Magnetohydrodynamic Simulation of Eruptive Solar Flares

Dec. 18, 2023 | Aerospace Project Research Associate, ISAS people

YAMASAKI Daiki / Dept. of Solar System Science, ISAS

Research Summary

Solar flares are rapid energy release phenomena in solar atmosphere. Coronal mass ejections (CMEs) are sometimes observed in association with solar flares. Since CMEs cause disturbances in electro-magnetic environment of interplanetary space, it is important to understand the onset mechanism of solar flares and associated plasma ejections in terms of space weather *1 study. To understand solar flares, quantitative diagnostics of coronal magnetic field is important. However, due to observational limitations, it is hard to detect coronal magnetic field directly. In this study, we focused on one large-scale flare event and performed magnetohydrodynamic modeling and simulation to reproduce the dynamics of flaring coronal magnetic field.

Fig.1
Fig. 1 (a) Full disk 304 Å image taken with SDO/AIA. (b) Flaring region, the location is indicated by green box in panel (a). (c) Extrapolated 3D coronal magnetic field, back ground grayscale correspond to photospheric magnetic field obtained from SDO/HMI.

Our target event is GOES X1 flare *2 observed on October 21, 2021. In Figure 1 (a), we display a full disk extreme ultra violet (EUV) image of 304 Å obtained with SDO *3 /AIA *4. Green box indicates the location of flaring region (see also panel (b) for more in detail). In Figure 1 (c), we show an extrapolated three-dimensional (3D) coronal magnetic field by using a photospheric magnetic field obtained from SDO/HMI *5 as a bottom boundary. At the center part of the flaring region, highly twisted field lines, which correspond to the releasable flare energy storage, are located.

Fig.2
Fig. 2 Temporal evolution of simulation results.

In Figure 2, we show our results of the simulation, we name this RUN A. Colored lines show the coronal magnetic field lines. Yellow lines correspond to the erupting twisted magnetic field. Under the yellow lines, we find magnetic reconnection between pink and green field lines. To quantitatively understand the contribution of the reconnection to the eruption, we performed another simulation, RUN B with reconnection suppression. In Figure 3, we show velocity electric current distributions of RUN A and B in panels (a-c) and (d-f), respectively. By comparing the results of RUN A and B, we found that the magnetic reconnection enhanced the acceleration of erupting magnetic field lines.

Fig.2
Fig. 3 (a-c) Comparison of velocity distribution of simulations RUN A and B. (d-f) Comparison of electric current distribution of simulations RUN A and B.

According to the previous research done by Dr. Forbes in 1990s, similar interpretation of acceleration of eruption by magnetic reconnection is reported by 2D simulation. This study extended this previous report into 3D and actual solar flare event study.
ISAS is now promoting the SOLAR-C project. SOLAR-C is a space mission which has a capability of spectroscopic observation in a wide range of wavelength in EUV with high temporal and special resolutions. It is expected that, in combination with our simulation, data provided by SOLAR-C will reveal energy conversion process from magnetic to thermal heat by magnetic reconnection in flaring regions.

Terminologies

  • *1 space weather : Predict or forecast the disturbances of electro-magnetic field, radiation, and high energetic particles caused by solar activities.
  • *2 GOES X1 flare : Extension of solar flare class defined by soft X-ray flux monitored by GOES satellite.
  • *3 SDO : Solar Dynamics Observatory, NASA’s space mission launched in 2010.
  • *4 AIA : Atmospheric Imaging Assembly, EUV imager on board SDO.
  • *5 HMI : Helioseismic and Magnetic Imager on board SDO.

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