We present the formation and eruption of a sigmoidal filament driven by rotating network magnetic fields (RNFs) near the center of the solar disk, which was observed by the one-meter aperture New Vacuum Solar Telescope (NVST) at Fuxian Solar Observatory (FSO) on 2018 July 12. Counterclockwise RNFs twist two small-scale filaments at their northeastern foot-point region, giving a rotation of nearly 200 degree within about 140 minutes. The motion of the RNF has a tendency to accelerate at first and then decelerate obviously, as the average rotation speed increased from 10 to 150 ,and then slowed down to 50 . Coalescence then occurs between filaments F1 and F2. Meanwhile the fine structures in the southwestern region of the filament was involved in another interaction of coalescence. The subsequent EUV brightening due to plasma heating is observed in the two interaction regions. These interacting structures, including F1, F2 and the fine structures in the southwestern region, eventually evolve into a larger-scale sigmoidal filament twisted in the same direction as the RNFs gave. The twist of the sigmoidal filament has exceeded 4π and the filament erupted finally. The motion of the sigmoidal filament keeps uniform until a nearby jet collides, causing the filament to erupt faster. These results provide evidence that RNF plays an important role in the formation and eruption of the sigmoidal filament. The phenomena also suggests that the kink instability is the trigger mechanism for the filament eruption.
In this paper, we study in detail the evolution of a mini-sigmiod originating in a cross-equatorial coronal hole, where the magnetic field is mostly open and seriously distinct from the closed background field above active-region sigmoids. The source region first appeared as a bipole, which subsequently experienced a rapid emergence followed by a long-term decay. Correspondingly, the coronal structure initially appeared as arc-like loops, then gradually sheared and transformed into continuously sigmoidal loops, mainly owing to flux cancellation near the polarity inversion line. The temperature…
It is recently noted that solar eruptions can be associated with the contraction of coronal loops that are not involved in magnetic reconnection processes. In this paper, we investigate five coronal eruptions originating from four sigmoidal active regions, using high-cadence, high-resolution narrowband EUV images obtained by the Solar Dynamic Observatory (SDO}). The magnitudes of the flares associated with the eruptions range from the GOES-class B to X. Owing to the high-sensitivity and broad temperature coverage of the Atmospheric Imaging Assembly (AIA) onboard SDO, we are able to identify bo…
Using observations from Solar Dynamics Observatory, we studied an interesting example of a sigmoid formation and eruption from small-scale flux canceling regions of active region (AR) 11942. Analysis of HMI and AIA observations infer that initially the AR is compact and bipolar in nature, evolved to sheared configuration consisting of inverse J-shaped loops hosting a filament channel over a couple of days. By tracking the photospheric magnetic features, shearing and converging motions are observed to play a prime role in the development of S-shaped loops and further flux cancellation leads to …
The dynamic properties of flare ribbons and the often associated filament eruptions can provide crucial information on the flaring coronal magnetic field. This Letter analyzes the GOES-class X1.0 flare on 2014 March 29 (SOL2014-03-29T17:48), in which we found an asymmetric eruption of a sigmoidal filament and an ensuing circular flare ribbon. Initially both EUV images and a preflare nonlinear force-free field model show that the filament is embedded in magnetic fields with a fan-spine-like structure. In the first phase, which is defined by a weak but still increasing X-ray emission, the wester…
We investigate two sympathetic filament eruptions observed by the New Vacuum Solar Telescope (NVST) on 2015 October 15. The full picture of the eruptions is obtained from the corresponding SDO/AIA observations. The two filaments start from active region NOAA 12434 in the north and end in one large quiescent filament channel in the south. The left filament erupts firstly, followed by the right filament eruption about 10 minutes later. Clear twist structure and rotating motion are observed in both filaments during the eruption. Both eruptions are failed, since the filaments firstly rise up, then…
