Numerical 3D constraints on convective eddy time-correlations : consequences for stochastic excitation of solar p modes

Abstract

A 3D simulation of the upper part of the solar convective zone is used to obtain information on the frequency component, chi_k, of the correlation product of the turbulent velocity field. This component plays an important role in the stochastic excitation of acoustic oscillations. A time analysis of the solar simulation shows that a gaussian function does not correctly reproduce the nu-dependency of chi_k inferred from the 3D simuation in the frequency range where the acoustic energy injected into the solar p modes is important (nu ~ 2 - 4 mHz). The nu-dependency of chi_k is fitted with different analytical functions which can then conveniently be used to compute the acoustic energy supply rate P injected into the solar radial oscillations. With constraints from a 3D simulation, adjustment of free parameters to solar data is no longer necessary and is not performed here. The result is compared with solar seismic data. Computed values of P obtained with the analytical function which fits best chi_k are found ~ 2.7 times larger than those obtained with the gaussian model and reproduce better the solar seismic observations. This non-gaussian description also leads to a Reynolds stress contribution of the same order as the one arising from the advection of the turbulent fluctuations of entropy by the turbulent motions. Some discrepancy between observed and computed P values still exist at high frequency and possible causes for this discrepancy are discussed.