By using a two-dimensional full-implicit-continuous-Euleri （FICE） scheme, the nonlinear propagation and evolution of gravity-wave packets in real atmosphere is simulated. The numerical results show that when an upgoing gravity-wave packet is generated in low mesosphere, it can propagate along its ray path before arriving at the height of mesopause, the nonlinearity and background atmospliere have little influence on its energy propagation path. However, when the wave packet arrives at low thermosphere, the wave packet and wave associated energy propagate almost horizontally, and its vertical propagation is halted. which departs obviously from the prediction of linear gravity-wave theory under WKB approximation in nondissipative case. A further discussion indicates that it is the vertical inhomogeneity of molecular viscosity that causes the restriction of upward energy propagation of the gravity-wave packet. Moreover, during the whole propagation, affected by the joint actions of nonlinearity, background temperaturc and dissipation, the dominant vertical wavelength of the wave packet decreases obviously with time. These indicate that the molecular viscosity especially the vertical inhomogeneity of molecular viscosity plays an important role in the nonlinear propagation of gravity-wave packets.
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