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SUMMARY:NLFFF modeling of a circular-ribbon flare - Dr. Gherardo Valori  (
 UCL MSSL)
DTSTART:20150601T150000Z
DTEND:20150601T160000Z
UID:TALK58590@talks.cam.ac.uk
CONTACT:Andrew Hillier
DESCRIPTION:On October 22\, 2011\, a circular ribbon\, shortly preceded by
  localized\ninner and remote compact brightening\, was observed in AR11324
  using\nSDO/AIA. The global evolution of such peculiarly shaped flares is\
 nbelieved to be caused by slipping reconnection at a coronal null point\,\
 nwith the circular ribbon being the footprint of the dome-shaped fan\, and
 \nthe inner and remote brightening tracing the two photospheric anchoring\
 nof the spine. The high spatial resolution and time cadence of AIA\nobserv
 ations give the unique opportunity to explore the details of this\nflare e
 vent\, which is globally agreeing with\, but not entirely explained\nby\, 
 the null/slipping reconnection model. In particular\, pre-flare\nbrighteni
 ng and a three-phase time evolution of EUV signals do not have\nstraightfo
 rward interpretations. Also\, the non-eruptive character of the\nflare mak
 es standard interpretations inadequate.\n\nIn this talk I will briefly int
 roduce the nonlinar-force-free field\n(NLFFF) extrapolaiton technique\, an
 d apply it to the interpretatin of\nthat event. In particular\, I will sho
 w how the combination of the NLFFF\nextrapolation with a topological analy
 sis based on quasi-separatrix\nlayers (QSL) allows to interpret the AIA ob
 servation of the dynamic of\nthe flare. In addition to the expected topolo
 gical features of a\nstandard circular-ribbon flare model\, we find a flux
  rope and a complex\nQSL internal to the dome\, which are connected with t
 he brightening\nlocations. Guided by the AIA observation\, we are able to 
 provide a\ncoherent description of the specific dynamic of this event that
 \, because\nof its non-eruptive nature\, has a peculiar reconnection patte
 rn. The\ndifferent peaks in the EUV signals are then explained by the cool
 ing of\nspecific sets of reconnected field lines that are matching both th
 e\nreconnection process evinced by our modeling and the multi-wavelengths\
 nobservations.\n\nThe combination of high-resolution observations with pow
 erful modeling\nand analysis techniques allow us to interpret very complex
  observations\nwith realistic models of the coronal field\, helping us to 
 deepen the\ntheoretical understanding of flare dynamics.\n
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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