The time-dependent evolution of an initial wave disturbance at the magnetospheric boundary as it is released in the presence of the sheared hydromagnetic flow in the magnetosphere is discussed for the simple case in which the shear in the Alfv¿n speed is uniform. The uniform-shear assumption allows explicit solutions to be obtained which are useful in explaining the recent observations of resonant Alfv¿n waves excited in the magnetosphere by a sudden impulse. ¿ American Geophysical Union 1988