Soar filament eruptions are often associated with solar flares and coronal mass ejections (CMEs), which are the major impacts on space weather. However, the fine structures and the trigger mechanisms of solar filaments are still unclear. To address these issues, we studied a failed solar active-region filament eruption associated with a C-class flare by using high-resolution H$α$ images from the New Vacuum Solar Telescope (NVST), supplemented by EUV observations of the Solar Dynamical Observatory (SDO). Before the filament eruption, a small bi-pole magnetic field emerged below the filament. An…
It is unclear whether successive filament eruptions at different sites within a short time interval are physically connected or not. Here, we present the observations of the successive eruptions of a small and a large filament in a tripolar magnetic field region whose coronal magnetic field showed as a fan-spine magnetic system. By analyzing the multi-wavelength observations taken by the Solar Dynamic Observatory (SDO) and the extrapolated three-dimensional coronal magnetic field, we find that the two filaments resided respectively in the two lobes that make up the inner fan structure of the f…
We present an investigation of partial filament eruption on 2012 June 17 in the active region NOAA 11504. For the first time, we observed the vertical splitting process during the partial eruption with high resolution narrow band images at 10830 . The active filament was rooted in a small sunspot of the active region. Particularly, it underwent the partial eruption in three steps, i.e. the precursor, the first eruption, and the second eruption, while the later two were associated with a C1.0 flare and a C3.9 flare, respectively. During the precursor, slow magnetic reconnection took place betwe…
To better understand magnetic structure and eruptive process of solar filaments, a solar active-region filament (labeled F2) eruption associated with a B-class flare was investigated by using high-resolution H$α$ data from the 1 m New Vacuum Solar Telescope (NVST), combined with EUV observations of the Solar Dynamical Observatory (SDO). The filament F2 was disturbed by another filament (labeled F1) eruption that experienced a whip-like motion. Before the filament F2 eruption, the Dopplergrams show that the southern and the northern parts of the filament F2 body exhibit blueshift and redshift a…
The active region magnetic field surrounding the filament plays an important role in filament formation, their evolution and disruption. We investigated a filament eruption that occurred in southern hemisphere of the Sun on July 08, 2011 using AIA and HMI data. The filament was located in a region close to the active region NOAA 11247 with its West-most footpoint anchored in the negative polarity plage region and the East-most in the positive polarity plage region. During observations, the magnetic flux was emerging in the active region and also in the plage regions. The flux emergence was sto…
We present the observations of three sympathetic filament eruptions occurring on 19 July 2015 namely F1, F2, and F3. The events were observed in UV/EUV wavelengths by Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory and by Global Oscillation Network Group telescope in Hα line. As filament F1 starts to erupt, a part of it falls close to the location of the F2 and F3 filaments. This causes the eruption of F2 and F3 during which the two filaments merge together and trigger a medium-class CME and a long-duration GOES C2.1 class flare. We discuss the dynamics and kinematics of th…
We investigate the interaction between two filaments and the subsequent filament eruption event observed from different view angles by Hinode, the Solar and Heliospheric Observatory (SOHO), and the Solar Terrestrial Relations Observatory (STEREO). In the event, the two filaments rose high, interacted with each other, and finally were ejected along two different paths. We measure the bulk-flow velocity using spectroscopic data. We find significant outflows at the speed of a few hundreds of km/s during the filament eruption, and also some downflows at a few tens of km/s at the edge of the erupti…
Successive Coronal Jets as Novel Facilitators for Filament Oscillation and Eruption
School of Physics and Astronomy, Yunnan University（云南大学物理与天文学院）；Yunnan Key Laboratory of the Solar physics and Space Science（云南省太阳物理与空间科学重点实验室）；School of Intelligence Science and Technology, Nanjing University（南京大学智能科学与技术学院）
Using multi-wavelength observation from SDO and STEREO, we investigated the mechanism of two successive eruptions (F1 & F2) of a filament in active region NOAA 11444 on 27 march, 2012. The filament was inverse `J' shaped and lying along a quasi-circular polarity inversion line (PIL). The first part of the filament (F1) erupted at ~2:30UT on 27 March 2012, the second part of the filament (F2) erupted at around 4:20 UT on the same day. A precursor/pre-flare brightening was observed below filament's main axis about 30 min prior to F1. The brightening was followed by a jet-like ejection below fila…
