The behaviors of a nonlinear quasi stationary ultra long wave system which includes the topographic

thermal and dissipative effects are investigated with the methods of chaotic dynamics. It’s found that depending upon the parameters the system can exhibit equilibrium states

periodic motions or even chaotic behaviors. The periodic motions have periods of about 30￣40 days

which are equivalent to the low frequency oscillation in the atmosphere. Based on the results of qualitative analysis

a criterion to judge the system’s behaviors is proposed. The value of the criterion is related to the topography

dissipation and diabatic heating.