Emergence and Evolution of Active Regions

1. Emergence and Evolution of Active Regions C. Birch, H. Schunker (MPS), D. C. Braun (NWRA)

2. Motivations • How does active region emergence work? • Where do AR come from? • How do emerging AR interact with convection? • What are the flows associated with AR? • Constrain dynamo models • Potentially rule out certain models (rising flux tubes?) • Converging flows associated with AR play a role in some dynamo models (e.g. Cameron & Schuessler, 2012)

3. Previous work • Pre-emergence case studies: • Braun (1995, Hankel analysis) • Jensen et al. (2001, time-distance) • Hartlep et al. (2011, acoustic power) • Ilonidis et al. (2011, time-distance) • Many others … • Statistical studies • Komm et al. (2009, 2011, rings, 100s of regions) • Birch et al. (2013, holography, ~100 regions one day before emergence) • Open questions remain

4. HMI Data selection • Presented by Hannah in previous talk • Additional constraints: • Less then 40 deg from central meridian • Duty cycle > 90% • Result: subsample of about 60 emerging AR

5. Helioseismic Holography • This talk: surface focusing measurements (lower turning point 3 Mm) • Strategy: • Carry out holography for disk passage of all emerging AR and quiet Sun control regions • find clear signals first and then think about inversions

6. Supergranulation is the dominant signal Blue = divergence; red= convergence Contours of B: 20, 40, 60 G

7. No clear signal in individual mapsNext step: ensemble averages (60 regions)

8. Average over AR IMPORTANT! Blue = flow towards emergence location Red = flow away from emergence location rms = 15 m/s

9. Average over QS IMPORTANT! Blue = flow towards emergence location Red = flow away from emergence location rms = 15 m/s

10. QS AR

11. Average over AR

12. Average over AR

13. Average over AR Converging flow! Note offset.

14. Zoom in t = -13 hr AR Max. flow 100 m/s Inner circle: 30 Mm radius

15. AR QS

16. Average over AR B contours 50, 100, 150 G

17. Average over AR

18. Average over AR

19. Zoom in t = 34 hr AR Max. flow 150 m/s Inner circle: 30 Mm radius

20. EW cut as a function of time:there is a feature before emergence m/s 30 m/s feature Noise ~ 10 m/s Lowest B contour 40 G Heavy contour 120 G

21. Quiet Sun noise level ~ 10 m/s m/s

22. NS cut shows converging flow before and during emergence m/s Lowest B contour 40 G Heavy contour 120 G

23. Quiet Sun: noise ~ 10 m/s m/s

24. Conclusions • There is a clear pre-emergence signature: • Near-surface flows of ~100 m/s • Converging to a location ~15 Mm East • Exists days before emergence • Flow pattern during emergence: • ~150 m/sprograde/equatorward flow in leading polarity • ~100 m/s NS converging flow between the polarities

25. Next steps • Refine the meaning of control region • pre-emergence signature dominated by preferential emergence location within the supergranulation pattern? • Control for supergranulation pattern. • Comparison with simulations?  Doug’s talk • Deep signal?  Doug’s talk

27. The end

28. QS11079 and AR11079

29. A single AR