Damped Coronal Loop Oscillations: Time‐dependent Results

Abstract

The excitation and damping oftransverse coronal loop oscillations is studied using a one-dimensional model ofa line-tied cylindrical loop. By solving the time-dependent magnetohydrodynamic (MHD) equations, we show how an initial disturbance produced in the solar corona induces kink-mode oscillations.We analyze the effect of the distur- bance on a loop with a nonuniform boundary layer and investigate the damping ofsuch a disturbance due to resonant absorption. We find that the period and attenuation time ofthe time-dependent results agree with the calculations of the corresponding quasi-mode (i.e., the kink mode resonantly coupled to Alfve´n modes) and that the resonant absorp- tion mechanism is capable ofdamping the oscillations almost immediately after the excitation. We study in detail the behavior ofsolutions in the inhomogeneous layer and show how the energy ofthe global oscillation is converted into torsional oscillations in the inhomogeneous layer. In addition, we estimate that the amplitude of the torsional oscillations is, for large magnetic Reynolds numbers and for thick layers, between 4 and 6 times the amplitude of the initial transverse motions. The implications ofthese results and their relationship with the observations are discussed.