Disentangling the Magnetic Flux Rope Topology from CMEs Do All Regular CMEs Contain Flux Ropes

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Disentangling the Magnetic Flux Rope Topology
from CMEsDo All Regular CMEs Contain Flux Ropes?
submitted to ApJ Letters
C. Jacobs1, N. Lugaz2, I. Roussev2 and S. Poedts1
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3-D Model of Magnetic Breakout in Idealized
Settings

• Model Features
• Multi-polar magnetic field is produced by
• Global, dipolar-type magnetic field resembling
  Sun at solar minimum.
• Pre-existing active region (outer spots with BR
  50 G).
• Newly emerged active region (inner spots with BR
  70 G).
• Steady state solar wind (Roussev et al., 2003).
• Coronal magnetic field is open beyond 2.5 RS.

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CME Driver Shearing Motions

• Inner spots are moved apart in finite time (30
  min) with speed 160 km/s (which is lt 3 of local
  VA).
• These shearing motions energize the magnetic
  field by creating field- aligned electric
  currents.
• Total separation of the charges is about 30o.
• Mechanism published in ApJ Letters, 2007,
  Roussev, Lugaz Sokolov

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Radial Flow Structure in Meridional Plane
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In-Situ Measurements at 15 RS

• Ejecta with
• High magnetic field strength.
• Low-density with a higher-density core.
• Smooth rotation of Bz.
• Decreasing speed.
• These properties are usually associated with flux
  ropes.

sheath
Flux rope fitting results in a cloudaxis along
the global current sheet (x-axis).
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3-D Structure of Coronal Magnetic Field at t 4
hr
BUT
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What Is New in This Idealized Simulation?

• Key Results
• This is not standard flux-rope type CME no
  twist.
• Magnetic field of CME has significant writhe.
• Foot-prints of erupting magnetic field are not
  localized on solar surface.
• There may be jumps in field line mapping on solar
  surface as a satellite flies through the CME.
• Passage of shock wave changes angle of overlying
  field in plane of shock surface.

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Why Is Magnetic Field So Complicated?

• Magnetic reconnection occurs at three sites
• Red field lines reconnect through current sheets
  formed at two pre-existing null points in NE and
  SW result of reconnection is blue field lines.
• Blue field lines are pushed equator-ward and
  reconnect to form the yellow field lines.

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Why Is Magnetic Field So Complicated? (Cont.)

• There is also reconnection from two other flux
  systems through the N and S parts of the current
  sheets in NE and SW
• Red field lines reconnect to form the blue field
  lines (one of which is highly kinked).

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Orientation of the flux rope vs. orientation of
the global field

• Dipolar instead of quadrupolar configuration
  (reverse global dipole field).
• Same methodology otherwise.

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Synthetic White Light Observations
t 30 min
t 2 hr
quadrupolar
dipolar
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Conclusions

• CMEs undergo major reconstruction as they evolve
  on the way out.
• Magnetic topology (null points, quasi-separators)
  plays an important role.
• Footprints of erupting magnetic field do not
  remain stationary as CME evolves.
• Not all iCMEs have the standard (highly twisted)
  flux-rope structure.
• Writhe instead of twist may result in the in-situ
  characteristics of a flux rope.
• Revision of magnetic cloud models may be
  required.
• Orientation of the background magnetic field and
  inclination of the inversion line may be keys to
  predict orientation of iCMEs.
• With this model, orientation of the flux rope
  is highly dependent on the orientation of the
  background field.
• More multi-spacecraft in-situ measurements of
  iCMEs are required to validate the theory.