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Magnetic configurations responsible for the coronal heating and the solar wind

Magnetic configurations responsible for the coronal heating and the solar wind. Hwanhee Lee 1 , Tetsuya Magara 1 1 School of Space research, Kyung Hee University. The 7 th Hinode Science Meeting in Takayama , Japan 13 Nov. 2013.

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Magnetic configurations responsible for the coronal heating and the solar wind

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  1. Magnetic configurationsresponsible forthe coronal heating and the solar wind Hwanhee Lee1, Tetsuya Magara1 1School of Space research, Kyung Hee University The 7thHinode Science Meeting in Takayama, Japan 13 Nov. 2013

  2. Key points of our study comparedto previous studies • Magnetic configurations Solar wind model Coronal heating model B photosphere • Previous works : simple magnetic configurations are assumed • Half-circle shaped loop • Cross sectional area is constant • Potential-field approximation We try to derive more detailed magnetic configurations

  3. Introduction • Two aspects of magnetic configurations • Global configuration : whole active region • Local configuration : individual coronal loop • Distributions of the following two parameters (1) Force-Free parameter : α (2) Flux-tube expansion rate : fex • Expansion profile of a coronal loop expanding outward • - Distribution of fexalong a loop

  4. Definitions of the parameters To investigate these magnetic configurations,we focus on two key parameters • Force-Free parameter • Flux-tube expansion rate Twist of magnetic field Expansion of magnetic field (A : cross sectional area)

  5. Model Description • Flux-emergence MHD simulation (Lee & Magara, submitted) • Basic equations: ideal MHD equations Initial state Magara (2013); An & Magara (2013) • Magnetic field : Gold-Hoyle profile Strongly twisted Weakly twisted , where r is the radial distance from the axis and b is field-line twist parameter Initial states of b=1(left) and b=0.2(right)

  6. Overview of evolution Strongly twisted case Weakly twisted case Initial state Late state

  7. Global magnetic configuration Distributions of α and fex in a whole active region

  8. Strongly twisted case In the α -distribution, inner loops form double J-shaped structure in the coronawhere strong electric current flows,while less current flowsalong outer loops • In the fex distribution, • large flux expansion rateisfound at the footpointsof outer loops

  9. Weakly twisted case In the α -distribution, strong electric current flows along short and low loops(inner part) • In the fex distribution, • long outer loops have large • flux expansion rate • at their footpoints

  10. Comparison to potential field(extrapolated from photospheric field)

  11. Distribution of flux expansion rate Strongly twisted case Weakly twisted case In the potential fields, not only outer but also inner loops have largeexpansion rate at their footpoints potential field potential field However in theemerging fields,outer loops tend to havelarge expansion rateat their footpoints emerging field emerging field

  12. 2. Local magnetic configuration Expansion profile of a coronal loop

  13. Expansion types of coronal loops Definition of flux expansion rate B B Sun Sun Exponential type A(s) A0 : cross-section of flux tube Parabolic type A(s) A0

  14. Expansion profile of a coronal loop • Example: Weakly twisted case, emerging field s Zb Range I Range II Range III Range IV s : the length of field line (unit: 2Hph) Zb : the height of field line element Exponential type Parabolic type

  15. Expansion profiles of various coronal loops • Outer loops are selected for each case • Strongly twisted case: emerging field • Weaklytwisted case: emerging field • Strongly twisted case: potential field • Weaklytwisted case: potential field • Range I (fex~ const.) is short and Range II is prominent in the emerging fields, • while Range I is wide and Range II is short in the potentialfields

  16. Conclusion Regardingthe global magnetic configurations, • In the strongly twisted case, inner part : - strong electric current flows in the corona- double-J shaped structure(observed as a sigmoid)outer part : large fex but small α at footpointsloops expand outward • In the weakly twisted case, inner part : - strong electric current flows near the surface- seaserpent structure (low loops)(not observed as a sigmoid)outer part : similar to the strongly twisted case

  17. Conclusion Regardingthe local magnetic configurations, • The expansion of a magnetic field is characterized by the exponential type near the photosphere (Range I)and parabolic type in the corona (Range III) • The Range II becomes prominentwhen the field is strongly confined by surrounding plasma (high plasma beta) • Transition from Range IIto Range III…magnetic field can determine its configurationby itself without being affected bysurrounding gas pressure (high plasma beta → low plasma beta) These detailed magnetic configurations probably contribute to developing realistic models for the coronal heating and solar wind generation.

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