Coronal mass ejections (CMEs) are closely related to eruptive filaments and usually are the continuation of the same eruptive process into the upper corona. There are failed filament eruptions when a filament decelerates and stops at some greater height in the corona. Sometimes the filament after several hours starts to rise again and develops into the successful eruption with a CME formation. We propose a simple model for the interpretation of such two-step eruptions in terms of equilibrium of a flux rope in a two-scale ambient magnetic field. The eruption is caused by a slow decrease of the …
A filament eruption on 2010 October 21 observed from three different viewpoints by the Solar Terrestrial Relations Observatory (STEREO) and the Solar Dynamic Observatory (SDO) is analyzed with invoking also data from the Solar and Heliospheric Observatory (SOHO) and the Kanzelhoehe Solar Observatory. The position of the filament just before the eruption at the central meridian not far from the center of the solar disk was favorable for photospheric magnetic field measurements in the area below the filament. Because of this, we were able to calculate with high precision the distribution of the …
Failed filament eruptions are solar eruptions that are not associated with coronal mass ejections. In a failed filament eruption, the filament materials usually show some ascending and falling motions as well as generate bright EUV emissions. Here we report a failed filament eruption that occurred in a quiet-Sun region observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. In this event, the filament spreads out but gets confined by the surrounding magnetic field. When interacting with the ambient magnetic field, the filament material brightens up and flows along…
A filament, a dense cool plasma supported by the magnetic fields in the solar corona, often becomes unstable and erupts. It is empirically known that the filament often demonstrates some activations such as a turbulent motion prior to eruption. In our previous study (Seki et al. 2017), we analysed the Doppler velocity of an Hα filament and found that the standard deviation of the line-of-sight-velocity (LOSV) distribution in a filament, which indicates the increasing amplitude of the small-scale motions, increased prior to the onset of the eruption. Here, we present a further analysis on this …
It is widely recognised that filament disappearances or eruptions are frequently associated with Coronal Mass Ejections (CMEs). Since CMEs are a major source of disturbances of the space environment surrounding the Earth, it is important to investigate these associations in detail for the better prediction of CME occurrence. However, the proportion of filament disappearances associated with CMEs is under debate. The estimates range from $\sim$10% to $\sim$90% and could be affected by the manners to select the events. In this study, we aim to reveal what parameters control the association betwe…
Solar eruptions occurring at different places within a relatively short time interval are considered to be sympathetic. However, it is difficult to determine whether there exists a cause and effect between them. Here we study a failed and a successful filament eruption following an X1.8-class flare on 2014 December 20, in which slipping-like magnetic reconnections serve as a key causal link among the eruptions. Reconnection signatures and effects are: at both sides of the filament experiencing the failed eruption, serpentine ribbons extend along chromospheric network to move away from the fila…
The magnetic breakout model has been widely used to explain solar eruptive activities. Here, we apply it to explain successive filament eruptions occurred in a quadrupolar magnetic source region. Based on the high temporal and spatial resolution, multi-wavelengths observations taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO), we find some signatures that support the occurrence of breakout-like external reconnection just before the start of the successive filament eruptions. Furthermore, the extrapolated three-dimensional coronal field also reveals th…
To better understand the dynamical process of active-region filament eruptions and associated flares and CMEs, we carried out a statistical study of 120 events observed by BBSO, TRACE, and t(SOHO/EIT) from 1998 to 2007 and combined filament observations with the NOAA's flare reports, MDI magnetograms, and LASCO data, to investigate the relationship between active-region filament eruptions and other solar activities. We found that 115 out of 120 filament eruptions are associated with flares. 56 out of 105 filament eruptions are found to be associated with CMEs except for 15 events without corre…
