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A Study of Magnetic Field Characteristics of Flaring Active Region Based on Nonlinear Force-free Field Extrapolation  

Johan Muhamad   Submitted: 2018-07-05 19:57

Coronal magnetic fields are responsible for the onset of solar flares and solar eruptions. However, the type of magnetic field parameters that can be used to measure the critical condition for a solar eruption is still unclear. As an effort to understand the possible condition for a solar flare, we have examined the non-dimensional parameter K introduced by Ishiguro & Kusano (2017), which contains information about magnetic twist distribution and magnetic flux in an active region (AR). We introduce a new parameter K*, as a proxy for K, and we have analyzed the evolution of K* during the flaring period of an AR using the nonlinear force-free field (NLFFF) extrapolated from the photospheric vector magnetic field data. Using data from the Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI), we have calculated K* for the AR NOAA 11158 during its three-day flaring period. We found that K* increased to a certain level before two large flares and decreased significantly after their onset. The results suggest that K* may be used as an indicator of the necessary condition for the onset of a solar eruption in the AR. Based on this result, we propose a new method to assess the possibility of a large solar eruption from an AR by combining the parameter K* and information about the magnetic energy of the AR.

Authors: Johan Muhamad, Kanya Kusano, Satoshi Inoue, Yumi Bamba
Projects: Hinode/SOT,SDO-AIA,SDO-HMI

Publication Status: ApJ (accepted)
Last Modified: 2018-07-06 11:04
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Magnetohydrodynamic Simulations for Studying Solar Flare Trigger Mechanism  

Johan Muhamad   Submitted: 2017-06-22 19:51

In order to understand the flare trigger mechanism, we conduct three-dimensional magnetohydrodynamic simulations using a coronal magnetic field model derived from data observed by the Hinode satellite. Several types of magnetic bipoles are imposed into the photospheric boundary of the Non-linear Force-Free Field (NLFFF) model of Active Region NOAA 10930 on 2006 December 13 to investigate what kind of magnetic disturbance may trigger the flare. As a result, we confirm that certain small bipole fields, which emerge into the highly sheared global magnetic field of an active region, can effectively trigger a flare. These bipole fields can be classified into two groups based on their orientation relative to the polarity inversion line: the so called opposite polarity (OP) and reversed shear (RS) structures as suggested by Kusano et al. We also investigate the structure of the footpoints of reconnected field lines. By comparing the distribution of reconstructed field lines and the observed flare ribbons, the trigger structure of the flare can be inferred. Our simulation suggests that the data-constrained simulation, taking into account both the large-scale magnetic structure and small-scale magnetic disturbance (such as emerging fluxes) is a good way to discover a flare producing AR, which can be applied to space weather prediction.

Authors: Johan Muhamad, Kanya Kusano, Satoshi Inoue, Daikou Shiota
Projects: Hinode/SOT,Hinode/XRT

Publication Status: Published in ApJ
Last Modified: 2017-06-28 08:41
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A Study of Magnetic Field Characteristics of Flaring Active Region Based on Nonlinear Force-free Field Extrapolation
Magnetohydrodynamic Simulations for Studying Solar Flare Trigger Mechanism

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