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Ring-diagram Frequency Comparisons

Ring-diagram Frequency Comparisons. RACHEL HOWE (February 2010 version). Introduction. Inferred ring frequencies vary with position on disk as well as activity. Different analyses and data produce slightly different results for frequencies and spatial variation.

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Ring-diagram Frequency Comparisons

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  1. Ring-diagram Frequency Comparisons RACHEL HOWE (February 2010 version)

  2. Introduction Inferred ring frequencies vary with position on disk as well as activity. Different analyses and data produce slightly different results for frequencies and spatial variation. Can we understand any of these differences? What effect, if any, does tracking rate have on frequencies? Since November, we have a few more data sets analyzed. What can we learn from these?

  3. Data Summary All data are from ring analysis of 15-degree dense-pack square patches tracked for 1664 min. SN(1) is original uncorrected Snodgrass-tracked data SN (2) is with distortion corrections SN(3) is with distortion corrections, Yale fitting code CR is Carrington-rate tracking, with offsets up to 0.9 microradian/sec.

  4. A reminder Even at disk center and low activity, MDI frequencies have varied over time, while GONG stays fairly stable.

  5. Analysis Frequencies provided by Deborah (MDI CO fits), Sushant (GONG CR tracking), Rick (Yale fits) and the GONG pipeline. Yale-code results interpolated onto the same k-bin grid as Boulder-code ones. (One bin=22.5 l) Compare ring frequency parameters patch-for-patch and bin-for-bin, discard modes present in less than 30% of whole dataset. Look at average frequency differences over all peaks, and difference as function of bin averaged over all longitudes.

  6. Old vs New Compare old and new MDI Snodgrass-tracked, CO-fitted frequencies for CR1988 and 2068, averaged over l<778, nu<4500 “Old” 2068 already had partial correction built-in.

  7. Old vs New by peak

  8. MDI vs GONG Compare new Snodgrass –tracked MDI with standard GONG. Remarkably similar for two rotations six years apart!

  9. MDI vs GONG peak by peak (Averages over all longitudes at three latitudes)

  10. MDI vs GONG: 2084 “Upside down” spacecraft rotates difference pattern.

  11. MDI (old) vs GONG No distortion correction. Note huge offset for 2019!

  12. CT vs CO fits Small non-uniform offset (orientation dependent?) even with distortion correction in place. (Much worse before corrections.)

  13. Differences by mode, CO vs CT

  14. CO vs CT fits (GONG)

  15. GONG vs MDI (CT fits)

  16. Carrington vs Snodgrass MDI data for Carrington-tracking tests has strongly radial dependence in its difference from other datasets.

  17. Carrington-rate tracking Differences are small, dominated by CMD

  18. Conclusions Tracking rate offset has a fairly small effect on the frequencies, but seems to be bigger away from central meridian. There may be something else funny about the Carrington tracking-rate test sets. (Scale error?) MDI after corrections is closer to GONG and more uniform than it used to be, but there are still differences with a distinct spatial pattern. CT vs CO shows significant differences, with hints of residual distortion effects.

  19. What Next? • Re-test of Carrington tracking effects on MDI Or skip straight to HMI when available? • Re-analysis of all MDI dynamics with improved distortion correction would be valuable (but not HMI priority.) Even better distortion correction would be even better. • Do CT vs CO differences matter? What will they look like for HMI?

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