Helicity as Ultimate Test of Surface Dynamo

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Helicity as Ultimate Test of Surface Dynamo
Alexei Pevtsov (National Solar Observatory) Dana
Longcope (Montana State University)
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Subphotospheric vs. (Near-) Surface Dynamo

• May operate in bulk (mean field D.) or at the
  bottom (overshoot) of the CZ.
• Field is generated by slow/large-scale flows.
• ARs fields.

• May operate at/near surface.
• Field is generated by (super-) granular
  convection.
• Quiet Sun salt-and-pepper fields.

(Emonet Cattaneo 2001)
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What is the Role of Surface Dynamo?

• Generates new magnetic field?
• Recycles magnetic field generated by subsurface
  dynamo?

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Chaotic (turbulent)
Helical

• Overshoot region (DeLuca Gilman 1991)
• Mean-field dynamo (Krause Radler 1980)
• Surface dynamo (Emonet Cattaneo 2001)

• Helical dynamo should result in hemispheric
  preference for sign of helicity
• Chaotic (turbulent) dynamo should show no
  hemispheric sign-preference for helicity.

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Seehafer, 1990 Pevtsov et al, 1995, Abramenko et
al, 1996 Longcope et al, 1998, Bao and Zhang,
1998, Pevtsov et al. 2001, Hagino and Sakurai,
2002 60-80, hemispheric helicity rule
Bao Zhang, 1998 84 - negative/northern, 81
positive/southern hemisphere. Pevtsov et al.
1995, 2001 Cycle22 76 - negative/N, 69 -
positive /S Cycle 23 63 - negative/N, 70 -
positive/S HSOS/HSP, 269 magnetograms,
1997-2000 76 show the same sign of helicity.

466 active regions, HSP observations during
1987-2000 Spearman cor. coef. -0.23 likelihood
of no correlation 2.5 x 10-7
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12 min x 5 repeats
ASP, Pevtsov Longcope (2001)
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What is the Role of Surface Dynamo?

• Generates new magnetic field?
• Recycles magnetic field generated by subsurface
  dynamo?

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• Problems
• ASP inversion does not work in very weak fields
• Atmospheric seeing effects (AO may introduce weak
  instrumental polarization)

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Chaotic
Helical
Duvall Gizon, 2000 (Coriolis force has effect
of supergranular flows)
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Pevtsov Neidig (2005)
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(No Transcript)
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Suggested Solar-B Observations

• Make vector magnetograms of quiet Sun areas at
  different
• latitudes and search for the hemispheric
  sign-asymmetry.
• Study helicity of magnetic concentration at the
  location
• of clumps of filament material.