Emergence and Evolution of Active Regions

A. C. Birch, H. Schunker (MPS), D. C. Braun (NWRA)

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)

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

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

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

Supergranulation is the dominant signal

Contours of B: 20, 40, 60 GBlue = divergence; red= convergence

No clear signal in individual mapsNext step: ensemble averages (60

regions)

IMPORTANT!Blue = flow towards emergence location

Red = flow away from emergence location

rms = 15 m/s

Average over AR

IMPORTANT!Blue = flow towards emergence location

Red = flow away from emergence location

rms = 15 m/s

Average over QS

QS AR

Average over AR

Average over AR

Converging flow!

Note offset.

Average over AR

Zoom in

t = -13 hr

AR

Max. flow 100 m/s

Inner circle: 30 Mm radius

AR QS

B contours 50, 100, 150 G

Average over AR

Average over AR

Average over AR

Zoom in

t = 34 hr

AR

Max. flow 150 m/s

Inner circle: 30 Mm radius

EW cut as a function of time:there is a feature before emergence

Lowest B contour 40 GHeavy contour 120 G

30 m/s featureNoise ~ 10 m/s

m/s

Quiet Sun noise level ~ 10 m/s

m/s

NS cut shows converging flow before and during emergence

Lowest B contour 40 GHeavy contour 120 G

m/s

Quiet Sun: noise ~ 10 m/s

m/s

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/s prograde/equatorward flow in leading

polarity– ~100 m/s NS converging flow between the

polarities

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

The end

QS11079 and AR11079

A single AR