Helioseismic measure of solar activity-meaning and applications

We analyze the antisymmetric part of the fine structure in the LOWL data, and find a remarkable agreement with the BBSO data taken during the 1986 activity minimum. For both, the P₄(cos θ) component of the Sun's asphericity is dominant. We discuss the importance of measuring this part of the fine structure as a global probe of the Sun's varying magnetic activity. The asphericity affects oscillation frequencies in a way that corrupts any inversion for the radial structure of the deep solar interior. The results of inversion of the original and cleansed data show that at the current minimal level of solar activity, the effect is within the errors. However, this is not true in the case of measurements taken in years of high activity. We mimic such measurements by adding in appropriate frequency shifts evaluated from 1989 BBSO data.