Solar oscillations with 13-day period

Reference is made to the solar observations made by Claverie et al. (1982) over a three-month period in the summer of 1981 which show oscillatory velocity with a period of 13.1 days and amplitude of 6.6 m/s. These investigators reject the possibility that they see the Doppler shift from a radial oscillation, because the amplitude is implausibly large. They also do not believe that their signal was induced by solar magnetic fields, since typical mean solar fields are too small. Photo-electric drift-scan measurements of the solar diameter and full-disk magnetograms taken at Kitt Peak National Observatory are examined here for evidence of variations corresponding to the velocity oscillations of the 13.1-day period. An upper limit on radius variations is reported which is a factor of six below the amplitude needed to explain the velocity observations as a radial oscillation. Attention is also given to the possible role of the rotation of large-scale surface magnetic features.