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

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

3. Spruit paper 3

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

5. 5 Simulations of the solar dynamo? Tremendous stratification –Not only density, also scale height change Near-surface shear layer (NSSL) not resolved Contours of  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 6 Brown et al. (2011) ASH code: anelastic spherical harmonics

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

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

9. Type of dynamo? 9 Use phase relation Closer to  2 dynamo Wrong for  dyn. Mitra et al. (2010) Oscillatory  2 dynamo

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

11. Turbulent sunspot origins?

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

13. 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 14

15. Sunspot decay 15

16. 512 3 vs 1024 3 resolution Rm/Re dependence? Here 40/80 and 95/190 Originally 18/36. 16

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

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

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

20. Why so strong? 20

21. Vertical fields survive downward flow 21

22. 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.