Variations of the solar acoustic high-degree mode parameters over solar cycle 23

The structural and dynamical properties of the Sun as well as the excitation and damping of the solar acoustic modes change with the solar cycle The first two manifest themselves as changes in the acoustic mode frequencies and frequency splittings While the last two are observed as changes in the mode amplitudes and lifetimes Using full-disk observations obtained with the Michelson Doppler Imager MDI on board the Solar and Heliospheric Observatory SOHO spacecraft we present the amplitude width frequency and frequency splitting variations of high-degree 100 l 1000 solar acoustic modes over most of solar cycle 23 using global helioseismology analysis techniques By looking at high-degree modes we focus on the properties of the near-surface solar region Following the methodology described in detail in Korzennik et al 2004 we have removed the known instrumental and observational effects that affect specifically high-degree modes as well as possible to infer unbiased estimates of high-degree mode parameters