THREE-DIMENSIONAL MAGNETOHYDRODYNAMIC MODELS OF TWISTED MULTITHREADED CORONAL LOOP OSCILLATIONS

Abstract

The multithreaded structure of active region coronal loops was deduced from past spectroscopic observations. Recent high-resolution observations by Transition Region and Coronal Explorer and Hinode satellites provided direct evidence that active region loops consist of multiple magnetic threads filled with plasma with higher density than neighboring loop material. High-resolution observations of loops near a flare site suggest that the threads are twisted or tangled, the magnetic field is not force free, and flows are present. To better understand these observations, we developed for the first time a three-dimensional magnetohydrodynamic model of twisted multithreaded loops that oscillate as a result of an impulsive event. The twist is induced by applying a rotating velocity field at the footpoint of the initially parallel set of threads, and parallel flow is included. The oscillations of the twisted loops are excited by a fast magnetosonic pulse. The evolution and the damping of the fast magnetosonic wave excited in the twisted multithreaded loop are compared to oscillations of a four-parallel-threaded loop. It was found that twisted loop oscillations result in filamented current and velocity structure that cannot be described by the fundamental kink mode. When parallel flow is present, the oscillation induces nonlinear compressive modulation of the flow and density in the threads. The twisted loop oscillates and damps faster than the parallel-threaded loop. The results of the study demonstrate the effects of the twist, internal loop structure, and flow on the evolution of the waves in coronal active region loops.