  We investigate the temporal evolution of impulsively generated perturbations
in a potential coronal arcade with an embedded loop. As the initial
configuration we consider a coronal loop, represented by a density enhancement,
which is unbounded in the ignorable direction of the arcade. The linearized
time-dependent magnetohydrodynamic equations have been numerically solved in
field-aligned coordinates and the time evolution of the initial perturbations
has been studied in the zero-beta approximation. For propagation constrained to
the plane of the arcade, the considered initial perturbations do not excite
trapped modes of the system. This weakness of the model is overcome by the
inclusion of wave propagation in the ignorable direction. The inclusion of
perpendicular propagation produces two main results. First, damping by wave
leakage is less efficient because the loop is able to act as a wave trap of
vertical oscillations. Second, the consideration of an inhomogeneous corona
enables the resonant damping of vertical oscillations and the energy transfer
from the interior of the loop to the external coronal medium.
