Solar oscillations with 13-day period

Abstract

Claverie et al.¹ have recently discussed solar observations made over a 3-month period in the summer of 1981 which show oscillatory velocity with 13.1-day period and 6.6 m s⁻¹ amplitude. Among alternative explanations they reject the possibilities that they see the Doppler shift from a radial oscillation, because the amplitude is implausibly large, and that their signal was induced by solar magnetic fields, as typical mean solar fields are too small. We have examined photoelectric drift-scan measurements of the solar diameter and full-disk magnetograms taken at Kitt Peak National Observatory for evidence of variations corresponding to the velocity oscillations of the 13.1-day period. We report here an upper limit on radius variations which is a factor of six below the amplitude needed to explain the velocity observations as a radial oscillation and we also consider the possible role of the rotation of large-scale surface magnetic features.