  We numerically investigate the excitation and temporal evolution of
oscillations in a two-dimensional coronal arcade by including the
three-dimensional propagation of perturbations. The time evolution of
impulsively generated perturbations is studied by solving the linear, ideal
magnetohydrodynamic (MHD) equations in the zero-beta approximation. As we
neglect gas pressure the slow mode is absent and therefore only coupled MHD
fast and Alfven modes remain. Two types of numerical experiments are performed.
First, the resonant wave energy transfer between a fast normal mode of the
system and local Alfven waves is analyzed. It is seen how, because of resonant
coupling, the fast wave with global character transfers its energy to Alfvenic
oscillations localized around a particular magnetic surface within the arcade,
thus producing the damping of the initial fast MHD mode. Second, the time
evolution of a localized impulsive excitation, trying to mimic a nearby coronal
disturbance, is considered. In this case, the generated fast wavefront leaves
its energy on several magnetic surfaces within the arcade. The system is
therefore able to trap energy in the form of Alfvenic oscillations, even in the
absence of a density enhancement such as that of a coronal loop. These local
oscillations are subsequently phase-mixed to smaller spatial scales. The amount
of wave energy trapped by the system via wave energy conversion strongly
depends on the wavelength of perturbations in the perpendicular direction, but
is almost independent from the ratio of the magnetic to density scale heights.
