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 maps Next 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

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

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 G Heavy contour 120 G 30 m/s feature Noise ~ 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 G Heavy 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