emergence and evolution of active regions
DESCRIPTION
Emergence and Evolution of Active Regions. 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 - PowerPoint PPT PresentationTRANSCRIPT
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