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Helicity as Ultimate Test of Surface Dynamo

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

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Helicity as Ultimate Test of Surface Dynamo

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

  2. 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. Subphotospheric vs. (Near-) Surface Dynamo (Emonet & Cattaneo 2001)

  3. What is the Role of Surface Dynamo? • Generates new magnetic field? • “Recycles” magnetic field generated by subsurface dynamo?

  4. Tornado: Hurricanes: 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.

  5. 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

  6. 12 min x 5 repeats ASP, Pevtsov & Longcope (2001)

  7. What is the Role of Surface Dynamo? • Generates new magnetic field? • “Recycles” magnetic field generated by subsurface dynamo?

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

  9. Chaotic Helical Duvall & Gizon, 2000 (Coriolis force has effect of supergranular flows)

  10. Pevtsov & Neidig (2005)

  11. 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.

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