Models of solar surface dynamics: impact on eigenfrequencies and radius

Abstract

We study the effects of different descriptions of the solar surface convection on the eigenfrequencies of p modes. 1D evolution calculations of the whole Sun and 3D hydrodynamic and magnetohydrodynamic simulations of the current surface are performed. These calculations rely on realistic physics. Averaged stratifications of the 3D simulations are introduced in the 1D solar evolution or in the structure models. The eigenfrequencies obtained are compared to those of 1D models relying on the usual phenomenologies of convection and to observations of the Michelson Doppler Imager instrument aboard the Solar Heliospheric Observatory (SoHO). We also investigate how the magnetic activity could change the eigenfrequencies and the solar radius, assuming that, 3 Mm below the surface, the upgoing plasma advects a 1.2 kG horizontal field. All models and observed eigenfrequencies are fairly close below 3 mHz. Above 3 mHz the eigenfrequencies of the phenomenological convection models are above the observed eigenfrequencies. The frequencies of the models based on the 3D simulations are slightly below the observed frequencies. Their maximum deviation is ≈3 μHz at 3 mHz but drops below 1 μHz at 4 mHz. Replacing the hydrodynamic by the magnetohydrodynamic simulation increases the eigenfrequencies. The shift is negligible below 2.2 mHz and then increases linearly with frequency to reach ≈1.7 μHz at 4 mHz. The impact of the simulated activity is a 14 mas shrinking of the solar layers near the optical depth unity.