Convective contributions to the frequencies of solar oscillations

TL;DR

This study quantifies how turbulent convection near the solar surface affects oscillation frequencies, highlighting the role of turbulent pressure and thermal differences in explaining observed frequency discrepancies.

Contribution

It provides a numerical analysis of the impact of turbulent convection on solar oscillation frequencies, emphasizing the effects of turbulent pressure and surface elevation.

Findings

Turbulent pressure supports the solar surface, elevating the photosphere by about 150 km.

High-frequency mode turning points are raised, affecting their frequencies.

Most observed frequency differences are explained by the effects of turbulent pressure and surface elevation.

Abstract

Differences between observed and theoretical eigenfrequencies of the Sun have characteristics which identify them as arising predominantly from properties of the oscillations in the vicinity of the solar surface: in the super-adiabatic, convective boundary layer and above. These frequency differences may therefore provide useful information about the structure of these regions, precisely where the theory of solar structure is most uncertain. In the present work we use numerical simulations of the outer part of the Sun to quantify the influence of turbulent convection on solar oscillation frequencies. Separating the influence into effects on the mean model and effects on the physics of the modes, we find that the main model effects are due to the turbulent pressure that provides additional support against gravity, and thermal differences between average 3-D models and 1-D models. Surfaces of constant pressure in the visible photosphere are elevated by about 150 km, relative to a standard envelope model. As a result, the turning points of high-frequency modes are raised, while those of the low-frequency modes remain essentially unaffected. The corresponding gradual lowering of the mode frequencies accounts for most of the frequency difference between observations and standard solar models. Additional effects are expected to come primarily from changes in the physics of the modes, in particular from the modulation of the turbulent pressure by the oscillations.