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					Twisted magnetic flux ropes: A breeding ground
                  for CMEs?


                          Sarah Gibson
 Collaborators: Yuhong Fan, Joan Burkepile, Giuliana de Toma, B. C. Low


          Sarah Gibson                                            October 2005
                                      Magnetic flux ropes
What’s a magnetic flux rope?
   Suggested definition: A set of magnetic field lines that wind at least one full turn about an axial field line

                                                                                           Spheromak-based

     Loosely wound

                                                   Tightly wound




                                                    Roussev (2003)
                                          (after Titov and Demoulin (1999))
      Amari et al. (2003)



                                                                                      After Gibson and Low (1998)
                                Magnetic flux ropes
Are there flux ropes in interplanetary space?
   Pretty well accepted




                                    Lepping et al. 1995
                                  Magnetic flux ropes

Are there flux ropes in the corona during the eruption of a
   coronal mass ejection (CME)?
   Also quite well accepted



Do flux ropes exist quiescently in the corona prior to the
   CME, or are they formed during eruption?
   Controversial




                                                                                  Amari et al., 2003




                                                                   Examples of models where rope
                                                                      forms during eruption



                                                             Lynch et al., 2004
                              Precursor magnetic flux rope
Theoretically compelling:


Precursor flux rope stores magnetic energy:


o   Coronal magnetic helicity very nearly conserved as a global quantity (Berger and Field, 1984)

o   Magnetically dominated plasma relaxes to minimum energy conserving helicity (Taylor, 1974, 1986)

o   Flux rope represent such a minimum energy state given enough helicity (Low, 1994)

o   Flux ropes “fundamental building blocks of magnetism in the solar atmosphere”? (Rust, 2003)



Precursor flux rope possesses the seeds of its own destruction:


•   Free energy stored in still-twisted magnetic fields is plausible CME driver (Low, 1999 )

•   Instabilities and loss of equilibria occur as thresholds are crossed for maximum flux or twist (Lin et

    al., 1998; Roussev et al., 2003; Linker, 2003; Fan, 2005; Toeroek et al., 2004)

•   Is there a threshold for maximum global helicity? (Zhang et al., 2005)
                            Precursor magnetic flux rope
Observationally compelling:

Coronal plasma gives us clues to field structure (flux frozen in highly conductive corona)

Many twisted-appearing structures in corona

Three-dimensional MHD models needed for meaningful comparison


I will present the case for a precursor flux rope, by comparing models to observations
before, during, and after the CME
                Evidence for a precursor flux rope: Before the CME
1.   Observations of quiescent corona are consistent with flux ropes as pre-CME magnetic
     configuration
     •   Filaments
     •   Cavities
     •   X-ray sigmoids




                                      QuickTime™ and a
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                              Before the CME: Filaments

Cool, dense, filament material supported by dips of winding rope




                                          Priest et al., 1989
                             Before the CME: Filaments

Three-dimensional flux rope model using photospheric boundary
         -- location of dips match observed filament location well.




                                             Van Ballegoiijen (2004)
                                Before the CME: Cavities

Filament viewed at the solar limb is surrounded by dark cavity
                                Before the CME: Cavities

Flux rope models predict such a cavity:


         •    Enhanced magnetic field in rope compensates for low gas pressure of cavity
         •    Requires thermal isolation from photosphere for longevity
         •    Circular cross-section, sharp boundary (magnetic flux surface/tangential field
              discontinuities)




          Low and Hundhausen, 1995                           Gibson et al., 2005
                              Before the CME: Sigmoids




                                              Active regions are significantly more likely to
                                              produce flares or CMEs when associated with
       QuickTime™ and a
  YUV420 codec decompressor                   sigmoid structures. (Canfield et al., 1999)
 are neede d to see this picture.




(Gibson et al., 2002):
                      Before the CME: Non-eruptive sigmoids

Dynamic evolution of flux rope field lying above and within separatrix surface relative to the
shorter, arcade-type field below and external to it, could result in tangential discontinuities,
leading to the the formation of electric current sheets along the separatrix surface (Parker,
1994; Titov and Demoulin, 1999; Low and Berger, 2000).




