ULF pulsations have been numerically studied in a new three-dimensional dipole model, which allows a realistic Alfven speed profile for the plasmasphere and outer magnetosphere in the tailward region. This model includes more realistic boundary conditions at the outer boundary, allowing for partial reflection at the magnetopause and escape of wave energy down the tail. We investigate how Pi2 modes develop in time when an impulse associated with the substorm onset is assumed. It is shown that discrete compressional modes, which are initially excited by the plasmasphere, persistently arise in the nightside region. Our numerical results suggest that Pi2 pulsations are strongly associated with these virtual resonances in the plasmasphere. Wave spectra are examined both at the equator and the ionosphere. We discuss and compare them with current theoretical and observational characteristics. ¿ 1999 American Geophysical Union