Helioseismic%20holography%20of%20Solar%20Subsurface%20Flows%20:%20progress%20

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Helioseismic holography of Solar Subsurface Flows
progress prospects
Doug Braun NWRA / CoRA

• NorthWest Research Associates
• Colorado Research Associates Division

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with input from
A. Birch C. Lindsey NWRA / CoRA
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outline

• calibrated (near-surface) flows CR1988
• supergranulation
• AR flows
• AR flows vs. depth travel-time asymmetries
• inversions
• zonal and meridional flows
• whats next?

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helioseismic holography
H- ingression
H egression
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phase-correlation holography
(space-frequency domain)
egression, ingression
correlation
correlation phase
travel-time perturbation
sensitive to refractive perturbations at focus
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phase-sensitive holography of flows
N
W
E
S
egressions and ingressions in 4 quadrants
e.g. E-W correlation phase
velocity
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calibrated near surface flows

• holography phase signatures for focus3Mm,
  calibrated from difference between two tracking
  rates
• nearly equivalent to inversion for 3Mm with
  following averaging kernel

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supergranulation
horizontal divergence
27-hr time averages
vertical vorticity
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vertical vorticity of SG as a result of Coriolis
force on divergence
confirms time-distance f-mode results of Duvall
Gizon (2000)
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power spectra of supergranulation (divergence)
in the fashion of Gizon, Duvall Schou (2003)
10 latitude strip _at_ B0
B 45

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Carrington rotation 1988
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vertical vorticity (smeared to 7.5)
vort vh (1/cosB) ?( cosB vB ) / ?L
(1/cosB)?vL / ?B
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(5.8 day-averaged) flow properties of ARs in
CR1988
For near-surface (e.g. 3Mm) ARs rotate faster
than quiet Sun (this shear can give rise to
bipolar vorticity signature) Inflows in plage
outflows in spots No net vorticity signatures
in ARs (but small number statistics?)
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horizonal divergence with depth (smeared to 1.0
deg)
focus 3 - 30 Mm
At all depths, outflow signatures from sunspots
dominate are these actual deep outflows?
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the showerglass FAQ

• what is it?
• its a hypothesis about possible strong, even
  dominant, contribution to helioseismic signatures
  (e.g. amplitude or phases) from surface magnetic
  fields
• why do you call it a showerglass?
• the phase and amplitude perturbations
  hypothesized vary significantly over small
  spatial scales, and may have consequences for
  imaging fine structure below the surface in a
  fashion similar to looking through a
  showerglass (see Lindsey Braun 2005a,b).
• whats this business about correcting it?
• the correction is an experiment, deriving from
  optical terminology. we are devising ways to
  assess the existence, and properties, of the
  hypothesized showerglass. measuring and removing
  a surface phase, derived from a magnetogram, is
  one such test. it is not a requirement for local
  helioseismology, or a suggested pipeline
  procedure.
• doesnt this phase subtraction just take out
  everything? or mostly everything?
• this is the subject of ongoing research. its
  designed to take out surface phases from the
  surrounding pupil (and not at the subsurface
  focus). if subsurface structure disappears
  when this is done, this may lead to a
  uniqueness problem how do we distinguish
  between a showerglass-caused feature and a real
  subsurface one?
• why should we care?
• if it exists, its probably telling us
  interesting physics about magnetic fields, it may
  have important diagnostic potential, we may also
  figure out how to detect weaker perturbations
  below it.

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assessing showerglass phase
Correlate surface signal with ingression or
egression (full pupil) focused at surface
making subsurface measurements
Correlate ingression (a quadrant) with egression
(opposite quadrant) focused at some depth
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horizontal flow signatures removing the phase
asymmetry
focus depth 3 Mm 5 Mm
7 Mm
raw data
showerglass phases removed
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horizontal flow inversions

• for now, not taking out phase asymmetries from
  the horizontal flow signatures
• will retain flexibility of whether or not this is
  done to assess the impact
• a full inversion taking into account horizontal,
  vertical flows, and magnetic effects will
  probably not be in place by HMI launch
• inversions have been explored for small-scale
  (supergranulation) and longitudinal averaged
  flows
• the latter is illustrated next

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zonal and meridional flows
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inversions

• multi-channel deconvolution algorithm (for 3D
  case)
• these rotation and meridional inversions are only
  1D (depth)
• averaging kernels (from Greens functions under
  Born approx.)
• OLA method
• regularization by hand
• solutions for two depths are shown (3Mm and 14
  Mm)

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zonal data and inversions
3 Mm
14 Mm
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zonal and meridional inversions
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HH code development needed for HMI

• fix astigmatism problem
• move to spherical coordinates
• inversions
• f mode
• higher frequencies

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larger (science-related) issues to address

• is there anything else other than AR divergence
  sigs., SG, zonal and meridional flows? (as if
  these werent enough!)
• travel-time asymmetries in magnetic regions
• understanding physics
• extracting flow signatures from other
  (interesting) effects
• vertical flows? directly? assume
  mass-conservation?
• combining or using surface flows in inversions,
  models

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further information
http//cora.nwra.com/dbraun
support
NASA (LWS and SRT programs) NSF (Stellar
Astronomy and Astrophysics program)