Rachel Howe University of Birmingham D Baker MSSL R KomM NSO R Bogart Stanford Introduction The Sun has flows at many scales from global rotation to flows around active regions and down to granules ID: 542522
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Slide1
Persistent structures in near-surface flows from ring diagrams
Rachel Howe, University of Birmingham
D. Baker, MSSL
R.
KomM
, NSO
R. Bogart, StanfordSlide2
Introduction
The Sun has flows at many scales, from global rotation to flows around active regions and down to granules.
Many of these show variations with solar cycle.
Here we are looking for persistent structures in local flow features over an extended period.Slide3
Differential rotation
2D rotation profile, based on RLS
inversions
Faster near equator, slower at polesSlide4
Analysis
Use synoptic maps of zonal/
meridional
flows from ring diagrams (GONG and HMI)
Average over all depths
At
each latitude, we subtract mean over all times/longitudes to remove biases and first-order temporal variations
Then plot residuals as longitude—time maps
Differential rotation causes features to drift in longitude from one rotation to the next.
Features (e.g., flows into active regions/remnants) persisting for more than one rotation will show up as diagonal streaks.Slide5
GONG zonal velocity
Note diagonal ‘grain’
Paired light-dark streaks suggest flows in or out of feature that drifts with differential rotation
.
Slope up == faster than Carrington rate
Slope down == slower than C.R.
Shallower slope means more difference.Slide6
GONG Meridional
velocity
Not much to see here – quieter at minimum?Slide7
MDI/HMI Magnetograms
(Timescale of GONG)Slide8
GONG zonal velocity
On HMI timescale.Slide9
HMI zonal velocity
Note strong stripes at high latitudes.Slide10
HMI meridional
velocity
Some grain visible here too.Slide11
HMI MagnetogramsSlide12
Differential rotation
Use cross-correlation analysis to translate stripes slope to rotation rate
Green –
Magnetograms
Black – Global inversions
Red – HMI ring
vx
correlation
Blue – GONG ring
vx
correlationSlide13
High-latitude vx
rewrapped with estimated velocitySlide14
High-latitude vx
rewrapped with est. velocity -5
nHZSlide15
Rewrapped HMI velocity
Use inferred rotation rate at each latitude instead of Carrington rate.
‘l=1’ structure at high latitudesSlide16
Discussion
Near-surface flows –especially zonal – show signatures of features persisting from a few to many rotations, migrating as would be expected from differential rotation.
Low latitudes traceable to active region/
plage
?
Rotation rate from magnetic features not quite the same as from flows – anchoring depth?
High latitudes – Hathaway giant cells
?
Looks like an l=1 structure,
anticorrelated
n/s.
Correlation analysis not good enough to pick
up changes in differential rotation.Slide17
HMI V sun-as-a-star
Daily variations Slide18
HMI IC sun-as-a-star
Daily variationsSlide19
Sun-as-a-Star
Use keywords (DATAMEAN) from JSOC database to form time series.
Line Core
= Continuum-Line Depth
Compare HMI Velocity with
BiSON
.All data interpolated to 45s cadence
HMI Continuum
HMI Line Core
AIA 1600
AIA 1700
BiSON Velocity
HMI VelocitySlide20
Coherence with HMI VSlide21
Phase relative to HMI V