Signatures of the Rise of Cycle 23

Abstract

During the rise of Cycle 23, we have found a sizable, systematic evolution of the Solar and Heliospheric Observatory/Michelson Doppler Imager solar oscillation frequencies implying significant changes in the spherically symmetric structure of the Sun's outer layers as well as in its asphericity up to a P18 Legendre distortion. We conducted a search for corresponding asymmetries in Ca II K data from Big Bear Solar Observatory. We found tight temporal and angular correlations of the respective asphericities up through P10. This result emphasizes the role of the magnetic field in producing the frequency changes. We carried out inversions of the frequency differences and the splitting coefficients assuming that the source of the evolving changes is a varying stochastic magnetic field. With respect to the most recent activity minimum, we detected a significant perturbation in the spherical part at a depth of 25-100 Mm, which may be interpreted as being a result of a magnetic perturbation, B2, of about (60KG)2 and/or a relative temperature perturbation of about 1.2 × 10-4. Larger, although less statistically significant, perturbations of the interior structure were found in the aspherical distortion.