The nature of the frequency spectrum of shear Alfvén waves in a solar coronal arcade

Frequency power spectra are computed theoretically for shear Alfvén waves excited in a solar coronal arcade by two separate perturbations, a cosine-modulated Gaussian perturbation and an impulsive driver. The arcade is assumed to consist of potential magnetic field lines embedded in a stratified plasma. It is shown that although the power spectra have discrete frequencies for each field line, a cumulative effect of many field lines of different widths/lengths in an arcade will be that of a continuous spectrum, if seen together as one entity. The nature of the frequency power spectra can constrain the size and the type of driver.