Far-side helioseismology with global mode frequencies from Sun-as-a-star and resolved observations

The frequencies of helioseismic modes vary with activity at a wide range of spatial and temporal scales. For global modes, we would expect the frequencies to be sensitive to activity at all longitudes, not just the visible ones, while most activity proxies include only activity on the Earth-facing side of the Sun. We present results from fitting p-mode spectra derived from 7-d segments of Sun-as-a-star helioseismic observations from the Birmingham Solar Oscillations Network covering 32 yr, and from 9-d segments of resolved-Sun observations from the Global Oscillations Network Group (GONG) covering 29 yr. The results show a clear dependence of the mode frequencies on solar activity, and the frequency dependence of the sensitivity to activity can also be seen. Because we use data segments that cover less than half of a solar rotation, we are able to test for the effect of activity on the solar far side. By fitting with a model that takes into account activity on the far side of the Sun, we show that the frequency shifts are indeed sensitive to activity from the whole Sun, not just the side facing the observer. We hope to extend this analysis to data from HMI and MDI when they become available.