Comparison of local frequency shifts between MDI velocity and intensity data

Abstract

We analyze the frequencies of high–degree p modes using velocity and intensity data from MDI. The study is carried out with the local helioseismic technique of ring diagrams. The resultant power spectra at several different positions on the solar disk are fitted with symmetric and asymmetric profiles to find the center–to–limb variation (CLV). Using symmetric profiles in the anaylsis produces significant differences in frequency between velocity and intensity with the differences increasing from disk center to the limb. The use of asymmetric peak profiles reduces these differences and in the 3 mHz band the frequencies agree reasonably well with each other.