We used long duration , high quality , unresolved ( Sun-as-a star ) observations collected by the ground based network BiSON and by the instruments GOLF and VIRGO on board the ESA/NASA SOHO satellite to search for solar-cycle-related changes in mode characteristics in velocity and continuum intensity for the frequency range between 2.5 mHz < \nu < 6.8 mHz .
Over the ascending phase of solar cycle 23 we found a suppression in the p -mode amplitudes both in the velocity and intensity data between 2.5 mHz < \nu < 4.5 mHz with a maximum suppression for frequencies in the range between 2.5 mHz < \nu < 3.5 mHz .
The size of the amplitude suppression is 13 \pm 2 per cent for the velocity and 9 \pm 2 per cent for the intensity observations .
Over the range 4.5 mHz < \nu < 5.5 mHz the findings hint within the errors to a null change both in the velocity and intensity amplitudes .
At still higher frequencies , in the so called H igh-frequency I nterference P eak s ( HIPs ) between 5.8 mHz < \nu < 6.8 mHz , we found an enhancement in the velocity amplitudes with the maximum 36 \pm 7 per cent occurring for 6.3 mHz < \nu < 6.8 mHz .
However , in intensity observations we found a rather smaller enhancement of about 5 \pm 2 per cent in the same interval .
There is evidence that the frequency dependence of solar-cycle velocity amplitude changes is consistent with the theory behind the mode conversion of acoustic waves in a non-vertical magnetic field , but there are some problems with the intensity data , which may be due to the height in the solar atmosphere at which the VIRGO data are taken .