Abstract
A time series of simultaneously measured velocity (V) and intensity (I) fluctuations of different spectral lines formed in the photosphere and low chromosphere is analysed. In order to separate the different patterns of motions (granulation, mesogranulation, gravity waves, acoustic waves) V-V and V-I phase difference spectra have been computed not only with respect to frequency v but also to the horizontal wavenumber kx. The V-V phase difference spectra of the Na Di line and two photospheric Fe I lines (5929.7A, 5930.2A) clearly show the existence of gravity waves in the solar atmosphere. The V-I phase spectra also exhibit the behaviour of gravity waves at high wavenumbers (kx≥1.7 Mm-1). At low wavenumbers one finds positive V-I phase differences. This we take as an indication for convective motions with a typical spatial scale of more than 5" (mesogranulation)
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