braun aia/hmi feb 2006 1 helioseismic holography of solar subsurface flows : progress &...
Post on 20-Dec-2015
218 views
TRANSCRIPT
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
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?
4Braun AIA/HMI Feb 2006
H- = ingression H+ = egression
helioseismic helioseismic holographyholography
5Braun AIA/HMI Feb 2006
phase-correlation phase-correlation holographyholography
egression, ingression:
correlation:
travel-time perturbation:
correlation phase:
(space-frequency domain)
sensitive to refractive perturbations at focus
6Braun AIA/HMI Feb 2006
phase-sensitive holography of phase-sensitive holography of flowsflows
egressions and ingressions in 4 quadrants:
e.g. E-W correlation phase:
velocity:
WEN
S
7Braun AIA/HMI Feb 2006
““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
8Braun AIA/HMI Feb 2006
supergranulation: supergranulation: horizontal divergencehorizontal divergence
vertical vertical vorticityvorticity
27-hr time averages
9Braun AIA/HMI Feb 2006
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)
10Braun AIA/HMI Feb 2006
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)
12Braun AIA/HMI Feb 2006
vertical vorticity vertical vorticity (smeared to (smeared to 7.57.5°)°)
vort vh = (1/cosB) ( cosB vB ) / L – (1/cosB)vL / B
13Braun AIA/HMI Feb 2006
(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?)
14Braun AIA/HMI Feb 2006
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?
15Braun AIA/HMI Feb 2006
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.
16Braun AIA/HMI Feb 2006
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
17Braun AIA/HMI Feb 2006
focus depth = 3 Mm 5 Mm 7 Mm
raw data
showerglass phases removed
horizontal flow signatures: horizontal flow signatures: removing the phase asymmetry
18Braun AIA/HMI Feb 2006
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
20Braun AIA/HMI Feb 2006
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)
23Braun AIA/HMI Feb 2006
HH code development HH code development needed for HMIneeded for HMI
fix astigmatism problem move to spherical coordinates inversions
f mode higher frequencies
24Braun AIA/HMI Feb 2006
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