Center-to-limb variation of the solar oscillation New results from MDI data

Using 17 hours of full-disk MDI Doppler data we have investigated the center-to-limb variation of the oscillatory wave spectrum of the solar photosphere. Power distributions in the khν-plane are calculated for fields of 20◦ × 20◦ on the Sun, centered at every 10◦ heliographic latitude. From the centerto-limb variation of the power in the f mode and the lowest 7 p modes we obtain information about the mean inclination of the oscillatory velocity vector with respect to the vertical direction. We find qualitative agreement with a model of adiabatic waves in an isothermal atmosphere, but generally the solar oscillations appear to be less inclined than the model oscillations. We find no indication for the existence of horizontal sound waves on the Sun.