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Understanding Solar Activity: Exploring Surface Phenomenon and Dynamo Waves

Explore the intricate dynamics of solar activity, from surface phenomena to the formation of sunspots. Dive into the thin flux tube paradigm, dynamo waves, and the role of magnetic fields in sunspot origins. Unravel the mechanisms driving solar activity and the implications for predicting solar behavior.

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Understanding Solar Activity: Exploring Surface Phenomenon and Dynamo Waves

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  1. Solar activity as a surface phenomenon Axel Brandenburg (Nordita/Stockholm) Kemel+12 Käpylä+12 Ilonidis+11 Warnecke+11 Brandenburg+11

  2. The thin flux tube paradigm Caligari et al. (1995) Charbonneau & Dikpati (1999)

  3. Spruit paper

  4. Standard dynamo wave New loop Differential rotation (faster inside) Cyclonic convection; Buoyant flux tubes Equatorward migration  a-effect

  5. Simulations of the solar dynamo? • Tremendous stratification • Not only density, also scale height change • Near-surface shear layer (NSSL) not resolved • Contours of W cylindrical, not spoke-like • (i) Rm dependence (catastrophic quenching) • Field is bi-helical: to confirm for solar wind • (ii) Location: bottom of CZ or distributed • Shaped by NSSL (Brandenburg 2005, ApJ 625, 539) • Formation of active regions near surface

  6. Brun, Brown, Browning, Miesch, Toomre ASH code: anelastic spherical harmonics Brown et al. (2011)

  7. Ghizaru, Charbonneau, Racine, … • Cycle now common! • Activity from bottom of CZ • but at high latitudes Racine et al. (2011)

  8. Dynamo wave from simulations Kapyla et al (2012)

  9. Type of dynamo? • Use phase relation • Closer to a2 dynamo • Wrong for aW dyn. Oscillatory a2 dynamo Mitra et al. (2010)

  10. Turbulent sunspot origins? Kosovichev et al. (2000) Theories for shallow spots: (i) Collapse by suppression of turbulent heat flux (ii) Negative pressure effects from <uiuj> vs BiBj

  11. Turbulent sunspot origins?

  12. Negative effective magnetic pressure instability • Gas+turb. press equil. • B increases • Turb. press. Decreases • Net effect?

  13. Much stronger with vertical fields • Gas+turb. press equil. • B increases • Turb. press. Decreases • Net effect?

  14. Self-assembly of a magnetic spot • Minimalistic model • 2 ingredients: • Stratification & turbulence • Extensions • Coupled to dynamo • Compete with rotation • Radiation/ionization

  15. Sunspot decay

  16. 5123 vs 10243 resolution • Rm/Re dependence? • Here 40/80 and 95/190 • Originally 18/36.

  17. Surface-filling magnetic activity Guedel (2004) Saturated activity naturally explained

  18. 3 times stronger stratification • Rm/Re dependence? • Here 40/80 and 95/190 • Originally 18/36.

  19. Imposed vs. self-assembly • Appearance of sunspot when coupled to radiation • Can be result of self-assembly when ~1000 G field below surface Rempel et al. (2009) Stein & Nordlund (2012)

  20. Why so strong?

  21. Vertical fields survive downward flow

  22. Conclusions • Interest in predicting solar activity • Cyclonic convection ( helicity) • Near surface shear  migratory dynamo? • Formation of active regions and sunspots by negative effective magnetic pressure inst.

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