Solar filaments/prominences exhibit rotational motion during different phases of their evolution from their formation to eruption. We have observed the rotational/vortical motion in the photosphere near the ends of ten filaments during their initial phase of eruption, at the onset of the fast rise phase. All the filaments were associated with active regions. The photospheric vortical motions we observed lasted for 4--20 minutes. In the vicinity of the conjugate ends of the filament the direction of rotation was opposite, except for two cases, where rotational motion was observed at only one en…
Using the observations from the Optical and Near-infrared Solar Eruption Tracer and the Solar Dynamics Observatory, we study an M5.7 flare in AR 11476 on 2012 May 10 and a micro-flare in the quiet Sun on 2017 March 23. Before the onset of each flare, there is a reverse S-shaped filament above the polarity inversion line. Then the filaments become unstable and begin to rise. The rising filaments gain the upper hand over the tension force of the dome-like overlying loops and thus successfully erupt outward. The footpoints of the reconnecting overlying loops successively brighten and are observed…
In this paper, we present a multi-wavelength analysis to mass-draining and oscillations in a large quiescent filament prior to its successful eruption on 2015 April 28. The eruption of a smaller filament that was parallel and in close, 350 proximity was observed to induce longitudinal oscillations and enhance mass-draining within the filament of interest. The longitudinal oscillation with an amplitude of 25 Mm and 23 km underwent no damping during its observable cycle. Subsequently the slightly enhanced draining may have excited a eruption behind the limb, leading to a feedback that further en…
We present here an interesting two-step filament eruption during 14-15 March 2015. The filament was located in NOAA AR 12297 and associated with a halo Coronal Mass Ejection (CME). We use observations from the Atmospheric Imaging Assembly (AIA) and Heliospheric Magnetic Imager (HMI) instruments onboard the Solar Dynamics Observatory (SDO), and from the Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO). We also use H-alpha data from the Global Oscillation Network Group (GONG) telescope and the Kanzelhoehe Solar Observatory. The filament shows a first st…
We describe a partial filament eruption on 11 December 2011 which demonstrates that the inclusion of mass is an important next step for understanding solar eruptions. Observations from the \textit{Solar Terrestrial Relations Observatory Behind} (STEREO-B) and the \textit{Solar Dynamics Observatory} (SDO) spacecraft were used to remove line-of-sight projection effects in filament motion and correlate the effect of plasma dynamics with the evolution of the filament height. Flux cancellation and nearby flux emergence are shown to have played a role in increasing the height of the filament prior t…
To investigate the factors that control the success and/or failure of solar eruptions, we study the magnetic field and 3-Dimensional (3D) configuration of 16 filament eruptions during 2010 July - 2013 February. All these events, i.e., erupted but failed to be ejected to become a coronal mass ejection (CME), are failed eruptions with the filament maximum height exceeding $100 Mm$. The magnetic field of filament source regions is approximated by a potential field extrapolation method. The filament 3D configuration is reconstructed from three vantage points by the observations of STEREO Ahead/Beh…
We investigate the eruption of a quiescent filament located close to an active region. Large-scale activation was observed in only half of the filament in the form of pre-eruption oscillations. Consequently only this half erupted nearly 30 hr after the oscillations commenced. Time-slice diagrams of 171 Å images from Atmospheric Imaging Assembly were used to study the oscillations. The oscillations were observed in several thin and long features connecting the filament spine to the chromosphere below. This study traces the origin of such features and proposes their possible interpretation. Smal…
Coronal mass ejections (CMEs) play a decisive role in driving space weather, especially, the fast ones (e.g., with speeds above $800$~km~s$^{-1}$). Understanding the trigger mechanisms of fast CMEs can help us gaining important information in forecasting them. The filament eruptions accompanied with CMEs provide a good tracer in studying the early evolution of CMEs. Here we surveyed 66 filament-accompanied fast CMEs to analyse the correlation between the trigger mechanisms, namely either magnetic reconnection or ideal MHD process, associated flares, and CME speeds. Based on the data gathering …
