The standard flare model in three dimensions I

strong-to-weak shear transition in post-flare loops

G. Aulanier, M. Janvier, B. Schmieder

    Research output: Contribution to journalArticle

    97 Citations (Scopus)

    Abstract

    Context. The standard CSHKP model for eruptive flares is two-dimensional. Yet observational interpretations of photospheric currents in pre-eruptive sigmoids, shear in post-flare loops, and relative positioning and shapes of flare ribbons, all together require three-dimensional extensions to the model.

    Aims. We focus on the strong-to-weak shear transition in post-flare loops, and on the time-evolution of the geometry of photospheric electric currents, which occur during the development of eruptive flares. The objective is to understand the three-dimensional physical processes, which cause them, and to know how much the post-flare and the pre-eruptive distributions of shear depend on each other.

    Methods. The strong-to-weak shear transition in post-flare loops is identified and quantified in a flare observed by STEREO, as well as in a magnetohydrodynamic simulation of CME initiation performed with the OHM code. In both approaches, the magnetic shear is evaluated with field line footpoints. In the simulation, the shear is also estimated from ratios between magnetic field components.

    Results. The modeled strong-to-weak shear transition in post-flare loops comes from two effects. Firstly, a reconnection-driven transfer of the differential magnetic shear, from the pre- to the post-eruptive configuration. Secondly, a vertical straightening of the inner legs of the CME, which induces an outer shear weakening. The model also predicts the occurrence of narrow electric current layers inside J-shaped flare ribbons, which are dominated by direct currents. Finally, the simulation naturally accounts for energetics and time-scales for weak and strong flares, when typical scalings for young and decaying solar active regions are applied.

    Conclusions. The results provide three-dimensional extensions to the standard flare model. These extensions involve MHD processes that should be tested with observations.

    Original languageEnglish
    Article numberA110
    Number of pages14
    JournalAstronomy and Astrophysics
    Volume543
    DOIs
    Publication statusPublished - Jul 2012

    Keywords

    • CORONAL MASS EJECTIONS
    • TWISTED FLUX TUBES
    • 26 JUNE 1992
    • RECONNECTION
    • Sun: flares
    • magnetohydrodynamics (MHD)
    • 2011 FEBRUARY 15
    • magnetic reconnection
    • ENERGY PARTITION
    • ACTIVE-REGION
    • PHOTOSPHERIC MAGNETIC-FIELD
    • Sun: UV radiation
    • SOLAR-FLARES
    • Sun: coronal mass ejections (CMEs)
    • EVOLUTION

    Cite this

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    title = "The standard flare model in three dimensions I: strong-to-weak shear transition in post-flare loops",
    abstract = "Context. The standard CSHKP model for eruptive flares is two-dimensional. Yet observational interpretations of photospheric currents in pre-eruptive sigmoids, shear in post-flare loops, and relative positioning and shapes of flare ribbons, all together require three-dimensional extensions to the model. Aims. We focus on the strong-to-weak shear transition in post-flare loops, and on the time-evolution of the geometry of photospheric electric currents, which occur during the development of eruptive flares. The objective is to understand the three-dimensional physical processes, which cause them, and to know how much the post-flare and the pre-eruptive distributions of shear depend on each other. Methods. The strong-to-weak shear transition in post-flare loops is identified and quantified in a flare observed by STEREO, as well as in a magnetohydrodynamic simulation of CME initiation performed with the OHM code. In both approaches, the magnetic shear is evaluated with field line footpoints. In the simulation, the shear is also estimated from ratios between magnetic field components. Results. The modeled strong-to-weak shear transition in post-flare loops comes from two effects. Firstly, a reconnection-driven transfer of the differential magnetic shear, from the pre- to the post-eruptive configuration. Secondly, a vertical straightening of the inner legs of the CME, which induces an outer shear weakening. The model also predicts the occurrence of narrow electric current layers inside J-shaped flare ribbons, which are dominated by direct currents. Finally, the simulation naturally accounts for energetics and time-scales for weak and strong flares, when typical scalings for young and decaying solar active regions are applied. Conclusions. The results provide three-dimensional extensions to the standard flare model. These extensions involve MHD processes that should be tested with observations.",
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    author = "G. Aulanier and M. Janvier and B. Schmieder",
    year = "2012",
    month = "7",
    doi = "10.1051/0004-6361/201219311",
    language = "English",
    volume = "543",
    journal = "Astronomy and Astrophysics",
    issn = "0004-6361",
    publisher = "EDP Sciences",

    }

    The standard flare model in three dimensions I : strong-to-weak shear transition in post-flare loops. / Aulanier, G.; Janvier, M.; Schmieder, B.

