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 ID: 273935
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Slide1
Emergence and Evolution of Active Regions
C. Birch, H.
Schunker
(MPS), D. C. Braun (NWRA)Slide2
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
)Slide3
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
remainSlide4
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 Slide5
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 inversionsSlide6
Supergranulation
is the dominant signal
Contours of B: 20, 40, 60 G
Blue = divergence; red= convergenceSlide7
No clear signal in individual maps
Next step: ensemble averages (60 regions)Slide8
IMPORTANT!
Blue = flow towards emergence location
Red = flow away from emergence location
rms
= 15
m/s
Average over ARSlide9
IMPORTANT!
Blue = flow towards emergence location
Red = flow away from emergence location
rms
= 15
m/s
Average over QSSlide10
QS ARSlide11
Average over ARSlide12
Average over ARSlide13
Converging flow!
Note offset.
Average over ARSlide14
Zoom in
t
= -13 hr
AR
Max. flow 100
m/s
Inner circle: 30 Mm radiusSlide15
AR QSSlide16
B contours 50, 100, 150 G
Average over ARSlide17
Average over ARSlide18
Average over ARSlide19
Zoom in
t
= 34 hr
AR
Max. flow 150
m/s
Inner circle: 30 Mm radiusSlide20
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/sSlide21
Quiet Sun noise level ~ 10
m/s
m/sSlide22
NS cut shows converging flow before and during emergence
Lowest B contour 40 G
Heavy contour 120 G
m/sSlide23
Quiet Sun: noise ~ 10
m/s
m/sSlide24
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 polaritiesSlide25
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 talkSlide26Slide27
The endSlide28
QS11079 and AR11079Slide29
A single ARSlide30