux rope core is depicted by orange field lines; ambient field lines are green. Bz (z = 0) is shown, with red (blue) corresponding to positive (negative) values. Left panels use a view similar to the observations (see paper I); right panels show a side view. The transparent grey-scales show a logarithmic distribution of |j|/|B| in the plane x = 0, outlining the locations of strongest currents. The sub-volume [−10, 16] × [−11, 11] × [0, 18] is used for all panels. (Kliem and Török 2006; Démoulin and Aulanier 2010), as has been shown under similar conditions in various simulations of erupting flux ropes (Török and Kliem 2007; Fan and Gibson 2007; Schrijver et al. 2008; Aulanier et al. 2010; Török et al. 2011). The right panels in Fig. 4 show that the trajectory of the flux rope is far from being vertical. Such lateral eruptions have been reported frequently in both observations and simulations (see, e.g., Williams et al. 2005; Panasenco et al. 2011; Yang et al. 2012), and are usually attributed to an asymmetric structure of the field overlying the erupting core flux. We believe that this causes the lateral rise also in our case. As the eruption continues, the trajectory of the flux rope becomes increasingly horizontal , resembling the so-called " roll effect " (Panasenco et al. 2011) and indicating that the rope cannot overcome the tension of the large-scale overlying field. Moreover, as a
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We report observations of a filament eruption, two-ribbon flare, and coronal mass ejection (CME) that occurred in Active Region NOAA 10898 on 6 July 2006. The filament was located South of a strong sunspot that dominated the region. In the evolution leading up to the eruption, and for some time after it, a counter-clockwise rotation of the sunspot...
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Context 1
... TD flux rope is stabilized by flux rooted towards the southern edge of the main polarity, and the rope is inclined with respect to the vertical, which is due to the asymmetry of the potential field surrounding it. Figure 4a shows that electric currents are present in the ambient field volume. The strongest current concentrations are located in the front of the flux rope and exhibit an X-shaped pattern in the vertical cut shown. ...
Context 2
... The QSLs are present in the configuration from the very beginning and arise from the complexity of the potential field. Their presence is evident also in the left panel of Fig. 4a: the green field lines show strong connectivity gradients in the northern part of the main polarity and in the vicinity of the western flux rope footpoint. It has been demonstrated that current concentrations form preferably at the locations of QSLs as a system containing such structures is dynamically perturbed (see, e.g., Aulanier, ...
Context 3
... twisting does not lead to the formation of a single twisted flux tube that rises exactly in vertical direction above the TD rope, as it was the case earlier studies (Amari et al. 1996;Török and Kliem 2003;Aulanier, Démoulin, and Grappin 2005). Rather, the twisting leads to a slow, global expansion of the fan-shaped field lines, as shown in Fig. 4. Since we are mainly interested in the destabilization of the flux rope, we did not study the detailed evolution of the large-scale field. We expect it to be very similar to the one described in Santos, Büchner, and Otto (2011), since the active region those authors simulated was also dominated by one main polarity, and the field ...
Context 4
... affected only by a fraction of the boundary flows and therefore get merely sheared (rather than twisted), which still leads to their slow expansion. As a result, the TD rope starts to rise, adapting to the successively decreasing magnetic tension of the overlying field (phase I in Fig. 3). This initial phase of the evolution is depicted in Fig. 4b. Note that some of the flux at the front of the expanding arcade reconnects at the QSL current layer, which can be expected to aid the arcade expansion to some degree. As can be seen in Fig. 3, the TD rope rises, after some initial adjustment, exponentially during this slow initial ...
Context 5
... of the TD rope after t ≈ 100 τ a can be associated with the development of the torus instability ( Kliem and Török 2006;Démoulin and Aulanier 2010), as has been shown under similar conditions in various simulations of erupting flux ropes Fan and Gibson 2007;Schrijver et al. 2008;Aulanier et al. 2010;Török et al. 2011). The right panels in Fig. 4 show that the trajectory of the flux rope is far from being vertical. Such lateral eruptions have been reported frequently in both observations and simulations (see, e.g., Williams et al. 2005;Panasenco et al. 2011;Yang et al. 2012), and are usually attributed to an asymmetric structure of the field overlying the erupting core flux. We ...
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Citations
... In the flux rope catastrophe theory, the onset of the eruption is approached as the loss of equilibrium of the coronal flux rope system. Before the onset, the flux rope should be static or quasi-static (Török et al., 2013;Liu, 2020), indicating that the flux rope system is in equilibrium. If the equilibrium is not disrupted, the net force on the flux rope will always be zero, so that its state of motion will remains unchanged, i.e., no eruption of the flux rope could occur. ...
