Formation of a Flare-Productive Active Region: Observation and Numerical Simulation of NOAA AR 11158
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We present a comparison of the Solar Dynamics Observatory (SDO) analysis of NOAA Active Region (AR) 11158 and numerical simulations of flux-tube emergence, aiming to investigate the formation process of this flare-productive AR. First, we use SDO/Helioseismic and Magnetic Imager (HMI) magnetograms to investigate the photospheric evolution and Atmospheric Imaging Assembly (AIA) data to analyze the relevant coronal structures. Key features of this quadrupolar region are a long sheared polarity inversion line (PIL) in the central δ-sunspots and a coronal arcade above the PIL. We find that these features are responsible for the production of intense flares, including an X2.2-class event. Based on the observations, we then propose two possible models for the creation of AR 11158 and conduct flux-emergence simulations of the two cases to reproduce this AR. Case 1 is the emergence of a single flux tube, which is split into two in the convection zone and emerges at two locations, while Case 2 is the emergence of two isolated but neighboring tubes. We find that, in Case 1, a sheared PIL and a coronal arcade are created in the middle of the region, which agrees with the AR 11158 observation. However, Case 2 never builds a clear PIL, which deviates from the observation. Therefore, we conclude that the flare-productive AR 11158 is, between the two cases, more likely to be created from a single split emerging flux than from two independent flux bundles.
KeywordsActive regions, magnetic fields Flares, relation to magnetic field Interior, convective zone
The authors thank K. Hayashi (Stanford University) for providing HMI data and P. Démoulin (Paris Observatory) for fruitful discussions. The authors are grateful to the anonymous referee for improving the manuscript and the SDO team for distributing HMI and AIA data. Numerical computations were carried out on Cray XC30 at the Center for Computational Astrophysics, National Astronomical Observatory of Japan. ST is supported by Grant-in-Aid for JSPS Fellows. This work was supported by a Grants-in-Aid for Scientific Research (B) “Understanding and Prediction of Triggering Solar Flares” (23340045, Head Investigator: K. Kusano) from the Ministry of Education, Science, Sports, Technology, and Culture of Japan.
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