braun aia/hmi feb 2006 1 helioseismic holography of solar subsurface flows : progress &...

Braun AIA/HMI Feb 2006 1

Helioseismic holography of Helioseismic holography of Solar Subsurface Flows :Solar Subsurface Flows :

progress & prospectsprogress & prospects

NorthWest Research AssociatesNorthWest Research Associates

Colorado Research Associates DivisionColorado Research Associates Division

Doug Braun

NWRA / CoRA

Braun AIA/HMI Feb 2006 2

A. Birch

C. Lindsey

NWRA / CoRA

with input from:with input from:

3Braun AIA/HMI Feb 2006

outlineoutline

““calibrated” (near-surface) flows calibrated” (near-surface) flows CR1988CR1988 supergranulationsupergranulation AR flowsAR flows

AR flows vs. depth: travel-time AR flows vs. depth: travel-time asymmetriesasymmetries

inversionsinversions zonal and meridional flowszonal and meridional flows

what’s next?what’s next?


H- = ingression H+ = egression

helioseismic helioseismic holographyholography


phase-correlation phase-correlation holographyholography

egression, ingression:

correlation:

travel-time perturbation:

correlation phase:

(space-frequency domain)

sensitive to refractive perturbations at focus


phase-sensitive holography of phase-sensitive holography of flowsflows

egressions and ingressions in 4 quadrants:

e.g. E-W correlation phase:

velocity:

WEN

S


““calibrated” near surface calibrated” near surface flowsflows

holography phase holography phase signatures for signatures for focus=3Mm, focus=3Mm, calibrated from calibrated from difference between difference between two tracking ratestwo tracking rates

nearly equivalent nearly equivalent to inversion for to inversion for 3Mm with 3Mm with following following averaging kernelaveraging kernel


supergranulation: supergranulation: horizontal divergencehorizontal divergence

vertical vertical vorticityvorticity

27-hr time averages


vertical vorticity of SG as a result vertical vorticity of SG as a result of of

Coriolis force on divergence:Coriolis force on divergence:

confirms time-distance f-mode results of Duvall & Gizon (2000)


power spectra of supergranulation power spectra of supergranulation (divergence)(divergence)

10° latitude strip @ B=0

B = 45°

in the fashion of Gizon, Duvall & Schou (2003)


Carrington rotation 1988Carrington rotation 1988


vertical vorticity vertical vorticity (smeared to (smeared to 7.57.5°)°)

vort vh = (1/cosB) ( cosB vB ) / L – (1/cosB)vL / B


(5.8 day-averaged) flow properties of (5.8 day-averaged) flow properties of ARs in CR1988ARs 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?)


horizonal divergence with depthhorizonal 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?


the showerglass FAQthe showerglass FAQ what is it?

it’s 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).

what’s 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.

doesn’t this phase subtraction just take out everything? or mostly everything?

this is the subject of ongoing research. it’s 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, it’s 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.


assessing showerglass assessing showerglass phasephase

Correlate surface signal with ingression or egression (full pupil) focused at surface

Correlate ingression (a quadrant) with egression (opposite quadrant) focused at some depth

making subsurface making subsurface measurementsmeasurements


focus depth = 3 Mm 5 Mm 7 Mm

raw data

showerglass phases removed

horizontal flow signatures: horizontal flow signatures: removing the phase asymmetry


horizontal flow horizontal flow inversionsinversions

for now, not taking out phase asymmetries for now, not taking out phase asymmetries from the horizontal flow signaturesfrom 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-inversions have been explored for small-scale (supergranulation) and longitudinal scale (supergranulation) and longitudinal averaged flowsaveraged flows

the latter is illustrated nextthe latter is illustrated next


zonal and meridional zonal and meridional flowsflows


inversionsinversions•multi-channel deconvolution algorithm (for 3D case)

•these rotation and meridional inversions are only 1D (depth)

•averaging kernels (from Green’s functions under Born approx.)

•OLA method

•regularization by hand

•solutions for two depths are shown (3Mm and 14 Mm)


zonal data and inversionszonal data and inversions3 Mm 14 Mm


zonal and meridional zonal and meridional inversionsinversions


HH code development HH code development needed for HMIneeded for HMI

fix astigmatism problem move to spherical coordinates inversions

f mode higher frequencies


larger (science-related) larger (science-related) issues to address:issues to address:

is there anything else other than AR divergence sigs., SG, zonal and meridional flows? (as if these weren’t 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


further information:further information:

http://cora.nwra.com/~dbraun

NASA (LWS and SR&T programs)

NSF (Stellar Astronomy and Astrophysics program)

supporsupport:t:

braun aia/hmi feb 2006 1 helioseismic holography of solar subsurface flows : progress &...

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