An investigation of the height distribution of the gas flow velocity in the solar granulation

With the aid of a 512-channel spectrophotometer records were made of profiles of spectral lines formed at different heights in the photosphere in order to obtain quantitative estimates of gas flow velocities within the granule cores and spaces between the granules in a quiet region at the solar disk center. The area of the scanning aperture was varied from 24 arc sec 2 to 0.3 arc sec 2, spatial samples were taken at steps of 0.235 sec of arc, and the spectral resolution was 0.01351 Å/pixel. A total of more than 3000 spectra were obtained from three scans of a length 8″.3; 4″.7 and 5″.2. Data handling involved digital averaging of the data as well as calculating the bisectors and Doppler shift, the last at 14–16 depth levels of spectral line profiles. The spectral-spatial analysis of a low-resolution record has shown that a preferential spatial period of granulation constitutes a set of discrete values and varies little with height. A drift of the gas flow in the horizontal direction with the velocity of ≈ 2 km s −1 is noted. On high-resolution records the velocity amplitude near the photospheric base reaches 2.7 – 3.5 km s −1 and decreases with height. The level h ≈ 200 km above τ (5000) = 1 is the boundary of velocities of a convective character, above which the velocity amplitude decreases considerably. There exists an inclined character of the gas flows, up to the level h ≈ 200 km at a larger angle to the vertical and a small angle for the middle and upper photosphere. The results obtained are discussed, by invoking the vortical character of the motion of the gas flows and a piston mechanism.