    In: Astronomy and Astrophysics, Vol. 543, A110, 07.2012.

    Research output: Contribution to journalArticle

    TY - JOUR

    T1 - The standard flare model in three dimensions I

    T2 - strong-to-weak shear transition in post-flare loops

    AU - Aulanier, G.

    AU - Janvier, M.

    AU - Schmieder, B.

    PY - 2012/7

    Y1 - 2012/7

    N2 - Context. The standard CSHKP model for eruptive flares is two-dimensional. Yet observational interpretations of photospheric currents in pre-eruptive sigmoids, shear in post-flare loops, and relative positioning and shapes of flare ribbons, all together require three-dimensional extensions to the model. Aims. We focus on the strong-to-weak shear transition in post-flare loops, and on the time-evolution of the geometry of photospheric electric currents, which occur during the development of eruptive flares. The objective is to understand the three-dimensional physical processes, which cause them, and to know how much the post-flare and the pre-eruptive distributions of shear depend on each other. Methods. The strong-to-weak shear transition in post-flare loops is identified and quantified in a flare observed by STEREO, as well as in a magnetohydrodynamic simulation of CME initiation performed with the OHM code. In both approaches, the magnetic shear is evaluated with field line footpoints. In the simulation, the shear is also estimated from ratios between magnetic field components. Results. The modeled strong-to-weak shear transition in post-flare loops comes from two effects. Firstly, a reconnection-driven transfer of the differential magnetic shear, from the pre- to the post-eruptive configuration. Secondly, a vertical straightening of the inner legs of the CME, which induces an outer shear weakening. The model also predicts the occurrence of narrow electric current layers inside J-shaped flare ribbons, which are dominated by direct currents. Finally, the simulation naturally accounts for energetics and time-scales for weak and strong flares, when typical scalings for young and decaying solar active regions are applied. Conclusions. The results provide three-dimensional extensions to the standard flare model. These extensions involve MHD processes that should be tested with observations.

    AB - Context. The standard CSHKP model for eruptive flares is two-dimensional. Yet observational interpretations of photospheric currents in pre-eruptive sigmoids, shear in post-flare loops, and relative positioning and shapes of flare ribbons, all together require three-dimensional extensions to the model. Aims. We focus on the strong-to-weak shear transition in post-flare loops, and on the time-evolution of the geometry of photospheric electric currents, which occur during the development of eruptive flares. The objective is to understand the three-dimensional physical processes, which cause them, and to know how much the post-flare and the pre-eruptive distributions of shear depend on each other. Methods. The strong-to-weak shear transition in post-flare loops is identified and quantified in a flare observed by STEREO, as well as in a magnetohydrodynamic simulation of CME initiation performed with the OHM code. In both approaches, the magnetic shear is evaluated with field line footpoints. In the simulation, the shear is also estimated from ratios between magnetic field components. Results. The modeled strong-to-weak shear transition in post-flare loops comes from two effects. Firstly, a reconnection-driven transfer of the differential magnetic shear, from the pre- to the post-eruptive configuration. Secondly, a vertical straightening of the inner legs of the CME, which induces an outer shear weakening. The model also predicts the occurrence of narrow electric current layers inside J-shaped flare ribbons, which are dominated by direct currents. Finally, the simulation naturally accounts for energetics and time-scales for weak and strong flares, when typical scalings for young and decaying solar active regions are applied. Conclusions. The results provide three-dimensional extensions to the standard flare model. These extensions involve MHD processes that should be tested with observations.

    KW - CORONAL MASS EJECTIONS

    KW - TWISTED FLUX TUBES

    KW - 26 JUNE 1992

    KW - RECONNECTION

    KW - Sun: flares

    KW - magnetohydrodynamics (MHD)

    KW - 2011 FEBRUARY 15

    KW - magnetic reconnection

    KW - ENERGY PARTITION

    KW - ACTIVE-REGION

    KW - PHOTOSPHERIC MAGNETIC-FIELD

    KW - Sun: UV radiation

    KW - SOLAR-FLARES

    KW - Sun: coronal mass ejections (CMEs)

    KW - EVOLUTION

    U2 - 10.1051/0004-6361/201219311

    DO - 10.1051/0004-6361/201219311

    M3 - Article

    VL - 543

    JO - Astronomy and Astrophysics

    JF - Astronomy and Astrophysics

    SN - 0004-6361

    M1 - A110

    ER -