TRI-PHONIC HELIOSEISMOLOGY - COMPARISON OF SOLAR P-MODE OBSERVED BY THE HELIOSEISMOLOGY INSTRUMENTS ABOARD SOHO

The three helioseismology instruments aboard SOHO observe solar p mode s in velocity (GOLF and MDI) and in intensity (VIRGO and MDI). Time se ries of two months duration are compared and confirm that the instrume nts indeed observe the same Sun to a high degree of precision. Power s pectra of 108 days are compared showing systematic differences between mode frequencies measured in intensity and in velocity. Data coverage exceeds 97% for all the instruments during this interval. The weighte d mean differences (V - I) are -0.1 mu Hz for l = 0, and -0.16 mu Hz f or l = 1. The source of this systematic difference may be due to an as ymmetry effect that is stronger for modes seen in intensity. Wavelet a nalysis is also used to compare the shape of the forcing functions. In these data sets nearly all of the variations in mode amplitude are of solar origin. Some implications for structure inversions are discusse d.