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Two Step Filament Eruption During 14-15 March 2015  

Ramesh Chandra   Submitted: 2017-04-30 18:36

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 Hα data from the Global Oscillation Network Group (GONG) telescope and the Kanzelhoehe Solar Observatory. The filament shows a first step eruption on 14 March 2015 and it stops its rise at a projected altitude ~125 Mm on the solar disk. It remains at this height for ~12 hrs. Finally it erupts on 15 March 2015 and produced a halo CME. We also find jet activity in the active region during both days, which could help the filament de-stabilization and eruption. The decay index is calculated to understand this two-step eruption. The eruption could be due to the presence of successive instability-stability-instability zones as the filament is rising.

Authors: R. Chandra, B. Filippov, R. Joshi, B. Schmieder
Projects: None

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2017-05-01 14:34
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Blowout Jets and Impulsive Eruptive Flare in a Bald-Patch Topology  

Ramesh Chandra   Submitted: 2016-10-06 19:20

Context. A subclass of broad EUV and X-ray jets, called blowout jets, have become a topic of research since they could be the link between standard collimated jets and CMEs. Aims. Our aim is to understand the origin of a series of broad jets, some accompanied by flares and associated with narrow and jet-like CMEs. Methods. We analyze observations of a series of recurrent broad jets observed in AR 10484 on 21-24 October 2003. In particular, one of them occurred simultaneously with an M2.4 flare on 23 October at 02:41 UT (SOLA2003-10-23). Both events were observed by ARIES Hα Solar Tower-Telescope, TRACE, SOHO, and RHESSI instruments. The flare was very impulsive and followed by a narrow CME. A local force-free model of AR 10484 is the basis to compute its topology. We find bald patches (BPs) at the flare site. This BP topology is present for at least two days before. Large-scale field lines, associated with the BPs, represent open loops. This is confirmed by a global PFSS model. Following the brightest leading edge of the Hα and EUV jet emission, we can temporarily associate it with a narrow CME. Results. Considering their characteristics, the observed broad jets appear to be of the blowout class. As the most plausible scenario, we propose that magnetic reconnection could occur at the BP separatrices forced by the destabilization of a continuously reformed flux rope underlying them. The reconnection process could bring the cool flux-rope material into the reconnected open field lines driving the series of recurrent blowout jets and accompanying CMEs. Conclusions. Based on a model of the coronal field, we compute the AR 10484 topology at the location where flaring and blowout jets occurred from 21 to 24 October 2003. This topology can consistently explain the origin of these events.

Authors: R. Chandra, C.H. Mandrini, B. Schmieder, B. Joshi, G.D. Cristiani, H. Cremades, E. Pariat, F.A. Nuevo, A.K. Srivastava, and W. Uddin
Projects: None

Publication Status: Accepted for the publication in A & A
Last Modified: 2016-10-12 12:19
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Peculiar Stationary EUV Wave Fronts in the eruption on 2011 May 11  

Ramesh Chandra   Submitted: 2016-02-29 20:03

We present and interpret the observations of extreme ultraviolet (EUV) waves associated with a filament eruption on 2011 May 11.The filament eruption also produces a small B-class two ribbon flare and a coronal mass ejection (CME). The event is observed by the Solar Dynamic Observatory (SDO) with high spatio-temporal resolution data recorded by Atmospheric Imaging Assembly (AIA). As the filament erupts, we observe two types of EUV waves (slow and fast) propagating outwards. The faster EUV wave has a propagation velocity of ~ 500 km s-1 and the slower EUV wave has an initial velocity of ~ 120 km s-1. We report for the first time that not only the slower EUV wave stops at a magnetic separatrix to form bright stationary fronts, but also the faster EUV wave transits a magnetic separatrix, leaving another stationary EUV front behind.

Authors: R. Chandra, P. F. Chen, A. Fulara, A. K. Srivastava, W. Uddin
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJ
Last Modified: 2016-03-01 10:07
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Sunspot Waves and Triggering of Homologous Active Region Jets  

Ramesh Chandra   Submitted: 2014-11-05 18:46

We present and discuss multi-wavelength observations of five homologous recurrent solar jets that occurred in active region NOAA 11133 on 11 December, 2010. These jets were well observed by the Solar Dynamic observatory (SDO) with high spatial and temporal resolution. The speed of the jets ranged between 86 and 267 km s-1. A type III radio burst was observed in association with all the five jets. The investigation of the over all evolution of magnetic field in the source regions suggested that the flux was continuously emerging on longer term. However, all the jets but J5 were triggered during a local dip in the magnetic flux, suggesting the launch of the jets during localised submergence of magnetic flux. Additionally, using the PFSS modelling of the photospheric magnetic field, we found that all the jets were ejected in the direction of open field lines. We also traced sunspot oscillations from the sunspot interior to foot-point of jets and found presence of ∼ 3 minute oscillations in all the SDO/AIA passbands. The wavelet analysis revealed an increase in amplitude of the oscillations just before the trigger of the jets, that decreased after the jets were triggered. The observations of increased amplitude of the oscillation and its subsequent decrease provides evidence of wave-induced reconnection triggering the jets.

