A GCM with cloud microphysics and its MJO simulation

The present study examines the Madden and Julian oscillation (MJO) appearing in a general circulation model (GCM) with full representation of cloud microphysics at 50 km horizontal resolution, and the MJO is compared with those of GCMs with conventional convective parameterizations. The present coarse-resolution GCM requires modifications of several parameters of cloud microphysics and an additional vertical mixing process in the lower troposphere to simulate the MJO reasonably well. The GCM with cloud microphysics only produces the relatively small-scale precipitation scattered in the tropic. The shallow convection added in the GCM helps moisten the lower troposphere and enhances low-level moisture convergence, and thus large-scale cloud clusters are generated effectively, resulting in a better simulation of MJO.