Abstract: By defining three flux vectors, the nonlinear advection terms in momentum equations are written into vorticity and divergence terms of the three vectors, which indicates that the vorticity or divergence can cause zonal or meridional wind to accelerate at the low frequency time scale. By convolving the momentum equations, the dynamical model is given to describe the low frequency oscillations. The low frequency flux vectors and the stream function and potential function of them are computed, which show us the interesting features of their spatial distribution and time variation.