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Register a new userTriggering Mechanism for the Filament Eruption on 2005 September 13 in Active Region NOAA 10808
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On 2005 September 13 a filament eruption accompanied by a halo CME occurred in the most flare-productive active region NOAA 10808 in Solar Cycle 23. Using multi-wavelength observations before the filament eruption on Sep. 13th, we investigate the processes leading to the catastrophic eruption. We find that the filament slowly ascended at a speed of 0.1km/s over two days before the eruption. During slow ascending, many small flares were observed close to the footpoints of the filament, where new magnetic elements were emerging. On the basis of the observational facts we discuss the triggering mechanism leading to the filament eruption. We suggest the process toward the eruption as follows: First, a series of small flares played a role in changing the topology of the loops overlying the filament. Second, the small flares gradually changed the equilibrium state of the filament and caused the filament to ascend slowly over two days. Finally, a C2.9 flare that occurred when the filament was close to the critical point for loss of equilibrium directly led to the catastrophic filament eruption right after itself.
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This paper presents a multiwavelength study of the M8.0 flare and its associated fast halo CME that originated from a bipolar active region NOAA 10759 on 2005 May 13. The source active region has a conspicuous sigmoid structure at TRACE 171 A channel as well as in the SXI soft X-ray images, and we mainly concern ourselves with the detailed process of the sigmoid eruption as evidenced by the multiwavelength data ranging from Halpha, WL, EUV/UV, radio, and hard X-rays (HXRs). The most important finding is that the flare brightening starts in the core of the active region earlier than that of the rising motion of the flux rope. This timing clearly addresses one of the main issues in the magnetic eruption onset of sigmoid, namely, whether the eruption is initiated by an internal tether-cutting to allow the flux rope to rise upward or a flux rope rises due to a loss of equilibrium to later induce tether cutting below it. Our high time cadence SXI and Halpha data shows that the first scenario is relevant to this eruption. As other major findings, we have the RHESSI HXR images showing a change of the HXR source from a confined footpoint structure to an elongated ribbon-like structure after the flare maximum, which we relate to the sigmoid-to-arcade evolution. Radio dynamic spectrum shows a type II precursor that occurred at the time of expansion of the sigmoid and a drifting pulsating structure in the flare rising phase in HXR. Finally type II and III bursts are seen at the time of maximum HXR emission, simultaneous with the maximum reconnection rate derived from the flare ribbon motion in UV. We interpret these various observed properties with the runaway tether-cutting model proposed by Moore et al. in 2001.
We report a detailed event analysis on the M6.6-class flare in the active region (AR) NOAA 11158 on 2011 February 13. AR 11158, which consisted of two major emerging bipoles, showed prominent activities including one X- and several M-class flares. In order to investigate the magnetic structures related to the M6.6 event, particularly the formation process of a flare-triggering magnetic region, we analyzed multiple spacecraft observations and numerical results of a flare simulation. We observed that, in the center of this quadrupolar AR, a highly sheared polarity inversion line (PIL) was formed through proper motions of the major magnetic elements, which built a sheared coronal arcade lying over the PIL. The observations lend support to the interpretation that the target flare was triggered by a localized magnetic region that had an intrusive structure, namely a positive polarity penetrating into a negative counterpart. The geometrical relationship between the sheared coronal arcade and the triggering region was consistent with the theoretical flare model based on the previous numerical study. We found that the formation of the trigger region was due to a continuous accumulation of the small-scale magnetic patches. A few hours before the flare occurrence, the series of emerged/advected patches reconnected with a preexisting fields. Finally, the abrupt flare eruption of the M6.6 event started around 17:30 UT. Our analysis suggests that, in a triggering process of a flare activity, all magnetic systems of multiple scales, not only the entire AR evolution but also the fine magnetic elements, are altogether involved.
The solar magnetic field in a flare-producing active region (AR) is much more complicated than theoretical models, which assume a very simple magnetic field structure. The X1.0 flare, which occurred in AR 12192 on 2014 October 25, showed a complicated three-ribbon structure. To clarify the trigger process of the flare and to evaluate the applicability of a simple theoretical model, we analyzed the data from Hinode/Solar Optical Telescope and the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, Atmospheric Imaging Assembly. We investigated the spatio-temporal correlation between the magnetic field structures, especially the non-potentiality of the horizontal field, and the bright structures in the solar atmosphere. As a result, we determined that the western side of the positive polarity, which is intruding on a negative polarity region, is the location where the flare was triggered. This is due to the fact that the sign of the magnetic shear in that region was opposite that of the major shear of the AR, and the significant brightenings were observed over the polarity inversion line (PIL) in that region before flare onset. These features are consistent with the recently proposed flare-trigger model that suggests that small reversed shear (RS) magnetic disturbances can trigger solar flares. Moreover, we found that the RS field was located slightly off the flaring PIL, contrary to the theoretical prediction. We discuss the possibility of an extension of the RS model based on an extra numerical simulation. Our result suggests that the RS field has a certain flexibility for displacement from a highly sheared PIL, and that the RS field triggers more flares than we expected.
The physical conditions leading the sunspot penumbra decay are poorly understood so far. We investigate the photospheric magnetic and velocity properties of a sunspot penumbra during the decay phase to advance the current knowledge of the conditions leading to this process. A penumbral decay was observed with the CRISP instrument at the Swedish 1m Solar Telescope on 2016 September 4 and 5 in active region NOAA 12585. During these days, full-Stokes spectropolarimetric scans along the Fe I 630 nm line pair were acquired over more than one hour. We inverted these observations with the VFISV code in order to obtain the evolution of the magnetic and velocity properties. We complement the study with data from instruments onboard the Solar Dynamics Observatory and Hinode space missions. The studied penumbra disappears progressively in both time and space. The magnetic flux evolution seems to be linked to the presence of Moving Magnetic Features (MMFs). Decreasing Stokes V signals are observed. Evershed flows and horizontal fields were detected even after the disappearance of the penumbral sector. The analyzed penumbral decay seems to result from the interaction between opposite polarity fields in type III MMFs and penumbra, while the presence of overlying canopies rules the evolution in the different penumbral sectors.
Four different methods are applied here to study the precursors of flare activity in the Active Region NOAA 10486. Two approaches track the temporal behaviour of suitably chosen features (one, the weighted horizontal gradient WGM, is generalised form the horizontal gradient of the magnetic field, GM; another is the sum of the horizontal gradient of the magnetic field, GS, for all sunspot pairs). WGM is a photospheric indicator that is a proxy measure of magnetic non-potentiality of a specific area of the active region, i.e. it captures the temporal variation of the weighted horizontal gradient of magnetic flux summed up for the region where opposite magnetic polarities are highly mixed. The third one, referred to as the separateness parameter, S(lf), considers the overall morphology. Further, GS and S(lf) are photospheric newly defined quick-look indicators of the polarity mix of the entire active region. The fourth method is tracking the temporal variation of small x-ray flares, their times of succession and their energies observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager instrument. All approaches yield specific pre-cursory signatures for the imminence of flares.
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