1. Solar Surface Magneto-Convection and Dynamo Action
Bob Stein
Michigan State University
East Lansing, MI, USA
Åke Nordlund
Niels Bohr Institute for Astronomy, Physics, and Geophysics
University of Copenhagen, DK

3. Weak Field Simulations
Initial conditions
Snapshot of granular convection (6x6x3 Mm)
Resolution: 25 km horizontally, km vertically
1G or 30G horizontal seed field imposed
Boundary conditions
Top boundary: B  potential field
Bottom boundary: inflows advect 1G or 30G horizontal field
Results
Flux emergence, convergence, fragmentation, cancellation, submergence

4. 3D Effects Inhomogeneous T (see only cool gas), Pturb Raises atmosphere 1 scale height

5. Magneto-Convection

6. Simulation Results: B Field lines

7. Flux Emergence & Disappearance

8. Field Distribution

9. Exponential Distribution

10. Exponential Distribution

11. Exponential Distribution

12. Exponential Distribution

13. Exponential Distribution

14. Strong “Flux Tubes” are dark, depressed & suppress flow

15. Stokes profiles new SVST, perfect seeing

16. Stokes Image - Quiet Sun Synthetic Observation - La Palma Telescope MTF + Excellent Seeing
Stokes V
Surface Intensity
6 Mm
6 Mm

17. Stokes Image - Quiet Sun Synthetic Observation - Perfect Telescope & Seeing
Stokes V
Surface Intensity
6 Mm
6 Mm

18. Magnetic “Flux Tubes” (top view)

19. Magnetic “Flux Tubes” (side view)

20. Magnetic field lines

21. Dynamo Action

22. Is there a local surface dynamo here?
Flux Emergence
Less cycle variation
slope = -2
Cycle variation

23. Dynamo Requirements
Magnetic field amplification by stretching and twisting
Diffusion to reconnect magnetic field lines and alter magnetic topology
Circulation to continue process

24. Magnetic Field Reorganization

25. Field Amplification Field is concentrated by diverging upflows
Field is stretched and twisted by vortical downflows

26. Vorticity

27. Work & Dissipation

28. Stratified convective flows have little re-circulation

29. Stratification Pumping Dorch & Nordlund (2000)
Initial
field
Most of the flux is INSIDE the convection zone
Relaxed
field

31. Stein & Nordlund, ApJL 1989

32. Fraction of fluid reaching surface

33. Surface and Global Field
Small scale flux is dominated by drag and is passively advected by the plasma flow.
Only a very small fraction of fluid ascending from the bottom of the convection zone reaches the surface
Much more flux and magnetic energy in the deep convection zone than at the surface.
Energy added to flux that visits the surface is tiny compared to the global energy.

34. Why NO Surface Dynamo? Little local re-circulation.
Magnetic field is carried to bottom of convection zone by downdrafts.
Re-circulation is global, time scale is long
Turnover time at bottom of convection zone is months.
Energy in surface field is small
Only small fraction of plasma starting up from bottom of convection zone reaches the surface.

35. Is there a Solar Surface Dynamo?
Answer: No.
There is a global dynamo process.
Small scale fields are dragged and dispersed.
Large scale fields are buoyant and feel
the differential rotation and coriolis force.

36. The End