We present a theoretical study on how Pi 2 pulsations are excited in the magnetosphere. When impulsive disturbances associated with the substorm onset are assumed at the tailward region, their propagation toward the sunward direction is investigated with a wave equation. In order to examine the effect of the plasmapause on the initial disturbances, we analytically solve the wave equation based on the model of a reasonable Alfven speed profile. The exact solution shows that virtual resonant states exist in the plasmasphere and plasmapause. We obtain the result that these unique modes strongly persist for arbitrary incoming impulses from the source in the magnetotail, which corresponds to the signature of Pi 2 pulsations. ¿ 1998 American Geophysical Union