Helioseismic Test of Nonhomologous Solar Radius Changes with the 11 Year Activity Cycle

Abstract

Recent models of variations of the Sun's structure with the 11 year activity cycle by Sofia et al. predict strong nonhomologous changes of the radius of subsurface layers, due to subsurface magnetic fields and field-modulated turbulence. According to their best model, the changes of the surface radius may be 1000 times larger than those at the depth of 5 Mm. We use f-mode oscillation frequency data from the SOHO MDI and measurements of the solar surface radius variations from SOHO and ground-based observatories during solar cycle 23 (1996-2005) to put constraints on the radius changes. The results show that the above model overestimates the change of the radius at the surface relative to the change at 5 Mm.