Study of p-mode excitation and damping rate variations from IRIS++ observations

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 v(n,l), heights H-n,H-l, and linewidths Gamma(n,l), taking into account the effects of the window function. These are used to infer variations in the velocity power <V-n,l(2) > and the energy supply rate (E)over dot(n,l) which relate to changes in the excitation and the damping of the modes. We find global changes over the range 2600 less than or equal to v less than or equal to 3600 muHz of about -26%, 11%, -11% for the heights, the linewidths, and the velocity power respectively, and a constant energy supply to the modes.