Filaments, the dense cooler plasma floating in the solar corona supported by magnetic fields, generally exhibit certain activations before they erupt. In our previous study (Seki et al. 2017 ), we observed that the standard deviation of the line-of-sight (LOS) velocities of the small-scale motions in a filament increased prior to its eruption. However, because that study only analyzed one event, it is unclear whether such an increase in the standard deviation of LOS velocities is common in filament eruptions. In this study, 12 filaments that vanished in Hα line center images were analyzed in a…
We report two sympathetic solar eruptions, including a partial and a full flux rope eruption in a quadrupolar magnetic region, where a large and a small filament resided above the middle and the east neutral lines respectively. The large filament first rose slowly at a speed of 8 km/s for 23 minutes and then it was accelerated to 102 km/s. Finally, this filament erupted successfully and caused a coronal mass ejection. During the slow rising phase, various evidence for breakout-like external reconnection has been identified at high and low temperature lines. The eruption of the small filament s…
The 2015 March 15 coronal mass ejection as one of the two that together drove the largest geomagnetic storm of solar cycle 24 so far was associated with sympathetic filament eruptions. We investigate the relations between the different filaments involved in the eruption. A surge-like small-scale filament motion is confirmed as the trigger that initiated the erupting filament with multi-wavelength observations and using a forced magnetic field extrapolation method. When the erupting filament moved to an open magnetic field region, it experienced an obvious acceleration process and was accompani…
On 2012 July 11, two solar filaments were observed in the northeast of the solar disk and their eruptions due to the interaction between them are studied by using the data from the Solar Dynamics Observatory (SDO), Solar TErrestrial RElations Observatory (STEREO) and Global Oscillation Network Group (GONG). The eastern filament (F1) first erupted toward the northeast. During the eruption of F1, some plasma from F1 fell down and was injected to the North-East part of another filament (F2), and some plasma of F1 fell down to the northern region close to F2 and caused the plasma to brighten. Mean…
We report on observations of conversion of bright filament strands into flare loops during 2012 August 31 filament eruption. Prior to the eruption, individual bright strands composing one of the legs of the filament were observed in the 171 A filter channel data of the Atmospheric Imaging Assembly. After the onset of the eruption, one of the hooked ribbons started to propagate and contract, sweeping footpoints of the bright filament strands as well as coronal loops located close by. Later on, hot flare loops appeared in regions swept by the hook, where the filament strands were rooted. Timing …
We present observations of the eruption and then reformation of a filament caused by its nearby emerging magnetic flux. Driven by the emerging magnetic flux, the emerged positive fluxes moved toward and cancelled with its nearby negative fluxes, where the negative ends of a filament channel beneath the filament and a bundle of left-skewed coronal loops overlying the filament were anchored. Complemented by the nonlinear force-free field extrapolation, we find that the coronal magnetic field lines associated with the filament channel and the emerging magnetic fields consist of sheared field line…
Filament eruption on 30 April - 1 May 2010, which shows the reconnection of one filament leg with a region far away from its initial position, is analyzed. Observations from three viewpoints are used for as precise as possible measurements of endpoint coordinates. The northern leg of the erupting prominence loop 'jumps' laterally to the latitude lower than the latitude of the originally southern endpoint. Thus, the endpoints reshuffled their positions in the limb view. Although this behaviour could be interpreted as the asymmetric zipping-like eruption, it does not look very likely. It seems m…
The stability of the magnetic field in the solar corona is important for understanding the causes of solar eruptions. Although various scenarios have been suggested to date, the tether-cutting reconnection scenario proposed by Moore et al.(2001) is one of the widely accepted models to explain the onset process of solar eruptions. Although the tether-cutting reconnection scenario proposed that sigmoidal field formed by the internal reconnection is the magnetic field in pre-eruptive state, the stability of the sigmoidal field has not yet been investigated quantitatively. In this paper, in order …
