Wilcox Solar Observatory, Stanford

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• Wilcox Solar Observatory, Stanford

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Solar eclipse HawaiiJuly 1989
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The Sun!
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Coronal Mass Ejections
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Coronal Mass Ejections
White light (SOHO/LASCO) solar limb coronagraph
image of CME. Inner corona and solar disk seen
in extreme ultraviolet (SOHO/EIT).
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The view from Earth
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3D and twisted.
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CME Onset Due to Loss of Confinement of Twisted
Magnetic Flux Ropes

• What triggers coronal mass ejections (CMEs)?
  This is a fundamental question in solar
  astrophysics that must be answered for space
  weather prediction.
• Magnetic twist can drive eruption. A 3D
  numerical simulation demonstrates that given
  enough twist, a magnetic flux rope can no longer
  be confined by the surrounding coronal magnetic
  field and will erupt in a CME.
• Twist in eruptions is observed. Twisted
  internal structure and motion consistent with the
  model has been observed in CMEs.

Observation of a CME by HAO Mauna Loa Solar
Observatory Mk4 white-light coronagraph
MHD Simulation from Fan (2005)
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Soft-X ray sigmoid brightening and associated
dimming
Fan and Gibson (in preparation)
Line-of-sight column integration of
Line-of-sight

• Looking down on flux rope we see it as it would
  appear on the solar disk
• Model predicts current sheets forming forward or
  backwards S shapes (depending on direction of
  flux rope twist)
• X-ray observations show such S shapes
• Model predicts twin density depletions within
  the S-shape (owl-eyes)
• Observations sometimes show such twin dimmings
  during eruptions

Line-of-sight column integration of
Soft-X ray image from Yohkoh satellite during the
onset of a CME
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Sigmoids
Sigmoids are generally visible in three ways
(Pevtsov, 2002)
persistent (long-lived)
transient (short-lived)
eruptive (transient sigmoid --gt cusp)
(Gibson et al., 2002)
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Magnetic flux rope observables X-ray sigmoids

• Sigmoid evolution -- evidence for flux rope
  before, during and after eruption (Gibson et al.,
  2004 2005)

eruptive (transient sigmoid --gt cusp)
persistent (long-lived)
transient (short-lived)
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