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Large-scale 3D MHD simulation on the solar flux emergence and the small-scale dynamic features in an active region  

Shin Toriumi   Submitted: 2012-01-16 06:23

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: S. Toriumi & T. Yokoyama
Projects: None

Publication Status: A&A (accepted)
Last Modified: 2012-01-16 14:09
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Dependence of the Magnetic Energy of Solar Active Regions on the Twist Intensity of the Initial Flux Tubes  

Shin Toriumi   Submitted: 2011-01-06 21:16

We present a series of numerical experiments that model the evolution of magnetic flux tubes with a different amount of initial twist. As a result of calculations, tightly twisted tubes reveal a rapid two-step emergence to the atmosphere with a slight slowdown at the surface, while weakly twisted tubes show a slow two-step emergence waiting longer the secondary instability to be triggered. This picture of the two-step emergence is highly consistent with recent observations. These tubes show multiple magnetic domes above the surface, indicating that the secondary emergence is caused by interchange mode of magnetic buoyancy instability. As for the weakest twist case, the tube exhibits an elongated photospheric structure and never rises into the corona. The formation of the photospheric structure is due to inward magnetic tension force of the azimuthal field component of the rising flux tube (i.e., tube's twist). When the twist is weak, azimuthal field cannot hold the tube's coherency, and the tube extends laterally at the subadiabatic surface. In addition, we newly find that the total magnetic energy measured above the surface depends on the initial twist. Strong twist tubes follow the initial relation between the twist and the magnetic energy, while weak twist tubes deviates from this relation, because these tubes store their magnetic energy in the photospheric structures.

Authors: Shin Toriumi, Takehiro Miyagoshi, Takaaki Yokoyama, Hiroaki Isobe, and Kazunari Shibata
Projects: None

Publication Status: PASJ (accepted)
Last Modified: 2011-01-07 18:24
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Two-step Emergence of the Magnetic Flux Sheet from the Solar Convection Zone  

Shin Toriumi   Submitted: 2010-03-16 14:48

We perform two-dimensional MHD simulations on the solar flux emergence. We set the initial magnetic flux sheet at z=-20,000 km in the convection zone. The flux sheet rises through the convective layer due to the Parker instability, however, decelerates beneath the photosphere because the plasma on the flux sheet piles up owing to the convectively stable photosphere above. Meanwhile, the flux sheet becomes locally unstable to the Parker instability again within the photosphere, and the further evolution to the corona occurs (two-step emergence model). We carry out a parameter survey to investigate the condition for this two-step model. We find that magnetic fluxes which form active regions are likely to have undergone the two-step emergence. The condition for the two-step emergence is 1021 - 1022 Mx with 104 G at z=-20,000 km in the convection zone.

Authors: Toriumi, S. and Yokoyama, T.
Projects: None

Publication Status: ApJ (accepted)
Last Modified: 2010-03-17 09:05
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Abstracts by Author
Large-scale 3D MHD simulation on the solar flux emergence and the small-scale dynamic features in an active region
Dependence of the Magnetic Energy of Solar Active Regions on the Twist Intensity of the Initial Flux Tubes
Two-step Emergence of the Magnetic Flux Sheet from the Solar Convection Zone

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