The effects of line-of-sight integration on multistrand coronal loop oscillations

Abstract

Observations have shown that transverse oscillations are present in a multitude of coronal structures. It is generally assumed that these oscillations are driven by (sub)surface footpoint motions. Using fully three-dimensional MHD simulations, we show that these footpoint perturbations generate propagating kink (Alfvénic) modes which couple very efficiently into (azimuthal) Alfvén waves. Using an ensemble of randomly distributed loops, driven by footpoint motions with random periods and directions, we compare the absolute energy in the numerical domain with the energy that is "visible" when integrating along the line of sight (LOS). We show that the kinetic energy derived from the LOS Doppler velocities is only a small fraction of the actual energy provided by the footpoint motions. Additionally, the superposition of loop structures along the LOS makes it nearly impossible to identify which structure the observed oscillations are actually associated with and could impact the identification of the mode of oscillation. © 2012. The American Astronomical Society. All rights reserved..