SSPVE Discussion Group B Question 5

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SSPVEDiscussion Group BQuestion 5

• To what extent is it possible to predict the
  emergence of active regions before they reach the
  photosphere, or to predict the rotation of an
  active region from behind the limb?

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Local Helioseismology

• Three major techniques
• Ring Diagrams
• Large-scale flows show kinetic helicity pattern
  below flare producers
• Time-Distance
• Sound speed signature seen before AR emergence
• Acoustic Holography
• Provides farside images of ARs

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Ring Diagrams - I

• Three-dimensional power spectrum of solar
  oscillations
• Subsurface flow displaces rings

No tracking for solar rotation
With tracking
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Ring Diagrams II

• Perform analysis over solar disk

• Invert for horizontal flows as function of
  location and depth

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Ring Diagrams -III

• Assuming incompressible flow and using solar
  model density
• Derive vertical velocity and fluid dynamics
  descriptors divergence, vorticity, helicity,
  enstrophy

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Vorticity below strong flare producers
AR 10069
AR 10486
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Correlation between kinetic helicity and flare
activity
Recently completed study of 408 ARs Must have
both a strong dipolar vorticity signal deep down
and a strong B for high flare activity. Low
activity can occur over a wide B range, but is
associated with low vorticty.
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Temporal behavior of kinetic helicity before a
flare
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Time-distance

• Sound is emitted from a location, travels down,
  and comes back up at some time later and some
  distance away from the source.
• The time and distance is influenced by the
  conditions of the plasma that the wave travels
  through.

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Constructing a T-D plot

• At a given time T, compute the cross-correlation
  between a point and annuli centered on the point
  with different radii D.
• Repeat for many values of T, plot
  cross-correlation amplitude as a function of T
  and D.
• Can be done approximately by taking the power
  spectrum of a filtered oscillation power
  spectrum.

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Observed time-distance diagram
Cross-correlation function is well described by a
Gabor wave packet
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T-D diagnostics

• Changes in travel time are related to subsurface
  conditions (sound speed, flows)
• Can be inverted to infer the conditions

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AR 10488 emergence
Sound speed from Time-Distance
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Farside imaging

• Uses acoustic holography
• Time reverse observed wave field to an impulse at
  a specific depth
• Depth can be located at the farside surface
• Presence of active region causes phase shifts

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Farside imagesof AR10808
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The answer

• We can see very large regions on the farside,
  giving up to 14 day warning before appearance on
  disk (or all-clear signal).
• We can see large regions form below the surface
  on the disk, giving 1-5 day warning.
• We are starting to see that specific flow
  configurations are likely activity producers and
  that there may be precursor temporal variations.
• BUT

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What do we need to do?

• More statistics, establish confidence levels.
• Better understanding of flare-related flow
  characteristics
• Tighter connection with surface observations
  what is the relation between the flow and the
  surface neutral line?
• Incorporation of subsurface flows into CME/Flare
  initiation models
• Energy analysis V vs B, is there a CME or SEP?
• Faster analysis
• Calibration of farside signal vs activity B
• Compare flows and vector magnetograms