M. S. Cunha, P. P. Avelino, W. J. Chaplin, T. L. Campante

The frequencies of the solar oscillations are known to vary in phase with the Sun's activity level. The solar cycle is accompanied by changes in the overall magnetic field as well as in the area covered by active regions, which can affect the wave propagation, hence, the oscillation frequencies, through direct and indirect effects. However, the importance of the different contributions is not well established. With this in mind, we developed an empirical model to estimate the spot-induced frequency shifts. The model assumes the sunspot properties, such as the time dependent latitudinal distribution and area and a characteristic induced phase difference that represents the local impact of a spot on the wave. We have applied our model to the sunspot daily records (from NGDC/NOAA) and synthetic sunspot data. By comparing the frequency shifts obtained with our model using real sunspot data with those observed, we are able to estimate that the contribution from spots to the observed frequency shifts is about 30%.