Solar Cycle Variations of p-Mode Frequencies
  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. We find that the smoothed scaled relative frequency change varies along the solar cycle for horizontal phase velocities higher than a critical value, which corresponds to a depth near the base of the convection zone. This phenomenon suggests that the physical conditions in a region near the base of the convection zone change with the solar cycle. 
Dean-Yi Chou, Alexander Serebryanskiy (Institute of Astronomy and   Dept. of Physics, Tsing Hua Univ., Hsinchu, Taiwan)