Topography, Diurnal Cycle and the MJO in the Maritime Continent

Understanding and simulating the multi-scale interactions between the diurnal cycle in the Maritime Continent (MC) and large-scale circulations remain a challenge to the atmospheric community. The problem is further exacerbated by the complex topography of the MC that are nor represented well in coarse resolution models. A series of numerical simulations using a popular regional model are conducted to understand the interactions between the topography, diurnal cycle and the MJO. The lower-resolution (LR, 12 km) simulation using cumulus parameterization captures the spatial distribution of precipitation well including the heavy rainfall areas, although precipitation is overestimate over land and is underestimated over ocean. The peak amplitude of diurnal precipitation in the LR simulation is 3 hours earlier than observation over land. However, the higher-resolution (HR, 4 km) simulation without cumulus parameterization captures the diurnal variability better than the LR. The MJO is also better organized in the HR than LR. Lower-resolution simulation in the absence of topography (LR-Flat) shows stronger diurnal cycle over land, but the MJO propagation remains unaffected. Higher-resolution simulation in the absence of topography (HR-Flat) shows weaker diurnal cycle over land and more organized MJO propagation across the MC. The amplitude and propagation of the MJO in the absence of diurnal cycle is also investigated. In particular, the diurnal cycle of moisture and zonal momentum budget during the passage of the MJO across the MC are discussed.