We present a study on the evolution of the small scale velocity field in a solar filament as it approaches to the eruption. The observation was carried out by the Solar Dynamics Doppler Imager (SDDI) that was newly installed on the Solar Magnetic Activity Research Telescope (SMART) at Hida Observatory. The SDDI obtains a narrow-band full disk image of the sun at 73 channels from H$α$ - 9.0 Å to H$α$ + 9.0 Å, allowing us to study the line-of-sight (LOS) velocity of the filament before and during the eruption. The observed filament is a quiescent filament that erupted on 2016 November 5. We deri…
We present the observations of a double-decker filament to study its formation, triggering, and eruption physics. It is observed that the double-decker filament was formed by splitting of an original single filament. During the splitting process, intermittent bright point bursts are observed in the filament channel, which resulted in the generation of the upper filament branch. The eruption of the newly formed double-decker filament was possibly triggered by two recurrent two-sided loop jets in the filament channel and the continuous mass unloading from the upper filament body. The interaction…
We analyze the observations of EUV loop evolution associated with the filament eruption located at the border of an active region. The event SOL2013-03-16T14:00 was observed with a large difference of view point by the Solar Dynamics Observatory and Solar Terrestrial Relations Observatory --A spacecraft. The filament height is fitted with the sum of a linear and exponential function. These two phases point to different physical mechanisms such as: tether-cutting reconnection and a magnetic instability. While no X-ray emission is reported, this event presents the classical eruption features lik…
The STEREO mission has been providing stereoscopic view of filament eruptions in EUV. The clearest view during a filament eruption is seen in He II 304 A observations. One of the main problems visualizing filament dynamics in He II 304 A is the strong background contrast due to surface features. We present a technique that removes background features and leaves behind only the filamentary structure, as seen by STEREO-A and B. The technique uses a pair of STEREO He II 304 A images observed simultaneously. The STEREO-B image is geometrically transformed to STEREO-A view so that the background im…
We study the formation and evolution of a failed filament eruption observed in NOAA active region 11121 near the southeast limb on November 6, 2010. We use a time series of SDO/AIA 304, 171, 131, 193, 335, 94 Å images, SDO/HMI magnetograms, plus ROSA and ISOON Hαimages, to study the erupting active region. We identify coronal loop arcades associated with a quadrupolar magnetic configuration, and show that the expansion and cancelation of the central loop arcade system over the filament is followed by the eruption of the filament. The erupting filament reveals a clear helical twist and develops…
We report on the rare eruption of a miniature H_alpha filament that took a surge form. The filament first underwent a full development within 46 minutes and then began to erupt 9 minutes later, followed by a compact, impulsive X-ray class M2.2 flare with a two ribbon nature only at the early eruption phase. During the eruption, its top rose, whereas the two legs remained rooted in the chromosphere and swelled little perpendicular to the rising direction. This led to a surge-like eruption with a narrow angular extent. Similar to the recent observations for standard and blowout X-ray jets by Moo…
To better understand the structures of active-region filaments and the eruption process, we study an active-region filament eruption in active region NOAA 11082 in detail on June 22, 2010. Before the filament eruption, the opposite unidirectional material flows appeared in succession along the spine of the filament. The rising of the filament triggered two B-class flares at the upper part of the filament. As the bright material was injected into the filament from the sites of the flares, the filament exhibited a rapid uplift accompanying the counterclockwise rotation of the filament body. From…
As one of the most common features in the solar atmosphere, filaments are significant not only in the solar physics but also in the stellar and laboratory plasma physics. With the New Vacuum Solar Telescope and the Solar Dynamics Observatory, here we report on multi-wavelength observations of eruptions of a small (30\arcsec) filament (SF) and its consequences while interacting with the ambient magnetic features including a large (300\arcsec) filament (LF). The eruptions of the SF drive a two-side-loop jet that is a result of magnetic reconnection between the SF threads and an over-lying magnet…
