Observational Study of Macroscopic Inhomogeneities in the Solar Atmosphere. III. Vertical Oscillatory Motions in the Solar Photosphere.

We have studied the Doppler displacements in two time sequences of spectrograms, one showing Fe I 5171.61, Mgi 5172.70 (b2), and Tii 5173.75 at the center of the solar disk, the other showing Fei 5324.19 at the limb. At the center we find that the velocity field consists mainly of short-lived oscillations of small elements of the solar atmosphere. The r.m.s. velocity amplitudes are 0.42 and 0.81 km/sec at low and high levels, respectively. The periods of the vertical oscillations cover roughly the range seconds, with a mean value around 242 sec. The periods seem to decrease with height in the atmosphere. An autocorrelation study shows also that the vertical velocity field is dominated by periodic oscillations, the time-correlation function having a strong positive peak at 300 seconds from the origin. The study of the time lags of oscillations between strong and faint lines suggests that they are of a type intermediate between progressive sonic waves (for the shorter periods) and standing waves (for the longer periods). Gradual transition from the first type to the second seems to occur during the life of a given oscillation. There is an indication that the individual oscillations are associated with individual granules. Near the limb, the observed horizontal motions consist of slowly changing velocities of the order of 0.5 km/sec in large surface elements, on which are superposed smaller random velocities of short duration. Oscillations rapidly disappear away from the center of the disk. The horizontal and vertical observable motions appear to be physically independent.