Numerical simulations of impulsively generated vertical oscillations in a solar coronal arcade loop

Abstract

Aims. The main aims of the paper are to carry out numerical simulations of the vertical oscillations in a coronal loop in order to determine their dependence on various parameters and to compare them with recent TRACE observations. Methods. We consider impulsively generated oscillations in a solar coronal arcade loop. The two-dimensional numerical model we implement in the ideal MHD regime includes the effects of nonlinearity and line curvature. We perform parametric studies by varying both the position and the width/strength of the pulse. Results. A pulse launched below a loop is in general found to excite multiple wave modes, in particular a vertical oscillation with many properties of a kink mode, fast mode oscillations and a slow mode pulse (or two slow mode pulses, depending on the location of the original pulse). From our parametric studies we deduce that wave periods and attenuation times of the excited waves depend on the position below the loop summit, as well as on the width of the pulse. Wider pulses launched closer to a foot-point and to the loop's apex trigger wave packets of longer period waves which are more strongly attenuated. A perturbed loop does not return to its initial state but is instead stretched, with its apex shifted upwards. As a result the perturbations propagate along the stretched loop and consequently stronger and wider pulses which stretch a loop more lead to longer period oscillations. A pulse located near one of the foot-points is found to excite a distortion mode leading to asymmetric oscillations which are distinct from the vertical or horizontal kink modes that have been identified in TRACE data. © ESO 2006.