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SOT observing modes for local helioseismology and data analysis

The seminar discusses SOT's high-resolution Dopplergrams for local helioseismology, offering insights into subsurface structures and flows. Topics include spatial and temporal resolutions, data analysis techniques, and the potential of joint observations with MDI for enhanced depth coverage in active regions.

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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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