Global Oscillations and Active Regions

Abstract

We present further estimates of the amplitude of the modulation of the solar global velocity signal caused by the passage of active regions across the solar disc. Using measurements of the profile of the K I It 769·9 nm line in the quiet Sun and in plages we find a global velocity variation of ~ 2 m s - 1 during the transit of a typical active region of area 3300 millionths of the hemisphere. However, during the period in which a velocity amplitude of 6 m s - 1 was reported by Claverie et al. (1982), the sunspot areas were exceptionally large and we confirm Schroter's (1984) result that the combination of spot 'and plage contributions is sufficient to account for the observed signal. The velocity modulation is thus attributable to surface inhomogeneities, not to the structure of the solar core.