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Context: There is a wide discrepancy in current estimates of the strength ofconvection flows in the solar interior obtained using different helioseismicmethods applied to observations from SDO/HMI. The cause for these disparitiesis not known. Aims: As one step in the effort to resolve this discrepancy, weaim to characterize the multi-ridge fitting code for ring-diagram helioseismicanalysis that is used to obtain flow estimates from local power spectra ofsolar oscillations. Methods: We updated the multi-ridge fitting code developedby Greer et al.(2014) to solve several problems we identified through ourinspection of the code. In particular, we changed the merit function to accountfor the smoothing of the power spectra, model for the power spectrum, and noiseestimates. We used Monte Carlo simulations to generate synthetic data and tocharacterize the noise and bias of the updated code by fitting these syntheticdata. Results: The bias in the output fit parameters, apart from the parameterdescribing the amplitude of the p-mode resonances in the power spectrum, isbelow what can be measured from the Monte-Carlo simulations. The amplitudeparameters are underestimated; this is a consequence of choosing to fit thelogarithm of the averaged power. We defer fixing this problem as it is wellunderstood and not significant for measuring flows in the solar interior. Thescatter in the fit parameters from the Monte-Carlo simulations is well-modeledby the formal error estimates from the code. Conclusions: We document anddemonstrate a reliable multi-ridge fitting method for ring-diagram analysis.The differences between the updated fitting results and the original resultsare less than one order of magnitude and therefore we suspect that the changeswill not eliminate the aforementioned orders-of-magnitude discrepancy in theamplitude of convective flows in the solar interior.

An improved multi-ridge fitting method for ring-diagram helioseismic analysis