Effect of the steady flow on spatial damping of small-amplitude prominence oscillations

Abstract

Aims. Taking account of steady flow in solar prominences, we study its effects on spatial damping of small-amplitude non-adiabatic magnetoacoustic waves in a homogeneous, isothermal, and unbounded prominence plasma. Methods. We model the typical feature of observed damped oscillatory motion in prominences, removing the adiabaticity assumption through thermal conduction, radiation and heating. Invoking steady flow in MHD equations, we linearise them under small-amplitude approximation and obtain a new general dispersion relation for linear non-adiabatic magnetoacoustic waves in prominences Results. The presence of steady flow breaks the symmetry of forward and backward propagating MHD wave modes in prominences. The steady flow has dramatic influence on the propagation and damping of magnetoacoustic and thermal waves. Depending upon the direction and strength of flow the magnetoacoustic and thermal modes can show both the features of wave amplification and damping. At the wave period of 5 min where the photospheric power is maximum, the slow mode shows wave amplification. However, in the absence of steady flow the slow mode wave shows damping. Conclusions. For the wave period between 5 min and 15 min, the amplification length for slow mode, in the case of prominence regime 1.1, varies between 3.4*10^11 m to 2*10^12 m. Dramatic influence of steady flow on small-amplitude prominence oscillations is likely to play an important role in both wave detection and prominence seismology.