Takashi SekiiNAOJ

SOT observing modes for local helioseismology and data analysis

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SOT and local helioseismology SOT provides high-resolution Dopplergra

ms and thus a great opportunity to study subsurface structure and flow (and a lot more) Spatial resolution 0.2” = 150km@disc centre

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High resolution powerspectrum MDI high-resolution power spectrum

No resonant p modes above ℓ≈2000 The f-mode frequency ∝ sqrt(ℓ)

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High resolution t-d diagram Sekii et al 2001: MDI(left) versus La Pal

ma SVST G-band (right, Berger et al 1998)

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How do we use SOT for local helioseismology? (1/2) Which line(s)?

Fe I 5576 (non-magnetic, photosphere) Mg I 5173 (magnetic, chromosphere) One of magnetic iron lines

Field of view the full unvignetted field: 240”x160”

2x2 summing: 　 OK except (perhaps) at high latitudes

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How do we use SOT for local helioseismology? (2/2) Cadence

1 min is the “standard” But there is no reason a higher cadence sho

uld hurt, except in terms of telemetry A higher cadence may be favoured in particul

ar for chromospheric wave study

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Data amount aspect A 12-hr run of single-line observation, 32

0”x160” FOV, 2x2 summing, 1-min cadance, JPEG compression

→ 　 ~9 Gbits

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Data analysis (1/3) Time-distance analysis1. Calibrated & tracked Dopplergrams

wavefield characterization, excitation study 、surface flow etc

2. Filtered Dopplergrams (phasespeed filter, averaging on segments etc)

3. Cross-covariance function4. Travel-time measurement5. Inversion for subsurface structure & flow

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Data Analysis (2/3) Inversion: Ray approximation

kernels for p-mode waves + MCD inversion How shall we incorporate f-mode

data? More sophisticated/realistic methods? It is still a developing subject

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Data analysis (3/3) Most of the scientific targets are achieve

d by the standard t-d analysis and its by-products

We may add “Simultaneous” observations with SP Multi-line observation for chromospheric wa

ves Observation with a photospheric magneti

c line (see the next slide)

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The first thing we would like to do A joint observation with MDI SOT field in the middle of MDI field QT & AR

Calibration (Doppler measurement, plate scale)

Combined data provides better depth coverage

Insight for t-d analyses in AR, using both magnetic and non-magnetic lines

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Time-distance analysis in ARs Doppler measurement based on FGs

MDI algorithm optimized for QT Does not affect SOT directly, since SOT can

use a non-magnetic line Does affect MDI-SOT joint observation

Oscillations in AR Scattering, changes in thermal structure, su

ppressed excitation Richard Wachter’s talk

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Summary High-resolution local-helioseismology by

SOT Time-distance inversion at the centre of t

he analysis