Understanding the Sun's Dynamo: Secrets of Solar Spots Revealed

2. Apologies from Ed and Karl-Heinz

8. SoFin@NOT

9. Near-surface shear layer:spots rooted at r/R=0.95? Benevolenskaya, Hoeksema, Kosovichev, Scherrer (1999) Pulkkinen & Tuominen (1998) • Df=tAZDW=(180/p) (1.5x107) (2p 10-8) • =360 x 0.15 = 54 degrees!

10. Forced large scale dynamo with fluxes geometry here relevant to the sun 1046 Mx2/cycle Negative current helicity: net production in northern hemisphere

11. Solar dynamos in the 1970s • Distributed dynamo (Roberts & Stix 1972) • Positive alpha, negative shear Yoshimura (1975)

12. Distributed dynamos • a max at 60 Mm depth • ht = 3x1012 cm2/s Krivodubskii (1984) 

13. In the days before helioseismology • Angular velocity (at 4o latitude): • very young spots: 473 nHz • oldest spots: 462 nHz • Surface plasma: 452 nHz • Conclusion back then: • Sun spins faster in deaper convection zone • Solar dynamo works with dW/dr<0: equatorward migr

14. Before helioseismology • Angular velocity (at 4o latitude): • very young spots: 473 nHz • oldest spots: 462 nHz • Surface plasma: 452 nHz • Conclusion back then: • Sun spins faster in deaper convection zone • Solar dynamo works with dW/dr<0: equatorward migr Brandenburg et al. (1992) Thompson et al. (2003) Yoshimura (1975)

15. Application to the sun:spots rooted at r/R=0.95 Benevolenskaya, Hoeksema, Kosovichev, Scherrer (1999) • Overshoot dynamo cannot catch up • Df=tAZDW=(180/p) (1.5x107) (2p 10-8) • =360 x 0.15 = 54 degrees!

16. Flux storage Distortions weak Problems solved with meridional circulation Size of active regions Neg surface shear: equatorward migr. Max radial shear in low latitudes Youngest sunspots: 473 nHz Correct phase relation Strong pumping (Thomas et al.) Arguments against and in favor? Tachocline dynamos Distributed/near-surface dynamo in favor against • 100 kG hard to explain • Tube integrity • Single circulation cell • Turbulent Prandtl number • Max shear at poles* • Phase relation* • 1.3 yr instead of 11 yr at bot • Rapid buoyant loss* • Strong distortions* (Hale’s polarity) • Long term stability of active regions* • No anisotropy of supergranulation Brandenburg (2005, ApJ 625, 539)

17. Origin of sunspot Theories for shallow spots: (i) Collapse by suppression of turbulent heat flux (ii) Negative pressure effects from <bibj>-<uiuj> vs BiBj

18. Build-up & release of magnetic twist Coronal mass ejections clockwise tilt (right handed)  left handed internal twist Upcoming work: • Global models • Helicity transport • coronal mass ejections • Cycle forecasts New hirings: • 4 PhD students • 4 post-docs (2yr) • 1 assistant professor • 2 Long-term visitors

19. Cycle dependenceof W(r,q)

20. Sunspots

21. How deep are sunspots rooted? • Solar activity may not be so deeply rooted • The dynamo may be a distributed one • Near-surface shear important Hindman et al. (2009, ApJ)

22. Near-surface shear layer Benevolenskaya, Hoeksema, Kosovichev, Scherrer (1999)

23. Flux emergence:observations & simulations Brandenburg (2005, ApJ) Hindman et al. (2009, ApJ)

24. Flux emergence: simulations and models • Active regions from an instability • Suppression of turbulent motions • Cooling, contraction, field amplification in preparation with Kleeorin & Rogachevskii

25. Winter School 11-22 January

26. http://spaceweather.com