We conduct numerical experiments of the quasi-biennial oscillation (QBO) using a 2-dimensionalmodel. An oscillation with period of about 600 days is obtained. The simulated oscillation is verysimilar to the observed QBO in many respects:
(1) The faster downward propagation of the westerly wind than that of the easterly is obtained.
(2) The westerly wind appears at first on the equator but the easterly spreads from the mid-latitude region.
(3) The meridional extent of the westerly wind at the initial onset in the upper layer is very narrow. We analyze the effects of wave transience, change of zonal phase velocity by wave self-acceleration mechanism and wave breaking in the model. The effects except wave self-acceleration are crucial in the present model.
The dependence of the results on the magnitude of the dissipation coefficients is examined. We have conducted some numerical experiments with different initial conditions. However, the same steady state solution is always obtained when the magnitude of the dissipation is large. In this case, it seems that no multiple equilibrium exists in spite of the nonlinearity of the system.