Abstract: By utilizing the barotropic vorticity equation including the effects of orography and horizontal diffusion, the linearized equation describing symmetric motion and that describing antisymmetric motion, and their analytic solutions, are presented. It can be found from the solutions that no matter what kind of motion may be, each solution consists of three waves, namely, Rossby wave related to initial values, marching wave propagating at Rossby wave velocity and stationary wave. The latter two of them are closely related to orography and horizontal diffusion.However, if the motion is symmetric at the initial instant, then the antisymmetric component of orography and of horizontal diffusion are likely to lead to the generation of antisymmetric motion. In the steady state, the symmetric flow is connected with symmetric orography and horizontal diffusion and the antisymmetric flow with antisymmetric orography and horizontal diffusion.Further, in order to verify the above analysis, three numerical experiments have been made. The results show that antisyrnmetric orography can produce antisymmetric motion. Finally, the interactions between the atmosphere of the Northern Hemisphere and that of the Southern Hemisphere are discussed.