Velocity Fields in the Solar Atmosphere. II. The Oscillatory Field.

From a systematic visual study of sets of "Doppler plates" obtained at the 13-foot spectroheliograph of the Mount Wilson Observatory during 1960 and 1961, the following results were derived: a) Vertical oscillatory motions were found in all medium-strong lines observed. The average period of the motions, about 290 sec, is a well-determined quantity for each spectral line. Slight, but apparently real, variations between the weaker and stronger lines observed suggest that the average period gradually decreases with increasing altitude in the line-forming regions of the upper photosphere. b) An oscillatory fluctuation of residual intensity was found in the cores of the stronger lines observed. The average period is somewhat shorter than that of the velocity oscillations and also exhibits an apparent decrease with increasing altitude. The two oscillations bear a definite phase relation to each other, indicating that they are physically connected. Intensity oscillations were not found in the weaker lines observed or in the core of Ha. These observations are discussed and compared with expectations for a plane wave propagating vertically through an isothermal atmosphere with an altitude-dependent radiative relaxation time.