Solar five-minute oscillations

Abstract

The stability of acoustic modes trapped in the solar envelope is studied in the framework of linearized perturbation theory, by incorporating the mechanical and thermal effects of turbulence on the mean flow through the eddy transport coefficients. Many of these acoustic modes are found to be overstable, with the most rapidly growing modes occupying a region centred around 3.2 mHz spread over a wide range of length-scales. The numerical results turn out to be in reasonable agreement with the observed power-spectrum of the five-mInute oscillations. It is demonstrated that these oscillations are most likely to be driven by a simultaneous operation of the k-mechanism and the turbulent conduction mechanism, the dominant contribution to the generation of self-excited acoustic waves arising from the turbulent mechanism.