Specifics of the solar photospheric convection at granulation, mesogranulation, and supergranulation scales

The power spectra of temperature and vertical velocity variations in the solar photosphere are calculated using the data obtained through observations of a nonperturbed region near the solar disk center in the neutral iron line lambda a parts per thousand 639.3 nm conducted at the 70 cm German Vacuum Tower Telescope (VTT) located in the Canary Islands (Spain). The variations of these spectra with altitude are analyzed. It is found that the primary power in the lower photosphere is localized in the range of frequencies that correspond to granulation with a peak at the lambda a parts per thousand 1.5-2.0 Mm scale and is reduced with altitude, the power spectrum maximum in the upper photospheric layers is shifted towards larger scales (Delta lambda a parts per thousand currency sign 1 Mm), and the power of variations of the vertical supergranulation velocity (lambda a parts per thousand 20-30 Mm) virtually does not change with altitude. An isolated mesogranulation regime (lambda a parts per thousand 5-12 Mm) is not found at any of the studied altitudes. The obtained results suggest that the convective structure of the solar photosphere at mesogranulation scales behaves like granulation: the mesostructures are a part of an extended distribution of granulation scales. It is shown that the supergranulation flows are stable throughout the entire photosphere and reach much higher altitudes than the granulation flows.