                                                                       QuickTime™ an d a
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                Evidence for a precursor flux rope: During the CME

2.   Observations of CME in eruption are consistent with flux rope precursor
     •   3 part eruption of CME (bodily eruption of filament and cavity)
     •   Transient sigmoid
     •   Transition to cusped post-flare loops behind eruption
                             During the CME: 3-part CME
 3-part CME a consequence of flux rope in many models




                                                               Linker et al., 2003

    Lynch et al. (2004)




                                            QuickTime™ and a
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Gibson and Low, 1998; 2000         Krall et al., 2001                                Fan and Gibson, 2005
                                      During the CME: 3-part CME
Cavity + filament exists before eruption (for days, weeks, or even months)
            -- evidence that flux rope also pre-exists CME




                                                                                             QuickTime™ and a
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 Mauna Loa Mk4 white light coronagraph image
 showing quiescent cavity: November 18, 1999




                                           CME eruption of cavity: November 19, 1999                         Gibson et al., 2005
                                   During the CME: 3-part CME
                      Cavity + filament observed to bodily erupt as 3 part CME




            August 8, 2001
                                                                 QuickTime™ and a
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Gibson et al., 2005
                                   During the CME: 3-part CME
                      Cavity + filament observed to bodily erupt as 3 part CME




                                                               QuickTime™ and a
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      February 4, 1999




Gibson et al., 2005
                          During the CMEs: Transient sigmoid
Current sheets form during eruption --> sigmoidal reconnecting field lines




                                                                              QuickTime™ an d a
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     Kliem et al., 2004




                                                                Fan, 2005; Gibson and Fan, 2005
                                  During the CMEs: Sigmoid-to-cusp
                                                           3D model (Titov & Demoulin, 1999)




                                                                     Roussev (2003)

When X-type point(s) exist prior to eruption below rope,
    simulations demonstrate a total eruption of the rope
            2D cartoon (Gilbert et al. 2001)

                                                                               QuickTime™ and a
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                                                                         are neede d to see this picture.




                                                                   (Toeroek and Kliem, 2005)
                                   During the CMEs: Sigmoid-to-cusp

•     Forms two ropes separated
      by cusped, sheared arcade
•     Sigmoid-separatrix-surface                      Gibson and Fan, 2005
      survives
•     Some dipped field erupts
      with upper rope, some
      shrinks back down with
      lower rope
•     Can break in this manner
      because
      •     3D
      •     NO X-line




    Adapted from Gilbert et al. 2001
                 Evidence for a precursor flux rope: After the CME

3.   Some post-CME observations appear inconsistent with total eruption of pre-existing flux
     rope
     •   Partially or non-erupting filaments
     •   Immediate reformation of long-lived X-ray sigmoid (sigmoid-->cusp-->sigmoid)
     •   Magnetic cloud charge state signatures




                      (Gibson et al., 2002):                              Gloeckler et al., 1999
                 After the CME: Partially or non-erupting filaments
Filaments are often observed to either not erupt, or only partially erupt with a CME (Gilbert,
2000; Pevtsov, 2002; Gibson et al., 2002)




                                      QuickTime™ and a
                                 YUV420 codec decompressor
                                are neede d to se e this picture.
             After the CME: Immediate reformation of sigmoid




Sigmoid-->cusp-->sigmoid
(Gibson et al., 2002)                                QuickTime™ and a
                                                YUV420 codec decompressor
                                               are neede d to see this picture.
                           After the CME: Magnetic charge states
•   Charge states of solar wind ions frozen in at coronal temperatures
•   Most magnetic clouds indicate only relatively hot coronal material -- no clear signature of cool filament material
•    Some cases that do imply cool material (He+ events) imply coexisting mixture of cool and hot material (Skoug
    et al., 1999; Gloeckler et al., 1999). These events are only seen during the rising phase of the solar cycle.
•   A recent case (Zurbuchen, private communication) demonstrates purely cold material -- this event had no
    associated flare
             First alternative: Flux rope formed during eruption

•   In three-dimensions combined with embedded sheared-field filament model could
    explain pre-CME quiescent filament (but what about long-lived cavity and non-
    eruptive sigmoid?)
•   Can explain 3-part CME (but what about the bodily erupting cavity?), (eruptive sigmoid?)-->cusp,
    and depending on location of pre-CME filament relative to reconnections, could explain either
    totally erupting, partially erupting, or non-erupting filament (but what about reformation of non-
    eruptive sigmoid?)
•   Explains why cold filaments rarely seen in magnetic cloud, since field lines making up the erupting
    rope were heated by reconnection during eruption (but what about observations of cold or mixed
    material in magnetic cloud?)




    De Vore and Antiochos, 2000                           Tokman and Bellan, 2002
             First alternative: Flux rope formed during eruption
•   In three-dimensions combined with embedded sheared-field filament model could explain pre-
    CME quiescent filament (but what about long-lived cavity and non-eruptive sigmoid?)

•   Can explain 3-part CME (but what about the bodily erupting cavity?), (eruptive
    sigmoid?)-->cusp, and depending on location of pre-CME filament relative to
    reconnections, could explain either totally erupting, partially erupting, or non-
    erupting filament (but what about reformation of non-eruptive sigmoid?)
•   Explains why cold filaments rarely seen in magnetic cloud, since field lines making up the erupting
    rope were heated by reconnection during eruption (but what about observations of cold or mixed
    material in magnetic cloud?)




