Solar five-minute oscillations of low, intermediate, and high degree

Abstract

The overstability of acoustic modes trapped inside the Sun is studied with mechanical and thermal effects of turbulence included in an approximate manner through the eddy diffusivities. Many of the acoustic modes are found to be overstable with the most rapidly growing modes occupying a region centred around 3.3 mHz and spread over a wide range of length-scales. The numerical results turn out to be in reasonable accord with the observed power-spectrum of the five-minute oscillations of arbitrary degree. It is demonstrated that these oscillations are most likely to be driven by a simultaneous operation of the κ-mechanism and the convective Cowling mechanism, the dominant contribution to the generation of self-excited acoustic waves arising from the turbulent diffusion.