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Surface Dynamo as Ultimate Test: Helicity and Solar Observations

This research delves into the role and mechanisms of surface dynamos in generating magnetic fields on the Sun, exploring helical and chaotic aspects and observational implications. The study investigates the generation and recycling of magnetic fields by surface dynamos in comparison to subsurface dynamos, considering factors like hemispheric preferences for helicity. Analysis is based on observations from various solar cycles and active regions. Challenges such as weak fields and seeing effects are also addressed, along with proposed observations to enhance understanding of solar dynamics.

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Surface Dynamo as Ultimate Test: Helicity and Solar Observations

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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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