Overstable solar oscillations of intermediate and high degree

Abstract

The stability of linear acoustic modes trapped in the solar envelope is investigated with the thermal and mechanical effects of turbulence on the mean flow incorporated through turbulent conductivity, viscosity and turbulent pressure. A number of these modes turn out to be overstable, and the most rapidly growing acoustic modes are found to occupy a region centred around 3.2 mHz and spread over a wide range of length scales. These numerical results are in reasonable accord with the observed power-spectrum of the five-minute oscillations.