The dynamics of the Madden-Julian oscillation

The dynamics of the Madden-Julian Oscillation (MJO) are explored using a highly simplified nonlinear shallow water numerical model. The model is formulated on an equatorial beta-plane in an atmosphere initially in radiative-convective equilibrium and at rest.

Observations suggest that the tropical atmosphere is only marginally unstable to moist convection. Accordingly, the convective parameterization in the model is based on the quasiequilibrium hypothesis. The essential idea is that convective clouds consume the convective available potential energy (CAPE) at almost the same rate as it is generated by large-scale processes, such as radiative cooling, and the surface fluxes of heat and moisture. The convective parameterization allows for both shallow non-precipitating and deep precipitating clouds.

The convection is driven by a maintained, localized sea surface temperature anomaly, and the resulting convection shows many of the characteristic features of the MJO. The role played by deep convection in drying the middle troposphere is found to play a central part in the dynamics of the oscillation.<