Authors: R. Chandra, G. R. Gupta, Sargam Mulay and Durgesh Tripathi
Projects: None

Publication Status: Accepted for publication in MNRAS
Last Modified: 2014-11-06 14:34
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Homologous Flares and Magnetic Field Topology in Active Region NOAA 10501 on 20 November 2003  

Ramesh Chandra   Submitted: 2010-11-08 20:43

We present and interpret observations of two morphologically homologous flares that occurred in active region (AR) NOAA 10501 on 20 November 2003. Both flares displayed four homologous Hα ribbons and were both accompanied by coronal mass ejections (CMEs). The central flare ribbons were located at the site of an emerging bipole in the center of the active region. The negative polarity of this bipole fragmented in two main pieces, one rotating around the positive polarity by ~ 110 deg within 32 hours. We model the coronal magnetic field and compute its topology, using as boundary condition the magnetogram closest in time to each flare. In particular, we calculate the location of quasiseparatrix layers (QSLs) in order to understand the connectivity between the flare ribbons. Though several polarities were present in AR 10501, the global magnetic field topology corresponds to a quadrupolar magnetic field distribution without magnetic null points. For both flares, the photospheric traces of QSLs are similar and match well the locations of the four Hα ribbons. This globally unchanged topology and the continuous shearing by the rotating bipole are two key factors responsible for the flare homology. However, our analyses also indicate that different magnetic connectivity domains of the quadrupolar configuration become unstable during each flare, so that magnetic reconnection proceeds differently in both events.

Authors: R. Chandra, B. Schmieder, C.H. Mandrini, P. Demoulin, E. Pariat, T. Torok, W. Uddin
Projects: SoHO-MDI,SoHO-LASCO,Yohkoh-HXT

Publication Status: Solar Physics (in press)
Last Modified: 2010-11-10 09:20
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Evidence of Magnetic Helicity in Emerging Flux and Associated Flare  

Ramesh Chandra   Submitted: 2009-06-05 01:59

The aim of this paper is to look at the magnetic helicity structure of an emerging active region and show that both emergence and flaring signatures are consistent with a same sign for magnetic helicity. We present a multi-wavelength analysis of an M1.6 flare occurring in the active region NOAA 10365 on 27 May, 2003, in which a large new bipole emerges in a decaying active region. The diverging flow pattern and the ``tongue'' shape of the magnetic field in the photosphere with elongated polarities are highly suggestive of the emergence of a twisted flux tube. The orientation of these tongues indicates the emergence of a flux tube with a right hand twist, i.e. positive magnetic helicity. The flare signatures in the chromosphere are ribbons observed in Hα by the MSDP spectrograph in the Meudon solar tower and in 1600 Å by TRACE. These ribbons have a `J' shape and are shifted along the inversion line. The pattern of these ribbons suggests that the flare was triggered by magnetic reconnection at coronal heights below a twisted flux tube of positive helicity, corresponding to that of the observed emergence. It is the first time that such a consistency between the signatures of the emerging flux through the photosphere and flare ribbons is clearly identified in observations. Another type of ribbons observed during the flare at the periphery of the active region by the MSDP and SOHO/EIT are related to the existence of a null point, which is found high in the corona in a potential field extrapolation. We discuss the interpretation of these secondary brightenings in terms of the ``breakout'' model and in terms of plasma compression/heating within large-scale separatrices.

Authors: R. Chandra, B. Schmieder, G. Aulanier, J.M. Malherbe
Projects: SoHO-EIT,SoHO-MDI

Publication Status: Solar Physics (accepted)
Last Modified: 2009-06-08 23:27
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Abstracts by Author
Two Step Filament Eruption During 14-15 March 2015
Blowout Jets and Impulsive Eruptive Flare in a Bald-Patch Topology
Peculiar Stationary EUV Wave Fronts in the eruption on 2011 May 11
Sunspot Waves and Triggering of Homologous Active Region Jets
Homologous Flares and Magnetic Field Topology in Active Region NOAA 10501 on 20 November 2003
Evidence of Magnetic Helicity in Emerging Flux and Associated Flare

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