Excitation of Longitudinal Modes in Solar Magnetic Flux Tubes by p-Modes

Abstract

This is a continuation of earlier work by Hasan (1997) on the interaction of longitudinal (sausage) waves in a slender flux tube with p-modes in the ambient medium. We use a realistic stratification for the flux tube and external atmospheres based upon the models of Hasan & Kalkofen (1994). The MHD equations for a thin flux tube are solved as an initial value problem incorporating radiative and convective energy transport. Our calculations confirm the linear prediction that the interaction is non-resonant. We find that the response (for a fixed order) increases with mode degree l up to a maximum and then falls off sharply as l increases. For the f-mode, l_max ~650. The amplitude of the oscillations tend to become stationary implying a balance between energy input from p-modes and losses through radiative damping and leakage from boundaries. Low order p-modes with degrees of several hundred appear to be most efficient for exciting longitudinal oscillations in flux tubes. The energy flux in these oscillations appears to be insufficient for chromospheric heating, but may contribute partially to the required flux.