Wave propagation in the photosphere

Using 32 minutes sequence of observation, brightness and velocity fluctuations in the wings of the Mg I line at 5172.7 A and Fe II line at 5197.578 A are analysed. The analysis of phase shifts and amplitude ratios leads to the following conclusions: (1) In the frequency range from (400 s)-1 to (130 s)-1, the existence of three modes of waves is found: internal gravity, evanescent and propagation acoustic waves which appear with increasing frequency. A satisfactory agreement for velocity between observations and theory in the range of horizontal wavelengths >5000 km with a theoretically local relaxation time β-1 approximately 80 s-40 s is obtained. The calculation of intensity fluctuations shows that the Mg I line is sensitive to temperature and density fluctuations while the Fe II line is only sensitive to temperature perturbation. For the best fit with the same value of β-1 to both lines (i.e., Fe II and Mg I) it is found necessary that the density effect should be taken into account for the Mg I intensity fluctuations. The relaxation time deduced from observed intensity fluctuations seems to decrease with the period of oscillation. This suggests the presence of a dissipation process. (2) For higher frequencies oscillations, the phase shift and the amplitude ratios are too small to be interpreted by propagating acoustic waves. (Auth.)