Something New About Frequency Shifts

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Presentation transcript:

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

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

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

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

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

Frequency shift sensitivity

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

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.

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

dn/dB, dn/dB2

dn/dB for 15-degree patches

MDI: coefficients color-coded by year

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

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

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

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

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.

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)

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.