Modeling the MJO in a cloud-resolving model with parameterized large-scale dynamics: vertical structure, radiation, and horizontal advection of dry air

Two Madden-Julian Oscillation (MJO) events, observed during October and November 2011 in the equatorial Indian Ocean during the DYNAMO field campaign, are studied in a cloud-resolving model using parameterized large-scale dynamics. Three parameterizations of large-scale dynamics --- the conventional weak temperature gradient (WTG) approximation, vertical mode based spectral WTG (SWTG), and damped gravity wave coupling (DGW) --- are employed. A number of changes to the implementation of the large-scale parameterizations, as well as the model itself, are made and lead to improvements in the results.

Simulations using all three methods, with imposed time-dependent radiation and horizontal moisture advection, capture the time variations in precipitation associated with the two MJO events well. The three methods produce significant differences in the large-scale vertical motion profile, however. WTG produces the most top-heavy profiles, while DGW's is less so, and SWTG produces a profile between the two, and in better agreement with observations.

Numerical experiments without horizontal advection of moisture suggest that that process significantly reduces the precipitation and suppresses the top-heaviness of large-scale vertical motion during the MJO active phases. Experiments in which a temporally constant radiative heating profile is used indicate that radiative feedbacks significantly amplify the MJO. Experiments in which interactive radiation is used produce agreement with observations that is much better than that achieved in previous work, though not as good as that with imposed time-varying radiative heating. Our results highlight the importance of both horizontal advection of moisture and radiative feedbacks to the dynamics of the MJO.