Wave propagation in the photosphere

Using a 32 minutes sequence of observation, brightness and velocity fluctuations in the wings of the Mgi line at 5172.7 Å and Fe ii line at 5197.578 Å are analysed. The analysis of phase shifts and amplitude ratios leads to the following conclusions:

(1)	In the frequency range from (400s)–1 to (130s)–1, we find the existence of three modes of waves: internal gravity, evanescent and propagating acoustic waves which appear with increasing frequency. A satisfactory agreement for velocity between observations and theory in the range of horizontal wavelengths \s>5000km with a theoretically local relaxation time –180s-40s is obtained. The calculation of intensity fluctuations shows that the Mgi 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 –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.
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