Tbe spatial and temporal evohltion of gravity wave packet interactions is studied numerically. It is shown that Igrougb tile resonant parametric excitation an upgoing gravity wave packet can cause the growth of two secondary waves from noise level up to a significanl inlensity in several bours The prbnary wave packet is apparently debrmed as it decays. Tile energy transfer among tile intenlcling waves is no longer reversible since their amplitudes are Iocalised Therefore the characteristic time for the interactions is of a parlicular significance: it represents a time during whicb the principal energy transfer arises. Beyond the cbaracteristic time the net energy transfer among the interacting waves becomes rather weak, but the local change in the wave energy densities can be Conlsiderable Only a part of the initial energy of the primary wave packet is transferred to the secondary waves during the parametric excilation. The amounts of energy, which each of the two secondary waves extract from the primary wave, are ditthrent, exhibiting a parameter preference in the energy transfer. 1he parametric excitation process can be completed in The propagation lime, For the resonant interaction with two gravity wave packets initially baying large amplitudes, the evolution tale is faster than that in the parametric excitation The primary wave packet can lose most of its energy and finally be reduced to a small fluetuation. The viscous dissipation not only decreases the wave energies but also strongly affects the local energy transfer among the interacting gravity wave packets.