The spectral and temporal characteristics of a ''giant'' Pc 2 (&tgr;~7 s) hydromagnetic wave event of duration ~110 s have been reanalyzed, as have the electromagnetic oscillations generated in the magnetosphere in an interval of about 45 min preceding and following the event. The event, which was recorded near local midnight at two mid-latitude locations, is, to the best of our knowledge, the largest such wave event reported to date. Previous analyses and interpretation of the event have centered on the bounce resonance generation of this packet of oscillations (Lanzerotti et al., 1986). The reexamination of the event, as well as other oscillations of the magnetoplasma, has caused us to identify six distinguishable spectral frequency bands which appear to encompass the Pc 2 wave packet and its evolution in time as well as to look at the development of the process as a whole. We present the details of these temporal and spectral studies and provide evidence that the Pc 2 event is probably produced by the gyroresonance swinging: amplification of the oscillatory magnetoplasma background in the frequency band ~0.1-0.2 Hz. The analysis suggests that the oscillatory background could be produced by impulse-like disturbances. The possible source(s) of such disturbances and their nature require further study. ¿ American Geophysical Union 1993