Solar Oscillations and Convection. II. Excitation of Radial Oscillations

Abstract

Solar p-mode oscillations are excited by stochastic, non-adiabatic gas pressure fluctuations, which are produced by small instantaneous local imbalances between the divergence of the radiative and conductive fluxes near the solar surface. We evaluate the expression for the radial mode excitation rate derived by Nordlund & Stein (1998) using numerical simulations of near surface solar convection. Excitation occurs mainly in the intergranular lanes and near the boundaries of granules. The frequency dependence of the mode excitation is due to effects of the mode structure and the pressure fluctuation spectrum. Excitation is small at low frequencies due to mode properties -- the mode compression decreases and the mode mass increases at low frequency. Excitation is small at high frequencies due to the pressure fluctuation spectrum -- pressure fluctuations become small at high frequencies because they are due to convection which is a long time scale phenomena compared to the dominant p-mode ...