                 Lynch et al., 2004


                                                                                              QuickTime™ an d a
                                                                                    TIFF (Uncompressed) decompressor
                                                                                       are need ed to see this p icture .


                                                                              Tokman and Bellan, 2002
             First alternative: Flux rope formed during eruption

•   In three-dimensions combined with embedded sheared-field filament model could explain pre-
    CME quiescent filament (but what about long-lived cavity and non-eruptive sigmoid?)
•   Can explain 3-part CME (but what about the bodily erupting cavity?), (eruptive sigmoid?)-->cusp,
    and depending on location of pre-CME filament relative to reconnections, could explain either
    totally erupting, partially erupting, or non-erupting filament (but what about reformation of non-
    eruptive sigmoid?)

•   Explains why cold filaments rarely seen in magnetic cloud, since field lines making
    up the erupting rope were heated by reconnection during eruption (but what about
    observations of cold or mixed material in magnetic cloud?)




                                                                                              QuickTime™ an d a
                                                                                    TIFF (Uncompressed) decompressor
                                                                                       are need ed to see this p icture .


          Lynch et al., 2004                                           Tokman and Bellan, 2002
          Second alternative: pre-existing flux rope totally erupts

•   Pre-eruption flux rope consistent with pre-CME quiescent filament and cavity (but what about
    non-eruptive sigmoid?)
•   Consistent with a totally erupting filament and eruptive sigmoid->cusp (but what about
    partial/non-erupting filaments, and reformation of long-lived sigmoid?)
•   Consistent with (rare) observations of cold filaments in magnetic cloud (but what about
    observations of hot or mixed material in magnetic cloud?)




    2D cartoon (Gilbert et al. 2001)                                        (Toeroek and Kliem, 2005)
     Third alternative: pre-existing flux rope that erupts only partially

•     Pre-eruption flux rope consistent with pre-CME quiescent filament and cavity, as well as non-
      eruptive sigmoid
•     Consistent with a totally erupting filament, partially eruptive filament, and non-eruptive
      filament, depending where filament mass lies relative to reconnection point, and also with an
      eruptive sigmoid-->cusp.
•     Consistent with reformation of long-lived sigmoid
•     Consistent with hot, mixed, or cold filaments in magnetic cloud, depending upon where
      reconnections take place


Consistent with observations, before, during, and after CME!




Adapted from Gilbert et al. 2001
                                       Conclusions

Quiescent, pre-eruption magnetic flux ropes in the corona


    •    Are a natural equilibrium state for a coronal magnetic field that is minimizing
         energy while conserving helicity (Taylor, 1974, 1986; Berger and Field, 1984; Low,
         1994; Rust, 2003)
    •    May form as an equilibrium state in the corona via photospheric motions (Amari,
         2000; Linker, 2003) or flux emergence (Fan and Gibson, 2004, 2005; Fan, 2005;
         Manchester et al., 2004b)
    •    Can produce a CME by losing equilibrium when flux or twist thresholds are crossed
         (Lin et al., 1998; Roussev et al., 2003; Linker, 2003; Fan, 2005; Toeroek et al.,
         2004)


The partial eruption of such a quiescent flux rope


    •    Can explain observations of the evolution of filaments, cavities, and sigmoids from
         their pre-eruption quiescent state, through the eruption, and to their post-eruption
         state.
                                         Doesn’t happen in 2D
•       In 3D, when the flux rope extends down to the
        photosphere so there is no pre-existing X-type point
        below the rope, the rope can break in two via internal
        reconnection




                                                                           QuickTime™ and a
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    •   However, 2D simulations show that the loss of
        equilibrium of the rope leads to its total eruption with
        current sheets forming below the rope




                               (Lin, 1998)                         Fan and Gibson, 2005)
Good-bye two-dimensional cartoons!




                                                                          QuickTime™ and a
                                                                        Video de compressor
                                                                   are neede d to see this picture.




  Tokman and Bellan (2004)


                                                http://solartheory.nrl.navy.mil/solartheory/erupt.html

                             Amari (2003)




  Van Ballegoiijen (2004)      Roussev (2003)                          Manchester et al. (2004a)
Good-bye two-dimensional cartoons!




  Tokman and Bellan (2004)


                                                http://solartheory.nrl.navy.mil/solartheory/erupt.html

                             Amari (2003)




  Van Ballegoiijen (2004)      Roussev (2003)                        Manchester et al. (2004a)

				
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posted:10/14/2012
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