SOT observing modes for local helioseismology and data analysis
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Transcript of SOT observing modes for local helioseismology and data analysis
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