Simultaneously Excited Narrow and Broad Quasiperiodic Fast-propagating Wave Trains in the Solar Corona

The response of a solar coronal plasma loop to an impulsive perturbation, demonstrating the simultaneous formation of guided and leaky fast magnetoacoustic wave trains, is numerically studied. The equilibrium magnetic configuration corresponds to a potential arcade. A loop is modeled by filling a bent magnetic flux bundle with a plasma denser than in the surrounding. The plasma parameter β is much lower than unity everywhere in the computational domain. The initial perturbation is a pulse of the plasma velocity of sausage symmetry. The extent of the velocity pulse along the field is about the minor diameter of the loop. The perturbation generates both a guided fast-mode disturbance along the loop and leaky fast waves that propagate outward into the ambient corona. Both guided and leaky fast waves are quasiperiodic. The external component experiences refraction, which, in the chosen equilibrium, turns the wave toward the vertical. The guided component consists of a leading dispersive precursor, composed predominantly of higher harmonics, followed by a trailing wave train, dominated by the fundamental harmonic. In the external medium, the higher harmonic precursor generates leaky fast perturbations, while perturbations in the trailing wave train are evanescent. Our results confirm that both narrow and broad quasiperiodic fast-propagating waves detected in the corona can be excited by the same spatially localised impulsive energy deposition. The narrow counterpart is associated with the guided component, while the broad component is caused by the leaky component.