In search of the solar cycle variations of p-mode frequencies generated by perturbations in the solar interior

Observations show that the solar p-mode frequencies change with the solar cycle. The horizontal phase velocity dependence of the relative frequency change, scaled by mode mass, provides depth information on the perturbation in the solar interior. Our model study suggests that variations of smoothed, scaled relative frequency change versus horizontal phase velocity might be able to detect the weak signals generated by the perturbation near the base of the convection zone. We find that the smoothed scaled relative frequency change, derived from SOHO MDI data, might show the evidence of solar cycle variations for horizontal phase velocities higher than a critical value, which corresponds to a depth near the base of the convection zone. The magnitude of temporal variations approximately correlates with solar activity. If these temporal variations are real signals, it suggests that the wave speed in a region near the base of the convection zone changes with the solar cycle. This change might be related to solar cycle variations of magnetic fields near the base of the convection zone.