A confined flare above filaments
aa r X i v : . [ a s t r o - ph . S R ] O c t Title of your IAU SymposiumProceedings IAU Symposium No. xxx, 2008A.C. Editor, B.D. Editor & C.E. Editor, eds. c (cid:13) A confined flare above filaments
K. Dalmasse , R. Chandra , B. Schmieder , and G. Aulanier LESIA, Observatoire de Paris, CNRS, UMPC, Univ. Paris Diderot,5 place Jules Janssen, 92190 Meudon, Franceemail: [email protected] Dept. of Physics, DSB Campus, Kumaun University, Nainital- 263 002, India
Abstract.
We present the dynamics of two filaments and a C-class flare observed in NOAA11589 on 2012 October 16. We used the multi-wavelength high-resolution data from SDO, as wellas THEMIS and ARIES ground-based observations. The observations show that the filamentsare progressively converging towards each other without merging. We find that the filamentshave opposite chirality which may have prevented them from merging. On October 16, a C3.3class flare occurred without the eruption of the filaments. According to the standard solar flaremodel, after the reconnection, post-flare loops form below the erupting filaments whether theeruption fails or not. However, the observations show the formation of post-flare loops above thefilaments, which is not consistent with the standard flare model. We analyze the topology of theactive region’s magnetic field by computing the quasi-separatrix layers (QSLs) using a linearforce-free field extrapolation. We find a good agreement between the photospheric footprints ofthe QSLs and the flare ribbons. We discuss how slipping or slip-running reconnection at theQSLs may explain the observed dynamics.
Keywords.
Filaments, flare, MHD
1. Introduction
Filaments are dark, elongated structures consisting of chromospheric plasma embeddedin the much hotter corona (van Ballegooijen & Martens 1989; Chae et al. ≈ et al. et al. et al. e.g. , T¨or¨ok & Kliem 2005). Confined flares also compriseflares induced by magnetic reconnection of different magnetic flux tubes, or magneticcoronal loops, for which no filament is present ( e.g. , Berlicki et al. et al. below the erupting filament,regardless of whether it is a successful or failed eruption.In this study, we present the evolution of two filaments and a confined flare observed1 K. Dalmasse & R. Chandra & B. Schmieder & G. Aulanierin NOAA 11589, which cannot be explained by the CSHKP model. We propose analternative flare scenario which accounts for the observed flare signatures and filamentsevolution during the flare.
2. Observations
Our study was performed by combining observations from the Solar Dynamic Observa-tory (SDO) satellite, the french T´elescope H´eliographique pour l’Etude du Magn´etisme etdes Instabilit´es Solaires (THEMIS), and an indian telescope of the Aryabhatta ResearchInstitute of observational Sciences (ARIES).NOAA 11589 appeared on 2012 October 10 at the heliographic coordinates N13 E61.The AR quickly developed into two decaying magnetic polarities (see Fig. 1a). During itson-disk passage, the AR was associated with large-scale magnetic flux cancellation, anda few localized magnetic flux emergence events.The flux cancellation in the internal part of the AR led to the formation of two filamentsof opposite chirality which eventually converged. However, the filaments did not mergeprobably due to their axial field being oriented in opposite direction along the PIL ( e.g. ,Schmieder et al. et al. et al. above the filaments contrary to what is expectedfrom the CSHKP model, and the filaments were not disturbed by the flare.
3. Analysis
Magnetic field extrapolation
To understand and explain the evolution of the filaments during the flare, we study themagnetic topology of the AR by means of an LFFF extrapolation ( ~ ∇ × ~B = α ~B , with α being the force-free parameter) to identify the key sites for the development of magneticreconnection that led to the flare.We only considered the global magnetic field of the AR because (i) the filaments werein plage regions where the magnetic field is weak, and thus, the currents are not wellmeasured, and (ii) the filaments did not seem to play any role in the flare.The extrapolations were performed using the fast Fourier transform method (Alis-sandrakis 1981) with a non-uniform grid of 1024 ×
351 points covering a domain of700 × . Within the set of performed extrapolations, we kept the solution α = 7 × − Mm − because it gave the best match with the northern loops of the AR(Fig. 1a), i.e. , the region where the flare was initiated.3.2. Topological analysis
The topology is then analyzed by computing the quasi-separatrix layers (QSLs; e.g. ,D´emoulin et al. confined flare above filaments Figure 1.
Central part of NOAA 11589. (a) Photospheric vertical magnetic field, B z , in greyscaleoverplotted with selected magnetic field lines from the extrapolation (black lines). (b) AIA171image showing some of the AR loops and the two observed filaments highlighted by black arrows. (see review by D´emoulin 2006). As separatrices, QSLs are preferential sites for particleacceleration (Aulanier et al. e.g. , D´emoulin et al. et al. et al. Q (Titov et al. Q -values ( Q ≫ Q at the photosphere. By plottingmagnetic field lines over the photospheric Q -map, we identified two double-C shapeQSLs, Q , , similar to Aulanier et al. (2005), and a circular-like one (overlaid with awhite circle), Q , similar to Masson et al. (2009). We find a few discrepancies betweenthe QSLs footprints, Q i , and the three flare ribbons of Fig. 2(b), R i . This is due to theassumptions made by extrapolating the AR’s magnetic field in LFFF, which do not modelthe highly-stressed filament magnetic fields, and which results in local modifications ofthe magnetic connectivity that slightly modifies the location and shape of the QSLs inour extrapolation. Nevertheless, there is a good qualitative agreement between the QSLsfootprints and the flare ribbons (Fig. 2).
4. Conclusion
From the previous analysis, it is clear that the magnetic field of AR 11589 presentsa complex topology formed by three entangled QSLs. Such a complex topology wasfavorable to the build-up of electric current layers and to the development of magneticreconnection at any of these QSLs. The flare might thus have been the result of the stressof, at least, one of the QSLs eventually triggering magnetic reconnection at all QSLs.Analyzing the AIA and HMI data prior to, and after the flare, we found signatures oflocalized, recurring magnetic flux emergence in the northern part of the AR — in theregion below Q , i.e. , between the western part of Q ,curv and the southern part of Q ,arc .Consequently, we propose that this episodic flux emergence was the driver of the C3.3 K. Dalmasse & R. Chandra & B. Schmieder & G. Aulanier Figure 2.
Central part of NOAA 11589. (a) Photospheric mapping of log Q displaying thephotospheric footprints of QSLs at 15:00 UT. (b) Flare ribbons at 16:25 UT. The footprints ofthree QSLs, labelled Q i , are identified with the three flare ribbons labelled R i . class flare: this continuous magnetic flux emergence may have stressed the magneticfield of Q , resulting in the formation of a strong thin current layer, at least, withinthis QSL. Eventually, this can trigger slipping or slip-running reconnection at Q (seeAulanier et al. Q and Q . This would have induced particle acceleration at all QSLs( e.g. , Masson et al. above these non-erupting filaments. References
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