First Ten Years of Hinode Solar On-Orbit Observatory by Toshifumi Shimizu Shinsuke Imada & Masahito Kubo

Author:Toshifumi Shimizu, Shinsuke Imada & Masahito Kubo
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

12.2.2 Consistency with Theoretical Model

We compared the observational findings described in Sect. 12.2.1 to the theoretical flare-trigger model based on the numerical simulations of Kusano et al. (2012, henceforth called “KB12 model” ). The basic idea of the model is similar to that of the emerging flux model ; a small-scale bipolar field (blue arcade in the upper schematic of Fig. 12.3) appears on the PIL of the global sheared magnetic field (red arcades in the upper schematic of Fig. 12.3). The shear angle θ 0 of the red magnetic arcades represents the deviation of the global magnetic fields in the AR from the potential field, and it characterizes the magnetic free energy stored in the corona. The azimuthal angle φ e represents a small-scale magnetic disturbance, which is critical for flare occurrence. KB12 systematically investigated the flux rope formation, occurrence of magnetic reconnection, and physical processes leading to flux rope eruption using ensemble simulations with different combinations of (θ 0, φ e ). The KB12 model proposed quantitative conditions for flare triggering based on the simulation results, which are summarized in the bottom plot of Fig. 12.3. There are two types of small-scale bipolar fields that can trigger a flare, i.e., the “flare-trigger field ”: the “opposite polarity (OP) type” and the “reversed shear (RS) type.” In the OP-type case, which is represented by the pink-colored diamonds in Fig. 12.3, the magnetic polarity pattern in the small-scale bipolar field is opposite to that of the global magnetic field, i.e., the azimuth angle φ e is around 180∘. Conversely, the RS-type case, in which the local magnetic shear in the small-scale bipolar field is opposite to the global magnetic shear in the AR (i.e., φ e is around 270∘), is represented by the blue-colored diamonds in Fig. 12.3.

Fig. 12.3Top: Schematic of the simulation setup in KB12. White/black regions represent positive/negative polarities of the magnetic field. The red and blue arrows represent the magnetic field lines in the pre-existing field and the small-scale injected field, which have rotation angles θ 0 and φ e with respect to the large-sale potential field, respectively. Bottom: Flare phase diagram that summarizes the simulation results. The diamond symbols indicate the regions where the eruption has occurred under the θ 0 and φ e conditions. The pink and blue diamonds indicate the types of dynamics considered “eruption-induced reconnection (OP-type)” and “reconnection-induced eruption (RS-type),” respectively. The yellow diamond corresponds to a special case where the potential field collapses because of reconnection with the small-scale injected field, which exhibits a completely antiparallel polarity compared with the initial potential field. The open square symbols indicate the regions where eruptions do not occur under the conditions

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