Helioseismic%20holography%20of%20Solar%20Subsurface%20Flows%20:%20progress%20 - PowerPoint PPT Presentation

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

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a full inversion taking into account horizontal, vertical flows, and ... OLA method. regularization by hand. solutions for two depths are shown (3Mm and 14 Mm) ... – PowerPoint PPT presentation

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


1
Helioseismic holography of Solar Subsurface Flows
progress prospects
Doug Braun NWRA / CoRA
  • NorthWest Research Associates
  • Colorado Research Associates Division

2
with input from
A. Birch C. Lindsey NWRA / CoRA
3
outline
  • calibrated (near-surface) flows CR1988
  • supergranulation
  • AR flows
  • AR flows vs. depth travel-time asymmetries
  • inversions
  • zonal and meridional flows
  • whats next?

4
helioseismic holography
H- ingression
H egression
5
phase-correlation holography
(space-frequency domain)
egression, ingression
correlation
correlation phase
travel-time perturbation
sensitive to refractive perturbations at focus
6
phase-sensitive holography of flows
N
W
E
S
egressions and ingressions in 4 quadrants
e.g. E-W correlation phase
velocity
7
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

8
supergranulation
horizontal divergence
27-hr time averages
vertical vorticity
9
vertical vorticity of SG as a result of Coriolis
force on divergence
confirms time-distance f-mode results of Duvall
Gizon (2000)
10
power spectra of supergranulation (divergence)
in the fashion of Gizon, Duvall Schou (2003)
10 latitude strip _at_ B0
B 45

11
Carrington rotation 1988
12
vertical vorticity (smeared to 7.5)
vort vh (1/cosB) ?( cosB vB ) / ?L
(1/cosB)?vL / ?B
13
(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?)
14
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?
15
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.

16
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
17
horizontal flow signatures removing the phase
asymmetry
focus depth 3 Mm 5 Mm
7 Mm
raw data
showerglass phases removed
18
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

19
zonal and meridional flows
20
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)

21
zonal data and inversions
3 Mm
14 Mm
22
zonal and meridional inversions
23
HH code development needed for HMI
  • fix astigmatism problem
  • move to spherical coordinates
  • inversions
  • f mode
  • higher frequencies

24
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

25
further information
http//cora.nwra.com/dbraun
support
NASA (LWS and SRT programs) NSF (Stellar
Astronomy and Astrophysics program)
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