Abstract
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.
Highlights
A number of studies have demonstrated that the Madden and Julian oscillation (MJO) simulation with a current general circulation model (GCM) depends on the convective parameterization (e.g., Lin et al 2006; Lee et al 2008; Frierson et al 2011)
With a coarse-resolution GCM with cloud microphysics, Yoshizaki et al (2012) and Takasuka et al (2015) obtained an MJO-like signal, their simulations were performed under idealized aquaplanet conditions
Holloway et al (2012) demonstrate that a high-resolution GCM with explicit cloud microphysics does not necessarily simulate a good MJO, rather it depends on the vertical distribution of simulated moisture anomalies in the MJO time scale, in the lower troposphere
Summary
A number of studies have demonstrated that the MJO simulation with a current general circulation model (GCM) depends on the convective parameterization (e.g., Lin et al 2006; Lee et al 2008; Frierson et al 2011). Holloway et al (2012) demonstrate that a high-resolution GCM with explicit cloud microphysics does not necessarily simulate a good MJO, rather it depends on the vertical distribution of simulated moisture anomalies in the MJO time scale, in the lower troposphere.
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