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Something New About Frequency Shifts

Get the latest insights on frequency shifts in helioseismology through Rachel Howe's LoHCo study. Explore background information, results from big rings, spline decomposition, and variations in sensitivity based on latitude and longitude. Join the discussion on the complexities of frequency shifts.

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Something New About Frequency Shifts

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  1. Something New About Frequency Shifts Rachel Howe LoHCo 30th Jan 2008

  2. Synopsis • A bit of background from global helioseismology • Results from big rings • Spline Decomposition for Depth Dependence • Latitude and Longitude variation of sensitivity • Discussion

  3. Two Things to Remember • Everything varies with everything else • It’s more complicated than that

  4. ACRIM (Woodard & Noyes 1985, 1988, Gelly, Fossat & Grec 1988) BiSON, Mark I (Palle et al. 1989, Elsworth et al. 1990) Courtesy G. Verner, 2006 Frequency shifts with solar cycle

  5. GONG l=50, n=10 frequency • From 108-day samples • Lines show best fits to activity indices: magnetic (solid), RF (dashed), sunspot (dotted)

  6. Frequency shift sensitivity

  7. Shifts Go Negative at High Frequency • Salabert et al., 2002

  8. Rings: Fitting the frequency shifts • Express frequencies as n=n0+a1rx+a2rx2+a3ry+a4ry2+a5B+a6B2 • Where • rx, ry are fractional distances from disk center, • B is magnetic index (mean unsigned field strength in patch). • Repeat fit for every patch, one CR at a time.

  9. Update on Ring-Diagram Results • dn/dx, dn/dx2, dn/dy, dn/dy2 from six years of GONG+ data. Shows obvious “seasonal” trends.

  10. dn/dB, dn/dB2

  11. dn/dB for 15-degree patches

  12. MDI: coefficients color-coded by year

  13. GONG MDI Disk-center, 0G frequency • MDI drifts or moves a long way! • Focus changes?

  14. Results from 30-degree patches • Shifts correlated with local magnetic index • Anticorrelated at high frequency

  15. dn/dB for large patches • Sensitivity decreases, changes sign at higher frequencies • (Mode conversion effect?)

  16. Depth dependence? • Signal is dominated by surface effects, which to first order are frequency-dependent • Asymptotic spline decomposition: Sdn/n=h1(n)+h2(n/L) Big Rings (CR1988) 15 deg Rings (CR1988) Global

  17. Decomposition: (S/n)dn/dB=H1(n)+H2(n/L) • Real depth dependence? Or just systematic error/inadequate model? • Should use n/L term in surface term for high-degree modes, but not enough dynamic range to fit properly. Big Rings 15 deg Rings Global

  18. Spatial Variation of Sensitivity • dn/dB Averaged over 6 years of GONG data at l=495, n=0 … 5 • Sensitivity of frequency to B varies with latitude (top) and CMD (bottom)

  19. Conclusions • Mode frequencies correlate well with activity indices in time and space. • Exact sensitivity varies with frequency – anticorrelations at high frequency. • Systematic errors make it hard to combine global and local results. (Or even big and small rings!) • Possible hint of structural changes varying with depth, but could be artifact.

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