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SOT observing modes for local helioseismology and data analysis

SOT observing modes for local helioseismology and data analysis. Takashi Sekii NAOJ. SOT and local helioseismology. SOT provides high-resolution Dopplergrams and thus a great opportunity to study subsurface structure and flow (and a lot more) Spatial resolution 0.2”

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SOT observing modes for local helioseismology and data analysis

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  1. SOT observing modes for local helioseismology and data analysis Takashi Sekii NAOJ

  2. SOT and local helioseismology • SOT provides high-resolution Dopplergrams and thusa great opportunity to study subsurface structure and flow (and a lot more) • Spatial resolution 0.2” = 150km@disc centre SOT17, Tokyo

  3. High resolution powerspectrum • MDI high-resolution power spectrum • No resonant p modes above ℓ≈2000 • The f-mode frequency ∝ sqrt(ℓ) SOT17, Tokyo

  4. High resolution t-d diagram • Sekii et al 2001: MDI(left) versus La Palma SVST G-band (right, Berger et al 1998) SOT17, Tokyo

  5. 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 SOT17, Tokyo

  6. How do we use SOT for local helioseismology? (2/2) • Cadence • 1 min is the “standard” • But there is no reason a higher cadence should hurt, except in terms of telemetry • A higher cadence may be favoured in particular for chromospheric wave study SOT17, Tokyo

  7. Data amount aspect • A 12-hr run of single-line observation, 320”x160” FOV, 2x2 summing, 1-min cadance, JPEG compression →~9 Gbits SOT17, Tokyo

  8. Data analysis (1/3) • Time-distance analysis • Calibrated & tracked Dopplergrams • wavefield characterization, excitation study、surface flow etc • Filtered Dopplergrams (phasespeed filter, averaging on segments etc) • Cross-covariance function • Travel-time measurement • Inversion for subsurface structure & flow SOT17, Tokyo

  9. 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 SOT17, Tokyo

  10. Data analysis (3/3) • Most of the scientific targets are achieved by the standard t-d analysis and its by-products • We may add • “Simultaneous” observations with SP • Multi-line observation for chromospheric waves • Observation with a photospheric magnetic line (see the next slide) SOT17, Tokyo

  11. 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 SOT17, Tokyo

  12. 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, suppressed excitation • Richard Wachter’s talk SOT17, Tokyo

  13. Summary • High-resolution local-helioseismology by SOT • Time-distance inversion at the centre of the analysis SOT17, Tokyo

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