S-R2-3
Simulation Study on Trigger Mechanism of Solar Flare and Plasmoid Ejection
シミュレーションで探る太陽フレアとプラズモイド放出のトリガー機構
Kanya Kusano, Yumi Bamba, and Tetsuya Yamamoto
草野完也, 伴場由美、山本哲也
Solar-Terrestrial Environment Laboratory, Nagoya University
Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
名古屋大学太陽地球環境研究所 〒464-8601 名古屋市千種区不老町
What triggers solar flares is not yet well understood, and the predictability of flare onset is still very muchlimited, although the forecasting of flare and coronal mass ejection is highly demanded to protect the healthof astronauts and satellite systems from severe space weather impacts. We have carried out a systematic
simulation study to clarify the physical condition for the onset of solar flare, based on the hypothesis thatthe emerging of magnetic flux onto the solar surface may trigger solar flares. As a result, it is found that
only two types of emerging flux can trigger solar flares. The simulations indicate that the causal
relationship between magnetic reconnection and plasmoid ejection is different between the cases that thedifferent types of emerging flux trigger flare, although the both cases result in a morphologically similar
dynamics. The simulatino results are well consistent with the data of two major flares observed by Solar
Optical Telescope aboard Hinode satellite.

1. Introduction
Solar flare may eject a large-scale plasmoid,and it sometimes forms coronal mass ejection in
the inter-planetary space. Although the energy
release process of flares is now believed to bedriven by magnetic reconnection, the fundamental
question “what triggers solar flares” is still open
to be answered. The understanding of trigger
mechanism of flares is important also for thespace weather forecast, because it is demanded topredict the flare onset in order to protect thehealth of astronauts on the orbit and the advanced
infrastructure from the impact of severe space
weather disturbance. However, the predictabilityof flare onset is still very much limited. In thisstudy, we have carried out a systematic
simulations to clarify the physical condition forthe onset of solar flares, based on the hypothesisthat the emerging of magnetic flux onto the solar
surface may trigger solar flares.
2. Simulation Model
The initial condition of simulation is given by
the linear force-free field, which is characterized
by the shear angle θ with reference to thepotential field. After the simulation starts, abi-pole field, which is oriented to the azimuth ϕ,is injected onto the center of magnetic arcade. We
have surveyed the parameter space 0≤θ<90° and0≤ϕ<360° in terms of 3D MHD simulation.
3. Results
As a result of systematic survey, it is found thatthe occurrence of flare is very sensitive to ϕ, andthat there are two different parametric windows inwhich the emerging flux can trigger flare eruption.
They are the cases for opposite polarity (OP) for
ϕ=180° and reversed shear (RS) for ϕ=270°,
respectively. In the case of OP, the emerging flux
forms elongated twisted rope by reconnecting two
sheared loops, and cause the eruption of plasmoid,which is followed by flare reconnection. On theother hand, in the case of RS, the emerging flux
reconnects with the originally sheared field, andcause the internal collapse of magnetic arcade. Asa consequence, flare reconnection is triggered.
Once flare reconnection proceeds, the both cases
result in similar dynamics, which is consistent
with the standard flare model.
4. Discussion and Conclusion
The simulation study reveals that there are twodifferent preferential magnetic configurations fortriggering flares. We have analyzed the magnetic
data observed by Solar Optical Telescope aboard
Hinode satellite. As a result, at least two flares
occurring on 2006 Dec. 13 and 2011 Feb. 13 arefound to be well consistent with this prediction.
The results strongly suggest us that small
reconnection caused by flux emerging maytrigger large-scale flare reconnection andplasmoid ejection [1].
References[1] K. Kusano, Y. Bamba, T. T. Yamamoto, to besubmitted.