sot observing modes for local helioseismology and data analysis
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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 and local helioseismology
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”

= [email protected] centre

SOT17, Tokyo

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

SOT17, Tokyo

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

SOT17, Tokyo

how do we use sot for local helioseismology 1 2
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

how do we use sot for local helioseismology 2 2
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

data amount aspect
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

data analysis 1 3
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

data analysis 2 3
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

data analysis 3 3
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

the first thing we would like to do
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

time distance analysis in ars
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

summary
Summary
  • High-resolution local-helioseismology by SOT
  • Time-distance inversion at the centre of the analysis

SOT17, Tokyo

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