Large-scale solar eruptive activities have a close relationship with coronal magnetic flux ropes. Previous numerical studies have found that the equilibrium of a coronal flux rope system could be disrupted if the axial magnetic flux of the rope exceeds a critical value, so that the catastrophe occurs, initiating the flux rope to erupt. Further studies discovered that the catastrophe does not necessarily exist: the flux rope system with certain photospheric flux distributions could be non-catastrophic. It is noteworthy that most previous numerical studies are under the ideal magnetohydrodynamic (MHD) condition, so that it is still elusive whether there is the catastrophe associated with the critical axial flux if magnetic reconnection is included in the flux rope system. In this paper, we carried out numerical simulations to investigate the evolutions of coronal magnetic rope systems under the ideal MHD and the resistive condition. Under the ideal MHD condition, our simulation results demonstrate that the flux rope systems with either too compact or too weak photospheric magnetic source regions are non-catastrophic versus varying axial flux of the rope, and thus no eruption could be initiated; if there is magnetic reconnection in the rope system, however, those flux rope systems could change to be capable of erupting via the catastrophe associated with increasing axial flux. Therefore, magnetic reconnection could significantly influence the catastrophic behaviors of flux rope system. It should be both the magnetic topology and the local physical parameters related to magnetic reconnection that determine whether the increasing axial flux is able to cause flux rope eruptions.
... They are huge structures that manifest themselves within some tens of minutes as clouds of magnetized plasma impulsively expelled from the Sun and subsequently propagating into interplanetary space (see e.g., Forbes, 2000). CMEs arise from usually complex and closed magnetic field structures in equilibrium that is disrupted due to some instability causing its eruption (e.g., emerging magnetic flux, remote reconfiguration of large scale magnetic field, or field rotation; see e.g., Török et al., 2013;Schmieder et al., 2015;Green et al., 2018). Instabilities in the solar magnetic field and their occurrence frequency are modulated by the 11-year activity cycle of the Sun. ...
The Sun, as an active star, is the driver of energetic phenomena that structure interplanetary space and affect planetary atmospheres. The effects of Space Weather on Earth and the solar system is of increasing importance as human spaceflight is preparing for lunar and Mars missions. This review is focusing on the solar perspective of the Space Weather relevant phenomena, coronal mass ejections (CMEs), flares, solar energetic particles (SEPs), and solar wind stream interaction regions (SIR). With the advent of the STEREO mission (launched in 2006), literally, new perspectives were provided that enabled for the first time to study coronal structures and the evolution of activity phenomena in three dimensions. New imaging capabilities, covering the entire Sun-Earth distance range, allowed to seamlessly connect CMEs and their interplanetary counterparts measured in-situ (so called ICMEs). This vastly increased our knowledge and understanding of the dynamics of interplanetary space due to solar activity and fostered the development of Space Weather forecasting models. Moreover, we are facing challenging times gathering new data from two extraordinary missions, NASA's Parker Solar Probe (launched in 2018) and ESA's Solar Orbiter (launched in 2020), that will in the near future provide more detailed insight into the solar wind evolution and image CMEs from view points never approached before. The current review builds upon the Living Reviews paper by Schwenn from 2006, updating on the Space Weather relevant CME-flare-SEP phenomena from the solar perspective, as observed from multiple viewpoints and their concomitant solar surface signatures.
... Once the tension is sufficiently reduced, a distinct second phase of evolution occurs where the flux rope enters an unstable regime characterized by a strong acceleration. Our simulation thus suggests a new mechanism for the triggering of eruptions in the vicinity of rotating sunspots [27]. 19 ...
There is a continuous need for an automated, computer based detection code that is able to isolate Coronal Mass Ejections (CME) from various observatories. Being bright, hot and fast plasma with large masses, CMEs are ejected from active regions of the solar corona in a variety of directions with an occurrence that implies that the solar corona is changing continuously. It is thought that CMEs are ejected into free space due to a sudden instability. Although the exact mechanism of CME generation is not clear yet, many studies focused on their behavior which require development of automatic detection utilities. In the present work, this task has been taken, where a computer code was written that aimed to detect and analyze CME events using images taken from the Large Angle and Spectrometric Coronagraph (LASCO) detector on board the Solar and Heliospheric Observatory (SOHO). Few selected examples of CMEs were studied by means of the present method using LASCO archived images. Selected CMEs were a group of 20 events from the years 2000, 2002, 2003, 2007 and 2013. The detection process was made using a Matlab program called cmeDetect. This program contained various functions that were written during this work for the task of analyzing CME events. The main detection method used in this work was based on bulk detection of CME events then track their motion. Analysis depended on LASCO images with resolution 512x512 pixels. Final analysis included CME heights, velocities, accelerations, masses, energies and directions of the detected events. Comparison with CDAW library was extensively made. The present cmeDetect code was able to detect and recognize welldefined CMEs but if they were with faint density the detection is either lost or decreased in efficiency. This was explained because the outer edge -the most important CME part- is about 3 to 7% less than the actual one.
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The rotation of sunspots around their umbral center has long been considered as an important process in driving coronal mass ejections (CMEs), but the specific mechanism remains unclear. Here with numerical magnetohydrodynamic simulations of both data-inspired and data-driven approaches, we show that the rotation of a large sunspot leads to a CME actually in a way distinct from the conventional view based on ideal instabilities of twisted flux rope. It is found that through the successive rotation of the sunspot the coronal magnetic field is sheared with a vertical current sheet created progressively, and once fast reconnection sets in the current sheet, the eruption is instantly triggered, with a highly twisted flux rope originating from the eruption. The simulations also revealed a slow-rise evolution phase sandwiched between the quasi-static energy-storage phase and the impulsive eruption-acceleration phase, and it enhances building up of the current sheet.
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