Study of the Solar Cycle Dependence of Low‐Degreep‐Modes with Michelson Doppler Imager and VIRGO

Abstract

Studying variations of observational properties of low-degree solar acoustic p-modes (radial, dipole, and quadrupole) with the activity cycle is important for understanding potential effects of the cycle in the deep interior, obtaining more accurate inversions for the sound speed and rotation, and also for estimating prospective investigation of stellar activity by asteroseismology. We have analyzed changes of low-degree p-mode parameters during the current solar cycle (number 23) by using velocity and intensity oscillation data from two instruments on the Solar and Heliospheric Observatory (SOHO): the Michelson Doppler Imager (MDI) and Variability of Solar Irradiance and Gravity Oscillations (VIRGO). We show a clear dependence of mode frequency, line width, frequency splitting, and line asymmetry on the solar cycle. Moreover, we demonstrate that these properties change differently for modes of different frequency, angular degree, and order. The greatest changes are observed for sectorial modes of frequencies higher than 3 mHz, corresponding to the fact that the most significant variations of the solar structure occur in low-latitude regions close to the solar surface.