Simulation study on the self-organization of sigmoidal structure and the onset of solar flares

K. Kusano, S. Inoue, T. Yamamoto, T. Yokoyama, T. Sakurai

Research output: Contribution to journalConference articlepeer-review


Although the recent observations strongly support the reconnection scenario, in which magnetic reconnection plays a key role for the energy liberate in flare processes, the onset mechanism of flares is not yet well understood. In order to clarify that, we have to explain not only the dynamics in the main phase of flares, but also the transition mechanism from pre-flare to main flare phase. It is an important test bench for this purpose to examine the causal relationship between the formation of sigmoids and the trigger of flares, because sigmoids are widely believed to be typical precursor phenomena for the several eruptive events. Aiming to understand the flare onset process from sigmoidal activity, the high-resolution simulation is developed to investigate the nonlinear evolution of a thin current sheet formed above the magnetic neutral line. The results indicate that the tearing mode instability growing on the thin current sheet, where the magnetic shear is steeply reversed, can drive both the self-organization of sigmoidal structure, and the impulsive onset of arcade eruption. The structure of sigmoid is shown to be consistent with the Taylor's minimum energy state, in which the torsional parameter α is limited by the eigenvalue decided geometrically. The simulation results strongly suggest that the nonlinearity of the tearing instability growing on the reversed-shear layer can play a role for the transition from pre-flare to flare phase. The consistency with the observation is also examined by comparing the vector magnetogram and the ultra-violet image of flares observed by the TRACE satellite. Based on the results, we predict that solar flares tend to occur from the reversed-shear region.

Original languageEnglish (US)
Pages (from-to)397-401
Number of pages5
JournalEuropean Space Agency, (Special Publication) ESA SP
Issue number596
StatePublished - 2005
Externally publishedYes
EventInternational Scientific Conference on Chromospheric and Coronal Magnetic Fields - Katlenburg - Lindau, Germany
Duration: Aug 30 2005Sep 2 2005

All Science Journal Classification (ASJC) codes

  • Aerospace Engineering
  • Space and Planetary Science


  • MHD
  • Sun: activity
  • Sun: flares
  • Sun: magnetic fields


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