The MJO and convectively coupled waves in a coarse resolution GCM with a simple multicloud parametrization

Three numerical simulations using different moisture gradients and different stratiform fractions are considered. The first experiment uses a large moisture gradient and a small stratiform fraction and provides an MJO-like example. It results in an intra-seasonal oscillation of zonal wavenumber two, moving eastward at a constant speed of roughly 5 m s⁻¹.

The second uses a weaker background moisture gradient and a large stratiform fraction and yields convectively coupled Rossby, Kelvin and two-day waves, embedded in and interacting with each other while the last one combines the small stratiform fraction and the weak background moisture gradient to yield a planetary scale (wavenumber one) second baroclinic Kelvin wave. While the two first experiments provide two benchmark examples that reproduce several key features of the observational record, the third one is more of a demonstration of a bad MJO model solution that exhibits very unrealistic features.