Solar variability and oscillations

Within this decade, observations of total solar irradiance have become good enough to permit us to study directly the solar luminosity variations on a wide range of time scales, up to several years. At the same time there has been considerable improvement in understanding the classical indicators of solar activity, such as UV and visible chromospheric lines, soft X‐rays, and radio fluxes. The observed variations include the effects of sunspots and plage (which induce “rotational modulation”), solar‐cycle effects, and signatures of global oscillations and convection. In addition new characteristic time‐scales (154 days and possibly 320 days) have been discovered but not explained. This review covers these developments and comments briefly on the subject of helioseismology, the study of the solar global oscillations.