Solar acoustic oscillations in a random density field

¹ Institute of Atomic and Molecular Physics, National Research Council, Via Moruzzi 1, 56124 Pisa, Italy
² Department of Environmental Physics, Technical University of Lublin, ul. Nadbystrzycka 40, 20-618 Lublin, Poland

Corresponding author: L. Nocera, nocera@ifam.pi.cnr.it

Received: 9 November 2000
Accepted: 2 April 2001

Abstract

The influence of a space-dependent random mass density field on the development of solar p-modes is investigated using analytical and numerical means. Using a perturbative approach, which is valid for a weak random field and small amplitude waves, we derive a linear dispersion relation whose solutions correspond to attenuated oscillations. The real part of the frequency of these oscillations exceeds the one of waves propagating in a medium without random density. We give an interpretation of the "unphysical" nature of the frequency shift and of the amplitude attenuation which is similar to Landau damping. The analytical findings are compared with the results of the numerical solution of a model wave equation. We find that, for weak random fields and for wavelengths which are a few times the correlation length of the random density fluctuations, numerical results agree with the analytical theory. Two practical formulas for deriving the correlation spectrum of the random density field from observations are also given.