Study of

11 years of low degree helioseismic data collected by the IRIS++ network (International Research of the Interior of the Sun) have been analyzed. The epoch covered (mid-1989 to end-1999) spans the maximum and the falling phase of solar cycle 22 and the rising phase of the current solar cycle 23. Annual timeseries with an overlap of 6 months are used to study the variations with solar activity of the p-mode frequencies $\nu_{n,\ell}$, heights $H_{n,\ell}$, and linewidths $\Gamma_{n,\ell}$, taking into account the effects of the window function. These are used to infer variations in the velocity power $$ and the energy supply rate $\dot{E}_{n,\ell}$ which relate to changes in the excitation and the damping of the modes. We find global changes over the range 2600 $\leq \nu \leq 3600~\mu$Hz of about -26%, 11%, -11% for the heights, the linewidths, and the velocity power respectively, and a constant energy supply to the modes