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

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. Disk-center, 0G frequency
MDI
GONG
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)
Big Rings
15 deg Rings
Global
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.

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.