Modulation of Maritime Continent convection by the MJO: differences between parametrized and explicit convection

Convection over the Maritime Continent has large impacts for local extreme weather, as well as for global weather and climate. However, this convection and its impacts are poorly represented in current weather and climate models. This is largely due to complex multi-scale interactions between convection and the ocean, intricate island coastlines and topography, equatorial waves, and larger-scale dynamics such as the Madden-Julian oscillation (MJO). In order to better understand the modulation of convection by the MJO, and its representation in current models, we developed a new modelling suite that couples the Met Office Unified Model to a thermodynamic mixed-layer ocean model with additional corrections to account for ocean dynamics. This allows two-way interactions between the atmosphere and ocean on convection-relevant timescales without the expense of a full dynamical ocean model. We present results from simulations of 10 DJF seasons over the Maritime Continent at grid spacings of 12km (with a mass flux convection scheme) and 2km (without).  

We investigated the modulation of large-scale convective heating and moistening by MJO phase in both models. We show that: 

• The 2km suite has more variability by MJO phase, and this variability is more realistic than that in the 12km suite when compared to observational data; 
• There is more variability in the type of convection (defined by the shape of heating/moistening profiles) between MJO phases in the 2km suite; 
• The dominant variation is between different types of convection in the two suites. 

We also present preliminary results on the modulation by the MJO of basic properties of the cloud field like feature size, and feature isotropy.