  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 2.5mHz < nu < 6.8mHz. 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 2.5mHz <nu< 4.5mHz with a maximum suppression for
frequencies in the range between 2.5mHz <nu< 3.5mHz. The size of the amplitude
suppression is 13+-2 per cent for the velocity and 9+-2 per cent for the
intensity observations. Over the range 4.5mHz <nu< 5.5mHz 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 High-frequency
Interference Peaks (HIPs) between 5.8mHz <nu < 6.8mHz, we found an enhancement
in the velocity amplitudes with the maximum 36+-7 per cent occurring for 6.3mHz
<nu< 6.8mHz. However, in intensity observations we found a rather smaller
enhancement of about 5+-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.
