NONLINEAR BALANCE ON AN EQUATORIAL BETA-PLANE

Extension of the nonlinear balance model to include the equator is exa mined here from a theoretical perspective. It is found that this model is ill-posed, in that zonally symmetric equatorial Kelvin waves of ar bitrary amplitude can occur. Two possible solutions are outlined. The zonally-averaged zonal momentum equation provides auxiliary informatio n that can be imposed on the flow. This equation can be solved simulta neously with the other parts of the problem. Alternatively, when small , isolated disturbances can be considered to have a negligible effect on the mean flow; one can simply assume that zonal means remain unchan ged.